MOTION FACTORS RELATED TO LOW BACK PAIN IN LACROSSE ATHLETES By JOSEPH G WASSER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2019
2019 Joseph G. Wasser
To my parents, Without you, none of my success would have been possible
4 ACKNOWLEDGMENTS I would first like to thank my mentor for helping me carry out this project and guiding me through this whole doctoral process. The amount of support, direction and patience you shared with me has been crucial from day one. I would also li ke to thank my parents and loved ones for their unwavering support and encouragement. There have been numerous highs and lows through this whole process, and your reassurance and belief in me gave me the strength and drive to do my best and achieve everyth ing I have put my mind to.
5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 4 LIST OF TABLES ................................ ................................ ................................ ........................... 7 LIST OF FIGURES ................................ ................................ ................................ ......................... 8 ABSTRACT ................................ ................................ ................................ ................................ ..... 9 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................. 11 Statement of the Problem ................................ ................................ ................................ ........ 13 Specific Aims ................................ ................................ ................................ .......................... 13 Specific Aim One ................................ ................................ ................................ ............ 14 Specific Aim Two ................................ ................................ ................................ ............ 15 Specific Aim Three ................................ ................................ ................................ .......... 15 2 LITERATURE REVIEW ................................ ................................ ................................ ....... 17 The Lacrosse Shot ................................ ................................ ................................ ................... 18 Low Back Pain an d Lacrosse ................................ ................................ ................................ .. 24 Kinematic Characteristics of Low Back Pain in Lacrosse ................................ ...................... 25 Motion Similarities with Other Sports ................................ ................................ .................... 28 Potential Functional Factors Associated with Low Back Pain in Lacrosse Athletes ............. 32 Sport Experience and Low Back Pain in Lacrosse ................................ ................................ 36 Working Model of Low Back Pain in La crosse Players ................................ ......................... 40 Application within Rehabilitation Science ................................ ................................ ............. 41 The Internal Classification of Functioning (ICF) Model ................................ ........................ 42 3 MATERIALS AND METHODS ................................ ................................ ........................... 46 Overview ................................ ................................ ................................ ................................ 46 Study Design ................................ ................................ ................................ ........................... 46 Participants ................................ ................................ ................................ ............................. 47 Recruitment ................................ ................................ ................................ ............................. 47 Sample Size Estimate ................................ ................................ ................................ ............. 48 Informed Consent ................................ ................................ ................................ ................... 48 Attrition ................................ ................................ ................................ ................................ ... 49 Study Outcomes ................................ ................................ ................................ ...................... 49 Participant Charac teristics ................................ ................................ ................................ ...... 49 Sport Experience and Lacrosse Position ................................ ................................ ................. 49 Pain Severity ................................ ................................ ................................ ........................... 50 Physical Function Tests ................................ ................................ ................................ .......... 51
6 Three Dimensional Motion Analysis ................................ ................................ ..................... 54 Crunch Factor Index: ................................ ................................ ................................ .............. 63 Statistical Analysis ................................ ................................ ................................ .................. 65 Protection of Human Subjects ................................ ................................ ................................ 66 4 RESULTS ................................ ................................ ................................ ............................... 68 Participant Characteristics ................................ ................................ ................................ ...... 68 Lacros se History ................................ ................................ ................................ ..................... 69 Musculoskeletal Pain ................................ ................................ ................................ .............. 70 Functional Testing ................................ ................................ ................................ .................. 70 Joint Angles a nd Range of Motion (ROM) ................................ ................................ ............ 72 Angular Velocities ................................ ................................ ................................ .................. 74 Timing of Peak Angular Velocities ................................ ................................ ........................ 76 Crunch Factor Index ................................ ................................ ................................ ............... 77 Odds Risk Analyses ................................ ................................ ................................ ................ 78 Regression Analyses ................................ ................................ ................................ ............... 78 Joint Angles and Range of Motion (ROM) and Onset of LBP ................................ ............... 80 Angular Velocities and Onset of LBP ................................ ................................ .................... 81 Single Leg Squat Kinematics and Onset of LBP ................................ ................................ .... 82 5 DISCUSSION ................................ ................................ ................................ ......................... 83 Limitations ................................ ................................ ................................ .............................. 93 Conclusion ................................ ................................ ................................ .............................. 95 LIST OF REFERENCES ................................ ................................ ................................ ............... 96 BIOGRAPHICAL S KETCH ................................ ................................ ................................ ....... 110
7 LIST OF TABLES Table page 2 1 Lacrosse Shooting Kinematics Among High School, Collegiate and Professional Players ................................ ................................ ................................ ................................ 22 3 1 Biomechanical Outcome Variables ................................ ................................ .................... 60 4 1 Participant characteristics of lacrosse players with and without low back pain. .............. 68 4 2 Playing history of lacrosse players with and wit hout low back pain.. ............................... 69 4 3 Self reported musculoskeletal pain at baseline and during follow up ............................... 70 4 4 Single leg squat kinematics of lacrosse participants with and without LBP. ................... 71 4 5 Functional testing of lacrosse participants with and without LBP. ................................ ... 72 4 6 J oint angles and range of motion generated during a lacrosse shot. ................................ .. 73 4 7 Maximal angular velocities during a dominant and non dominant lacrosse shot. ............. 75 4 8 Temporal patterns of maximal segmental angular velocities during a dominant and non dominant lacrosse shot. ................................ ................................ ............................... 76 4 9 Crunch Factor Index. ................................ ................................ ................................ ......... 77 4 10 Odds risk analyses for development of LBP and sport participation. ................................ 78 4 11 Odds risk analyses for presence of LBP and lacrosse position played. ............................. 78 4 12 Hierarchal regression analyses for kinematic parameters of a lacrosse shot ..................... 79 4 13 Stride length, joint angles and range of motion generated during a lacrosse shot ............. 80 4 14 Maximal angular velocities, Crunch Factor Index and development of LBP. ................... 81 4 15 Single leg squat kinematics of lacrosse participants who developed LBP and those who did not. ................................ ................................ ................................ ....................... 82
8 LIST OF FIGURES Figure page 2 1 Phases and events of the lacrosse shot. ................................ ................................ .............. 20 2 2 Potential physical pathways to low back pain with lacrosse shooting ............................... 35 2 3 Potential factors that may contribute to low back pain in lacrosse athletes. ...................... 41 2 4 Lacrosse Low Back Pain (LBP) within ICF Disability Model ................................ .......... 44 3 1 Study flow diagram ................................ ................................ ................................ ............ 46 3 2 t maneuver from start to finish ................................ ...................... 51 3 3 Should Flexibility Test. ................................ ................................ ................................ ...... 52 3 4 Motion camera setup for shooting ................................ ................................ ..................... 56 3 5 Phases and events of the lacrosse shot ................................ ................................ ............... 57 3 6 Retroreflective marker placement on athlete ................................ ................................ ..... 58
9 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Deg ree of Doctor of Philosophy MOTION FACTORS RELATED TO LOW BACK PAIN IN LACROSSE ATHLETES By Joseph G. Wasser August 2019 Chair: Heather K. Vincent Major: Rehabilitation Science Introduction : Low back pain (LBP) and motion alterations can occur in athletes who engage in high speed throwing motions. Therelationship between LBP and shooting motion in lacrosse players is not yet known. Purpose : To determine the effect of chronic LBP and factors associated with pain on lacrosse shooting bio mechanics. Study Design : Controlled laboratory study Methods : Lacrosse players (n=127) were stratified into 2 groups based on back pain symptoms (LBP or no pain). Three dimensional motion capture of overhead throws was used to collect data on knee, pelvis, trunk, and shoulder kinematics aswell as crosse stick (the stick capped with a strung net) and ball speed. Functional measures were collected for shoulder ROM, hi p flexibility and single leg squat performance. Results : Effects on shot kinematics were identified at the pelvis, trunk, and shoulders within the cohort of players who reported LBP. Players with pre existing LBP performed their dominant lacrosse shots w ith slower angular velocities at the pelvi s, trunk, and shoulders (p<.05) Lead knee flexion was significantly larger for dominant lacrosse shots (p<.05), and transverse pelvis and shoulder ROM were significantly decreased (p<.05). Functional outcomes have identified
10 that players with pre existing LBP perform single leg squ ats with greater medial lateral knee ROM (p<.05), maximal hip flexion (p<.05), hip flexion ROM (p<.05), and pelvic drop (p<.05) on their non dominant leg (lead leg during lacrosse shot). Participants who did not participation in other sports, had a 4.6x increase in developing LBP (p<.05). Predictors of LBP onset were identified with higher peak pelvic accelerations (p<.05), and pelvic acceleration at maximal lateral trunk tilt (p<.05). De ficits in dominant shoulder internal rotation provided signficiant contribution to LBP severity (p<.05). Conclusion : Lacrosse players with existing LBP have slower peak pelvic, trunk, and shoulder angular velocities and greater knee flexion during a shot motion than players with no pain. Side asymmetries during a lacrosse shot have not been identified as a factor to infl uence the development of LBP, however significantly higher pelvic acceleration is an identifiable risk factor in players who developed LBP. Lack of multi sport participation is identified as contributory factors to the onset of LBP in lacrosse athletes.
11 C HAPTER 1 INTRODUCTION Low back pain (LBP) is one of the most common musculoskeletal issues in the United States. It is estimated the lifetime prevalence of LBP in the general adult population is 85 90%. (Trainor and Wiesel, 2002) In the athletic population, LBP occurs in approximately 10 15% of young athletes and up to 30% in aging athletes. (Graw and Wiesel, 2008) Evidence suggests that the prevalence o f LBP depends on the sport. Specifically, 27% of wrestlers and football players who train with heavy spine loads report LBP, but 50 86% of gymnasts who engage in high velocity, high spine rotational motion suffer from chronic back pain symptoms. al., 20 00; De Luigi, 2014) A concerning trend is that pain episodes recur in children and adolescents, between 7 and 16 years of age, with overuse related back injuries recurring in 26 33% of cases Recurrent pain may set in motion chronic pain sequelae that young athletes may carry with them i nto adulthood. Up to 38% of younger athletes with LBP have radiographic findings of lumbar spondylolysis, compared to a 3.5 6% occurance in the general population. (Ladenhauf et al., 2013; Papanicolaou et al., 1985; Rossi and Dragoni, 1990) The prevalence rates of spondylolysis among younger athletes (<16 years of age) va ries; lacrosse ranks third among a variety of sports sampled with an estimated 9.4% of lacrosse players who have this diagnosis. (Ladenhauf et al., 2013) Conservative treatment is generally recommended for those who develop spondylolysis, and can involve restriction from play. In some cas es, as much as 30% of playing time could be lost due to spondylolysis (Bahr, 2009; McCarroll et al., 1986) There is a negative impact of LBP on the quality of life (QoL) for children and adults, reflected by lower self reported physical functioning and physical health scores. Girls reported a higher disability and lowe r QoL than boys in the domains of physical and emotional functioning, psychosocial health, physical health
12 summary scores, and pediatric QoL. (Macedo et al., 2015) These results can also be applied to the adult population, wher e back pain may be more important than knee pain in adults older than 50, with respect to QoL. (Kim et al., 2015) Lacrosse is the fastest growing sport at the high school and collegiate level, with more than half of the players competing being 15 years and younger. (Putukian et al., 2014) The complexities of lacrosse include fast paced running, cutting, agility high velocity rotational motions, while stra tegizing, multi tasking and decision making (Vincent and Vincent, 2018) A key movement in this sport is the overhead throw, as it is used for passing, clearing and shooting to score. Lacrosse athletes must perfo rm precise motions under challenging demands, and must catch and throw a ball using a small pocketed crosse. Like other overhead athletes, lacrosse players develop fast ball speeds by generating forces at the start of the shot and transferring that energy along the kinetic chain to ball release. (Millard and Mercer, 2014; Weber et al., 201 4) There are several factors that can affect force development and timing of the mechanics, including the presence of musculoskeletal pain. High forces generated by the shooting motion itself may place excessive mechanical stress on the body and can lea d to the development of musculoskeletal pain/injury. The lumbar spine and associated musculature transfer energy of the throwing motion from the lower to the upper body via rapid rotation, and these anatomical structures are involved with the acceleration and deceleration of the upper body during a shot. (Glazier, 2010; Weber et al., 2014) In a previous project, the lead and senior author studied the relationships of LBP in lacrosse athletes on shooting motion. Significant restrictions in trunk and shoulder motions were evident in high school throu gh collegiate lacrosse players who experience LBP. (Wasser et al., 2016a) Moreover, these restrictions in motion contribute to slower ball
13 speed, which can impact lacrosse performance. Further research is needed to identify prospective risk factors in throwin g motion and develop back health programs in the lacrosse population. Statement of the Problem G rowth in lacrosse is among the fastest of American sports and much of this growth is occurring in the younger demographic. ( NFHS Participation Statistics 2006 2018) Despite the public interest and spread of lacrosse across the country, the science of sport performance the impact on health domains is not yet keeping pace. While many reported lacrosse injuries are acute and potentially unavoidable ( e.g., inadvertent collisions, stick and ball contacts and acute sprains and strains), many injuries are also chronic (e.g., LBP, patellofemoral pain) (Warner et al., 2018) Chronic LBP occur s across the age spectrum of players and can be avoidable if the mechanisms underlying the pain are understood. LBP may contribute to loss of playing time due to sub par performance with the basic throwing and shooting motions and for physical recovery. Con straint of the throwing motion decreases player effectiveness on the field. This is the initial point that could lead to a negative cascade which includes decreased enjoyment of the game, potential to withdraw participation in other physical activity and a decrease in QoL. (Jackson et al., 201 1) This cascade can carry over adolescent/high school level. (McCarroll et al., 1986) Specific Aims Three specific aims and related hypotheses were generated to determine the effect of chronic LBP and factors associated with pain on lacrosse shooting biomechanics. Male and female lacrosse players (10 21 years of age) provide d sport playing histories, lacrosse experience an d numerical pain ratings. Shoulder, hip and hamstring flexibility w ere measured and comprehensive motion analysis of the shot motion of the dominant and non dominant sided w ere
14 be captured. Players were prospectively followed over six months and new back r elated injuries or pain episodes will be documented. Th e specific aims and hypotheses we re as follows: Specific Aim One To determine the effect of pre existing LBP on key kinematics of the lacrosse shot motion in lacrosse athletes. H 01 : It is hypothesized that athletes with pre existing LBP would demonstrate less total excursion from pelvis to shoulder, less angular velocity transfer from pelvis to trunk, greater lateral trunk lean (Wasser et al., 2016a) and greater knee flexion compared to asymptomatic player s at baseline H 02 : It is hypothesized that athletes with pre existing LBP would have less symmetry between the peak angular velocities of the hip and trunk and timing of these velocities between the dominant and non dominant side would be different than those from asymptomatic players at baseline H 03 : It is hypothesized that athletes with pre existing LBP would shoot the ball at higher speeds, have greater crank back of the shoulders over the pelvis, relatively shorter stride length and h interaction between lateral trunk tilt and acceleration of shoulders over trunk) than asymptomatic players at baseline Rationale Existing LBP may cause self constraint of rotational movement and core stabiliz ation to mitigate mechanical stress on the painful spine; therefore the angular excursions of the pelvis, trunk and shoulders w ould be lower and stab ilization with knee flexion would be greater in the presence of LBP than without pain. Asymmetric pelvis an d trunk angular velocities and timing of peak velocities will contribute to asymmetric torsional, axial and compressive stresses at the spine that could be related to pain. Moreover, athletes who engage in excessive axial rotation about the spine and great er Crunch Index values at high velocities would be at greater risk for onset of LBP over time.
15 Specific Aim Two To determine differences in physical function factors associated with lumbar spine health (single leg squat performance, hip and shoulder flexib ility) between lacrosse athletes with LBP and those without. H 01 : It is hypothesized that athletes with pre existing LBP would demonstrate lower flexibility of the hip and shoulder than asymptomatic players at baseline H 02 : It is hypothesized that athlete s with pre existing LBP would demonstrate less shoulder external rotation than asymptomatic players at baseline H 03 : It is hypothesized that athletes who exhibit excessive lateral pelvic drop and hip adductio n during a single leg squat would develop LBP as they continue to play lacrosse. Rationale Low flexibility about the hip may restrict stride length and pelvis rotation in the transverse plane. Moreover, relatively low shoulder external rotation restricts the degree of crank back during the shot prep aration. Low flexibility infers that the power for the shot must be generated by other sites along the kinematic chain. The single leg squat test can also be used to determine the movement control provided by the gluteal muscle group, and the inability to control single legged motions can contribute to pelvic drop and asymmetric forces acting at the low back. These asymmetric forces if not corrected may lead to the onset of LBP. Specific Aim Three To identi fy the contribution of player factors (anthropometrics, field position, lacrosse playing volume, sport participation, shooting motion features) to the onset of LBP in lacrosse athletes. H 01 : It is hypothesized that players whos e positions shoot with the high est volumes during play ( e.g., midfi eld or attack) will have a higher odds risk of reporting LBP than players who shoot less (defense, long stick midfield or goalie). H 02 : It is hypothesized that players who are currently participating in sports additional to lacrosse throughout the year wil l have a lower prevalence of LBP compared to players who participate only in lacrosse. H 03 : It is hypothesized
16 that key features of shooting motion (body segment orientation, peak angular velocities, timing of peak angular velocities) and player characteri stics may predict the severity of LBP. Rationale Chronic back pain symptoms may develop over time due to repetitive mechanical stresses at the spine. (Wasser et al., 2017) Midfielders and attack are most often the shooting positions on the field. It is likely that the higher volume of throwing exposure may be related to development of LBP. Particip ation in other sports in addition to lacrosse may confer protective benefits against overuse injury through comprehensive development of the musculoskeletal system. Finally, specific motion factors that place high mechanical stress on the spine, coupled w ith player characteristics such as player position, age, sex, body size and flexibility about the hip or shoulder may contribute to the onset of LBP over time. While each factor alone may load the lumbar spine, it is likely that a clustering of features be tter predicts the onset of LBP than each factor alone.
17 CHAPTER 2 LITERATURE REVIEW In the United States, lacrosse continues to increase in popularity, with a 225% increase in participation from 2001 to 2016. ( US Lacrosse Participation Report n.d.) Among youth players (14 and under), there has been a 106% increase in participation over the past 10 years. ( US Lacrosse 2016 Participation Suvey 2016) This growth in the younger age bracket is the highest among all reported l evels in the spor t (youth, high school, college, and professional). High school lacrosse participation among boys and girls has increased of 17.5% over the last five years, to reach a total of 210,217 players for the 2017 2018 school year, ( 2017 2018 High School Athletics Participation Survey 2018) Lacrosse gained the greatest percentage of there has been an 11. 4% increase in lacrosse participation over the past five years. ( NFHS Participation Statistics 2006) Though few collegiate lacrosse players achieve professional status, there was a 54 .2 % spike in professional lacrosse growth from 2015 to 2016. ( US Lacrosse 2016 Participation Suvey 2016) This expansion may be explained by an increasing demand of lacrosse fandom and women to continue to particip ate in lacrosse like their male counterparts who have two professional leagues in North America (Major League Lacrosse (est. 2001) and the National Lacrosse League (est. 1987)). ( US Lacrosse Participation Report n.d.) For those who do not reach professional status, ther e is club lacrosse, which is the most ac tive level of lacrosse following college. ( US Lacrosse 2016 Participation Suvey 2016) These post collegiate clubs include several leagues for both men and women and host numerous annual tournaments for all
18 rica, and 46 ( US Lacrosse: Post College n.d.) The Lacrosse Shot Irrespective of age or skill level, t he re are basic motions of the sport include running, shooting and throwing, cutting and pivoting, and jump landings. The biomechanics of running, cutting and pivoting and jump landings as stand alone actions are well researched (Jones et al., 2014; Kuni et al., 2014; Nicola and Jewison, 2012) Our laboratory has recently advanced the understanding of the mechanics of the lac rosse shot. (Vincent HK, Chen C, Zdziarski LA, Montes J, & V incent KR, 2015; Wasser et al., 2016a) This motion will be the focus of the research project and the relationship with LBP related motion characteristics among players of different skill levels and age. One of the first motions learned in the sport is t he standard overhead shot. The motion bears similarities to other sport actions, such as throwing a ball, swinging a bat, and swinging a golf club. Precision and mechanics of a lacrosse shot depends on the appropriate muscle activation patterns, adequate r otation of the shoulders over the pelvis, and sequencing of peak body segment rotational velocity and positioning toward the goal. (Atwater, 1979; Fleisig et al., 1999; Glazier, 2010; Kageyama et al., 2014; Weber et al., 2014) Among throwing sports a threat on the field if they are able to successfully execute a shot or throw equally well with both arms. Bilateral shooting ability increases unpredictability against the defense and im proves chances of scoring. Offensive and defensive players perform shooting or throwing motions in varying amounts, depending on practice or competition and sta kes involved in the game. Irrespective of player position, those attempting to score run toward the goal while changing directions, cutting (dodging) or spinning and may need to shoot from either their dominant or
19 non dominant side. Thus, a goal for developing players is to practice shooting from all directions from both the right and left arms. Thus Symmetry Index, which is a calculation comparison of the performance on the dominant and non dominant sides (where 100 is the highest possible score and 0=no symmetry at all). S imilar movement patterns and timing sequences exist for each shot regardless of which side a player shoots From initial lead foot contact to ball release, lacrosse players transfer energy during sequential rotation of body segments or joints from the lower body to the upper body fo r ball launch. Lacrosse players develop fast ball speeds by generating initial forces at the start of the shot and transferring that energy along the kinetic chain from the lower body to ball release, similar to other overhead athletes like baseball pitch ers. (Millard and Mercer, 2014; Weber et al., 2014) These patterns occur during sho ts from both dominant and non dominant sides, but the angular velocities and segment or joint excursions are often less from the non dominant side. (Vincent et al., 2015) To standardize shooting motion comparisons between sides and between players of varying skill and age, we and others (John A. Mercer and Jason H. Nielson, 2 012; Wasser et al., 2015) have defined the key phases and events that comprise a shot, details of which are shown in Figure 2 1 ( following page). The three phases include the crank back, acceleration and follow through. The crank back is the initial pr eparatory movement that reflects the wind up that precedes the acceleration of the crosse. Immediately after crank back, there is a drive forward with the lead foot. A key event of the lead foot plant initiates the acceleration phase. The acceleration pha se is comprised of increasing angular veloci ties of the body segments (pelvis trunk, shoulders) and crosse to prepare for ball release. The ball release is the key event that ends the acceleration phase. The final phase of the lacrosse shot is follow thro ugh. This phase
20 involves the trunk to pelvis crossover motion and a deceleration of the body segment rotations. The maximal shoulder to pelvis crossover is the final event of the lacrosse shot. The starting point of the motion is the lead foot plant event (at 0%). The point of ball release is defined the end of the shot (at 100%). Follow through occurs after the ball release (>100% of the throw cycle). (D ick, 2013) Specific kinematic events are therefore expressed as a percent of the shot cycle. All descriptions for joint angulations and events are previously published (Vincent 2015). Figure 2 1. Phases and events of the lacrosse shot. Photo courtesy of author. Our laboratory compared shooting mechanics among high school, collegiate and professional players (Vincent et al., 2015) Table 2 1 (page s 22 23 ) provides the data from this cross sectional comparative study. Table 2 1 shows that non dominant side shots generated slower ball speeds, even among the professional players Non dominant shots of professional
21 players were, on average, 13% faster than the dominant shots of high school and collegiate players. Fast angular velocities contribute to fast ball speed s, as has been shown in other sports like baseball. (Kageyama et al., 2015) Professionals generated the highest ball speeds with a combination of higher angular velocities and earlier peaks of these velocities at the pelvis, trunk, shoulders and crosse compared to younger players. Unlik e collegiate and high school players, professional players were able to symmetrically produce high angular velocities at the pelvis, trunk, shoulders and crosse on both their dominant and non dominate sides. Generally, we have observed that older players w ith more playing experience tend to have higher Symmetry Index values compared to less experienced younger players. The timing at which these peak angular velocities occur are achieved is critical for performance and relationship to musculoskeletal injury. In other sport motions such as the golf swing or baseball pitch, the timing of peak angular velocities (from the start of the motion to the ball contact or release) should occur in sequence from the pelvis, trunk and shoulder. (Cole and Grimshaw, 2016; Holt and Oliver, 2016) In cases where the timing sequence is not as expected, the rotational forces can stress areas of the kinematic chain at which this rotation and energy transfer from lower to upper body occurs such as the lumbar spine. Moreover, other segments of the kinemati c chain must compensate to achieve the action. LBP occurs with baseball and golf, where timing of peak velocities of pelvis, trunk and shoulder is relatively early, late or out of sequence. (Mun et al., 2015) This summation of speeds principle is of particular importance in lacrosse, where poor sequence timing can produce excessive forces at sites along the kinematic chain that are not accustomed to, or prepared for, these stresses.
22 Table 2 1. Lacro s se Sho o ting Kinematics Among High School, Colle g iate and Professional Players Crank Back ( ) Pelvis Trunk Shoulders Crosse (/s) Follow Through (+) Ball Speed (km/hr) High School Dominant Side 30.6 9.7 Peak Angular Velocity (/s) 582 110 698 152 923 197 1540 365 57.3 15.7 112 16 Temporal Pattern (% of Shot Cycle) 62 11 74 11 83 9 Non Dominant Side 21.2 10.1 Peak Angular Velocity (/s) 483 157 578 179 796 191 1347 334 53.6 18.9 95 16 Temporal Pattern (% of Shot Cycle) 67 27 79 18 46 12 Collegiate Dominant Side 32.6 5.6 Peak Angular Velocity (/s) 594 158 700 139 909 163 1677 360 49.8 13.6 112 15 Temporal Pattern (% of Shot Cycle) 45 15 63 7 70 10
23 Table 2 1. Continued Crank Back ( ) Pelvis Trunk Shoulders Crosse (/s) Follow Through (+) Ball Speed (km/hr) Collegiate Non Dominant Side 27.3 12.8 Peak Angular Velocity (/s) 492 225 563 202 759 211 1410 457 51.2 15.4 100 16 Temporal Pattern (% of Shot Cycle) 58 18 75 14 70 11 Professional Dominant Side 39.2 8.2 Peak Angular Velocity (/s) 562 101 727 107 995 118 2046 244 49.8 13.6 138 7 Temporal Pattern (% of Shot Cycle) 43 17 58 17 79 12 Non Dominant Side 24.9 11.7 Peak Angular Velocity (/s) 561 115 759 211 951 79 1789 274 57.2 15.5 127 18 Temporal Pattern (% of Shot Cycle) 46 12 70 11 94 13
24 Low Back Pain and Lacrosse High school lacrosse surveillance data show that back injuries occur at a rate of 60 to 80 cases per 1000 athletic exposures. (Hinton et al., 2005) These statistics incorporate injuries causes by both acute contact and noncontact mechanisms. There are noncontact mechanisms of injury or chronic pain that are the most relevant to our researc and men s lacrosse, compiled estimates indicate that 18.1% 29.6% are noncontact injuries. (Kerr et al., 2017b) A one year epidemiological study of lacrosse injuries in youth reported that 3.8% and 14.1% of injuries in girls and boys, respectively, involved the trunk (Kerr et al., 2018b) A similar study in high school lacrosse found that 4.0% and 7.6% of all reported injuries ov er a 3 year period occurred at the back/trunk (Hinton et al., 2005) Among adult women, 6.1% to 12.0% of in j uries occurred at the trunk/back during games and practices, respectively, over a 16 year surveillance period (Dick et al., 2007) A challenge of understanding the relationship of LBP and shooting biomechanics is determining whether p ain influences mechanics or whether mechanics influence pain onset and severity. First, musculoskeletal or joint pain can affect force development or sequence timing in overhead throwing activity. (Laird et al., 2014; Wasser et al., 2016a) Second, significant rotational forces generated by high velocity throwing moti on may increase mechanical st resses on the body at specific sites where the transfer of energy changes from linear to rotational, such as the lumbar spine. (Ferdinands et al., 2009; Schilling et al., 2013) In adolescent male tennis players, where injuries to the low back account for the greate st loss of playing time, the lumbar spine undergoes significant loading during a tennis serve. (Campbell et al., 2014, 2013) For a fast throwing motion, the athlete prepares by cocking the throwing shoulder posteriorly (activating deltoids, teres major, latissimus dorsi) and shooting side abdominal and trunk muscles (rectus & transversus abdominis, internal & external obliques, erector spinae,
25 serratus anterior) engage. The lead foot then plants in front of the body and lower body muscles activate to provide a stable base of support (gluteal muscles, quadriceps, hamstrings, gastrocnemius, and tibalis anterior). (Millard, n.d.) During the acceleration phase, contralateral trunk and core muscles are activated to rotate the shoulders horizontally and the leg muscles of the driving leg (largely biceps femoris and gluteal muscles) help to move the athlete forward in a linear fashion These low back structures are involved with the acceleration and deceleration of the upper body during a shot. (Glazier, 2010; Weber et al., 2014) Kinematic Characteristics of Low Back Pain in Lacrosse Specific motion features may contribute to LBP onset and severity in lacrosse. From the foot plant to the ball release, the following features are potential culprits for study: forward and lateral trunk lean, stride length, knee flexion, shoulder external rotation, pelvis to shoulder cross over, and angular velocity and timing asymmetries between dominant and non dominant limbs. We acknowledge that these features are not necessarily mutually exclusive; in fact, there may be a yet undetermined interaction between features that is more representative of the unique mechanical demands of the shot. In t he methods section, we will propose a new measure compressive and shearing loads of the golf swing with lateral flexion and axial rotation). (Glazier, 2010) To expand our understanding of the relationship between LBP and lacrosse motions, our labo ratory investigated of the effect of LBP on lacrosse shooting in a small cross sectional study (n=24) involving players from high school through collegiate. (Wasser 2016a). We detected significant differences in peak angular velocities of the trunk between players with (515253 /s) and without LBP (677198 /s). Moreover, a significant difference between the incremental change in angular velocity from pelvis to trunk was found for players who reported LBP (8783
26 /s) compared to those without pain (15177 /s). S ignificantly less total range of motion () of the pelvis and shoulder (83.6 24.5 vs. 75.9 24.5), and less knee flexion at ball release (160.6 8.4 vs. 151.1 13.0) were detected between players with and without mild to moderate LBP respecti vely (Wasser et al., 2016a) Ball speed was 90.6 7.2 km/h and 103.3 24.7 km/hr in the groups with and without LBP respectively. Those with chronic mild to moderate pain shot the lacrosse ball with greater knee flexion and slower peak trunk angular veloci ties. There was also less incremental increase in angular velocities from pelvis to trunk between player s with and without LBP LBP severity impacted several kinematic variables including trunk and shoulder peak angular velocities and knee flexion at ball release. (Wasser et al., 2016b) Another striking finding was that greater LBP severity was related to greater knee flexion (B= 2.9 (95%CI: 5.1 to 0.8), p=0.01), decreased peak angular velocity of the shoulders (B= 41.4 (95%CI: 81.4 to 1.4), p=0.04), and peak angular velocity of the trunk (B= 34.5 (95%CI: 66.9 to 1.9), p=0.03). These f indings could suggest that flexing more at the knee can provide additional stabilization support spine rotation in players with LBP. Limited evidence from studie s on lacrosse and other sports, such as softball and tennis, show that the co activation of low er extremity muscle groups (biceps femoris, rectus femoris, gastrocnemius) and core (rectus abdominis, external obliques and lumbar erector spinae) may be essential for stabilization of the lower body as the upper body rotates over the pelvis. (Chow et al., 2003; Millard and Mercer, 2014; Oliver et al., 2011) The greater knee flexion during a lacrosse shot in players with LBP may improve their base of support and facilitate the stabilization effect at the core. The prese nce of pain may change normal muscle activation of the muscles of the trunk responsible for the control of spine rotation and rotational velocity. During axial rotation, LBP activation of the mulitifidus and longissimus muscles allows these muscles to act as stabilizers.
27 (Kuriyama and Ito, 2005) LBP may also increase pelvis stiffness and thereby negatively affect the transfer of energy and negatively impact pelvis to trunk angular rotational velocities. (Sung, 2013) In relation to lacrosse shooting, the kinematic variables that would represent lumbar and pelvic position would include anterior pelvic tilt and anterior tilt ex cursion during the shot. The relative position of the trunk to the pelvis could be represented by trunk flexion The peak velocities and timing of the peak velocities of the pelvis and trunk anterior tilt would be informative of the energy transfer sequenc e from the lower to the upper body for the lacrosse shot. It is also possible that maximal lateral trunk lean coupled with maximal pelvic tilt during repetitive shooting interact to cause LBP. Two possible interpretations to our initial findings exist: 1) players may self restrict excursion of high velocity rotational motions that may exacerbate pain, or 2) the motion itself over time caused the back pain to develop. Shooting motions require effective and efficient timing and coordination of angular veloci ties of the proximal to distal segments to optimize ball speed. Disparities in the timing or velocities can disrupt overall coordination and reduce performance. (Urbin et al., 2013) Wh ile we did not detect differences in the timing of peak angular velocities between players with and without LBP, maximal angular velocities of the trunk were significantly lower in the participants with LBP. Normal kinematic sequence and coordination were thus altered during the lacrosse shot, and the forces that were produced in the throwing motion may be transferred to distal body segments which may lead to injury elsewhere. (Whiteley, 2007) Rest rictions in pelvis or torso transverse rotation may require compensatory engagement of distal musculature to generate power for the shot. This shift increases the mechanical stress to distal segments, such as the upper arm. This paper was the first step to identifying the relationship between LBP and shooting mechanics in lacrosse players.
28 Motion Similarities with Other Sports Our evidence linking LBP and lacrosse mechanics is similar to other sports that involve throwing a ball or using a lever arm to thro w or hit a ball at high velocities. Tennis is characterized by serving motion, return serves or groundstrokes. Baseball involves pitching a ball with accuracy and speed to a catcher, or throwing a ball from the field to a base. Golf involves the swing moti on that is preparatory for striking a golf ball over a long distance during a drive. The findings of these papers below have helped to shape the meth ods and variables selected for this dissertation. Tennis Investigation of the biomechanics of tennis play ers detected small motion differences between players with and without LBP. In one study compared serving kinematics and found that players with LBP demonstrated greater lateral pelvic tilt, lower lumbar and pelvic ROM and lower anterior pelvic tilt compar ed with healthy players. Time to peak knee extension was earlier in players with LBP, but peak knee and hip flexion angles did not differ. (Campbell et al., 2014) In contrast, Campbell et al. (2015; N=19) found that average values of key motion parameters in forehand or backhand groundstroke did not di ffer in young players with or without pain (N=12). (Ca mpbell et al., 2015) Among tennis players who had recently experienced LBP, core and extensor muscle activation during a serve were significantly lower than those in players with no LBP. Moreover, abdominal endurance and co activation of core and extens or muscles during a tennis serve were reduced in players who experienced a LBP episode within the last week (Correia et al., 2016) ; t his is a c linically relevant finding. A deficit in core stabilization is predictor of potential LBP onset with repeated pelvis to trunk rotation. (Chow et al., 2003; Millard and Mercer, 2014; Oliver et al., 2011) A high level of co re stabilization is required to control high speed rotational motions during sport.
29 Baseball. T he prevalence of LBP among active baseball players ranges between 3% and 15%. (Dick et al., 2007b) The execution of a high volume of pitches may be related to the onset of LBP. Pitching motion is complex and requires appropriate activation of the core musculature to produce a well timed motion with forces minimized at the extremities. The spine, core and back musculature are involved with acceleration and deceleration of rotational motions. In a recent review, we proposed potential mechanisms linking baseball play to LBP, including aberrant motion of pitching, fielding, and swinging, improper timing, high lumbar stress due to mechanical loading and deficits to lumbopelvic stability (Wasser et al., 2017) Similar kinematics exist between a baseball pitch and a lacrosse shot. (Wasser et al., 2015) In baseball, stride length and shoulder external rotation may impact the forces acting at the spine. An ideal stride length allows for proper positioning and timing of whole body kinematic s during the pitching motion, allowing for critically efficient transfer of energy from the legs to the upper body and to the ball. (Calabrese, 2013a; Escamilla et al., 2007; Wight et al., 2004) In a study investigating stride length on elbow torque in youth pitchers, there was a significant association with peak elbow va rus torque. (Tocci et al., 2017) Though this study investigated kinematics and peak elbow torques for bot h fastba ll and change up pitches, the authors found that longer stride lengths in both conditions had significant associations with higher peak elbow It should be noted that lower skill level has been associated with the decreased utilization of the pelvis and legs in pitching mechanics, therefore compensatory motions at the arm are developed, which could also place higher loads on the elbow. Dun et al. found that aging professional pitc h ers exhibited a shorter stride length, with equivalent ball velocities. (Dun et al., 2007) M anipulati on of stride length by 25% can challenge baseball throwing mechanics and influence low body effort. (Ramsey and
30 Crotin, 2016) Pitchers wit h shorter stride lengths use greater trunk transverse momentum following lead leg contact, while longer strides generates greater forward momentum, causing a moderate effect of transverse momentum following lead leg contact. (Ramsey and Crotin, 2016) This increase in stride length is thought to reduce orthopedic risk to the throwing arm, however this may also increase strain to the low back. Werner et al. reported conflicting evidence as stride length had no association with elbow torque in baseball pitchers (Werner et al., 2002 ) These results were supported by Crotin et al, who reported that a difference of 24% body height difference in stride length results in a 7% timing difference in the instant of lead foot contact. (Crotin et al., 2015) Even with height difference s, the timing of maximal external shoulder rotation or acceleration phase is not affected (Crotin et al., 2015) Thes e results may not fully be applicable to the lacrosse population due to the unique inclusion of a fixed arm lev er (crosse). Kinematic deficits at the hip and pelvis due to long stride lengths in lacrosse players may be compensate d at the spine but the sequence of timing for throwing kinematics will remain. (Crotin et al., 2015) Hip and pelvic motion deficits in baseball pitchers can also exist in lacrosse shooting and may be related to the onset of LBP. (Holt and Olive r, 2016) Different strategies however, are used between these two sports to achieve the ball release; often, lacrosse shots occur while running or approaching the goal, whereas baseball pitchers start from a static standing position. For both sports, p eak rotational velocities for the pelvis occur early (from 40 55% of the movement cycle), followed by the trunk (60 80% of the motion) and finally the shoulder (from 90 100% of the motion) and lastly the arm or crosse. (Vincent and Vincent, 2018) Unlike baseball, lacrosse players use a crosse as the main lever arm to launch the ball. Crosses come in different lengths and weights depending on the position. It is imperative then, that the rotation of
31 the added weigh t of the crosse forward during acceleration and deceleration in follow through be appropriately controlled and sequenced to minimize added stress on the lumbar spine. Golf. Epidemiological studies show ~25% of golf all injuries involve the low back (Batt, 1992; Lindsay and Vandervoort, 2014; McHard y et al., 2006) with incidence rates ranging from 18.2% to 54% (McHardy et al., 2007; Sugaya et al., 1999) Similar to both lacrosse and tennis, angula r velocities from the pelvis, trunk, shoulder and lever arm (golf club) sequentially increase during a golf swing. The golf swing is complex, as it involves compressive, shearing and torsional loads on the spine. The lateral flexion coupled with axial spin e rotation are believed to be injury risks. (Cole and Grimshaw, 2014) Similar to lacrosse, golfers approach their shot (downswing) with powerful rotations from an already rotated backswing (shoulder to pelvis crossover). The spinal forces and torsion experience d by golfers are very high; compressive loads reach 7,584 N), shear loading reaches 596 N lateral bending is significant and rotational loads on the L3 L4 segments are high (Hosea et al ., 1990; Lindsay and Vandervoort, 2014) The compressive forces in golfers are estimated to reach eight times body weight, with ca daver studies indicating disc prolapse occurring at ~5,500 N of compression. (Adams and Hutton, 1982) With respect to the structure and anatomy of the spine the vertebral annulus and facet joints limit lumbar spine rotation posteriorly but allow for significant flexion and extension with moderate lateral bending. (Gluck et al., 2008) The lumbar spine has a very small rotational ROM. Loading the lumbar spine with a high amount of torque and an accompanied lateral f LBP, tissue damage. (Glazier, 2010) W ith repetitive loading of the lumbar spine in golf swings, the risks to LBP and back injury increase. Studies of golf swing
32 motion show that players with symptomatic LBP use more lateral side bending on the backswing, and have trunk flexion velocities dur ing the downswing that are two times slower than players without pain. (Lindsay and Horton, 2002) M oreover, the prescence of LBP appears to limit rotational trunk ROM during a swing in golfers experiencing LBP (Lindsay and Horton, 2002) During their cross sectional study, it was found that during neutral stance, the golfers with pain had less trunk rotation during the swing than players without, inferring that the relative spine rotation was elevated during the backswing. In contrast, Tsai et al. reported minimal differences in trunk kinematics between golfers with and without LBP (Tsai et al., 2010) Excessive transverse spine rotation is a risk factor contributing to LBP. (Gluck et al., 2008) Thus, decreasing the rotation of a players back swing and the relative amount of spinal rotation (or torsion) successfully eliminates LBP in professional golfers (Bulbulian et al., 2001; Grimshaw and Burden, 2000) From the performance perspective there does not appear to be a negative effect on swing performance with a 20% restriction o f a back swing. (Bulbulian et al., 2001) These collective papers related to LBP in golfers have helped to develop our measures in lacrosse shooting and may provide insight on injury prevention techniques. Potential Functional Factors As sociated with Low Back Pain in Lacrosse Athletes Several physical function characteristics may modify stresses acting at the lumbar spine. These include poor hip and core stability poor hip and trunk flexibility, and knee instability. Laird et al., publis hed a meta analysis of the evidence of lumbopelvic kinematics in individuals with and without LBP. (Laird et al., 2014) There were 35 studies included in this meta analysis. Key measures were lordosis, range of motion ( ROM ) relative hip and lumbar contributions to trunk flexion extension, pelvic angle position ROM, and kinematic s of lumbar movement and proprioception.
33 Relatively poor hip stability The task of completing the single leg squat assesses a fundamental athletic requirement to control the body over a single planted leg. This task can reveal deficits in hip and core stability as well as trunk control. (Agresta et al., 2017; Claiborne et al., 2006; Willson et al., 2006; Zeller et al., 2003) The inability to control the body through this motion has been associated with other common athletic injuries, such as patellofemoral pain syndrome and ACL injury. (Dierks et al., 2008; Souza and Powers, 2009) Muscle activation during a single leg squat involves activation of all four quadriceps muscles, rectus femoris, gluteal muscles, all three hamstring muscles (semitendinosus, semimembranosus, and biceps femoris), erector spinae, external obliques gastrocnemius, and soleus. (Eliassen et al., 2018) Abnormalities in this test include excessive kne e valgus and hip adduction (related to poor hip stability ), pelvic drop, and lateral trunk lean. These issues are risk factors for LBP and chronic back injury. (Haddas et al., 2016; McGregor and Hukins, 2009) T runk lean and asymmetries on functional screening tests such as the single leg squat should be addressed to reassure lumbop elvic strength and stability in order to redu ce the forces loading the spine when participating in athletics. It should not be confused with sport specific trunk lean, as it provides a competitive advantage in overhead throwing athletes though spinal loading forces are increased on the contralateral side. (Oyama et al., 2013) Among active adolescents, the single leg squat performance appears different among individuals of differing maturity (prepubescent vs pub escent vs post pubescent). (Agresta et al., 2017) Single leg squat performance significantly improves with advancing age. This improvement is likely due to sensorimotor improvements as been observed between male and female participants. (Graci et al., 2012) Females engage in less trunk flexion and more trunk and pelvis rotation toward the stable limb side when compared to
34 their male counterparts. Moreover, female subjects had greater hip adduction, knee abduction and knee valgus angle than males (Mendiguchia et al., 2011; Zeller et al., 2003) For lacrosse players, the inability to maintain a strong lower body base during a dynamic repetitive ac tivity like a shot to the goal may increase the risk of LBP in these players. Shoulder flexibility and shoulder to pelvis r otation. There is strong, but untested, potential for shoulder external rotation deficits to impact lacrosse shooting. Chalmers et al. provided a clinical review of pitching mechanics and pitching injuries. G lenohumeral internal rotational deficit and relatively low tot al rotational range of motion about the shoulder are risk factors for injury. (Chalmers et al., 2017) Less rotation means less potential energy is being put into the throw at the shoulder. Energy from elsewhere, including rotation about the spine, may be used to offset shoulder inflexibility. Oyama et al. found that pitchers who had improper timing of trunk rotation in the throwing sequence had greater maximal shoulder external rotation and proximal shoulder forces. (Oyama et al., 2014) In lacrosse, there may be a relationship between low shoulder flexibility and suboptimal sequencing of trunk rotati on (especially in players with less skill) with long er stride lengths, greater lateral trunk lean and fast er rotation s about the spine to produce fast ball speed during a shot. Excessive torques could develop in the lumbar spine as a result. I t can be theo rized that due to the fixed arm of a crosse, the forces and compensation strategies avoid the shoulder and impact the low back or trunk. An important poi nt to understanding LBP in high speed rotational sport is to examine shoulder pelvic integration. Par k et al. investigated the maximal rotational angles of the shoulder relative to the pelvis between age matched subjects with and without recurrent LBP during trunk twisting activity. (Park et al., 2012) Though the shoulder girdle rotation excursio n was not different between the two groups, pelvic girdle rotation was lower in individuals with LBP. (Park
35 et al., 2012) Sung (2014) compared shoulder and pelvis kinematics in participants with and without LBP and identified d eficits in pelvis transverse range of motion and pelvic angular velocity in people with LBP (Sung, 2014) W e have found restrictions of angular velocity transfer from the pelvis to the trunk, and reductions in pelvis and shoulder total excursion in the transverse plane in lacrosse players with LBP compared to players with no pain. (Wasser et al., 2016b) For the lacrosse athlete, high shoulder external rotation flexibility could increase potential energy that becomes kinetic energy during the acceleration phase of the shot. Low shoulder external rotation flexibility indicates that the potential energy must be generated by other means, including increasing trunk to pelvis rotationa l velocity during crank back or by faster elbow extension before ball release, or both. This may increase mechanical stress at the lumbar spine. Figure 2 2 provides an overview of key physical factors that may contribute to LBP in lacrosse athletes. Figure 2 2. Potential physical pathways to low back pain with lacro s se sho o ting A final point, LBP is associated with impairment in kinesthetic sense of the spine. (Koumantakis et al., 2002; La Touche et al., 2018) For example, in a study by McDowell et al.,
36 proprioception and compensatory trunk and hip motions following slip perturbation were compared between individuals with and without LBP. (McDowell et al., 2018) While reaction times were not different between the two groups, the control group flexed more at the trunk and there was a negativ e correlation between reaction time and trunk flexion among individuals with LBP. Moreover, Taimela et al. found that LBP impairs the ability to detect change in lumbar position. This finding has implications for player safety in lacrosse. A delayed kinesthetic response at the spine is not sufficient to protect against sudden and unexpected rotational loading, as occurs during running and shooting. Failure to qu ickly respond to changes in lumbar spine position may subject the spinal structures to unanticipated motions and movements where forces could not be controlled or stabilized with proper muscle activation. Sport Experience and Low Back Pain in Lacrosse Spo rt participation is being established as a modifier of chronic injury risk in overhead sport. (Guddal et al., 2017; Post et al., 2017) Sport specific experience in lacrosse in young and experienced players and participation in other sports is not w ell described. Anecdotally, a typical high school player in this Florida region engages in seasonal play, with 3 6 days of practice a week, for an estimated two hours per practice or game. Youth players, depending on the school, may engage in middle school level play, with 2 5 practices per week for practice durations of 1 2 hours per practice or game. Club teams can play all year, with varying practice volume and competitive play. In an epidemiological study by Hinton et al., the frequency of back/trunk in juries in high school boys and girls lacrosse players are reported to occur 5.0 7.6% and 2.8 4.0%, respectively. Back injuries were reported to occur due to indirect force (33% in girls and 44% in boys) and were musculotendinous strains by nature. This c aused boys and girls to miss 120 days and 39 days of lacrosse participation, respectively. (Hinton et al., 2005) It is possible
37 that players who specialize in lacrosse, play at high volumes throughout the year and though they do not play other sports can still develop overuse injury in the low back. In a 16 year collegiate epidemiological study, Di ck et al. reported all injuries and lacrosse players. (Dick et al., 2007) Division I lacrosse athletes play ed two more regulation games per year than Division II and II I Division I lacrosse also participates i n five more practice sessions compared to Division II, and 12 more practice sessions th an Division III. During this 16 year time period, trunk/back injuries comprised 6.1 % and 12% of all injuries with 2.5% of all injuries as low back strains. (Dick et al., 2007; Kerr et al. 2018a) These rates were much higher compared to high school lacrosse players. Though the physicality of lacrosse play differs between sexe s due to different game rules and regulations there are a variety of proposed mechanisms for chronic, atraumati c LBP. These mechanisms are predominantly overuse and aberrant mechanics. Over 60% of injuries during lacrosse occur during the second half of the season indicating that many develop over time and with repetition of motions (Harwood, n.d.) One study determined the activity profile of high leve l lacrosse players in Australia and calculated player workloads (PL; c alculated as the square root of the sum of the squared instantaneous rate of change in acceleration in the anterior posterior, mediolateral, and vertical vectors using GPS and accelerometers ) PL were determined in midfield, attack, and defense. Though midfielders had the shortest amount of playing time per match (36. 2 13. 2 min), they had the largest relative PL (9.91.5 PL/min) compared to attack (8.22.1 PL/min) and defense (7.62.7 PL/min). (Polley et al., 2015) This is important as there are greater overall physical demands for midfielders (distance covered across the field, playing both off ensive and defe nsive roles shooting passing and clearing) than other positions These repetitive demands over a season or over multiple teams may accumulate overload and
38 contribute to chronic injuries. A major limitation with determining overuse injury mechanisms is an inadequate level of surveillance to address the evidence gap. A ccording to one study, only 62.4% of overuse injuries were reported to surveillance programs. (Kerr et al., 2017a) Additionally, most epidemiological studies report injuries relative to athletic exposure (e.g., a traditional reporting of injuries per 1000 athletic exposures) ; h owever this style of reporting is insufficient to capture chronicity of an injury that may be present over multiple exposures but is not likely to keep a player out from participation altogether. Currently, early sport specialization has been progressi vely increasing in youth athletes. (Jayanthi et al., 2013) Early specialization is defined as the focus on one sport, usually at the exclusion of any others an d often year round. (Brenne r and Council on Sports medicine and Fitness, 2016) Though the concept is relatively new, solid evidence has shown that early sport specialization incrases the risk for higher injury rates compared to variation in sport participation (Jayanthi et al., 2013) E arl y sport specialization increases risk of overuse injuries (OR 1.27 4.0; p< 0.05 ) (Fabricant et al., 2016) but lowers the risk for acute injuries (Pasu lka et al., 2017) and the injury rates vary by age, sex and sport (Brenner and Council on Sports medicine and Fitness, 2016) Participating in multiple sports introduces cross training and differing physical cognitive, affective, and psycho social environments. (Ct et al., 2009; Pasulka et al., 2017) US Lacrosse recognizes that early specialization leads to overuse injuries. The organization encourages participation in multiple sports and discourages specializing too early before puberty, preferably until 15 16 years of age based on research from The American Academy of Pediatrics (AAP). n is Too Soon to While there is likely a need to have some degree of sport specialization to attain high level skill, research indicates that delaying sport specialization until late adolescence
39 may optimize success while minimizing risk for injury. (Jayanthi et al., 2013; Moesch et al., 2011 ) Researchers are currently identifying risks of specialization for specific sports; unfortunately, lacrosse has yet to be investigated. It can be surmised that b enefits of participating in different sports across different seaons may help improve neuromotor coordination for the complexities of lacrosse motions on the field, optimize motor patterns for both non dominiant and dominant sides and strengthen muscles all over the body. The downstrteam effect could be improved shooting motion and buttressing of the spine. In addition to specialization, multiple factors such as cumulative training volume, intensity, and frequency all increase risk of injury. (Colby et al., 2017; Rose et al., 2008) For example, a dolescent girls (<17 years of age) wh o participated in greater than 16 hours of sport/activity a week had 1.88 greater odds of having a history of stress fracture than those who participated in <4 hours. Furthermore, for every hour of high impact activity per week, there was a significant in crease in odds of stress fractures in adolescent girls (<17 years of age) (Loud et al., 2005) Among overhead athletes, increased volume has bee n correlated to increased injury and pain. (Black et al., 2016; Lazu et al., 2019; Zaremski et al., 2017) Though an increase playing volume >2hrs/day fo r tennis players (Abrams et al., 2012) and higher throwing volumes in baseball pitchers have been correlated to increase elbow and shoulder pain, (Lazu et al., 2019) factors such as intensity and improper workload monitoring and reporting m ay have greater impact on the development of musculoskeletal pain. (Black et al., 2016) While research into certain sports have shown specific advers impact on physical health (delayed maturation, height, menarche onset) the evid ence in lacrosse is not yet available. This is a significant gap in the literature, as the threshold at which oversue injuries occur among lacrosse players at various skill levels is not yet known.
40 Working Model of Low Back Pain in Lacrosse Players The development of LBP in the general population is due to several risk factors and the relative impact of each of these factors may vary on an individual basis. (Ganesan et al., 2017) Among lacrosse athletes, there are several additional sport related factors that could contribute to LBP onset (Figure 2 3 ). First, players are subjected to unique mec hanical demands including repetitive high torsional, compressive and axial loading at the spine and asymmetrical high speed rotational movement, especially with shooting or throwing. Shooting requires high angular velocities, appropriate timing of peak ang ular velocities of body segments during a shot and appropriate body positioning relative to the target. Second, lacrosse experience may increase the spine stresses through intermittently high playing volumes during different seasons and overall cumulative playing time through growth and development. Because shooting volume is player position dependent, specific field positions may predispose players to LBP such as midfield or attack. Third, there are likely physical factors in this LBP model that may be ass ociated with pain onset in lacrosse players: low flexibility of the hip and hamstring, low shoulder flexibility (external rotation), body weight and high percentage of lean body mass. We acknowledge that these factors are not necessarily mutually exclusiv e. It is likely that factors overlap and some modulate the other. For example, the mechanical stress on the lumbar spine from high velocity shooting is modulated by the amount of experience (the more playing time, the more exposures to shooting related str ess) and by player body size (greater muscle mass produces stronger muscle actions and faster angular rotational velocities of the pelvis and trunk). This proposed research will systematically examine the contribution of each of these factors on LBP onset and severity.
41 Figure 2 3. Potential factors that may contribute to low back pain in lacrosse athletes Application within Rehabilitation Science The project has direct applications within the field of rehabilitation science to develop interventions among young athletes that prevent injury, improve physical well being, reduce bodily pain and optimize performance. When chronic LBP occurs in an athletic population, athletic performance declines and rehabilitation programs are i mplemented to address the potential mechanisms underlying pain. (Trainor and Trainor, 2004) A multidis ciplinary team often collaborates to find solutions and establish goals. (Monticone et al., 2014) Unfortunately, rehabilitation strategies for lacrosse athletes with LBP have not yet been optimized due to severa l factors, including lack of comprehensive determination of kinematic risk factors. Identification of sport specific characteristics of the lacrosse shooting motion and secondary risk factors pertaining to lacrosse play will advance efforts to improve preh abilitation and prevent LBP. Initial papers are emerging to show the importance of core and back strength in lacrosse
42 and what exercise prehabilitation programs can be used from players under 11 through collegiate levels. (Vincent and Vincent, 2018) Current practice in the sport of lacrosse typically involves early emphasis development of stick skills, speed work and learning the game. It is not common for young players to participate in conditioning and strength ening to increase spine durability. Sport or training standards for young athletes that emphasize strength, endurance, and dynamic stability of the postural hip, and core stability muscles are lacking Thus, many players may not be adequately prepared for the mechanical demands of beginning a lacrosse career or for intermittent seasonal play. Upon completion of this study, we will apply these findings toward: 1) refinement of risk factors for LBP in young lacrosse athletes, and 2) development of conditioning exercises for lacrosse prehabilitation LBP prevention programs. Thus, our efforts will help provide the foundation from which structured prevention programs can be created. These improvements sho uld significantly improve quality of life by maintaining longevity in lacrosse participation without any secondary pains and injuries related to the low back. The findings can help advance the understanding of methods to improve function in an understudied active population. The Internal Classification of Functioning (ICF) Model In 1965, the introduction of a disability model by Saad Nagi, allowed for a more structured and organized implementation of clinically based research into the clinical setting. (Nagi, 1965; Snyder et al., 2008) A schematic of disease and injury impact on individual well being from the cellular level to complex in teraction and relation of that individual in society provides a roadmap for improvements in clinical practice, research and health care policy. (Jette, 2006, 1994; Verbrugge and Jette, 1994) Since the introduction of the Nagi disablement model, several other models have been produced with each sequential model improving upon the previous. ( National Advisory Board for Medical Rehabilitation Research. Res earch Plan for the
43 National Center for Medical Rehabilitation Research. 1993) Currently, we are using the Internal Classification of Functioning (ICF) Model, introduced by the World Health Organization in 1980. This model itself has been revised severa l times since its inception, most recently in 2001. (Jimnez Buuales et al., 2002) It is widely recognized around the world for classifying and identifying the inter relationship of several domains (Figure 2 4 following page ) involving a disorder fro m which a population may be suffering. We determine d kinematic and musculoskeletal risk factors associated with LBP in the lacrosse population using the shooting motion as a marker of performance. The ICF model will cting the population of young lacrosse players. The impact of LBP on the domain of Functions and Structures include lean muscle mass volume and percent. Higher volumes of lean mass and muscle are related to greater strength and faster angular velocities of movement. (Tapking et al., 2018) Low flexibility (or range of motion) about the shoulder and hip may reduce efficiency o f the shooting kinematics and thus transfer mechanical stress to the lumbar spine. Neurom uscular control can be reflected by the asymmetric movements generated by shooting motion by both limbs, excessive motion about the pelvis and spine with poor hip and core stability, and restricted motions for lacrosse players with LBP. In the cases of compromised function, structures of the lumbar vertebra are at risk of damage and overwhelming stress that can lead to the development of conditions such as stress fractu res, disc degeneration and spondylolisthesis. Figure 2 4 provides the ICF Disability Model summary. In this model under the domain of Activities, LBP can decrease participation in other sporting activities. A modifier of Activities and Participation is la crosse participation/volume of play. Other modifiers and factors that impact the influence of LBP as a health condition include environmental factors related to lacrosse participation, such as the access to and use of medical
44 and coaching personnel as we ll as safe training facilities and playing fields. It is possible that some players in certain geographic regions do not have access to higher quality training facilities or maintained fields, or have medical personnel available on the field to assist. Coa ching experience and knowledge drive training practices and behaviors, and some coaches do not emphasize prehabilitation to improve player durability pre season or in season. Figure 2 4. Lacrosse Low Back Pain (LBP) within ICF Disability Model Lastly, Personal Factor determinates such as age, sex, body mass index (BMI), lacrosse playing volume (club teams, official school teams and other) and career aspirations (i.e. collegiate lacrosse) have the potential to influence LBP in the lacrosse popula tion. For example, a 14 year old male attack player with ambitions of becoming a collegiate level player may be concurrently participating in his high school team and his club team during spring to summer seasons H e is also beginning to develop more muscl e mass and his shooting speed has increased considerably over the last year. These Personal Factors are all potential factors that
45 contribute to greater mechanical loading at the spine and a greater likelihood of pain onset. These domains are all interre lated and can influence other domains. Functional, kinematic, and self reported measures selected for these studies will address each of the domains of the ICF model.
46 CHAPTER 3 MATERIALS AND METHODS Overview This study address ed a scientific evidence gap for a growing athletic population. This project use d a cross sectional and prospective observational study design to determine the factors that relate to musculoskeletal pain in lacrosse players across the age spectrum. Participants completed an init ial baseline testing and were followed for six months to document wheth er LBP developed Study Design Figure 3 1. Study flow diagram A six month prospective study was used to determine what motion related factors may influen ce the onset of musculoskeletal pain in male and female lacrosse players aged 10 21 years of age. Figure 3 1 provides the study flow. The primary study outcomes were presence of LBP LBP severity and lacrosse related biomechanics (of the shooting motion). S econdary outcomes
47 include d potential modifiers of pain (lacrosse experience, play volume, position or body segmental rotational velocity and physical function measures ). Participants Potential participants were recruited to participate in the study from the central Florida region (N=100). Parental informed consent and child assent for participants under 18 and informed consent for participants greater than 18 were obtained after the s tudy details and potential risks were reviewed. The number of participants was chosen to allow stratification of the results based on age, sex and player position (attack, midfield, defense) for statistical analysis and a large number is necessary for mean ingful analysis. Inclusion: Males and females between 10 21 years of age Currently playing lacrosse in organized school or club teams Exclusion: Aged <10 or > 21 years Currently being treated for an acute injury (e.g., new sprain, strain, fracture) Recr uitment Potential participants were recruited from central Florida and beyond using flyers, the University of Florida Department of Orthopaedics and Rehabilitation website and other public places in the central Florida region. Permission was obtained from the Alachua County School Board to distribute UF approved flyers about the study in public schools. The advertisements direct ed potential participants to contact the study coordinator for further screening and for scheduling of the testing session. The stu dy coordinator, or another member of the research team, describe d the study and verif ied that the candidate me t the inclusion and exclusion criteria. If the
48 candidate agree d to participate, the coordinator describe d the study in detail and answer ed any que stions. Sample Size Estimate This study was powered to detect significant differences in all measures of Hypothesis 1, Aim 1 (that players with LBP would have less total transverse excursion from pelvis to shoulder, less angular velocity transfer from pelv is to trunk, greater lateral trunk lean and greater knee flexion compared to players with no pain). This decision was based on the available evidence to date for this specific population and related measures and to a close motion of a tennis serve (Campbell et al., 2014; Wasser et al., 2016a) For all the following measures, to detect differences in players with and without LBP with a power of 0.80 and an level of 0.05, the sample sizes were determined using methods described by Rosner. (Rosner, 1995) Using means and standard deviations of transverse excursion from pelvis to trunk in a lacrosse shot (158.3 0.28 [n=16 no pain] and 126.2 34.0 [n=8 pain]), a sample of 18 players per group were needed. Using data on angular velocity transfer from pelvis to trunk (151/s 77 /s [n=16 no pain] and 87/s 83/s [n=8 pain]), a sample of 20 players were needed per group Peak knee flexion data during a shot (160.6 8.4 [n=16 no pain] and 151.1 13.0 [n=8 pain]) were used to determine that 21 players were needed per group to find significant differences in this measure. Finally, among tennis players who performed a serve motion with pain (n=7) and without pain (n=13), the lateral tilt was 3.9 6.0 and 4.5 7.0, respectively; a total of 10 players per group wer e needed to detect differences in tilt based on presence of back pain. (Campbell et al., 2014) Informed Consent Upon contact from an interested candid ate, the Study Coordinator review ed the main details in the informed consent document. The candidate either agree d to participate, think about
49 participating and decide at a later time, or decline d If the participant remain d interested, informed consent wa s obtained by the principal investigator during the testing visit. After complet ing the informed consent process, participants underwent testing with the study team. Attrition The percent of participants who do not respond to the two, four or six month f ollow up contacts were tracked. The attrition was expressed for the total cohort and expressed as a percent of the age groups (10 14 years; 15 18 years, >19 years) and as a percent of male versus female participants to indicate whether there was greater vu lnerability of loss to follow up among specific subgroups. Study Outcomes Primary and secondary study outcomes were collected during the initial motion testing visit and at the follow up time points at month 2, month 4 and month 6. Main outcomes include d back pain severity and lacrosse motion biomechanics during shooting a ball. Secondary measures include d physical fun ction assessments of hip flexor and iliotibial band flexibility and shoulder internal and external rotation, single legged squat performance, and lacrosse and other sport experience. Participant Characteristics Player age was self reported. Height and wei ght was obtained using a medical grade stadiometer. Body mass index (BMI) was calculated as: BMI = body weight (kg)/ height (m) 2 Sport Experience and Lacrosse Position Pain presence may be related to several features of lacrosse experience, including nu mber of current weekly lacrosse playing sessions (training duration) (Kujala et al., 1992) position and participation in other sports during the year. (Cole and Grimshaw, 2016; Fett et al., 2017; Quinn
50 and Bird, 1996; Wasser et al., 2017) A study specific survey was developed to determine key information about the playing experience of each participant. Questions were adminis tered electronically using REDCap. (Harris et al., 2009) Questions included quantification of current practice ses sions or games and annual seasons of play (spring, fall, summer or all year play). The player position was categorized to offense (midfield, attack) and defense (defense and goalie); players could select if they played more than one position or have been s witched to another position over the last year. Players were asked to document the sports they participated in over basketball, football, volleyball, golf, soccer, cycling, swimming, martial arts, equestrian, softball and other. Pain Severity Self reported occurrence of any musculoskeletal pain due to acute injury or overuse were collected If pain was present, the participant was asked to further characterize the pain by providing a number from 1 10 using the 11 point Numerical Pain Rating scale (NRS pain ). This scale has anchors of 0 (no pain) to 10 (worst imaginable pain). The NRS pain is an accepted outcome measure as described in the Initiative on Methods, Measur ement, and Pain Assessment in Clinical Trials (IMMPACT). (Dworkin et al., 2008) Participants were asked to rate their average NRS pain scores separately at the lumbar spine, shoulders, hips, knees, ankles and feet over the last week. Recall reporting of pain ratings using the NRS pain over a week has shown to be highly agreeable to momentary pain ratings and does not reach a ceiling effect of pain as shown by commonly used visual analogue scales. (Jamison et al., 2006) The lumbar spine was the primary pain site studied and discussed in this study.
51 Physical Function Tests The presence of, or worsening of, back pain might be related to several physical functional impairments that shift mechanical stresses to the lumbar spine. These factors could include low hip and low shoulder external flexibility. Three clinical tests were hip flexor test and shoulder internal extern al rotation while lying supine. (Hurd et al., 2011; Z aremski et al., 2013) Figure 3 2 Thomas ( Photo courtesy of author ) ip Flexor Test This test evaluate d the tightness of the hip flexors (Figure 3 2 ) Evidence indicate d that there is moderate strength evidence that relates hip flexor tightness with the presence of low back pain, (Moradi et al., 2015) and this tightness is related to a lifetime prevalence of low back pain in athletes. (Kujala et al., 1992) To conduct the test, the participant
52 lie d supine, with bo th knees brought to the chest. Keeping the back flat against the table, the participant dro p p ed one leg into extension followed by the knee dropping into flexion. The test was cons idered positive for tightness if the leg being tested did not remain on the table The intraclass coefficient for the Thomas test is 0.97 (95% confidence interval of 0.91 0.99). (Kim and Ha, 2015) Figure 3 3. Should Flexibility Test (Photo courtesy of author). Shoulder internal and external r otation Passive shoulder internal and external rotation was measured using a goniometer of the dominant and non dominant limbs (Figure 3 3 ) ( Moreno Perez 2018, Zaremski 2014) Each player lie d supine on a clinical table with the shoulder abducted at 9 0 degrees and the elbow flexed to 90 degrees. The goniometer was anchored by hand on the ulnar styloid and the olecranon. The forearm was placed in a pronated position for
53 the testing. The tester h e re stabilization of the scapula as the humerus was rotated in the glenohumeral joint anteriorly and posteriorly. The greatest internal and external rotation magnitude were documented at the point at which the scapula motion was appreciated upon visual insp ection. A total arc of motion was determined by adding the internal and external rotations. This test was used in athletes with upper extremity motions in racquet sports and general overhead throwing athletes (McConnell et al., 2012; Moreno Prez et al., 2018) and in a small pilot study of lacrosse players in our laboratory (Zaremski et al., 2013) Among healthy tennis players and baseball pitchers, previou s studies have shown internal rotation to range from 52.5 75.0 degrees and external rotation to range 97.8 130 degrees (Hurd et al., 2011; Moreno Prez et al., 2018) Arcs of motion for these populations has ranged from 136 146 degrees, (Ellenbecker et al., 2002; McConnell et al., 2012; McConnell and McIntosh, 2009) and among male high school lacrosse players averaged 160.9 degrees (with an average of 98.4 degrees external rotation and 60.4 degrees of internal rotation, respectively). (Zaremski et al., 2013) Single l eg s quat A single leg squat has been a commonly used functional task that can assess movement patterns in an athletic population. (Lewis et al., 2015) The task consists of squatting with one leg, as low as possible and then returning to a standing single leg position. When evaluating a single leg squat, muscle function is evaluated to id entify knee stability. The task is challenging for individuals of all physical skill levels and is used to determine quality of functional movement and postural orientation. (Ageberg et al., 2010) Among healthy individuals, ordinal scale intra rater reliability scores ranged from 0.38 to 0.94 and inter rater reliability was reported as 0.68 (0.46
54 and four of the six novice clinicians used to evaluate SLS were able to measure properly for clinical use. For frontal plane knee measurements, intra rater reliability r anged from 0.88 to 0.98 with interrater reliability of 0.99 (0.97 1.00), both are considered good agreement and clinically significant. (Poulsen and James, 2011) The ordinal scale has been identified unreliable between raters due to inherent subjectivity. (Chmielewski et al., 2007) Evaluating single leg squat by the entire movement versus evaluati ng each segment (trunk, pelvis, and hips) individually, the kappa coefficients were higher for specific segment evaluation (0.23 0.53; fair to moderate agreement) vs the entire movement (0 0.55; poor to moderate agreement), however neither evaluation metho d met the criteria to be clinically significant. When evaluating the single leg squat with a values and percent agreement were > 0.90 and 96%, respectively, betw een 3 examiners. (Ageberg et al., 2010) Increased medial lateral knee movement is indicative of poor knee stability during dynamic movements. Another cross sectional study assessed reliability and validity of clinicians ratings compared with 3D motion capture. (Barker Davies et al., 2018) While subjective ratings can vary between reviewers, a 3D evaluation is considered the (Munro et al., 2012) Overall interrater intersession reliability and intersession reliabilities for 3D evaluations were extremely high (0.83 1.00 and 0.82 0.97, respectively). (Nakagawa et al., 2014) Three Dimensional Motion Analysis The kinematics of shooting a lacrosse ball encompass ed the secondary outcomes of over a period of four years, whereby sport motions that had similar features to that of the lacrosse shot were studied. Motion capture protocols that have bee n used and validated in throwing
55 motions like baseball and golf were used as references for the development of the ball shooting lacrosse protocol (Fleisig et al., 1999; Meister et al., 2011) The initial development phase of motion capture in 2014 included the creation of a 44 retroflecive marker system that included anatomical landmarks for placement, the crosse and the ball. During testing and retesting during 2014 2015, the marker set was streamlined to include a total of 27 mark ers (Figue 3 6, page 59) including the crosse and the ball. We first published this marker system in 2015, and then used this in a cross sectional study to document differences in shooting motion among high school through professional level players with an d without low back pain. (Vincent et al., 2015; Wasser et al., 2016b) During s hooting, reflective markers were applied to anatomical landmarks and body segments using the streamlined marker system Kinematics were derived from the marker da ta using standard rigid body mechanics equations implemented within commercially available software (Visual3D, C motion, Inc). Motion capture s etup After pilot testing using a variety of camera heights, positions and numbers, we repeatedly obtain ed our m easures of interest using the infrared camera arrangement shown in the experimental setup in Figure 3 4 with minimal noise and virtually no data loss. Infrared cameras were arranged to capture motion from the participant, crosse and ball. A testing area wa s used that is approximately 7.6 meters X 9.5 meters in size. Motion was captured using high speed optical motion cameras (Motion Analysis Corp, Santa Rosa, CA, USA) that were sampling at a rate of 200Hz. On the lengthwise side of the testing area, a high speed camera (Elixim, Casio) was used to document the shooting trials at a capture frequency rate of 300 frames per second.
56 Figure 3 4. Motion camera setup for shooting. Shooting a ball at goal t arget was evaluated by using a high speed 12 camera optical motion analysis system (Motion Analysis Corp, Santa Rosa, CA, USA). The standard overhead shot was chosen for this analysis as this is one of the very first skill s learned in the sport and its variability is less than other shots such as the sidearm or underhand. (Macaulay et al., 2017) Dominant and non dominant side shot motions were captured. Key measures inclu de d the peak angular velocities of the pelvis, trunk, shoulder and crosse. Additional kinematic measures include d peak shoulder abduction excursion and angle, shoulder to pelvis crossover angles at crank back and follow through and ball velocity. These me asures are similar to those reported for the golf swing and the baseball pitch. (Meister et al., 2011) The timing of these events were determined as a percent of the shot cycle. Phases and events of the Lacrosse s hot The description of the phases and events of a lacrosse shot by Mercer and Nielson (John A. Mercer and Jason H. Nielson, 2012) are expanded
57 in this work. Three main phases related to the lacrosse shot are used reliably in motion analysis. These three phases are the crank back, acceleration and follow through (see Figure 3 5 ) Figure 3 5. Phases and events of the lacrosse shot. Stick figure of player from Cortex software during a lacrosse shot sequence. During the crank back, the shooting limb winds up and the body stores potential energy. After crank back, the lead foot drives forward and prepares for foot plant. A key event of the lead foot plant identified by the heel or toe marker being within a 3mm threshold of the ground, then triggers the acceleration phase identified as the frame or frame following the stick being perpendicular wit h the ground The acceleration phase consists of increasing the angular velocities of the body segments (pelvic, trunk, shoulders) and crosse to prepare for ball release. (Vincent et al., 2015) The release of the ball is the key event that ends the acceleration phase. Finally, the last phase of the lacrosse shot is the follow through. Here, there is a forward
58 crossover motion of the trunk to pelvis and a deceleration of the body segment rotations. The final event of the lacrosse shot is the greatest magnitude of shoulder to pelvis crossover. Hence, the starting point of the shooting motion was the lead foot plant event (0%) and the ball release was the end of the shot (1 00%). Follow through occurs after the ball release (>100% of the throw cycle) (Dick, 2013) Specific kinematic events were expressed as a percent of the shot cycle. Marker System for motion c apture The marker systems for the lacrosse shot are shown in Figure 3 6 (following page) Reflective markers were applied bilaterally directly on the skin, on the following anatomical landmarks: acromion processes, lateral epicondyles of the elbow, midway between the ulnar and radial styloid processes, third metacarpal, posterior superior iliac spines, anterior superior iliac spines, greater trochanters, latera l femoral epicondyles, lateral malleoli, heels and great toes. A marker was placed on the right scapula as an offset. Markers and reflective tape were also placed on the stick end of the crosse, the crosse shaft, and the right and left sides of the head. A standard lacrosse ball (National Operating Committee on Standards for Athletic Equipment [NOCSAE] approved) was completely covered in reflective tape for the analysis. Figure 3 6. Retroreflective marker placement on athlete. (Photo courtesy of author )
59 Preparation for s hooting Each player were permitted a five minute warm up period of shooting at the simulated goal target in the laboratory. Participants perform ed overhead shots with both the dominant and non dominant arms within the camera capture vol ume area. The standard overhead shot was selected because it is easily replicated by players and has discrete events from which analysis can be developed. Moreover, it is one of the very first basic skills that a player learns in the sport of lacrosse. Par ticipants w o r e non cleated athletic shoes and use d their own crosses. The use of personal shoes and sticks reduce d the possibility of altered motion due to unfamiliar equipment. The order of shooting arm testing was the same for all participants, with the dominant arm first and the non dominant arm second. To determine the dominant arm, each participant was asked with which arm they use to write. Each player was provided a set of standardized instructions to release the ball with as much speed and accuracy as possible, without compromising form for the sake of speed. Accuracy was defined as the ability of the player to have the ball hit within the simulated goal target. High speed film of the motion was captured using an independent camera (Exilim, Casio Tokyo, Japan ) stationed in the frontal plane of the participant. If the ball did not land in the goal target, the trial was not included in the analysis. Three trials were captured on the dominant and non dominant sides, and were averaged to determine the typical performance of each side. Kinematics Kinematics were derived from the marker data using standard rigid body mechanics equations implemented within commercially available software ( MATLAB; R2011b, The Mathworks Inc, Natick, MA ). Based on the conceptual model of the development of back pain or injury provided in Chapter 2, a series of kinematic variables were calculated from the software, and these are provided in Table 3 1
60 Table 3 1. Bio m echanical Outcome Variables Variable Relation t o Conceptual Model Determination Angulations & Orientation Stride Length Relation to hip flexor flexibilty; if low flexibility, stride length may be low and similar to baseball, energy input int o the shot must be derived from the upper body rotation about the spine Distance between the heel markers of the trailing foot and lead foot Knee Flexion Relation to mechanical stress on low back; increased knee flexion at BR, FC, and total ROM may be a compensatory motion to alleviate the strain at the low back Angulation between the upper and lower leg segments in the saggital plane Foot Position Relative to the Goal Relation to mechanical stress on low back; similar to baseball, a closed foot position necessitates more upper body rotation about the spine to position trunk toward the net at ball release and an open foot position may indicate early hip roation and loss of sequence. Define open ) or closed position Pelvic Tilt Relation to mechanical stress on low back; high peak pelvic tilt angle may elevate stresses on the low back Angulation of pelvic plane during a lacrosse shot (at foot contact (FC) and at ball release(BR)) Pelvic Tilt Excursion Relation to mechanical stress on low bac k; high pelvic tilt excursion may place high stress on the low back Displacement between maximum and minimum pelvic tilt
61 Table 3 1. Continued Variable Relation t o Conceptual Model Determination Shoulder Internal/External Rotation Deficts in internal/external rotation may force compensatory motions of the pelvis and trunk Goniometer measurements of internal and external rotations will be made for both shoulders. Peak Angular Velocities and Timing of Velocities Peak Rotational Velocities of the Pelvis, Trunk, and Shoulders High forces generated by the shooting motion itself may place mechanical stresses on the body and may contribute to the development of musculoskeletal pain or injury. Peak angular velocities at each segment through the shooting motion. Peak Timing of Rotational Velocities of the Pelvis, Trunk, and S h oulders Restrictions in rotation of body segments engaged in earlier phases of the shot (ie, pelvis) may increase the mechanical demands to segments engaged later in the shot. Time (% of shot cycle) where peak angular velocities occur. Segmental Interactions X Factor (Crank Back & Follow Through) Relation to mechanical stress on low back; while a higher X Factor may provide more potential energy into the shot, this shoulder to pelvis separation also creates more rotational motion at the lumbar spine Degrees of separation between the pelvis segment and the line created by markers of the acromion processes Crunch Factor Index Relat ion to mechanical stress on low back; lateral tilt with relation to velocity has been reported to stress the lumbar spine unilaterally. The index will identify the impact of trunk angular acceleration and trunk lean with respect to potential onset of LBP. Lateral and sagittal trunk tilt angle to trunk angular acceleration.
62 Angulations and o rientation In the sagittal plane, trunk lean at ball release and trunk flexion excursion throughout the cycle were determined. The excursion of the trunk during the shot cycle was determined from the difference in the maximum and minimum trunk lean angles. Anterior pelvis tilt at ball release and its maximum throughout the cycle was determined. In the transverse plane, the ROM of the pelvic ti lt during the cycle was determined from the difference in the maximum and minimum angles. ROM values of knee flexion were calculated. In the sagittal plane, the knee flexion angle was determined at two time points, foot contact and ball release. The ROM of knee flexion during the shot cycle was determined from the difference in the maximum and minimum knee flexion angles of the lead leg. Stride length was determined by measuring the distance between lead foot and trailing foot. Additionally, foot orientatio n was identified for both the lead foot and trailing foot at initial foot contact. Foot orientations was assessed relative to the target (goal) with positive orientations indicating a closed position and negative orientations indivating an open position Peak angular velocities and timing of v elocities T he maximum angular velocity and the time (expressed as percent of the shot cycle) at which the maximum angular velocity occurs was determined for pelvis, trunk, and shoulders during a lacrosse shot. These phases and events were streamlined from an earlier description ( Mercer & Nielson, 2012). Segmental i nteractions The two anterior superior iliac spines create d was created by the two acromion processes. Shoulder to pelvis crossover was defined as the amount of li ne crossover that occurred from crank back to follow through. The total angular excursion from foot contact to maximal shoulder to pelvis crossover in the transverse plane was calculated as negative (shoulder line crossing back over pelvis line in crank ba ck) or positive (shoulder line crossing forward over the pelvis during follow through). In
63 preparation for a shot, the throwing arm abducts, and the torso turns away from the target and is positioned for acceleration (crank back phase). This shoulder to pe lvis crossover was defined as negative, as the rotation is away from the target on the net. As the crosse is brought forward for the shot during the acceleration phase, the throwing arm moves anteriorly toward the target. After the ball release event the s houlder to pelvis crossover continue s This crossover was defined as positive as the rotation occurred toward the target on the net (follow through phase). A novel outcome measure being created for this study was We propose d to expand what was known about trunk motion and trunk tilt angle in high speed rotation motions such as those of a golf swing (Cole and Grimshaw, 2014) Using the published concept of the Crunch Index as a gui de (instantaneous product of lateral bending angle and trunk rotation velocity), we model ed our Index score to include variables that represent the stresses that are applied to the lumbar region. The proposed foundation for Crunch Factor Index incorporat ed two distinct features of movement: 1) the magnitude of maximal lateral trunk tilt, and 2) pelvic acceleration at the time of maximal lateral trunk tilt. The interaction of these factors were the basis of the novel Crunch Factor Index. The instantaneous pr oduct of maximal lateral bending angle of the trunk and pelvic rotation acceleration at the time point of maximal lateral bending, was calculated for the Crunch Factor Index. Crunch Factor Index: All measures were release. Lateral trunk tilt, or lateral trunk flexion is a potential factor contributing to back pain or injury among rotational and overhead sports. (Campbell et al., 2013; Cole and Grimshaw, 2014; Trunk Lean (3 1)
64 Glazier, 2010) In golf, high compressive loads are produced in the lumbar spine region from backswing to ball contact, so we inferred that a comparable time frame to assume high compressive loading occurs in lacrosse would prior to ball release. (Glazier, 2010) Events after ball release were not be calculated for this study, though we acknowledge d that the eccentric forces used to dissipate forces might contribute to the onset of LBP. LBP has been rep orted in baseball and golf, where timing of peak velocities of pelvis, trunk and shoulder is relatively early, late or out of sequence. (Mun et al., 2015) As such, the second factor we include d in the calculation was F inally, the interaction of pelvic acceleration at the time of maximal ipsilateral lateral trunk tilt was calculated. Preliminary analys e s compar ed the interaction, or our Crunch Index, highlight ed a higher magnitude for individuals with reported LBP (LBP) compared to healthy controls (CON) who were age, position, and gender matched (LBP: 69724.7317315.89 vs CON: 21782.1033639.94). Upon further inspection, players with LBP seem ed to compensate for a lower pelvic acceleration at the time of maximal lateral trunk tilt (LBP: 1913.071057.39 m/s 2 vs CON: 4258.511464.78 m/s 2 ) with an increased ipsilateral trunk tilt prior to ball release (LBP: 14.635.53 vs CON: 5.669.17). It wa s also noted that healthy controls had a peak pelvic acceleration that were not n oticeably different from pelvic acceleration at the time of maximal 2 4258.511464.78 m/s 2 ). For players with reported LBP, pelvis acceleration at maximal lateral trunk tilt were remarkably lower than their maximal pelvis acceleration of their lacrosse shot 2 2 ). A compact average difference in the timing (% of shot cycle) of maximal pelvic accele ration and maximal lateral trunk tilt was seen in CON subjects compared to LBP subjects (CON:
65 14.9%8.4 vs LBP: 91.3%102.75). We c onduct ed these analyses with a larger cohort of subjects to attempt to determine if these findings were clinically significant. Statistical Analysis All statistical analyses were completed using the Statistical Package for the Social Sciences (SPSS version 24; Chicago, IL) software. (http://www 01.ibm.com/software/analytics/spss/products/statistics/index.h tml. Published August 26, 2014. Accessed December 1, 2014) To assess baseline characteristics of the overall sample and player positional characteristics, several techniques were used, including analysis of variance (ANOVA) for continuous variables and Chi 2 ) for categorical values. Chi square for frequency distributions was used for demographics and presence of LBP. Continuous data that were not normally distributed (Shapiro Wilk Test; p>0.05) were to be log transformed prior to analysis. The pri mary analyses for Aims 1 and 2 used a general linear model approach. These analyses assess ed the main effects of LBP on biomechanical variables. Specifically, to test Hypotheses 1 and 2 for Aim 1, independent variables include d presence of pain (LBP or no LBP) and for Hypothesis 3 the independent variable were those players who develop ed pain over time (LBP at month 6, or no pain by month 6). Dependent variables included all biomechanical parameters. For the hypotheses in Aim 2, the independent variable wa s the presence of pain (LBP or no LBP). Significant effects o n pain status would indicate that the difference in outcomes was dependent on LBP. To test the hypotheses of Aim 3, odds ratios will be calculated for presence of LBP for player position and for athletes who participate in sports additional to lacrosse. To address Hypothesis 3 of Aim 3, a hierarchal regression analysis procedure was used to determine the
66 greatest contributors to the variance of the model for back pain severity. Separate successi ve models were generated to first account for player characteristics such as age and sex. Then, we enter ed in player position, years of play, participation in other sports, and various biomechanical factors to determine the percent o f variability in LBP se verity that could be accounted for by the entered predictors. A p value was established priori at 0.05 for all statistical tests. d was calculated for effect size and represents a standardiz ation of differences between two d has several established thresholds identifying small ( d =0.20), medium ( d =0.50), and large ( d =0.80) effect sizes. (Cohen, 1988) Protection of Human Subj ects Exercise and testing r isks To minimize risk of physical injury during testing, the study team provide d standardized instructions for each of the testing maneuvers and provide d spotters for each test. Informed c onsent The form was written in simple, easy to understand language. Potential participants who ha d impaired vision ha d the consent document read to them, followed by encouragement to ask questions and for discussion. There was time for the patient to consider the risks and benefits before making the ir decision to join. A copy of the signed and dated consent form was given to participants. Confidentiality Data was used only in aggregate, and no identifying characteristics of individuals were published or presented. Confidentiality of data was maintained by using research identification numbers that uniquely identify each individual. All appropriate measures were ta ken to prevent unauthorized use of study information. Data other than demographic information d id not use names as an identifier. The research ID number was used on all study case forms. Paper research records were locked in the UF Health Orthopedics and S ports Medicine Institute (OSMI; room 1135). Electronic data were protected behind encrypted
67 firewalls of the UF Clinical Translational Science Institute Research Electronic Data Capture System (REDCap Vanderbilt University, Nashville, TN ). Only the study team members ha d access to these files. Data collection and s torage Data was collected systematically for each participant. Each participant had an individual folder and electronic case report forms that was completed using the REDCap service throug h the Clinical Translational Science Institute. Storage of gait analyses data was completed using a password protected, encrypted repository for data collection and storage in the Department of Orthopaedics and Rehabilitation
68 CHAPTER 4 RESULTS Particip ant Characteristics Table 4 1 summarizes participant demographics. Participants (N=128) enrolled ranged in age from 10 to 21 Participants were 62.5% male, and 92.2% right hand dominant. There were significant differences regarding age, weight, and BMI bet ween the No Back Pain and LBP groups. No significant differences were found between the two groups for proportions of individuals who participated in any other sports. Table 4 1. Participant characteristics of lacrosse players with and without low back pa in at baseline All Participants (N=127 ) Low Back Pain (N=11 ) No Back Pain (N=116 ) p Age 16.4 3.0 18.4 2.1 16.1 3.1 *<0.01 Height (cm) 169.0 13.3 172.8 8.9 168.4 13.8 0.18 Weight (kg) 64.1 15.0 71.3 11.6 62.9 15.2 *0.03 BMI (kg/m 2 ) 22.2 3.1 23.8 2.2 21.9 3.2 *0.02 Gender (n,%) 0.51 Male 80 (62.5) 10 (55.6) 70 (63.6) Female 48 (37.5) 8 (44.4) 40 (36.4) Dominant Side (n, %) 0.57 Right 118 (92.2) 16 (88.9) 102 (92.7) Left 10 (7.8) 2 (11.1) 8 (7.3) Other Sport Participation (n, %) Running 17 (13.3) 2 (11.1) 15 (13.6) 0.77 Baseball 1 (0.8) 1 (0.9) 0.69 Basketball 21 (16.4) 2 (11.1) 19 (17.3) 0.52 Football 22 (17.2) 1 (5.6) 21 (19.1) 0.19 Volleyball 9 (7.0) 2 (11.1) 7 (6.4) 0.47 Golf 16 (12.5) 2 (11.1) 14 (12.7) 0.85 Soccer 19 (14.8) 2 (11.1) 17 (15.5) 0.63 Cycling 4 (3.1) 4 (3.6) 0.41 Swimming 6 (4.7) 6 (5.5) 0.31 Martial Arts 2 (1.6) 2 (1.8) 0.56 Equestrian 2 (1.6) 1 (5.6) 1 (0.9) 0.14 Other 15 (23.8) 3 (33.3) 12 (22.2) 0.47 Multiple Sports 61 (47.7) 8 (44.4) 53 (48.2) 0.769 No Additional Sports 37 (28.9) 7 (38.9) 30 (27.3) 0.314
69 Lacrosse History Table 4 2 provides lacrosse history for all participants. Overall, players participated fo r an average of 6.3 years, and we re currently playing between 3 4 lacrosse sessions per week. Approximately two thirds of participants indicated playing all year and during spring and s ummer seasons. Midfield was the most commonly position played, and goalie was the least commonly played position. Less than one fourth of the participants changed their position in the last year. No significant differences were found between the No Back P ain and LBP groups for years of lacrosse play, number of lacrosse sessions per week, lacrosse positions played, or seasons played. Table 4 2. Playing history of lacrosse players with and without low back pain at baseline Values are mean SD or percent o f the group. All Participants (N=127) Low Back Pain (N=11 ) No Back Pain (N=116 ) p Years of play 6.3 3.1 6.7 2.9 6.2 3.1 0.0 7 Current Sessions (#/wk) 3.6 2.0 3.3 2.2 3.7 19.1 0.1 4 Spring 8 (6.3) 1 (5.6) 7 (6.4) Fall & Spring 36 (28.1) 7 (38.9) 29 (26.4) Fall & Summer 2 (1.6) 2 (1.8) Spring & Summer 41 (32.0) 6 (33.3) 35 (31.8) All Year 41 (32.0) 4 (22.2 37 (33.6) 0.7 6 Lacrosse Positions Played (n, %) Midfield 41 (32.0) 5 (27.8) 36 (32.7) Attack 27 (21.1) 3 (16.7) 24 (21.8) Defense 23 (18.0) 3 (16.7) 20 (18.2) Goalie 4 (3.1) 4 (3.6) Multiple Positions 33 (25.8) 7 (38.9) 26 (23.6) 0.6 6 Changed Position in Last Year (n,%) 30 (23.6) 5 (27.8) 25 (22.9) 0.6 5 No participants reported playing fall or summer as their only seasons of play
70 Musculoskeletal Pain Table 4 3 contains self reported musculoskeletal pains (NRS pain ) at baseline and during the 2, 4, and 6 month follow ups. The musculoskeletal pain reporte d most frequently at baseline was located at the low back (14.1% of participants). During follow up, development of LBP was the most frequently reported (6.3% of participants) musculoskeletal pain. Table 4 3. Self reported musculoskeletal pain at baseline and during follow up. Baseline Hip Knee Ankle Foot Back n (%) 7 (5.5%) 16 (12.5%) 12 (9.4%) 7 (5.5%) 18 (14.1%) NRS Pain at site 2.4 1.1 3.5 1.9 2.7 1.2 3.4 1.3 3.4 1.3 Follow Hip Knee Ankle Foot Back n (%) 5 (3.9%) 5 (3.9%) 4 (3.1%) 8 (6.3%) NRS Pain at site 6.0 1.7 4.0 2.0 3.0 1.4 3.0 1.2 Functional Testing Table 4 4 summarizes dominant and non dominant single leg squat kinematics of lacrosse participants with and without pre existing LBP for the player cohort who initiated testing in 2017 and completed in 2019 (n=73). Participants with LBP had significantly larger hip flexion range of motion (ROM) during a dominant single leg squat compared to participants without LBP (p = 0 .0 0 1 d =1.07 ). During a non dominant single leg squat, participants with LBP exhibited significantly larger medial lateral knee ROM (p=0.0 15 d =0.91 ), maximal hip flexion (p=0.0 3 3 ; d =0.62 ), and hip flexion ROM (p=0.01 3 d =0.92 ).
71 Table 4 4. Single leg squat kinematics of lacrosse participants with and without pre existing LBP at baseline Values are means SD. S medial lateral ROM represents the addition of the knee or hip adduction and abduction to create total medial lateral ROM. No Low Back Pain Low Back Pain (n=62) (n=11) p Dominant Single Leg Squat Max Knee Flexion (), sagittal 74.3 13.2 79.2 18.6 0.29 Knee Flexion ROM (), sagittal 73.7 14.8 80.3 16.7 0.19 Max Knee Abduction (), frontal 7.8 5.6 7.9 3.5 0.94 Max Knee Adduction (), frontal 2.2 5.7 5.2 7.6 0.12 Knee Total Medial Lateral ROM (), frontal 9.9 5.2 13.1 6.0 0.07 Max Hip Flexion (), sagittal 57.4 16.6 67.3 11.2 0.06 Hip Flexion ROM (), sagittal 56.4 15.9 70.7 10.1 *<0.01 Max Hip Abduction (), frontal 13.9 7.0 17.2 4.0 0.14 Max Hip Adduction (), frontal 1.6 5.0 1.3 2.9 0.06 Hip Total Medial Lateral ROM (), frontal 15.5 5.9 15.9 4.3 0.84 Max Pelvic Drop (), frontal 7.3 4.2 6.2 3.9 0.41 Pelvic Drop ROM (), frontal 11.5 4.6 12.0 5.1 0.73 Non Dominant Single Leg Squat Max Knee Flexion (), sagittal 73.7 15.5 77.9 16.6 0.42 Knee Flexion ROM (), sagittal 73.1 15.9 78.1 15.9 0.34 Max Knee Abduction (), frontal 7.5 5.5 10.1 5.7 0.15 Max Knee Adduction (), frontal 2.7 6.3 4.6 6.8 0.36 Knee Total Medial Lateral ROM (), frontal 10.2 5.7 14.8 4.3 *0.02 Max Hip Flexion (), sagittal 55.6 16.8 64.3 10.4 *0.03 Hip Flexion ROM (), sagittal 54.6 16.2 67.8 12.3 *0.01 Max Hip Abduction (), frontal 12.8 6.8 15.7 5.2 0.18 Max Hip Adduction (), frontal 1.7 4.8 0.7 4.5 0.51 Hip Total Medial Lateral ROM (), frontal 14.5 5.4 16.4 5.3 0.29 Max Pelvic Drop (), frontal 3.0 6.0 5.7 6.6 0.19 Pelvic Drop ROM (), frontal 10.9 4.5 13.9 4.5 *0.05
72 Table 4 dominate sides of lacrosse participants with and without LBP. No significant differences were found by back pain group for either measure. Table 4 5. Functional testing of lacrosse participants with and without LBP at baseline Values are means SD. Shoulder ROM measured with shoulder positioned at 90 No Low Back Pain Low Back Pain (n=62) (n=11) p Thomas Hip Flexor Test (% Positive Tests) Dominant Side Hip Flexor 9 (14.5%) 0.18 Non Dominant Side Hip Flexor 7 (11.3%) 1 (9.1%) 0.83 Dominant Shoulder Range of Motion (ROM) Internal Rotation () 68.2 19.4 53.5 13.9 0.18 External Rotation () 85.4 22.2 88.8 17.8 0.93 Total Arc Of Motion () 153.6 25.8 142.3 18.2 0.37 Non Dominant Shoulder Range of Motion (ROM) Internal Rotation () 71.0 17.7 61.5 15.9 0.11 External Rotation () 83.3 21.4 81.3 14.1 0.94 Total Arc Of Motion () 154.3 25.6 142.8 17.6 0.23 Joint Angles and Range of Motion (ROM) Table 4 6 provides all kinematic orientations and ROM parameters generated during the lacrosse throwing motion. We did not detect a significant interaction between limb side (dominant v non dominant) and LBP on any joint angle or ROM. Participants with LBP did exhibit differences in pelvic and shoulder orientation at foot contact (p<0.05) with both dominant and non dominant shots (Co d values ranged from 0.41 0.60 and 0.43 0.51, respectively) Furthermore, participants with LBP produced significantly less transverse ROM at the pelvis (p = 0.0 0 1 d =0.73 ) and shoulder (p = 0.0 18 d =0.47 ) with a dominant lacrosse shot. Additionally, there was more sagittal knee flexion ROM in participants with LBP performing a dominant shot (p=0.0 15 d = 0.36 ). These differences in ROM, however, were not evident with a non dominant shot. In the non dominant
73 shot, participants with LBP exhibited significantly lower sagittal trunk lean ( p=0.0 4 4 d = 0.66 ) Investigation into kinematic differences between dominant and non dominant shots revealed differences with crank back ( p = 0.0 0 d = 0.54), pelvic ( p=0.0 69 d = 0.33) and shoulder ( p = 0.0 0 d = 0.58) orientation at foot contact, and trunk flexion at ball release ( p=0.0 36 d = 0.31) Furthermore, shot side differences in total ROM were evident in transverse ROM at the pelvis ( p =0.01; d = 0.54), shoulders ( p = 0.0 0. d = 0.67), and total shoulder and pelvis ROM ( p = 0.0 0 d = 0.41) Table 4 6. J oint angles and range of motion generated during a lacrosse shot. Values are means SD. S Dominant Shot Non Dominant Shot No Low Back Pain Low Back Pain No Low Back Pain Low Back Pain S hot S ide Side* LBP (n=116 ) (n=11 ) p (n=116 ) (n=11 ) p p p Stride length (cm) 95.40 16.25 98.56 22.86 0.94 89.98 18.61 87.73 26.40 0.92 *0.02 0.47 Stride to height ratio 0.43 8.113 0.43 12.10 0.82 98.56 22.86 98.56 22.86 0.36 *0.02 0.41 Shoulder to pelvis separation Crank back () 28.97 10.41 30.63 10.65 0.92 22.73 12.77 24.62 10.87 0.39 *<0.01 0.95 Follow through () 49.18 16.67 51.57 15.00 0.81 46.59 14.71 48.41 19.26 0.46 0.32 0.92 Joint Angles Lead foot angle at FC () 28.97 21.22 23.71 11.84 0.43 28.38 20.32 13.25 20.20 *0.01 0.13 0.16 Lead foot angle at BR () 26.82 19.07 21.98 19.25 0.43 24.57 19.61 10.58 23.98 *0.02 *0.05 0.15 Knee flexion angle at FC () 156.42 13.32 161.73 8.95 0.27 161.14 10.26 164.34 8.62 0.40 0.07 0.61 Knee flexion angle at BR () 152.06 10.94 150.10 17.02 0.44 14 9 .30 11.25 147.03 14.61 0.56 0.17 0.95 Pelvic tilt at FC () 11.07 22.71 15.47 5.92 0.41 8.58 26.63 16.11 7.89 0.18 0.83 0.71 Pelvic tilt at BR () 24.12 8.48 22.10 6.60 0.57 21.28 9.59 20.33 7.39 0.85 0.14 0.73 Pelvic rotation at FC () 73.61 21.26 58.79 27.51 *0.01 65.18 23.77 53.70 32.22 *0.03 *0.07 0.63 Pelvic rotation at BR () 3.92 14.75 6.18 11.99 0.69 9.38 16.20 6.30 18.86 0.30 0.32 0.34 Trunk flexion at BR () 18.42 12.79 13.86 13.84 0.35 14.69 12.14 9.48 11.83 0.39 *0.04 0.89 Shoulder Rotation at FC () 95.74 22.82 80.22 36.52 *<0.01 80.26 24.88 66.54 37.52 *<0.01 *<0.01 0.79 Shoulder Rotation at BR () 0.14 12.37 1.59 10.89 0.84 3.38 14.10 0.20 16.26 0.10 0.64 0.29
74 Table 4 6. Continued Dominant Shot Non Dominant Shot No Low Back Pain Low Back Pain No Low Back Pain Low Back Pain Shot Side Side* LBP (n=116 ) (n=11 ) p (sig) (n=116 ) (n=11 ) p p p Range of Motion (ROM) Transverse lead foot rotation () 2.15 11.08 1.73 15.92 0.96 3.80 11.71 2.67 21.11 0.65 0.52 0.98 Sagittal knee flexion ROM () 22.48 8.08 26.33 12.66 *0.02 23.27 8.45 26.15 12.82 0.12 0.85 0.76 Transverse pelvis ROM () 70.10 19.11 53.04 26.80 *<0.01 56.48 23.16 47.99 35.02 0.16 *0.01 0.22 Pelvic tilt ROM () 16.36 21.14 10.64 5.45 0.39 17.40 26.55 7.35 4.07 0.09 0.40 0.65 Sagittal trunk lean ROM () 35.28 14.13 29.108 15.31 0.13 34.51 13.35 26.18 11.90 *0.04 0.77 0.59 Transverse shoulder ROM () 96.97 23.18 83.19 33.94 *0.02 78.23 26.80 69.77 39.53 0.15 <*0.01 0.50 Total pelvis & shoulder ROM ()^ 78.15 20.82 82.64 18.43 0.71 69.91 19.36 73.03 19.61 0.89 *<0.01 0.59 ^ = additive ROM in the transverse plane from foot contact to follow through FC= Foot Contact BR= Ball Release Angular Velocities Table 4 7 shows segmental angular velocities during dominant and non dominant lacrosse shots in participants with and without LBP. No significant interaction was detected with angular velocities between limbs (dominant v non dominant) and presence of LBP. However, during a dominant shot, participants with LBP produced significantly lower peak angular velocities at the pe lvis (p<0. 0 01 ; Co d =0.82 ), trunk (p = 0.0 0 1 ; d =0.54 ), and shoulders (p = 0.0 05 ; d =0.40 ) compared to those without LBP. During a non dominant shot, participants with LBP produced lower peak pelvic angular velocities (p=0.04 2 ; d =0.45 )
75 and higher ball velocity (p=0.0 48 d =0.03) compared to players without LBP. There were also s ignificant differences in peak angular velocities between the dominant and non dominant sides at the pelvis (17.7% slower; p = 0 .001 d = 0.58 ), trunk (1 6.4% slower; p< 0 .001 d = 0.65 ), shoulders (15.1% slower; p= 0 .001 d = 0.60 ), and ball velocity (13.8% slower; p<0.001 d = 0.56 ) regardless of prescence of LBP Lastly, the dominant side produced a significantly higher incremental cha nge in angular velocity from the pelvis to the trunk (p=0.0 36 d = 0.37 ) compared to the non dominant side. Table 4 7. Maximal angular velocities during a dominant and non dominant lacrosse shot. Values are means SD. *significant at Domi nant Shot Non Dominant Shot No Low Back Pain Low Back Pain No Low Back Pain Low Back Pain S hot S ide Side* LBP (n=116 ) (n=11 ) p (n=116 ) (n=11 ) p p p Maximal angular velocity Pelvis (/s) 563.4 141.6 441.8 155.3 *< 0.01 467.0 154.3 393.2 175.0 *0.04 *<0.01 0.28 Trunk (/s) 666.2 156.7 561.3 223.5 *<0.01 543.8 181.3 487.4 205.7 0.13 *<0.01 0.34 Shoulders (/s) 877.4 202.8 772.9 303.9 *<0.01 738.6 206.7 694.3 246.9 0.19 *<0.01 0.33 Crosse (/s) 1393.9 400.5 1377.2 426.4 0.27 1285.9 413.8 1273.0 420.4 0.26 0.06 0.94 Incremental change in angular velocity Pelvis to trunk (/s) 102.8 68.0 119.4 97.8 0.70 77.8 67.2 94.2 67.5 0.62 *0.04 0.97 Trunk to shoulders (/s) 211.7 81.0 211.6 108.3 0.63 195.1 67.5 206.9 64.0 0.94 0.407 0.64 Shoulders to crosse (/s) 516.1 311.1 604.4 203.5 0.66 544.9 283.6 578.8 284.2 0.65 0.975 0.56 Ball velocity (km/h) 99.2 24.3 102.3 33.7 0.22 85.8 23.2 86.5 25.9 *0.05 *<0.01 0.66
76 Timing of Peak Angular Velocities Table 4 8 summarizes the timing at which peak angular velocities of the pelvis, trunk, and shoulders occur. No significant limb side by back pain interaction was detected with the timing values. Main effects of ba ck pain revealed different timing of peak angular velocities (% of shot cycle) during non dominant shooting with the pelvis (p =0 0 0 4 d = 0.43 ) and trunk (p= 0 .029 ; d = 0.39 ) peaking significantly later in the shot cycle for individuals with LBP. Limb side main effects included differences in timing at the pelvis (p=0.02 1 d = 0.27 ), trunk (p = 0.0 02 d = 0.37 ), and shoulders (p = 0. 0 0 3 d = 0.53 ). Table 4 8. Temporal patterns of maximal segmental angular ve locities during a dominant and non dominant lacrosse shot. Values are expressed as a percent (%) of the shot cycle. Values are means SD. Dominant Shot Non Dominant Shot No Low Back Pain Low Back Pain No Low Back Pain Low Back Pain S hot S ide Side* LBP (n=116 ) (n=11 ) p (n=116 ) (n=11 ) p p p Crank Back 8.6 59.9 19.9 36.2 0.29 3.1 85.8 34.3 106.9 0.38 *0.02 0.15 Pelvis 60.1 21.3 64.8 29.9 0.15 72.5 56.6 114.9 127.1 *<0.01 *0.02 0.32 Trunk 72.5 11.4 73.8 20.2 0.49 77.8 19.4 87.6 29.4 *0.03 *<0.01 0.17 Shoulders 80.4 11.7 81.9 19.2 0.48 90.6 22.7 92.4 32.5 0.75 *<0.01 0.99 Follow Through 202.2 44.4 202.0 56.4 0.65 192.2 46.5 185.2 152.2 0.71 0.23 0.78
77 Crunch Factor Index Table 4 9 (below) summarizes results of the Crunch Factor Index. Participants with LBP had a significantly lower Crunch Factor Index values than those with no pain (p=0.0 42 ; d = 0.39 ). Table 4 9. All Participants No Pain Low Back Pain (n=127 ) (n=116 ) (n=1 1 ) p Peak Pelvis Acceleration (/s 2 ) 4320.2 1282.2 4350.9 1248.0 4139.1 1497.3 0.4 7 Peak Pelvis Acceleration (%) 56.4 76.6 55.6 78.5 61.2 66.0 0.75 Pelvis Acceleration @ Max Lateral Trunk Lean (/s 2 ) 2098.7 2164.0 2179.9 2210.1 1620.9 1856.0 0.06 Peak Lateral Trunk Lean () 6.2 5.7 5.9 5.7 7.8 5.9 0.3 8 Peak Lateral Trunk Lean (%) 23.9 71.2 20.7 67.1 43.0 92.3 0.2 1 Acceleration difference between peak pelvic acceleration and pelvic acceleration @ max lateral trunk lean (/s 2 ) 2221.5 2052.8 2171.1 2083.5 2518.2 1892.8 0.1 4 Timing difference between peak lateral trunk lean and peak pelvic acceleration (%) 85.1 105.4 81.7 105.2 104.7 107.4 0.3 1 14547.8 21487.7 15605.7 22463.1 8325.1 13311.5 *0.04 acceleration (/s 2 ) @ peak lateral trunk lean ()
78 Odds Risk Analyses Table 4 10 present the results of odds ratio analysis for sport participation, in addition to lacrosse, and developing LBP. Participants who did participated in lacrosse only had significantly higher odds of developing LBP compared to participants who did participant in at least one other sport. (p=0.0 4 5) Table 4 10. Odds risk analyses for development of LBP and sport participation. OR p 95% CI Basketball (n=21) 0.741 0.76 0.083 6.130 Soccer (n=19) 0.810 0.85 0.094 6.980 Running (n=17) 0.929 0.95 0.107 8.055 No Other Sport Participation (n=37) 4.583 *0.05 1.036 20.285 Table 4 11 presents the results of odds risk analysis for lacrosse playing position and developing LBP. There were no positions that significantly increased or decreased the odds of developing LBP. No players who played the goalie position developed LBP in our study, and were subsequently removed from analysis. Table 4 11. Odds risk analyses for presence of LBP and lacrosse position played. OR p 95% CI Attack (n=27) 0.717 0.62 0.192 2.682 Midfield (n=41) 0.791 0.68 0.262 2.388 Defense (n=23) 0.900 0.88 0.238 3.406 Multiple Positions (n=33) 2.056 0.18 0.723 5.844 Regression Analyses A portion of our aims was to quantify the contribution of specific lacrosse shooting kinematics on the statistical variance of LBP severity. The results of these age and sex adjusted regression models are shown in Table 4 12. There were no significant kin ematic variables
79 contributing to LBP severity. Dominant shoulder internal rotation was a significant functional measure contributing to LBP severity (p=0.02) Table 4 12. Hierarchal regression analyses for kinematic parameters of a lacrosse shot. Each line represents a different model. All models were first adjusted for age and sex, and then the kinematic measures were added in in the later steps of each model. Model R R 2 R 2 Change Significant F B (CI) Body Segment Orientation 1. Shoulder Rotation @ FC 0.763 0.582 0.063 0.184 0.468 ( 0.042 0.009) 2. Pelvic Rotation @ FC 0.720 0.519 0.000 0.929 0.028 ( 0.029 0.032) Range of Motion (ROM) 3. Pelvis (in transverse plane) 0.730 0.534 0.015 0.529 0.058 ( 0.022 0.040) 4. Shoulders (in transverse plane) 0.728 0.530 0.011 0.583 0.446 ( 0.35 0.021) 5. Lead Knee (in sagittal plane) 0.779 0.607 0.089 0.111 0.019 ( 0.009 0.076) 6. Trunk Lean (in sagittal plane) 0.791 0.625 0.107 0.077 0.234 ( 0.084 0.005) Peak angular velocity 7. Pelvis 0.721 0.520 0.001 0.854 0.058 ( 0.006 0.005) 8. Trunk 0.759 0.576 0.057 0.209 0.446 ( 0.007 0.002) 9. Shoulder 0.784 0.615 0.096 0.095 0.525 ( 0.005 0.0004) 10. Ball Speed 0.725 0.526 0.007 0.661 0.210 ( 0.047 0.030) 11. Crunch Factor Index 0.754 0.568 0.011 0.578 0.121 (0.000 0.000) 12. Max Trunk Tilt (in frontal plane) 0.746 0.557 0.000 0.987 0.003 ( 0.099 0.100) 13. Max Pelvic Acceleration 0.749 0.562 0.005 0.725 0.078 ( 0.001 0.000) 14. Pelvic acceleration at max trunk tilt (in frontal plane) 0.748 0.56 0.003 0.766 0.062 (0.000 0.000) 15. Dominant Shoulder Internal Rotation 0.902 0.814 0.282 *0.02 0.780 ( 0.129 0.013) 16. Non Dominant Shoulder Internal Rotation 0.813 0.662 0.130 0.18 0.500 ( 0.101 0.013) 17. Dominant Shoulder External Rotation 0.171 0.029 0.017 0.276 0.001 ( 0.001 0.004) 18. Non Dominant Shoulder External Rotation 0.123 0.01 0.003 0.664 0.001 ( 0.004 0.003)
80 Joint Angles and Range of Motion (ROM) and Onset of LBP Table 4 13 presents joint angles and joint ROM values during the lacrosse shot for participants who developed LBP with no LBP reported at baseline, compared to those who did not. No kinematic variables were significantly difference between these two groups. Table 4 13. Stride length, joint angles and range of motion generated during a lacrosse shot. Values are means SD. S 0.05 No Pain Developed Low Back Pain Developed (n=1 19 ) (n=8) p(sig) Stride length (cm) 95.4 17.3 103.7 17.0 0.28 Stride to height ratio 0.57 0.1 0.60 0.1 0.34 Shoulder to pelvis separation Crank back () 29.3 10.5 27.9 9.7 0.74 Follow through () 49.25 16.4 53.51 16.8 0.42 Joint Angles Lead foot angle at FC () 27.6 19.9 38.2 22.5 0.19 Lead foot angle at BR () 25.3 18.8 39.8 19.8 0.07 Knee flexion angle at FC () 157.4 12.9 153.3 13.0 0.59 Knee flexion angle at BR () 151.8 12.3 151.7 5.3 0.90 Pelvic tilt at FC () 11.7 21.9 12.2 3.8 0.96 Pelvic tilt at BR () 23.8 8.2 24.0 8.9 0.98 Pelvic rotation at FC () 71.0 22.7 78.9 22.9 0.33 Pelvic rotation at BR () 4.2 14.45 5.6 13.5 0.84 Trunk lean at BR () 17.8 13.1 18.1 12.2 0.95 Shoulder Rotation at FC () 93.2 25.7 98.4 25.4 0.49 Shoulder Rotation at BR () 0.1 12.2 0.1 11.4 0.94 Range of Motion (ROM) Transverse lead foot rotation () 10.1 26.6 6.3 4.9 0.54 Sagittal knee flexion ROM () 22.8 8.7 23.9 5.7 0.81 Transverse pelvis ROM () 67.3 20.6 72.3 20.4 0.65 Pelvic tilt ROM () 15.8 20.9 13.5 7.9 0.83 Sagittal trunk lean ROM () 34.7 14.6 37.1 8.2 0.91 Transverse shoulder ROM () 95.3 25.2 96.5 25.5 0.90 FC= Foot Contact BR= Ball Release
81 Angular Velocities and Onset of LBP Table 4 14 describes the maximal angular velocities and Crunch Factor Index between participants who developed LBP and those who did not. Participants who developed LBP had a significantly higher maximal pelvic acceleration (p = 0.0 04 d = 1.48 ) during their baseline testing and a significantly higher pelvic acceleration at maximal lateral trunk tilt (p=0.02 4 d = 0.79) Table 4 14. Maximal angular velocities, Crunch Factor Index and development of LBP. Values are means SD. S No LBP Developed LBP Developed (n=1 19 ) (n=8) p (sig) Maximal angular velocity Pelvis (/s) 541.2 147.2 623.9 138.9 0.26 Trunk (/s) 647.0 168.4 714.1 160.5 0.52 Shoulders (/s) 862.63 221.9 901.3 184.0 0.86 Crosse (/s) 1380.5 409.3 1543.2 397.4 0.55 Timing of maximal angular velocity Pelvis (%) 63.5 37.6 60.9 23.9 0.82 Trunk (%) 72.7 12.9 72.3 13.6 0.84 Shoulders (%) 81.0 12.8 74.1 14.5 0.15 Ball velocity (km/h) 99.9 25.9 108.1 26.9 0.61 Maximal lateral trunk tilt 6.3 5.9 4.3 3.1 0.46 Maximal pelvic acceleration 4227.1 1252.3 5782.9 800.9 *<0.01 Pelvic acceleration @ maximal lateral trunk tilt 1989.7 2109.5 3811.1 2461.5 *0.02 14577.2 21829.6 14086.3 16413.3 0.72 2 ) @ peak lateral trunk lean ()
82 Single Leg Squat Kinematics and Onset of LBP Table 4 15 presents the kinematic differences of the hip, knee, and pelvis during a dominant and non dominant single leg squat between participants who developed LBP and those who did not. No significant differences were found in any variable between the p articipants who developed LBP and the group that did not. Table 4 15. Single leg squat kinematics of lacrosse participants who developed LBP and those who did not. Values are means SD. S lateral ROM represents t he added knee or hip adduction and abduction No LBP Developed LBP Developed (n=119 ) (n=8) p (sig) Dominant Single Leg Squat Max Knee Flexion (), sagittal 75.0 14.3 74.5 9.9 0.82 Knee Flexion ROM (), sagittal 75.1 15.2 67.3 13.0 0.24 Max Knee Abduction (), frontal 7.7 5.2 8.5 7.4 0.35 Max Knee Adduction (), frontal 2.8 6.0 0.2 5.6 0.91 Knee Medial Lateral ROM (), frontal 10.6 5.5 8.3 1.9 0.38 Max Hip Flexion (), sagittal 58.5 16.6 65.0 6.9 0.59 Hip Flexion ROM (), sagittal 58.2 16.3 64.2 10.8 0.64 Max Hip Abduction (), frontal 1.2 4.9 0.5 2.7 0.87 Max Hip Adduction (), frontal 14.4 6.9 14.3 5.1 0.90 Hip Medial Lateral ROM (), frontal 15.6 5.7 14.7 3.9 0.77 Max Pelvic Drop (), frontal 7.1 4.2 7.2 4.0 0.92 Pelvic Drop ROM (), frontal 11.6 4.7 10.6 4.2 0.62 Non Dominant Single Leg Squat Max Knee Flexion (), sagittal 74.2 15.9 77.2 10.9 0.86 Knee Flexion ROM (), sagittal 73.8 16.2 74.2 11.6 0.83 Max Knee Abduction (), frontal 8.0 5.6 6.3 4.7 0.50 Max Knee Adduction (), frontal 2.9 6.3 4.7 8.9 0.31 Knee Medial Lateral ROM (), frontal 10.9 5.8 11.0 4.3 0.83 Max Hip Flexion (), sagittal 56.6 16.4 63.7 11.2 0.51 Hip Flexion ROM (), sagittal 56.3 16.1 62.6 21.8 0.55 Max Hip Abduction (), frontal 1.6 4.7 1.9 5.6 0.83 Max Hip Adduction (), frontal 13.3 6.7 12.4 5.8 0.64 Hip Medial Lateral ROM (), frontal 14.9 5.5 13.7 0.9 0.50 Max Pelvic Drop (), frontal 3.4 6.2 3.8 6.8 0.89 Pelvic Drop ROM (), frontal 11.4 4.7 11.0 4.0 0.71
83 CHAPTER 5 DISCUSSION To our knowledge, this is the largest investigation into the development and effect of LBP on shooting performance in lacrosse players. Our primary aim was to determine kinematic effects of pre existing LBP on key kinematics of the lacrosse shot motion in lacrosse athletes. Initial hypotheses focused on aspects of player orientation and transfer of motion from the lower body to th e upper body during a lacrosse shot. Existing LBP may cause constraint of rotational movement and increase core stabilization to mitigate mechanical stress on the painful spine. This would subsequently lead to decreased angular excursions of the pelvis, tr unk and shoulders. Moreover, we predict ed asymmetric pelvic and trunk angular velocities an d timing of peak velocities would contribute to asymmetric torsional, axial and compressive stresses at the spine that could be related to pain. Furthermore, lower b ody stab ilization with knee flexion would be elevated in players with LBP. The results of our study indicated no differences in lateral trunk lean, total excursion from pelvis to shoulder, or angular velocity transfer from pelvis to trunk, in lacrosse play ers with pre existing low back pain. Moreover, we were able to determine that lead knee flexion differences existed between symptomatic and asymptomatic participants. These results will be further discussed. We did not find any differences in lateral tru nk lean, angular velocity transfer from the pelvis to the trunk in players with pre existing LBP and no pain. W e a lso found no differences in total pelvis to shoulder excursion between these two groups In related literature, deficits in pelvis transverse range of motion and pelvic angular velocity were detected in people with LBP (Sung, 2014) In our pilot study involv ing lacrosse players with LBP, restrictions of angular velocity transfer occurred from the pelvis to the trunk, and reductions in pelvi s and shoulder total excursion existed in players with LBP (Wasser et al., 2016b) Our current study did not show
84 similar differences to our pilot study ; however we recognize that our previous sample size may not been large enough to confir m these results. Though differences in transfer of angular velocity and total pelvis to shoulder excursion were insignificant findings between symptomatic and asymptomatic participants in this current study, we did determine that peak angular velocity at t he pelvis, trunk, and shoulder segments were significantly slower. The significant decreases in angular velocities may negate distinguishable impacts to transfer of energy due to already lessened velocities. No significant differences in lateral trunk lea n were detected between players with and without LBP This finding was not a major surprise because although studies of the golf swing, a similar high speed rotational sport indicated players who experience d LBP used more lateral side bending during the b ackswing (Lindsay and Horton, 2002) other studies indicated minimal differences in trunk kinematics. (Tsai et al., 2010) While inconclusive in golf, our study is the fir st to determine that the prescence of LBP does not influence a lacrosse players lateral trunk lean during a shot. We anticipated lacrosse players with pre existing LBP would exhibit greater knee flexion at baseline than those without LBP due to restrictions in trunk flexion With additional knee flexion, players may improve their base of support and increase players ability to stabilize and support spine rotation while experiencing LBP. At foot contact (FC) and ball release (BR), no differences were identifi ed with knee flexion angle. However, players with LBP had greater sagittal knee flexion ROM during their dominant shot. This result supports our previous pilot study which indicated similar results. (Wasser et al., 2016b) Previous research h as indicated the importance of co activating lower extremity and core musculature for low body stability as the upper body rotates over the pelvis. (Chow et al., 2003; Millard and Mercer, 2014; Oliver et al., 2011) While we did not measure muscle activity of the lower extremity during the
85 shot motion, the deeper knee flexion peak angle and greater flexion ROM indicate that the lower extremity suggest that the lead leg was used for stabilization. Lacrosse players develop fast ball speeds by transferring that energy along the kinetic chain from the lower body to ball release. (Millard and Mercer, 2014; Weber et al., 2014) W e investigated limb side differences between peak angular velocities and timing of these peak velocities at the hip and trunk in the population of players with reported LBP. Asymmetric pelvis and trunk angular velocities and timing of peak velocities were hypothesized to contribute to asymme tric torsional, axial and compressive stresses at the spine that could be related to pain in the lacrosse population. S ignificant ly lower peak velocities and delayed timing of peak velocities at the hip, trunk, and shoulders between lacrosse shots from the dominant and non dominant side were present. Previous literature supports this finding, with angular velocities a nd segment or joint excursions being less on the non dominant side. (Vincent et al., 2015) These differences remained irrespective of LBP. This finding implies that the execution of the motion on the non dominant side is not a coordinated or sequencial motion with players essentially shooting with a pushing motion of their arms rather than gene rating rotational motion. For dominant shots, players with LBP shot with significantly lower pelvic, trunk, and shou lder angular velocities. Only pelvic angular velocity was significantly less during non dominant shots in players with LBP Also, the peak v elocities of the pelvis and tru n k occurred significantly later in the lacrosse shot with non dominant shots. T hus, th e segmental angular velocities and to some extrent, the timing, may be related to LBP in lacrosse players Significantly lower angular velo cities during a non dominant shot may not provide large enough magnitudes of compressive and torsional forces at the low back to elicit pain or injury. To summarize, the magnitude of side specific
86 (dominant v non dominant) effects of LBP on a la crosse sho t are mutually exclusive due to significantly different motion patterns. We attempted to determine the influence of baseline ball speed, shoulder to pelvis crossover (crank back), and stride length on the development of LBP over a period of 6 months. We anticipated that athletes who engage in excessive axial rotation about the spine and generated greater Crunch Index values would be at a greater risk for onset of LBP over time. Ball velocity was not significantly impacted between players who experienced LBP and those who did not. This was a surprising result, as we hypothesized the LBP would impair production of fast angular velocities of the body segments and transfer of energy to the crosse and ball. It is apparent players with LBP find methods to compensate for lower angular segmental velocities in the prescence of LBP to generate fast ball speeds This could indicate that there are pe rformance factors here that we did not capture that could contribute to maintained or higher ball speeds. Utilization of different muscle activation patterns or greater motor unit activation with less joint excursion/segmental rotation could be captured wi th the incorporation of EMG. W e were able to follow up with players at several time periods after their baseline testing (2, 4, and 6 months). The most frequently reported area of pain and injury was at the low back. W e predict ed ball speed to be a risk fa ctor for developing LBP over time due to the amount of force and speed tha t player would need to generate, especially at the anatomical locations where rotational motion is great est Though players who subsequently developed LBP shot 8.2% faster than those players who did not develop pain, this was not statistically significant after co varying for age, gender, and position played. We investigated relative to preexisting LBP and onset of pain One could surmise tha t due to pain at the low back, the extent of pelvis to shoulder
87 crossover (crank back) would be limited, but this wa s not the case. Players with LBP were not limited with their ability to crank back during the lacros se shot. Moreover, there was no differen ce in timing of when this crank back occurred from FC to BR Our previous research also indicated no significant difference in crank back between subjects with and without LBP. (Wasser et al., 2016b) Furthermore, we anticipated that asymptomatic participants with higher crank back measures would develop LBP during our 6 month follow up period. Contrary to our hypothesis, players who developed LBP actually had less crank back (4.5% less), but this was not a statistically significant finding. Though our h ypothesis was not supported, it is possible that motions of a arms and the use of a fixed lever (crosse) may explain this finding. During a lacrosse shot, arm position may be extended posterior to the trunk with an abducted shoulder thus creating a longer lever arm with out chang in g shoulder to pelvis crossover Add itionally, the use of a solid, fixed crosse and the physical limitation presented from holding the crosse with both hands, non dominant shoulder horizontal adduction ROM may restrict the extent of a players should to pelvis crossover. Therefore, crank bac k itself may not elevate the risk of developing LBP. Differences in stride length and s tride to height ratio were not different based on preexisting LBP. We hypothesized that participants with a relativ ely shorter stride length would develop LBP by six mo nths. Unfortunately, this prediction was not supported. P articipants who did develop LBP by six months exhibited larger stride lengths (8.7% longer) compared to those who remained asymptomatic, but this difference was not statistically significant. Therefo re stride length as a standalone measure did not seem to be important in the onset of LBP Though we predicted that stride length may influence development of LBP, these results would indicate
88 that motions higher up the kinematic chain (ie. knee, hip, and core in stability) may be more responsible for the development of LBP. A novel aspect of this study wa established y, however, subsequent literature has shown that this calculation has been largely inconclusive in detecting the impact unilateral loading at the low back and lumbar spine during rotational sporting activity. (Glazier, 2010) Our innovative approach estimates (I would say estimates here i nstead) t he stress at the low back as an interaction of max lateral trunk tilt prior to BR and pelvic acceleration at the time point of maximal lateral trunk tilt. We suggest that t his time point functionally represents one of the highest rotational and sh ear stress aspects of the shot. P reliminary data initially indicated players who had existing LBP had a significantly larger we predicted that not only would players with existing LBP but those players who subsequently developed LBP will have a significantly larger value during baseline testing. Contrary to our hypothesis, significantly lower in participants with pre existing LBP ; however, it was not a predi ctive factor in the onset of LBP over time. values in players with pre existing LBP could largely be explained by a lower pelvic acceleration a t maximal lateral trunk tilt ( the timing of maximal lateral trunk tilt was 25.6% l ater in participants with LBP ) Given that LBP impairs production of fast pelvic angular velocity acceleration would be reduced P articipants who developed LPB over six months had a 9 1.5% faster pelvic acceleration at maximal lateral trunk tilt during ini tial testing. Moreover, maximal pelvic acceleration was also significantly faster for those who developed LBP (36.8% faster) compared to those who did not. This is an interesting finding as differences in maximal pelvic velocity
89 between study groups were n ot significant. This suggests that maximal velocity of transverse or pelvic rotation itself is not a risk factor; it may be more important to examine how the player achieves that maximal velocity by measuring acceleration S ignificantly faster acceleration at the pelvis likely increased torque and lateral flexion at the lumbar spine This mechanical mechanism has been presented in previous literature as a very common mechanism of LBP, t issue damage. (Gluck et al., 2008) Physical function factor effects (flexibi l ity / stability) on lumbar spine health among lacrosse athlete s w ere examined Low flexibility about the hip may restrict stride length and pelvis rotation in the transverse plane. We evaluated hip flexibility for lacrosse players and hypothesized that players with LBP would demonstrate lower hip flexibility. Hip fle xibility did not differ by preexisting LBP and our hypothesis was not supported This would suggest sagittal plane hip flexibility itself may not be associated with back pain in the general lacrosse population. We further attempted to find if the presence of LBP was related to shoulder flexibility in the lacrosse population. Shoulder flexibility was not associated with LBP in this cohort which did not support our hypothesis. Though we had hypothesized that relatively low shoulder external rotation m ay rest rict the degree of crank back during the shot, the use of a fixed crosse may limit the impact of reduced shoulder flexibility in the sport of lacrosse L iterature has noted that baseball pitchers with improper trunk rotation sequences had greater maximal s houlder external rotation and proximal shoulder forces (Oyama et al., 2014) There was a wide range of experience variability in our subjects, and we combined male and female players (which in itself can change the amount of crank back possible at the shoulder for females. However, we were surprised to discover th at greater low back NRS Pain scores were related to dominant shoulder internal rotation deficits. An interpretation of this finding is that
90 players with ROM deficits at the shoulder may compensate with increased ROM at the pelvic, trunk, and shoulder segmen ts during follow through This potential explanation may direct the focus of future research to potential underlying mechanisms of pain during the eccentric portion of the lacrosse shot (ie. follow through). The single leg squat test was intended to challenge participants and determine quality of functional movement and postural orientation. (Ageberg et al., 2010) The single leg squat test can also be used to determine the movement control provided by the gluteal muscle group, and the inability to control single legged motions can contr ibute to pelvic drop and asymmetric forces acting at the low back. Features of the s ingle leg squat performance were measured to determine if excessive lateral pelvic drop and hip adduction would lea d to the development of LBP in lacrosse players over time Players with LBP demonstrated no differences in key motion features ( lateral pelvic drop or hip adduction ) during a single leg squat. However, players with pain had significantly larger hip flexion excursion and dropped into a deeper squat than players w ith no pain. S ingle leg squat features did not predict the development of LBP in the following six months as they continue to play lacrosse. These results would need further analysis before suggesting the inability of a single leg squat test to predict LBP onset. Analysis would consist of bracketing age and evaluating depth of squat, as less coordinated players were unable to/did not execute squats with appreciable depth. With respect to non dominant squat performance, participants with LBP exhibited signi ficantly more medial lateral movement at the knee (knee along with a higher maximal hip flexion angle and overall hip flexion excursion during their non dominant squat performance. This wobble reflects the inability to stabilize the non dominant knee, and is due to sub optimal gluteal activation and/or strength, which is important for both knee and pelvic stability in the frontal plane. (Kim et al., 2016) Players with
91 LBP performed single leg squat s with 9% and 6.8% greater knee flexio n excursion respectively which w ould assist with a greater compensatory upper body anterior lean with a deeper squat Though greater knee flexion by itself is a simple characteristic of a lacrosse player with LBP, the addition of poor knee and pelvic stability may introduce a risk factor to strain and injury at the low back, pelvis and knee. I njury prevention and rehab ilitative efforts must be made to address stability deficits at the knee and pelvis by improving neuromuscular activation and emphasizing gluteal strengthening programs, especially for participants who are still maturing. Our final aim was to detect contr ibutory factors for the onset of LBP in lacrosse athletes. Midfielders and attack are most often the shooting positions on the field. We hypothesized that the higher volume of throwing exposure would be related to development of LBP. It is hypothesized tha t these field positions, which shoot high v olumes during play and are identified to most likely sustain injury (Barber Foss et al., 2018) We were unable to s upport our predic tion that LBP onset is position related. This can potentially be explained by the game strategy these players play with Those who play the attack position may have more constrained shooting motions due to limited space to move between def ending players and the need to shoot quickly, which would impact the amount of force that could potentially be produced. Midfielders, though likely to shoot the most, may shoot significantly less than those in the attack position. The bigger explanation ma y be due to gender and age differ e nces. As players mature, they will likely get stronger and shoot with higher segmental velocities. Moreover, male players shoot with higher velocities compared to their age matched female counterpart. (Zdziarski et al., 2014) Further analysis between genders and players, grouped by age, may highlight that older ma le attack and midfield position players would develop LBP compared to other positions on the field of play.
92 Evidence is rapidly growing surrounding the increased risk for higher injury rates with early sport specialization, which we can further attest in the sport of lacrosse. (Jayanthi et al., 2013) While US Lacrosse has recognized this evidence, and made suggestions to avoid sport specialization until 15 16 years of age, there will still remain a population of lacrosse players who specialize early. Participat ion in other sports in addition to lacrosse is theorized to provide protective benefits against sport specific injury due to cross training and experiencing different physical cognitive, affective, and psycho social environments. (Ct et al., 2009; Pasulka et al., 2017) Over 4 5 % of all participants were multi sport athletes, meaning th ey participated in at least one sport in addition to lacrosse The most common sports that lacrosse players partic ipated in we re football (17.2%), basketball (16.4%), running (13.3%), soccer (14.8%), and golf (12.5%). With the rising concern over sport spe cialization as a factor for development of overuse injuries (Jayanthi et al., 2013) we hypothesized that players who we re currently participating in sports in addition to l acrosse throughout the year would have a lower prevalence of LBP compared to players who participate only in lacrosse. We are able to support this hypothesis. Players who only participated in lacrosse had a 4.6 fold increase in the odds of de veloping LBP. We are unable to single out a specific sport that may reduce the odds of developing LBP. This significant finding has significant implications for the growing population of lacrosse players under the age of 16. As we have seen in previous li terature the increase of overuse injuries for athletes increase by 27%, these statistics have also been noted to vary by age, sex, and sport. (Brenner and Council on Sports M edicine and Fitness, 2016; Fabricant et al., 2016) We are the first to identify that sport specialization in lacrosse may present a higher injury rate compared to other sports.
93 Specific motion factors that place high mechanical stress on the spine, coupled with player characteristics such as player position, age, sex, body size and flexibility about the hip or shoulder may contribute to the onset of LBP over time. While each fact or alone may load the lumbar spine, it is likely that a clustering of features better predicts the onset of LBP than each factor alone. High rotational forces generated by high velocity throwing motion may increase mechanical stresses on the body at specif ic sites, such as the low back. (Ferdinan ds et al., 2009; Schilling et al., 2013) We were unable to determine any key features of the lacrosse shooting motion that predicted the severity of LBP. Though no specific kinematics are noted to predict severity of LBP, this would also indicate that p redictors to LBP severity may not be entirely related to lacrosse shot kinematic factors. Limitations L imitations of this study deserve comment Though we followed lacrosse athletes prospectively, functional and kinematic measures were only collected at baseline. Future investigations should include regular kinematic follow up. Moreover, a larger sample size of lacrosse players who developed LBP during follow up would improve study power and give a better understanding of risk factors that may predispose lacrosse athletes to develop LBP. T here are differences in shot motions between male and female lacrosse players. These differences are largely be due to equipment and game strategy. The crosse used by female lacrosse players have a shallow pocket to cra dle the lacrosse ball, potentially forcing them to restrict their shot motions to prevent from losing possession of the ball. Moreover, due to rule restrictions and the lack of helmets and protective pads, as seen in the male population, contact injuries are significantly reduced. The combination of male and female players in our analysis may skew our overall results as each gender sustain injuries at different rates, (Kerr et al., 2018b) and perform shots with significantly lower velocities. (Zdziarski et al.,
94 2014) Moreover, developmental maturity is an important factor to consider for this age range. Differences i n developmental maturity can be highlighted by occuring at different times (females sooner than males), and having different effects (males having an advantage in size, strength and power) between genders. (Malina et al., 2015) Though the prevalence of LBP in lacrosse players were not different among genders, and we considered gender differences with o ur analysis, future studies should stratify into kinematic risk factors specifically for musculoskeletal injury and pain in the female lacrosse population. Lastly, considerations for volume of lacrosse and other sport participation could be further investi gated. Though we assessed years of lacrosse play, lacrosse session/week, and whether participants participated in other sports, we did not fully track participants lacrosse play and play in other sports for a long duration of time more than one year Thes e details could reveal sport participation volume factors that may predispose athletes to overuse injuries as some times during the year may have larger participation in sporting activities than other times Further research should aim to determine wrist, elbow, and shoulder kinematics in lacrosse players as the utilization of these segments could explain areas where players might compensate for LBP or they may further influence LBP (ie. Shoulder flexibility). Additional research should als o include stratifying female lacrosse motions and determine the relationship of pain onset to mechanics in this population. Although both males and females participate in the sport of lacrosse, numerous physiological, technical, and sport specific differen ces are evident that need to be investigated further. Lastly, a specific focus on events and motions during follow through are highly encouraged. With a large portion of low back injuries in lacrosse having a muscle tendon strain mechanism, (Dick et a l., 2007) this may relate to eccentric forces during the follow through phase. In other overhead sports like pitching, the follow through is the second
95 most stressful phase of a throw due to its eccentric demand on the body. (Calabrese, 2013b) This study was designed to identify contributory factors for LBP onset for events leading up to ball release, more impactful results may be identified for events following ball release. Conclusion Lacrosse players with existing LBP have slower peak pelvic, trunk, and shoulder angular velocities and greater knee flexion during a shot motion than players with no pain. There were no differences in dominant nondominant asymmetry patterns based on LBP. S ignificantly higher pelvic acceleration is a distinguishable risk factor in players who developed LBP. Lack of multi sport participation is identified as contributory factors to the onset of LBP in lac rosse athletes. With further age stratification and analysis, data will likely reveal subgroups of players who may benefit from training and injury prevention programs, and those players who develop pain should consider improving strength and stability aro und the core.
96 LIST OF REFERENCES 2017 2018 High School Athletics Participation Survey, 2018. The National Federation of State High School Associations. Abrams, G.D., Renstrom, P.A., Safran, M.R., 2012. Epidemiology of musculoskeletal injury in the tennis player. Br. J. Sports Med. 46, 492 498. https://doi.org/10.1136/bjsports 2012 091164 Adams, M.A., Hutton, W.C., 1982. The mechanics of prolapsed intervertebral disc. Int. Orthop 6, 249 253. Ageberg, E., Bennell, K.L., Hunt, M.A., Simic, M., Roos, E.M., Creaby, M.W., 2010. Validity and inter rater reliability of medio lateral knee motion observed during a single limb mini squat. BMC Musculoskelet. Disord. 11, 265. https://doi.org /10.1186/1471 2474 11 265 Leg Squat Performance in Active Adolescents Aged 8 17 Years. J. Strength Cond. Res. 31, 1187 1191. https://doi.org/10.1519/JSC.0000000000001617 Atwater, A.E. 1979. Biomechanics of overarm throwing movements and of throwing injuries. Exerc. Sport Sci. Rev. 7, 43 85. Bahr, R., 2009. No injuries, but plenty of pain? On the methodology for recording overuse symptoms in sports. Br. J. Sports Med. 43, 966 972. http s://doi.org/10.1136/bjsm.2009.066936 Barber Foss, K.D., Le Cara, E., McCambridge, T., Hinton, R.Y., Kushner, A., Myer, G.D., 2018. Level and Sex Specific Injury Prevention Strategies. Clin. J. Sport Med. Off. J. Can. Acad. Sport Med. 28, 406 413. https://doi.org/10.1097/JSM.0000000000000458 Barker Davies, R.M., Roberts, A., Bennett, A.N., Fong, D.T.P., Wheeler, P., Lewis, M.P., 2018. Single leg squat ratings by clinicians are reliable and predict excessive hip internal rotation moment. Gait Posture 61, 453 458. https://doi.org/10.1016/j.gaitpost.2018.02.016 Batt, M.E., 1992. A survey of golf injuries in amateur golfers. Br. J. Sports Med. 26, 63 65. Black, G.M., Gabbett, T.J., Cole, M.H ., Naughton, G., 2016. Monitoring Workload in Throwing Dominant Sports: A Systematic Review. Sports Med. Auckl. NZ 46, 1503 1516. https://doi.org/10.1007/s40279 016 0529 6 Brenner, J.S., Council on Sports medicine and Fitness, 2016. Sports Specialization a nd Intensive Training in Young Athletes. Pediatrics 138. https://doi.org/10.1542/peds.2016 2148
97 Bulbulian, R., Ball, K.A., Seaman, D.R., 2001. The short golf backswing: effects on performance and spinal health implications. J. Manipulative Physiol. Ther. 2 4, 569 575. https://doi.org/10.1067/mmt.2001.118982 Calabrese, G.J., 2013a. Pitching mechanics, revisited. Int. J. Sports Phys. Ther. 8, 652 660. Calabrese, G.J., 2013b. P itching mechanics, revisited Int. J. Sports Phys. Ther. 8, 652 660. Sullivan, P., Straker, L., Elliott, B., Reid, M., 2014. Back pain in tennis players: a link with lumbar serve kinematics and range of motion. Med. Sci. Sports Exerc. 46, 351 357. https://doi.org/10.1249/MSS.0b013e3182a45cca livan, P., Elliott, B., Reid, M., 2013. Lumbar loading in the elite adolescent tennis serve: link to low back pain. Med. Sci. Sports Exerc. 45, 1562 1568. https://doi.org/10.1249/MSS.0b013e31828bea5e Elliott, B., Reid, M., 2015. Lumbar Mechanics in Tennis Groundstrokes: Differences in Elite Adolescent Players With and Without Low Back Pain. J. Appl. Biomech. https://doi.org/10.1123/jab.2015 0122 Chalmers, P.N., Wimmer, M.A., Verma, N.N., Cole, B.J., Romeo, A.A., Cvetanovich, G.L., Pearl, M.L., Chalmers, P.N., Wimmer, M.A., Verma, N.N., Cole, B.J., Romeo, A.A., Cvetanovich, G.L., Pearl, M.L., 2017. The Relationship Between Pitching Mechanics and Injury: A Review of Current Concepts. Sports Health 9, 21 6 221. https://doi.org/10.1177/1941738116686545 Chmielewski, T.L., Hodges, M.J., Horodyski, M., Bishop, M.D., Conrad, B.P., Tillman, S.M., 2007. Investigation of clinician agreement in evaluating movement quality during unilateral lower extremity functiona l tasks: a comparison of 2 rating methods. J. Orthop. Sports Phys. Ther. 37, 122 129. https://doi.org/10.2519/jospt.2007.2457 Chow, J.W., Shim, J.H., Lim, Y.T., 2003. Lower trunk muscle activity during the tennis serve. J. Sci. Med. Sport Sports Med. Aust. 6, 512 518. Claiborne, T.L., Armstrong, C.W., Gandhi, V., Pincivero, D.M., 2006. Relationship between hip and knee strength and knee valgus during a single leg squat. J. Appl. Biomech. 22, 41 50. Cohen, J., 1988. Statistical power analysis for the behavioral sciences, 2nd ed. ed. L. Erlbaum Associates, Hillsdale, N.J. Colby, M.J., Dawson, B., Heasman, J., Rogalski, B., Rosenberg, M., Lester, L., Peeling, P., 2017. Preseason Workload Volume and High Risk Periods for Noncontact Injury Across Multiple Australian Football League Seasons. J. Strength Cond. Res. 31, 1821 1829. https://doi.org/10.1519/JSC.0000000000001669
98 Cole, M.H., Grimshaw, P.N., 2016. The Biomechanics of the Modern Golf Swing: Implications for Lower Back Injuries. Sports Med. Auckl. NZ 46, 339 351. https://doi.org/10.1007/s40279 015 0429 1 related low back pain. Spine J. Off. J. North Am. Spine Soc. 14, 799 807. https://doi.org/10.1016/j.spinee.2013.09.019 Correia, J.P., Oliveira, R., Vaz, J.R., Silva, L., Pezarat Correia, P., 2016. Trunk muscle activation, fatigue and low back pain in tennis players. J. Sci. Med. Sport 19, 311 316. https://doi.org/10.1016/j.jsams.2015.04.002 Ct, J., Lidor, R., Hackfort, D., 2009. ISSP p osition stand: To sample or to specialize? Seven postulates about youth sport activities that lead to continued participation and elite performance. Int. J. Sport Exerc. Psychol. 7, 7 17. https://doi.org/10.1080/1612197X.2009.9671889 Crotin, R.L., Bhan, S. Ramsey, D.K., 2015. An inferential investigation into how stride length influences temporal parameters within the baseball pitching delivery. Hum. Mov. Sci. 41, 127 135. https://doi.org/10.1016/j.humov.2015.03.005 i, L.J., 2000. Back injuries in the young athlete. Clin. Sports Med. 19, 663 679. De Luigi, A.J., 2014. Low back pain in the adolescent athlete. Phys. Med. Rehabil. Clin. N. Am. 25, 763 788. https://doi.org/10.1016/j.pmr.2014.06.004 Dick, R., 2013. Head pr Dick, R., Lincoln, A.E., Agel, J., Carter, E.A., Marshall, S.W., Hinton, R.Y., 2007. Descriptive Association Inju ry Surveillance System, 1988 1989 through 2003 2004. J. Athl. Train. 42, 262 269. Dick, R., Sauers, E.L., Agel, J., Keuter, G., Marshall, S.W., McCarty, K., McFarland, E., 2007b. egiate Athletic Association Injury Surveillance System, 1988 1989 through 2003 2004. J. Athl. Train. 42, 183 193. Dierks, T.A., Manal, K.T., Hamill, J., Davis, I.S., 2008. Proximal and distal influences on hip and knee kinematics in runners with patellofem oral pain during a prolonged run. J. Orthop. Sports Phys. Ther. 38, 448 456. https://doi.org/10.2519/jospt.2008.2490 Dun, S., Fleisig, G.S., Loftice, J., Kingsley, D., Andrews, J.R., 2007. The relationship between age and baseball pitching kinematics in pr ofessional baseball pitchers. J. Biomech. 40, 265 270. https://doi.org/10.1016/j.jbiomech.2006.01.008
99 Dworkin, R.H., Turk, D.C., Wyrwich, K.W., Beaton, D., Cleeland, C.S., Farrar, J.T., Haythornthwaite, J.A., Jensen, M.P., Kerns, R.D., Ader, D.N., Brandenb urg, N., Burke, L.B., Cella, D., Chandler, J., Cowan, P., Dimitrova, R., Dionne, R., Hertz, S., Jadad, A.R., Katz, N.P., Kehlet, H., Kramer, L.D., Manning, D.C., McCormick, C., McDermott, M.P., McQuay, H.J., Patel, S., Porter, L., Quessy, S., Rappaport, B. A., Rauschkolb, C., Revicki, D.A., Rothman, M., Schmader, K.E., Stacey, B.R., Stauffer, J.W., von Stein, T., White, R.E., Witter, J., Zavisic, S., 2008. Interpreting the clinical importance of treatment outcomes in chronic pain clinical trials: IMMPACT rec ommendations. J. Pain Off. J. Am. Pain Soc. 9, 105 121. https://doi.org/10.1016/j.jpain.2007.09.005 Eliassen, W., Saeterbakken, A.H., van den Tillaar, R., 2018. C omparison of bilateral and unilateral squat exercises on barbell kinematics and muscle activation Int. J. Sports Phys. Ther. 13, 871 881. Ellenbecker, T.S., Roetert, E.P., Bailie, D.S., Davies, G.J., Brown, S.W., 2002. Glenohumeral joint total rotation range of motion in elite tennis players and baseball pitchers. Med. Sci. Sports Exerc. 34, 2052 2056. https://doi.org/10.1249/01.MSS.0000039301.69917.0C Escamilla, R.F., Barrentine, S.W., Fleisig, G.S., Zheng, N., Takada, Y., Kingsley, D., Andrews, J.R., 2007. Pitching biomechanics as a pitcher approaches muscular fatigue during a simulated baseball game. Am. J. Sports Med. 35, 23 33. https://doi.org/10.1177/0363546506293025 Fabricant, P.D., Lakomkin, N., Sugimoto, D., Tepolt, F.A., Stracciolini, A., Kocher, M.S., 2016. Youth sports specialization and musculoskeletal injury: a systematic review of the literature. Phys. Sportsmed. 44, 257 262. https://doi.org/10.1080/00913847.2016.1177476 Ferdinands, R.E.D., Kersting, U., Marshall, R.N., 2009. Three dimensional lumbar segment kinetics of fast bowling in cricket. J. Biomech. 42, 1616 1621. https://doi.or g/10.1016/j.jbiomech.2009.04.035 Fett, D., Trompeter, K., Platen, P., 2017. Back pain in elite sports: A cross sectional study on 1114 athletes. PloS One 12, e0180130. https://doi.org/10.1371/journal.pone.0180130 Fleisig, G.S., Barrentine, S.W., Zheng, N., Escamilla, R.F., Andrews, J.R., 1999. Kinematic and kinetic comparison of baseball pitching among various levels of development. J. Biomech. 32, 1371 1375. Ganesan, S., Acharya, A.S., Chauhan, R., Acharya, S., 2017. Prevalence and Risk Factors for Low Bac k Pain in 1,355 Young Adults: A Cross Sectional Study. Asian Spine J. 11, 610 617. https://doi.org/10.4184/asj.2017.11.4.610 https://www.uslacrosse.org/rules/girls rules (accessed 7.26.19).
100 Glazier, P.S spine pathology in cricket fast bowlers? Sports Med. Auckl. NZ 40, 809 815. https://doi.org/10.2165/11536590 000000000 00000 Gluck, G.S., Bendo, J.A., Spivak, J.M., 2008. The lumbar spine and low back pain in golf: a literature review of swing biomechanics and injury prevention. Spine J. Off. J. North Am. Spine Soc. 8, 778 788. https://doi.org/10.1016/j.spinee.2007.07.388 Graci, V., Van Dillen, L.R., Salsich, G.B., 2012. G ender differences in trunk, pelvis and lower limb kinematics during a single leg squat. Gait Posture 36, 461 466. https://doi.org/10.1016/j.gaitpost.2012.04.006 Graw, B.P., Wiesel, S.W., 2008. Low back pain in the aging athlete. Sports Med. Arthrosc. Rev. 16, 39 46. https://doi.org/10.1097/JSA.0b013e318163be67 Grimshaw, P.N., Burden, A.M., 2000. Case report: reduction of low back pain in a professional golfer. Med. Sci. Sports Exerc. 32, 1667 1673. Guddal, M.H., Stensland, S.., Smstuen, M.C ., Johnsen, M.B., Zwart, J. A., Storheim, K., 2017. Physical Activity Level and Sport Participation in Relation to Musculoskeletal Pain in a Population Based Study of Adolescents: The Young HUNT Study. Orthop. J. Sports Med. 5, 2325967116685543. https://do i.org/10.1177/2325967116685543 Haddas, R., Sawyer, S.F., Sizer, P.S., Brooks, T., Chyu, M. C., James, C.R., 2016. Effects of Volitional Spine Stabilization and Lower Extremity Fatigue on Trunk Control During Landing in Individuals With Recurrent Low Back P ain. J. Orthop. Sports Phys. Ther. 46, 71 78. https://doi.org/10.2519/jospt.2016.6048 Harris, P.A., Taylor, R., Thielke, R., Payne, J., Gonzalez, N., Conde, J.G., 2009. Research electronic data capture (REDCap) -a metadata driven methodology and workflow p rocess for providing translational research informatics support. J. Biomed. Inform. 42, 377 381. https://doi.org/10.1016/j.jbi.2008.08.010 Sport 97. Hinton, R.Y., Linco ln, A.E., Almquist, J.L., Douoguih, W.A., Sharma, K.M., 2005. Epidemiology of lacrosse injuries in high school aged girls and boys: a 3 year prospective study. Am. J. Sports Med. 33, 1305 1314. https://doi.org/10.1177/0363546504274148 Holt, T., Oliver, G.D ., 2016. Hip and upper extremity kinematics in youth baseball pitchers. J. Sports Sci. 34, 856 861. https://doi.org/10.1080/02640414.2015.1076163 Hosea, T., Garr, C., Galli, K., 1990. Biomechanical Analysis of the Golfers Back. Sci. Golf Proc. World Sci. C ongr. Golf 43 48.
101 How Soon is Too Soon to Specialize? [WWW Document], 2016. US Lacrosse. URL https://www.uslacrosse.org/blog/how soon is too soon to specialize (accessed 7.25.19). Hurd, W.J., Kaplan, K.M., Eiattrache, N.S., Jobe, F.W., Morrey, B.F., Kauf man, K.R., 2011. A profile of glenohumeral internal and external rotation motion in the uninjured high school baseball pitcher, part I: motion. J. Athl. Train. 46, 282 288. Jackson, J.K., Shepherd, T.R., Kell, R.T., 2011. The influence of periodized resist ance training on recreationally active males with chronic nonspecific low back pain. J. Strength Cond. Res. Natl. Strength Cond. Assoc. 25, 242 251. https://doi.org/10.1519/JSC.0b013e3181b2c83d Jamison, R.N., Raymond, S.A., Slawsby, E.A., McHugo, G.J., Bai rd, J.C., 2006. Pain assessment in patients with low back pain: comparison of weekly recall and momentary electronic data. J. Pain Off. J. Am. Pain Soc. 7, 192 199. https://doi.org/10.1016/j.jpain.2005.10.006 Jayanthi, N., Pinkham, C., Dugas, L., Patrick, B., Labella, C., 2013. Sports specialization in young athletes: evidence based recommendations. Sports Health 5, 251 257. https://doi.org/10.1177/1941738112464626 Jette, A.M., 2006. Toward a common language for function, disability, and health. Phys. Ther. 86, 726 734. Jette, A.M., 1994. Physical disablement concepts for physical therapy research and practice. Phys. Ther. 74, 380 386. Jimnez Buuales, M.T., Gonzlez Diego, P., Martn Moreno, J.M., 2002. [International classification of functioning, disabil ity and health (ICF) 2001]. Rev. Esp. Salud Publica 76, 271 279. John A. Mercer, Jason H. Nielson, 2012. Description of Phases and Discrete Events of the Lacrosse Shot. Sport J. Jones, P.A., Herrington, L.C., Munro, A.G., Graham Smith, P., 2014. Is there a relationship between landing, cutting, and pivoting tasks in terms of the characteristics of dynamic valgus? Am. J. Sports Med. 42, 2095 2102. https://doi.org/10.1177/0363546514539446 Kageyama, M., Sugiyama, T., Kanehisa, H., Maeda, A., 2015. Difference B etween Adolescent and Collegiate Baseball Pitchers in the Kinematics and Kinetics of the Lower Limbs and Trunk During Pitching Motion. J. Sports Sci. Med. 14, 246 255. Kageyama, M., Sugiyama, T., Takai, Y., Kanehisa, H., Maeda, A., 2014. Kinematic and Kine tic Profiles of Trunk and Lower Limbs during Baseball Pitching in Collegiate Pitchers. J. Sports Sci. Med. 13, 742 750.
102 Kerr, Z.Y., Lincoln, A.E., Caswell, S.V., Klossner, D.A., Walker, N., Dompier, T.P., 2018a. Epidemiology of National Collegiate Athletic 2009 10 Through 2014 15. J. Sport Rehabil. 27, 118 125. https://doi.org/10.1123/jsr.2016 0124 Kerr, Z.Y., Lincoln, A.E., Dodge, T., Yeargin, S.W., Covassin, T.M., Nittoli, V.C., Mensch, J., Roos, K.G., Dompier, T.P., 291. https://doi.org/10.1249/MSS.0000000000001422 Kerr, Z.Y., Lynall, R.C., Roos, K.G., Dalton, S.L., Djoko, A., Do mpier, T.P., 2017a. Descriptive Epidemiology of Non Time Loss Injuries in Collegiate and High School Student Athletes. J. Athl. Train. 52, 446 456. https://doi.org/10.4085/1062 6050 52.2.15 Kerr, Z.Y., Quigley, A., Yeargin, S.W., Lincoln, A.E., Mensch, J., Caswell, S.V., Dompier, T.P., 2014/15 academic years. Inj. Epidemiol. 4, 6. https://doi.org/10.1186/s40621 017 0104 0 Kim, D., Unger, J., Lanovaz, J.L., Oates, A.R., 2016. The Relationship o f Anticipatory Gluteus Medius Activity to Pelvic and Knee Stability in the Transition to Single Leg Stance. PM R 8, 138 144. https://doi.org/10.1016/j.pmrj.2015.06.005 Kim, G. M., Ha, S. M., 2015. Reliability of the modified Thomas test using a lumbo plevi c stabilization. J. Phys. Ther. Sci. 27, 447 449. https://doi.org/10.1589/jpts.27.447 Kim, W., Jin, Y.S., Lee, C.S., Bin, S. I., Lee, S.Y., Choi, K.H., 2015. Influence of Knee Pain and Low Back Pain on the Quality of Life in Adults Older Than 50 Years of A ge. PM R 7, 955 961. https://doi.org/10.1016/j.pmrj.2015.03.002 Koumantakis, G.A., Winstanley, J., Oldham, J.A., 2002. Thoracolumbar proprioception in individuals with and without low back pain: intratester reliability, clinical applicability, and validity. J. Orthop. Sports Phys. Ther. 32, 327 335. https://doi.org/10.2519/jospt.2002.32.7.327 Kujala, U.M., Salminen, J.J., Taimela, S., Oksanen, A., Jaakkola, L., 1992. Subject characteristics and low back pain in young athletes and nonathletes. Med. Sci. Sports Exerc. 24, 627 632. Kuni, B., Crdenas Montemayor, E., Bangert, Y., Rupp, R., Ales, J., Friedmann Bette, B., Schmitt, H., 2014. Impaired jump landing after exercise in recreational and in high performance athletes. J. Strength Cond. Res. 28, 2306 2313. https://doi.org/10.1519/JSC.0000000000000431 Kuriyama, N., Ito, H., 2005. Electromyographic functional analysis of the lumbar spinal muscles with low back pain. J. Nippon Med. Sch. Nippon Ika Daigaku Zasshi 72, 165 173.
103 La Touche R., Grande Alonso, M., Cuenca Martnez, F., Gnzlez Ferrero, L., Suso Mart, L., Paris Alemany, A., 2018. Diminished Kinesthetic and Visual Motor Imagery Ability in Adults With Chronic Low Back Pain. PM R. https://doi.org/10.1016/j.pmrj.2018.05.025 Lade nhauf, H.N., Fabricant, P.D., Grossman, E., Widmann, R.F., Green, D.W., 2013. Athletic participation in children with symptomatic spondylolysis in the New York area. Med. Sci. Sports Exerc. 45, 1971 1974. https://doi.org/10.1249/MSS.0b013e318294b4ed Laird, R.A., Gilbert, J., Kent, P., Keating, J.L., 2014. Comparing lumbo pelvic kinematics in people with and without back pain: a systematic review and meta analysis. BMC Musculoskelet. Disord. 15, 229. https://doi.org/10.1186/1471 2474 15 229 Lazu, A.L., Love, S.D., Butterfield, T.A., English, R., Uhl, T.L., 2019. THE RELATIONSHIP BETWEEN PITCHING VOLUME AND ARM SORENESS IN COLLEGIATE BASEBALL PITCHERS. Int. J. Sports Phys. Ther. 14, 97 106. Lewis, C.L., Foch, E., Luko, M.M., Loverro, K.L., Khuu, A., 2015. Diff erences in Lower Extremity and Trunk Kinematics between Single Leg Squat and Step Down Tasks. PloS One 10, e0126258. https://doi.org/10.1371/journal.pone.0126258 Lindsay, D., Horton, J., 2002. Comparison of spine motion in elite golfers with and without lo w back pain. J. Sports Sci. 20, 599 605. https://doi.org/10.1080/026404102320183158 Lindsay, D.M., Vandervoort, A.A., 2014. Golf related low back pain: a review of causative factors and prevention strategies. Asian J. Sports Med. 5, e24289. https://doi.org /10.5812/asjsm.24289 Loud, K.J., Gordon, C.M., Micheli, L.J., Field, A.E., 2005. Correlates of stress fractures among preadolescent and adolescent girls. Pediatrics 115, e399 406. https://doi.org/10.1542/peds.2004 1868 Macaulay, C.A.J., Katz, L., Stergiou, P., Stefanyshyn, D., Tomaghelli, L., 2017. Kinematic and kinetic analysis of overhand, sidearm and underhand lacrosse shot techniques. J. Sports Sci. 35, 2350 2356. https://doi.org/10.1080/02640414.2016.1267385 Macedo, R.B., Coelho e Silva, M.J., Sousa, N .F., Valente dos Santos, J., Machado Rodrigues, A.M., Cumming, S.P., Lima, A.V., Gonalves, R.S., Martins, R.A., 2015. Quality of life, school backpack weight, and nonspecific low back pain in children and adolescents. J. Pediatr. (Rio J.) 91, 263 269. htt ps://doi.org/10.1016/j.jped.2014.08.011 Malina, R.M., Rogol, A.D., Cumming, S.P., Coelho e Silva, M.J., Figueiredo, A.J., 2015. Biological maturation of youth athletes: assessment and implications. Br. J. Sports Med. 49, 852 859. https://doi.org/10.1136/bj sports 2015 094623 McCarroll, J.R., Miller, J.M., Ritter, M.A., 1986. Lumbar spondylolysis and spondylolisthesis in college football players. A prospective study. Am. J. Sports Med. 14, 404 406. https://doi.org/10.1177/036354658601400513
104 McConnell, J., Don nelly, C., Hamner, S., Dunne, J., Besier, T., 2012. Passive and dynamic shoulder rotation range in uninjured and previously injured overhead throwing athletes and the effect of shoulder taping. PM R 4, 111 116. https://doi.org/10.1016/j.pmrj.2011.11.010 Mc Connell, J., McIntosh, B., 2009. The effect of tape on glenohumeral rotation range of motion in elite junior tennis players. Clin. J. Sport Med. Off. J. Can. Acad. Sport Med. 19, 90 94. https://doi.org/10.1097/JSM.0b013e31819b9cd1 McDowell, C., Smyk, M., S ung, P.S., 2018. Compensatory strategy between trunk hip kinematics and reaction time following slip perturbation between subjects with and without chronic low back pain. J. Electromyogr. Kinesiol. Off. J. Int. Soc. Electrophysiol. Kinesiol. 43, 68 74. htt ps://doi.org/10.1016/j.jelekin.2018.09.005 McGregor, A.H., Hukins, D.W.L., 2009. Lower limb involvement in spinal function and low back pain. J. Back Musculoskelet. Rehabil. 22, 219 222. https://doi.org/10.3233/BMR 2009 0239 McHardy, A., Pollard, H., Luo, K., 2007. One year follow up study on golf injuries in Australian amateur golfers. Am. J. Sports Med. 35, 1354 1360. https://doi.org/10.1177/0363546507300188 McHardy, A., Pollard, H., Luo, K., 2006. Golf injuries: a review of the literature. Sports Med. Au ckl. NZ 36, 171 187. Meister, D.W., Ladd, A.L., Butler, E.E., Zhao, B., Rogers, A.P., Ray, C.J., Rose, J., 2011. Rotational biomechanics of the elite golf swing: benchmarks for amateurs. J. Appl. Biomech. 27, 242 251. Mendiguchia, J., Ford, K.R., Quatman, C.E., Alentorn Geli, E., Hewett, T.E., 2011. Sex differences in proximal control of the knee joint. Sports Med. Auckl. NZ 41, 541 557. https://doi.org/10.2165/11589140 000000000 00000 Millard, B., n.d. Examination of Lower Extremity Muscle Activity during an Overhand Lacrosse Shot in Females 74. Overhand Lacrosse Shot. J. Hum. Kinet. 41, 15 22. https://doi.org/10.2478/hukin 2014 0028 Moesch, K., Elbe, A. M., Hauge, M. L.T., Wikman, J.M., 2011. Late specialization: the key to success in centimeters, grams, or seconds (cgs) sports. Scand. J. Med. Sci. Sports 21, e282 290. https://doi.org/10.1111/j.1600 0838.2010.01280.x
105 Monticone, M., Ambrosini, E., Rocca, B., Magni, S., Brivio F., Ferrante, S., 2014. A multidisciplinary rehabilitation programme improves disability, kinesiophobia and walking ability in subjects with chronic low back pain: results of a randomised controlled pilot study. Eur. Spine J. Off. Publ. Eur. Spine Soc. E ur. Spinal Deform. Soc. Eur. Sect. Cerv. Spine Res. Soc. 23, 2105 2113. https://doi.org/10.1007/s00586 014 3478 5 Moradi, V., Memari, A. H., ShayestehFar, M., Kordi, R., 2015. Low Back Pain in Athletes Is Associated with General and Sport Specific Risk Factors: A Comprehensive Review of Longitudinal Studies. Rehabil. Res. Pract. 2015, 850184. https://doi.org/10.1155/2015/850184 Moreno Prez, V., Elvira, J., Fernandez Fernandez, J., Vera Garcia, F.J., 2018. A COMPARATIVE STUDY OF PASSIVE SHOULDER ROTATION RANGE OF MOTION, ISOMETRIC ROTATION STRENGTH AND SERVE SPEED BETWEEN ELITE TENNIS PLAYERS WITH AND WITHOUT HISTORY OF SHOULDER PAIN. Int. J. Sports Phys. Ther. 13, 39 49. Mun, F., Suh, S.W., Park, H. J., Choi, A., 2015. Kinematic relationship between rota tion of lumbar spine and hip joints during golf swing in professional golfers. Biomed. Eng. Online 14, 41. https://doi.org/10.1186/s12938 015 0041 5 Munro, A., Herrington, L., Carolan, M., 2012. Reliability of 2 dimensional video assessment of frontal plan e dynamic knee valgus during common athletic screening tasks. J. Sport Rehabil. 21, 7 11. Nagi, G., 1965. Some conceptual issues in disability and rehabilitation., Sociology and Rehabilitation. American Sociological Association. Nakagawa, T.H., Moriya, .T .U., Maciel, C.D., Serro, F.V., 2014. Test retest reliability of three dimensional kinematics using an electromagnetic tracking system during single leg squat and stepping maneuver. Gait Posture 39, 141 146. https://doi.org/10.1016/j.gaitpost.2013.06.011 National Advisory Board for Medical Rehabilitation Research. Research Plan for the National Center for Medical Rehabilitation Research., 1993. National Institutes of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Washington, DC. NFHS Participation Statistics, 2006. The National Federation of State High School Associations. Nicola, T.L., Jewison, D.J., 2012. The anatomy and biomechanics of running. Clin. Sports Med. 31, 187 201. https://doi.org /10.1016/j.csm.2011.10.001 Oliver, G.D., Plummer, H.A., Keeley, D.W., 2011. Muscle activation patterns of the upper and lower extremity during the windmill softball pitch. J. Strength Cond. Res. Natl. Strength Cond. Assoc. 25, 1653 1658. https://doi.org/10 .1519/JSC.0b013e3181db9d4f
106 Oyama, S., Yu, B., Blackburn, J.T., Padua, D.A., Li, L., Myers, J.B., 2014. Improper trunk rotation sequence is associated with increased maximal shoulder external rotation angle and shoulder joint force in high school baseball p itchers. Am. J. Sports Med. 42, 2089 2094. https://doi.org/10.1177/0363546514536871 Oyama, S., Yu, B., Blackburn, J.T., Padua, D.A., Li, L., Myers, J.B., 2013. Effect of excessive contralateral trunk tilt on pitching biomechanics and performance in high sc hool baseball pitchers. Am. J. Sports Med. 41, 2430 2438. https://doi.org/10.1177/0363546513496547 Papanicolaou, N., Wilkinson, R.H., Emans, J.B., Treves, S., Micheli, L.J., 1985. Bone scintigraphy and radiography in young athletes with low back pain. AJR Am. J. Roentgenol. 145, 1039 1044. https://doi.org/10.2214/ajr.145.5.1039 Park, W. H., Kim, Y.H., Lee, T.R., Sung, P.S., 2012. Factors affecting shoulder pelvic integration during axial trunk rotation in subjects with recurrent low back pain. Eur. Spine J. Off. Publ. Eur. Spine Soc. Eur. Spinal Deform. Soc. Eur. Sect. Cerv. Spine Res. Soc. 21, 1316 1323. https://doi.org/10.1007/s00586 012 2280 5 Pasulka, J., Jayanthi, N., McCann, A., Dugas, L.R., LaBella, C., 2017. Specialization patterns across various you th sports and relationship to injury risk. Phys. Sportsmed. 45, 344 352. https://doi.org/10.1080/00913847.2017.1313077 Polley, C.S., Cormack, S.J., Gabbett, T.J., Polglaze, T., 2015. Activity profile of high level Australian lacrosse players. J. Strength C ond. Res. 29, 126 136. https://doi.org/10.1519/JSC.0000000000000599 Post, E.G., Trigsted, S.M., Riekena, J.W., Hetzel, S., McGuine, T.A., Brooks, M.A., Bell, D.R., 2017. The Association of Sport Specialization and Training Volume With Injury History in You th Athletes. Am. J. Sports Med. 45, 1405 1412. https://doi.org/10.1177/0363546517690848 Poulsen, D.R., James, C.R., 2011. Concurrent validity and reliability of clinical evaluation of the single leg squat. Physiother. Theory Pract. 27, 586 594. https://doi .org/10.3109/09593985.2011.552539 Putukian, M., Lincoln, A.E., Crisco, J.J., 2014. Sports lacrosse. Curr. Sports Med. Rep. 13, 334 340. https://doi.org/10.1249/JSR.0000000000000092 Quinn, S., Bird, S., 1996. Influence o f saddle type upon the incidence of lower back pain in equestrian riders. Br. J. Sports Med. 30, 140 144. Ramsey, D.K., Crotin, R.L., 2016. Effect of stride length on overarm throwing delivery: Part II: An angular momentum response. Hum. Mov. Sci. 46, 30 3 8. https://doi.org/10.1016/j.humov.2015.11.021
107 Rose, M.S., Emery, C.A., Meeuwisse, W.H., 2008. Sociodemographic predictors of sport injury in adolescents. Med. Sci. Sports Exerc. 40, 444 450. https://doi.org/10.1249/MSS.0b013e31815ce61a Rosner, B.A., 1995. Fundamentals of Biostatistics. Duxbury Press. Rossi, F., Dragoni, S., 1990. Lumbar spondylolysis: occurrence in competitive athletes. Updated achievements in a series of 390 cases. J. Sports Med. Phys. Fitness 30, 450 452. Schilling, J.F., Murphy, J.C., B onney, J.R., Thich, J.L., 2013. Effect of core strength and endurance training on performance in college students: Randomized pilot study. J. Bodyw. Mov. Ther. 17, 278 290. https://doi.org/10.1016/j.jbmt.2012.08.008 Snyder, A.R., Parsons, J.T., Valovich Mc Leod, T.C., Curtis Bay, R., Michener, L.A., Sauers, E.L., 2008. Using disablement models and clinical outcomes assessment to enable evidence based athletic training practice, part I: disablement models. J. Athl. Train. 43, 428 436. https://doi.org/10.4085/ 1062 6050 43.4.428 Souza, R.B., Powers, C.M., 2009. Differences in hip kinematics, muscle strength, and muscle activation between subjects with and without patellofemoral pain. J. Orthop. Sports Phys. Ther. 39, 12 19. https://doi.org/10.2519/jospt.2009.288 5 Sugaya, H., Tsuchiya, A., Moriya, H., Morgan, D.A., 1999. Low Back Injury in Elite and Professional Golfers: An Epidemiologic and Radiographic Study. Sci. Golf Proc. 83 91. Sung, P.S., 2014. A kinematic analysis for shoulder and pelvis coordination during axial trunk rotation in subjects with and without recurrent low back pain. Gait Posture 40, 493 498. https://doi.org/10.1016/j.gaitpost.2014.06.001 Sung, P.S., 2013. Disability and back muscle fatigability changes following two therapeu tic exercise interventions in participants with recurrent low back pain. Med. Sci. Monit. Int. Med. J. Exp. Clin. Res. 19, 40 48. Tapking, C., Armenta, A.M., Popp, D., Herndon, D.N., Branski, L.K., Lee, J.O., Suman, O.E., 2018. Relationship between lean bo dy mass and isokinetic peak torque of knee extensors and flexors in severely burned children. Burns J. Int. Soc. Burn Inj. https://doi.org/10.1016/j.burns.2018.09.007 Tocci, N.X., Howell, D.R., Sugimoto, D., Dawkins, C., Whited, A., Bae, D., 2017. The Effe ct of Stride Length and Lateral Pelvic Tilt on Elbow Torque in Youth Baseball Pitchers. J. Appl. Biomech. 33, 339 346. https://doi.org/10.1123/jab.2016 0305 Trainor, T.J., Trainor, M.A., 2004. Etiology of low back pain in athletes. Curr. Sports Med. Rep. 3 41 46. Trainor, T.J., Wiesel, S.W., 2002. Epidemiology of back pain in the athlete. Clin. Sports Med. 21, 93 103.
108 Tsai, Y. S., Sell, T.C., Smoliga, J.M., Myers, J.B., Learman, K.E., Lephart, S.M., 2010. A comparison of physical characteristics and swing mechanics between golfers with and without a history of low back pain. J. Orthop. Sports Phys. Ther. 40, 430 438. https://doi.org/10.2519/jospt.2010.3152 Urbin, M.A., Fleisig, G.S., Abebe, A., Andrews, J.R., 2013. Associations between timing in the basebal l pitch and shoulder kinetics, elbow kinetics, and ball speed. Am. J. Sports Med. 41, 336 342. https://doi.org/10.1177/0363546512467952 US Lacrosse 2016 Participation Suvey, 2016. US Lacrosse. US Lacrosse Participation Report, n.d. U.S Lacrosse. US Lac rosse: Post College, n.d. US Lacrosse. Verbrugge, L.M., Jette, A.M., 1994. The disablement process. Soc. Sci. Med. 1982 38, 1 14. Vincent, H.K., Chen, C., Zdziarski, L.A., Montes, J., Vincent, K.R., 2015. Shooting motion in high school, collegiate, and p 448 458. https://doi.org/10.1080/14763141.2015.1084034 Vincent, H.K., Vincent, K.R., 2018. Core and Back Rehabilitation for High speed Rotation Sports: Highlight on Lacrosse. Curr. Sports Med. Rep. 17 208 214. https://doi.org/10.1249/JSR.0000000000000493 Warner, K., Savage, J., Kuenze, C.M., Erkenbeck, A., Comstock, R.D., Covassin, T., 2018. A 2009 Through 2015 2016. J. Athl. Train. https://doi.org/10.4085/1062 6050 312 17 Wasser, J.G., Chen, C., Vincent, H.K., 2016a. Kinematics of Shooting in High School and Collegiate Lacrosse Players With and Without Low Back Pain. Orthop. J. Sports Med. 4. https://doi.org/10.1177/2325 967116657535 Wasser, J.G., Chen, C., Vincent, H.K., 2016b. Kinematics of Shooting in High School and Collegiate Lacrosse Players With and Without Low Back Pain. Orthop. J. Sports Med. 4, 2325967116657535. https://doi.org/10.1177/2325967116657535 Wasser, J. G., Chen, C., Zdziarski, L.A., Vincent, H.K., 2015. Kinematics of Overhead Throwing Motions in Professional Lacrosse and Baseball Players: 3506 Board #267 May 30, 9. Med. Sci. Sports Exerc. 47, 952. https://doi.org/10.1249/01.mss.0000479324.69566.4d Wasser J.G., Zaremski, J.L., Herman, D.C., Vincent, H.K., 2017. Prevalence and proposed mechanisms of chronic low back pain in baseball: part i. Res. Sports Med. Print 25, 219 230. https://doi.org/10.1080/15438627.2017.1282361 S.J., Bedi, A., 2014. The biomechanics of throwing: simplified and cogent. Sports Med. Arthrosc. Rev. 22, 72 79. https://doi.org/10.1097/JSA.0000000000000019
109 Werner, S.L., Murray, T.A., Hawkins, R.J., Gill, T.J., 2002. Relationship between throwing mecha nics and elbow valgus in professional baseball pitchers. J. Shoulder Elbow Surg. 11, 151 155. Whiteley, R., 2007. Baseball Throwing Mechanics as They Relate to Pathology and Performance A Review. J. Sports Sci. Med. 6, 1 20. Wight, J., Richards, J., Hall S., 2004. Influence of pelvis rotation styles on baseball pitching mechanics. Sports Biomech. 3, 67 83. https://doi.org/10.1080/14763140408522831 Willson, J.D., Ireland, M.L., Davis, I., 2006. Core strength and lower extremity alignment during single leg squats. Med. Sci. Sports Exerc. 38, 945 952. https://doi.org/10.1249/01.mss.0000218140.05074.fa Zaremski, J.L., Seay, A., Montero, C., Vincent, K.R., Vincent, H.K., 2013. Shoulder Passive Range of Motion in High School Lacrosse Players: An Exploratory Pil ot Study of Arm Dominance and Presence of Pain. PM&R 5, S217. https://doi.org/10.1016/j.pmrj.2013.08.325 Zaremski, J.L., Wasser, J.G., Vincent, H.K., 2017. Mechanisms and Treatments for Shoulder Injuries in Overhead Throwing Athletes. Curr. Sports Med. Rep 16, 179 188. https://doi.org/10.1249/JSR.0000000000000361 Zdziarski, L.A., Chen, C., Slater, C.D., Vincent, K.R., Montero, C., Vincent, H.K., 2014. Sex Differences in Pelvic and Trunk Rotation During a Lacrosse Throw: 2708 May 30, 1. Med. Sci. Sports Exe rc. 46, 727. https://doi.org/10.1249/01.mss.0000495669.49710.aa Zeller, B.L., McCrory, J.L., Kibler, W.B., Uhl, T.L., 2003. Differences in kinematics and electromyographic activity between men and women during the single legged squat. Am. J. Sports Med. 31 449 456. https://doi.org/10.1177/03635465030310032101
110 BIOGRAPHICAL SKETCH Originally from Miami, FL., Joseph received his Doctor of Philosophy at the University of Florida in the Rehabilitation Science Joseph's academic training began with exercise physiology; receiving his Bachelor of Science from the University of Florida in May 2012 During his doctoral training, his research reside d in the biomechanics of individuals who present injury or conditions that may inh ibit their performance and activity. Goals of his works are to identify kinematic risk factors in the development of low back pain and using those risk factors to develop protocols for prevention and rehabilitation. From a personal perspective, Joseph is committed to advancing treatments for chronic low back pain. After years of back pain and debility, he underwent spine fusion in 2016 He can related outcomes t hat can help drive changes in rehabilitation and exercise as medicine.