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Does Warming Up Influence Shoulder Stiffness or External Rotation in Healthy, Non-Elite Tennis Players?

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Does Warming Up Influence Shoulder Stiffness or External Rotation in Healthy, Non-Elite Tennis Players?
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Peterson, Daniel
Tillman, Mark ( Mentor )
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Gainesville, Fla.
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University of Florida
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English

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Does Warming Up Influence Shoulder Stiffness or External Rotation in
Healthy, Non-Elite Tennis Players?

Daniel S. Peterson, Jeff T. Wight, Guy B. Grover, and Mark D. Tillman


ABSTRACT


Background


During overhead motion sports, massive loads are placed on the shoulder. Research has shown that these loads

are closely associated with stiffness and flexibility at the shoulder. Understanding the way tension and

flexibility change is crucial for assessment as well as the importance of warming up. The purpose of this study was

to investigate changes in stiffness and range of motion (ROM) about the shoulder before and after a sport

specific warm-up.



Methods


Amateur tennis athletes (11 males and 11 females) were tested for both external motion and torque about

the shoulder. Both dominant and non-dominant arms were taken to a maximum external position and were

measured for torque at the shoulder and maximum ROM. Subjects then completed a tennis specific warm-

up consisting of light stretching, dry tennis serves, and finally several live serves. Subjects were again tested for

ROM and torque.



Results


A two-way ANOVA was carried out (pre/post warm-up, dominant/non-dominant arms) showing significantly

larger post warm-up ROM, as well as larger torque values on the dominant arm. T-tests were also performed

to determine differences between pre- and post-warming up trials of each arm. Dominant arm external rotation

was shown to significantly increase while the non-dominant arm ROM did not. Tests of the onset of stiffness

(when the shoulder reached 2 Nm of torque) and slope of the angle/torque graph were calculated as measures

of stiffness, and neither showed any significant changes between arms or across warm-up trials. Within each

trial, subjects completed three measured external ROM repetitions. Significant differences were shown between

the first and third repetition within trials.





Interpretation


These findings show the importance of warming up as a tool to immediately increase ROM. Studies have shown

that overhead sport athletes with larger ROM about the shoulder are less susceptible to injury. Also, these results

are important to clinicians or therapists who are assessing ROM. Due to changes in the internal workings of

the shoulder as well as increased comfort of the subject, the arm's ROM is dynamic when "cold" and may

change significantly even within repetitions of the same trial.



INTRODUCTION


The balance between mobility and stability in the shoulder is one of great complexity. Even in normal

movements people can experience pain and dislocations due to the relative instability of the joint. Athletes

who participate in activities involving overhead arm motions, such as throwing in baseball or serving in tennis,

put themselves at an especially high risk for shoulder-related injuries. Overhead motions are particularly

damaging due both to the extreme loads they place on the shoulder, as well as the severe arm positions which

are associated with these loads. These repetitive loads and exaggerated ranges of motion can cause significant

injury to athletes, and it is important to understand the circumstances around their occurrence.



Dynamic motions can be described by two measures: range of motion (ROM) and stiffness (torque required

to produce that ROM). Differences in ROM have been well documented and are highly variable both between

and within individuals. The variability in passive ROM is attributed to several factors, one of which being

the experience level of the athlete. Kilber, Chandler, Livingston, & Roetert (1996) showed that subjects who

have been participating in overhead motions for extended periods often show a decrease in internal

rotation. Moderate negative correlations between dominant internal rotation and both age and years of play

were reported. This is probably due to posterior capsule tightness, resulting from chronic microtraumatization of

the surrounding structures (Schmidt-Wiethoff, Rapp, Mauch, Schneider, & Appell 1996). It is unclear if

these adaptations are normal, but some studies have shown negative effects associated with lack of internal

rotation, including increased injury (Chandler, Kibler, Uhl, Wooten, Kiser, & Stone, 1990).



Differences in ROM have also been observed between athletes of different sports. Chandler et al. (1990) noted

that tennis athletes, when compared to other athletes, showed significantly different internal and external ranges

of motion. These tennis athletes were shown to be tighter in internal rotation and looser in external rotation for

both the dominant and non-dominant arms (Williford, East, Smith, & Burry, 1986).



Differences have also been shown within overhead-motion athletes (Ellenbecker & Mattalino, 1999). Research

has shown that while baseball pitchers had no significant difference between extremities in total ROM, tennis

athletes showed significantly less dominant arm total ROM (Ellenbecker, Roetert, Bailie, Davies, & Brown,

2002). These changes in ROM can have significant implications resulting in chronic injuries. Specifically, a

reduced internal ROM has been shown to be associated with increased injury and pain (Chandler et al.,





1990; Ellenbecker et al., 2002).


There have been some discrepancies in measured changes of external ROM. After testing professional tennis

athletes, Schmidt- Wiethoff et al. (1996) determined that there was indeed an increase in external rotation,

while Ellenbecker & Roetert (2003) noted that while internal rotation of non-dominant shoulders was less,

external rotation between dominant and non-dominant arms were not different.



As there are some differences between dominant and non-dominant arms, changes in ROM can also be

expected between athletes and non-athletes. In addition to shoulder stretching completed by most athletes,

the violent motions experienced during play induce changes in ROM. Both dominant and non-dominant shoulders

of experienced tennis athletes have been shown to have lesser internal ROM when compared to non-athletes

(Borsa, Dover, Wilk, & Reinold 2006).



Stiffness of the shoulder is another important factor in the assessment of dynamic motion. For overhead-

motion sports, similar external ranges of motion are necessary. Due to individual differences in shoulder stiffness,

the process in which this ROM is reached is extremely varied (Chow, Wight, Grover, Tillman, 2006). For this reason

it is important to note how to best measure these differences as well as the way in which they change.



Stretching has been shown to have an impact on stiffness and flexibility. Although benefits have been variable

with regards to certain activities, specifically maximal contractions, stretching has been recognized as a potential

way to decrease injury and increase performance in overhead motions such as pitching and tennis serving

(Fowles, Sale, & MacDougall, 2000; Young & Elliott 2001; and Nelson & Kokkonen 2001). As integral elements

of overhead-motion athletics, the shoulder and elbow joint have been scrutinized to determine how

stretching influences overhead sports mechanics and affects ROM and strength. However, most previous studies

have not taken into account the immediate changes in stiffness due to stretching. Most studies consider passive

ROM but neglect the change in ROM associated with warming up. Some studies have shown benefits but

were focused only on the lower body (Weijer, Gomiak, & Shamus 2003; Williford et al., 1986). Also, these

studies included a different type of "warm-up" than is often associated with overhead motion. A warm-up of the

lower body usually consists of superficial and deep-heat modalities, or repetitive exercises at low intensity, such

as jogging, bicycling (Taylor, Waring, & Brashear, 1995) and stair climbing (Hubley, Kozey, & Stanish,

1984; Wessling, Davane, & Hylton, 1987; and Williford et al., 1986).With overhead sports, a warm-up is geared

more toward in-game activity. For example, warming up the shoulder for a tennis match more often

includes stretching followed by some practice swings and light serves, followed by full speed serves. This is the

type of warm-up that was integrated into the present study.



The purpose of the study described here was to determine if any differences in stiffness or flexibility (ROM)

occurred within tennis athletes before and after warming up. The immediate effect of warming up on changes in

ROM on the shoulder may have implications in both clinical and research settings. If there are in fact differences

in pre and post collections, it would provide insight as to how data should be collected in the future. In addition,






when analyzing progress and recovery of shoulder injuries, it is important to know how best to assess ROM.

Further, changes in stiffness and flexibility may give insight into how important stretching really is in

injury prevention.



METHODS


Participants


A total of 22 participants, with an average height and weight of 174.5 � 10.7 cm and 69.2 � 12.9 kg,

respectively, were measured for pre- and post-external ROM changes. Subjects included 11 males and 11

females, and all were in good health. None of the subjects had sustained significant shoulder injuries in

recent months. All subjects had some experience with tennis, though the experience level ranged from two months

to several years. Most of the subjects were chosen from sport and recreation tennis classes on campus.

Other subjects were recruited from non-sport classes, provided they had "moderate tennis experience."



Apparatus and Instrumentation


The device used in this study (shown in Figures 1 and 2) was previously fabricated in conjunction with

ongoing projects at the University of Florida. Its specific purpose is to provide an accurate measure of both ROM

and stiffness. This equipment was used by seating the subject in a chair with the arm abducted to 90 degrees.

The weight of the arm was supported by a piece of PVC pipe (5" diameter) held in place by rollers on a post.

The subject's arm was inserted through the PVC, and secured by a bicycle tire tube that was inflated to secure

the humerus. The axis of the humerus was aligned with the center of a bicycle wheel and was horizontally

adducted 150 to align with the scapular plane. The forearm was flexed and the wrist strapped to a bar extending

from the perimeter of the bicycle wheel. A potentiometer (Model 536, Spectrol Electronics, City of Industry, CA)

was used to measure the rotation of the wheel. The wheel was manually rotated into maximum internal or

external rotation by a line connected to the perimeter of the wheel down through a pulley. A load cell (Model

SBO-3000, Transducer Technologies, Temecula, CA) was used to measure the force required to attain the ROM.

A strap also surrounded the shoulder in order to reduce rotation about the scapula. The data were amplified

before being processed by a Labview program running on a laptop computer.































Figure 1. Instrumentation


Figure 2. Subject in External Rotation


Procedure


The duration of testing was approximately 45 minutes per subject. Subjects were given informed consent

paperwork, then measured for height and weight. Each subject was then seated and familiarized with the

procedure.The height of the arm support and bike wheel was adjusted to insure that the arm was abducted to

90 degrees and the axis of the humerus was in line with the center of the wheel. A horizontal bar from the

outer diameter of the wheel was then strapped to the wrist of the subject. For smaller subjects, the seat was

raised with supports for alignment purposes.Each subject was instructed to execute one practice rotation to

become comfortable with the position of maximal external ROM. Maximal ROM was determined by the subject as

the point of an "intense stretch without significant pain." The order of testing (external, internal dominant and





non-dominant) was randomized. The subject was then instructed to execute three recorded maximum

rotation repetitions. A repetition began with the forearm perpendicular to the ground. The arm was taken

to maximum rotation by way of a line tied to the outer rim of the bicycle wheel. The subject's arm was then

brought back to the starting position. Each subject then underwent external and internal maximum rotations for

both arms. During internal rotation, the shoulder was secured to the chair to reduce scapular motion. Then

the subject was instructed to warm-up as he or she normally would before a tennis match. Subjects

stretched slightly, executed several "dry" serves and finally hit several live serves until they reached "game

status." Subjects were then retested for all measures (internal and external rotation) for both arms.



Data Analysis


The data collected corresponded to a series of three repetitions, all with synchronized force and ROM data. The

force data were multiplied by the distance from the bicycle wheel axis to the bar which was placed on the wrist.

This calculation yields torque, which is necessary to standardize forearm lengths between subjects. To

facilitate analysis, it was necessary to split the data into three separate repetitions. Once this was done, ROM

and torque were extrapolated for each repetition.



RESULTS


Due to difficulties with the amplifier and load cell, the data from 8 of the 22 subjects had to be dropped from

the study. In the process of comparing these remaining 14 subjects, several significant changes in maximum

external rotation emerged. For each measure (Max External ROM, Max Torque, Slope, and Onset) a two way

ANOVA was performed comparing dominant and non-dominant arms with pre and post warm-up repetitions.

To further analyze specific differences between arms, T-tests were used to compare dominant pre- versus

post-warm-up, non-dominant pre- versus post-warm-up, Dominant pre- versus non-dominant pre- and

dominant post- versus non-dominant post-. All data were taken from the third repetition from each trial.



Maximum External Rotation


As seen in Figure 3, the repeated-measures two way ANOVA comparing dominant and non-dominant arms with

pre and post warm-up maximum ranges of motion showed a significant difference between pre- and post- warm-

up of both arms, with post-warm-up having larger external ROM. No significant difference was shown

between dominant and non-dominant arms (Table 1).



When T-tests were run, dominant arm post-warm-up maximum external ROM were significantly larger than

pre-warm-up external ROM. Also, dominant arm pre-warm-up ROM were shown not to be significantly larger

than non-dominant ROM.Neither non-dominant pre- vs. post- ranges nor pre-warm-up dominant vs. non-

dominant ranges were shown to be significantly different.





Maximum Torque


The repeated-measures two-way ANOVA showed significantly larger dominant arm torques when compared to

the non-dominant arm.



T-tests revealed dominant arms to have undergone significantly more torque during the post-warm-up reps than

non-dominant arms. There were no significant differences shown between pre- versus post- repetitions of

either dominant or non-dominant arms.



Stiffness/Onset


Stiffness may be defined as the slope of the curve relating torque and rotation angle (Novotny, Wooley, Nichols,

& Beynnon, 2000). The two points designated to determine this slope are the angles corresponding to a torque of

1 and 2 Nm. Only limited amounts of data were available within this range, and no significant difference in

stiffness could be identified for any of the test conditions. Onset of stiffness was also calculated. This measure

was described as the angle at which 2 Nm of torque was reached. Onset also showed no significant

statistical differences in any of the testing areas.



Finally, to determine the possible changes associated with loosening within the three trial-repetitions, a t-test

was run to determine differences between the first and third repetitions within each trial. This test

showed significantly larger third repetition ROMs compared to first repetitions of that same trial.



Table la: Data Analysis

TWO-WAY ANOVA


Condition
p Condition p


Maximum Angle (�) Onset (�)

(All) Dom vs. non-dom
p = 0.283 (All) Dom vs. non-dom p = 0.332


(All) Pre vs. post p = 0.038a (All) Pre vs. Post p = 0.095

Associations p = 0.259 Associations p = 0.215

Maximum Torque (Nm) Slope (�/Nm)

(All) Dom vs. non-dom p =0.04 a (All) Dom vs. non-dom p = 0.410

(All) Pre vs. post p = 0.387 (All) Pre vs. Post p = 0.320

Associations p = 0.637 Associations p = 0.289






Table 1b: Data Analysis

T-Tests; Mean (SD)

Type Pre Post p=

Maximum Angle (�)


Dom 107.08 (14.32) 114.65 (10.30) 0.041a


Non-Dom 105.53 (8.24) 109.38 (10.79) 0.145


p= 0.685 0.113


Onset (�)


Dom 88.7 (17.1) 97.6 (12.407) 0.076


Non-Dom 88.2 (12.8) 91.97 (15.9) 0.280


p= 0.88 0.188


Maximum Torque (Nm)


Dom 7.4415 (4.66) 7.74 (4.04) 0.753


Non-Dom 4.95 (2.45) 5.67 (2.66) 0.093


p= 0.069 0.038a


Slope (�/Nm)


Dom 6.53 (2.24) 13.59 (14.40) 0.304


Non-Dom 6.15 (2.61) 6.35 (1.35) 0.795


p= 0.814 0.354


Table 1c: Data Analysis

First to Third Rep Variability (�)

Average Number p

1st Rep Average 107.34 (13.2) p <.001


3rd Rep Average 110.43 (12.1)


*A forearm rotation of 0� was designated as 90� of shoulder abduction with the ulna/radius parallel to the

ground.

(a, Significant difference)






Change in Maximum ROM (pre and post warm-up)


116
114
S112
a 110
S108

< 106


114.65


107.06 109.38__

. . _----


105.53 -
104 * Dominant Arm
102 * Non-dominant Arm
100
1 2
Pre/Post


Figure 3. Changes in maximal external rotation from pre- to post-warm-up trials.



DISCUSSION


Though there were some difficulties encountered in the collection of data, several important points can be taken

from this study. With regards to maximal external rotation, the dominant arm showed a significant increase from

pre- to post-warm-up while the non-dominant arm did not. Though not significant, there was a change between

non-dominant arm averaging 105.50 before warming up and 109.00 after. Extensive "whole body" warm ups can

lead to increases in core muscle temperature, which increases and prolongs connective tissue and

musculotendinous extensibility (Lehmann, Masock, Warren, & Koblanski, 1970). In this study, the focus was not

the "whole body" warm-up, but rather stressed the changes due to the more specific tennis warm-up. This

tennis warm-up consisted of several light serves, followed by full speed serves until the subject felt to be at "in-

game status." Since the change associated with the non-dominant arm was not significant, the difference

in dominant arm ROM is most likely due to the stretching involved with the practice serves as opposed to any

whole-body warm-up that did occur.



There was no significant difference between dominant and non-dominant arms in pre-warm-up external

rotation. Research on this topic has been mixed, some showing that highly trained overhead athletes show

larger ranges of motion of the dominant arm (Young & Elliott 2001; Lehmann et al., 1970), and others showing

no difference (Nelson & Kokkonen 2001). Subjects in the studies noted, however, were professional, while in

the current study the subjects tested were of a much lower caliber.



The subjects tested consisted of a wide variety of individuals. Due to different pain tolerances and differences

in anatomy, the torque required to reach maximum ROM varied greatly. For this reason, the "onset" of stiffness

was also calculated. This onset was determined to be the angle at which two Nm were reached. This measurement

is important because it removes the factor of excess force being applied to the arm to reach large ROM. Measure

of onset closest to significance (p = 0.076) was the dominant arm's onset pre- to post-warm-up. This






difference, though not significant, is notable. Since the maximum torque, which correlates to the maximum

external ROM, was not significantly different pre- to post-warm-up, it should not have had a large effect on

the difference in maximum ROM. Therefore, barring differences in torque properties of the arm through the

ROM, differences in onset should mirror differences in maximal ROM. Wight et al. showed that the arm's

stiffness values do in fact stay relatively constant through the ROM (Chow et al., 2006). Large standard

deviations associated with the maximum torque values, however, may have complicated these results, as

some subjects did in fact experience larger maximal torques pre- to post-warm-up. The significant

difference between post-dominant and post-non-dominant maximum torque may have resulted from the

subjects' level of comfort in compromised arm positions. Subjects' dominant arms may be more accustomed

to extreme ROM as they are exposed to them when serving.



The slope data collected varied greatly within and between subjects. This measure was calculated by choosing

two points along the x-axis of the angle/torque graph, corresponding to one and 2 Nm. In short, this method

detects changes in distance traveled (in degrees) between two set torque measurements. Novotny et al. (2000),

also using torque as a measurement, designated one Nm as the "onset of stiffness" and measured from that point

to 4 Nm as the stiffness range. When comparing across subjects, standardization of forces by converting to torque

is necessary. For many of the subjects, inexperience, low pain tolerance, and hesitance to move through a full

ROM, caused extremely low maximum torque values. These problems limited the data to the smaller range of one

to 2 Nm. For follow-up studies, extensive familiarization would be necessary to ensure the subject is very

comfortable with the setup and arm motions.



In addition, to ensure comfort of the subject, a non-threatening apparatus is helpful. Subjects with their arm

in compromised situations under control of a machine may experience apprehension and tightening of the shoulder.

If available, EMG measurements on the rotator cuff muscles could show whether muscle stiffness would in fact

affect these measurements. As reported by Novotny et al. (2000), repeated testing may improve familiarization

with the apparatus.



The large changes in first to third repetitions within trials underscore the variability of ROM testing.

Though differences were quite varied, as a whole the third repetition was larger than the first by approximately

30. Some of the variance may be attributed to the subjects becoming more familiar with the motion and limits

of their shoulder ROM, though a trial repetition was incorporated into the procedure to eliminate this problem.



In future studies, more familiarization measures should be incorporated into the procedure. When studying

less experienced athletes who often are accustomed to extreme ROM, it is recommended that the subjects be

made as comfortable as possible with the apparatus, the motion, and the amount of stiffness in the joint that elicits

a thorough stretch. Also, additional adjustments should be made to the seating device to allow better measures

of small individuals.





CONCLUSION


A tennis-specific warm-up was shown to produce significant changes in external rotation about the shoulder.

No significant differences between pre- and post-non-dominant arms were shown, implying that the change was

due to the stretch/serving, as opposed to any whole-body warm-up that occurred. No significant differences in

the stiffness were shown as measured by slope of the torque vs. angle graph. A change in onset of stiffness (2

Nm) between pre- and post-warm-up on the dominant arm was shown, though not to a significant level (p =

0.076). Significant differences in the maximum torque used to bring subjects to their maximum angle were

also shown, but only between dominant and non-dominant arms. The difference in maximum torque within pre/

post repetitions of either arm was shown not to be significant.



The fact that there were indeed changes in ROM not due to whole body warm-up shows the importance

of standardizing warm-up procedure if ROM testing or analysis is to be completed. When testing subjects it is

crucial to know whether any warm-up has been completed, as results will be strongly influenced. Significant

changes can be seen within multiple repetitions of one measurement trial. Specifically when trainers or

other clinicians are assessing ROM for clearance to play, close attention must be paid to the number of

maximum stretch repetitions applied. Also, as shown by previous studies, increased ROM in the shoulder may

reduce injury when competing in overhead motion sports. This study shows the possible increase in ROM, and

further decrease in injury that could stem from thorough, sport specific stretching.






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