Effects of a 4-Month Season on Glenohumeral

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Journal of Strength and Conditioning Research, 2002, 16(1), 92–96 q 2002 National Strength & Conditioning Association

Effects of a 4-Month Season on Glenohumeral Joint Rotational Strength and Range of Motion in Female Collegiate Tennis Players TODD S. ELLENBECKER1

AND

E. PAUL ROETERT2

Physiotherapy Associates Scottsdale Sports Clinic, Scottsdale, Arizona 85258; 2United States Tennis Association, Key Biscayne, Florida 33149. 1

ABSTRACT The purpose of this study was to examine the effects of a 4month season of collegiate tennis on glenohumeral joint internal and external rotation strength and range of motion in female collegiate tennis players. Eleven female collegiate tennis players were isokinetically tested to assess glenohumeral joint internal and external rotation strength with 908 of abduction on a Cybex 6000 isokinetic dynamometer. Subjects were also measured for internal and external rotation range of motion using a universal goniometer with 908 of abduction. Measurements were taken before and immediately after a 4-month season of competitive collegiate tennis play. A repeated-measures analysis of variance showed no significant difference in internal or external rotation strength or range of motion between pre- and postseason measures. Results from this study show that, despite 4 months of competitive tennis play, changes in rotational strength and range of motion did not occur. These data have implications for clinicians as well as strength and conditioning professionals designing rehabilitation and preventative conditioning programs for athletes in this population.

Key Words: shoulder, isokinetics, testing, tennis Reference Data: Ellenbecker, T.S., and E.P. Roetert. Effects of a 4-month season on glenohumeral joint rotational strength and range of motion in female collegiate tennis players. J. Strength Cond. Res. 16(1):92–96. 2002.

Introduction

T

he demands of collegiate competitive tennis play on the human shoulder frequently result in the development of muscular imbalance and overuse injuries (3, 4, 11, 15). Previous studies have identified significantly greater dominant arm internal rotation strength, with no significant strength difference between extremities for glenohumeral joint external rotation (1, 3, 4). This muscular adaptation occurs secondary to the specific functions of the rotator cuff dur-

92

ing tennis-specific movement patterns. The rotator cuff functions to provide both acceleration of the humerus during the tennis serve and forehand as well as eccentric deceleration during follow-through (16). Decreases in dominant limb glenohumeral joint internal rotation range of motion have been consistently measured in the literature (6, 10, 18). The loss or decrease in dominant limb glenohumeral joint internal rotation range of motion is perpetuated by years of tennis play and number of competitive events (6, 10, 18). The effects of selective restriction of glenohumeral joint capsular flexibility have been experimentally studied and found to have deleterious effects on humeral head shear and cause abnormal anterior and superior translation of the humeral head (8). The presence of glenohumeral joint muscular imbalance, coupled with the range of rotational motion required during the overhead serve and groundstrokes and the repetitive demands required for successful skill acquisition and competition, place the glenohumeral joint at risk for injury (11). To address these musculoskeletal adaptations, clinicians and strength and conditioning professionals have recommended strength and flexibility exercises (17, 19). The challenge of implementing these exercises throughout a player’s competitive cycle and the difficulty in implementing conditioning and preventative strength programs often limits their effectiveness. The purpose of this study was to determine whether glenohumeral joint rotational strength or range of motion changes occur during a 4-month season of competitive Division I collegiate tennis play in female players.

Methods Subjects Eleven elite female collegiate tennis players were recruited from two NCAA Division I tennis teams. Prior approval by the Institutional Review Board for the use

Glenohumeral Joint Changes in Tennis Players 93

of Human Subjects was obtained for the investigation and consent was obtained before participation. Subjects were free from any upper extremity musculoskeletal injury for the past year and had no history of surgery in either of their upper extremities. Subjects were not involved in any formal strength training during the 4-month training season. Instrumentation A calibrated Cybex 6000 (Cybex, Ronkonkoma, NY) isokinetic dynamometer and upper body testing table were used for all isokinetic testing in this investigation. The mechanical and physiological reliability of the Cybex 6000 isokinetic dynamometer has been previously studied and deemed acceptable for both experimental and clinical use (20). A Cybex upper body ergometer (UBE) was used for subject warm-up and preparation and a standard universal goniometer was used for all joint range-of-motion measurement. Procedure Subjects were tested in early January, immediately before resumption of the primary competitive season of college tennis. Subjects underwent the exact testing sequence immediately after the conclusion of the regular season of college tennis in early May. Before testing, all subjects performed a 5-minute warm-up on the UBE at a level of 600 kpm in a clockwise direction (right hand view). After the warm-up, subjects were positioned in a supine position on a plinth with 908 of glenohumeral joint abduction. The universal goniometer axis was aligned with the long axis of the humerus, with the distal-most tip of the olecranon being the superficial landmark for alignment. The stationary arm of the goniometer was placed in a vertical orientation perpendicular to the floor, with the moving arm aligned with the lateral aspect of the ulna (6, 13). From the anatomical zero rotation position in 908 of abduction, the subjects were asked to maximally rotate their shoulder. Stabilization of the scapulothoracic joint was provided by the tester via a posteriorly directed containment force by the tester’s hand on the coracoid and anterior aspect of the acromion. No allowance of scapular protraction was permitted. Once the subject achieved a stable end-point position, the angle was recorded. No passive overpressure was applied, and the force of gravity provided a consistent load to facilitate endpoint determination. Internal rotation range of motion was measured immediately after external rotation using identical landmarks and stabilization. The reliability of this technique for glenohumeral joint rotation range-of-motion measurement has previously been demonstrated (6). Total rotation range of motion was calculated by combining the maximal internal and external rotation measurements for each extremity independently (10, 18).

Figure 1. Isokinetic testing setup.

Immediately after range of motion measurement, subjects were placed on the upper body testing table, with stabilization at the pelvis and mid-thoracic levels. The glenohumeral joint was abducted 908, with the dynamometer input axis aligned with the long axis of the humerus (Figure 1). A range of motion of 0–908 of external rotation and 0–658 of internal rotation was set and enforced through the use of end stops. Gravity correction of the Cybex 6000 dynamometer for the pattern of internal/external rotation is not recommended by the manufacturer and therefore not used. Testing consisted of 4 gradient submaximal warm-up repetitions, followed by 5 maximal concentric repetitions that were recorded for data generation. Testing was performed at speeds of 90, 210, and 3008·s21, in that order. Testing order of speeds was not randomized in an effort to improve reliability (22). Starting limb was randomized to minimize the effects of a learning bias. Thirty seconds of rest was allowed between testing speeds for all subjects. Statistical Analyses Data analysis was performed using a repeated-measures analysis of variance (ANOVA) to test for main effect differences in pre- and postseason range of motion and isokinetic strength. The level of significance was set at p # 0.05. The mean age of the subjects in this study was 19.18 6 1.83 years. The average body weight was 149.00 6 20.31 lb (67.57 1 9.21 kg). The average number of years of competitive tennis play by the women in this study was 9.82 6 1.99 years.

Results Results of the repeated-measures ANOVA and effect size calculation are presented in Table 1. No significant difference between pre- and postseason glenohumeral joint range of motion or strength was found. Tables 2 and 3 contain the pre- and postseason glenohumeral internal and external rotation range of motion and

94 Ellenbecker and Roetert Table 1. Analysis of variance (ANOVA) for the dependent variables muscular strength and range of motion for glenohumeral joint interval and external rotation in elite female tennis players. Source

Sum of squares

df

Mean squares

F

p-value

Effect size

Time (pre/post) Error (time) Time 3 rotation Error (time 3 rotation)

141.84 539.53 12.02 81.60

1 10 1 10

141.84 53.95 12.02 8.16

2.63

0.136

0.42

1.47

0.253

0.02

Table 2. Pre- and postseason glenohumeral joint internal and external rotation passive range of motion from the elite female tennis players.*

Motion Preseason External rotation W/908 Abd. Internal rotation W/908 Abd. Total rotation (ER 1 IR) Postseason External rotation W/908 Abd. Internal rotation W/908 Abd. Total rotation (ER 1 IR)

Dominant arm

Nondominant arm

Mean 6 SD

Mean 6 SD

101.09 6 9.14

95.27 6 6.36

48.91 6 10.18 150.00

60.82 6 8.47 156.09

98.91 6 7.06

96.45 6 7.38

48.64 6 9.23 147.55

60.36 6 5.61 156.81

* All measures in degrees.

strength descriptive data respectively. Table 4 contains the external/internal rotation ratios that are formed by dividing each subject’s concentric external rotation strength parameter by the corresponding internal rotation parameter.

Discussion The results of this study show no significant changes in glenohumeral joint rotational strength or range of motion patterns after a 4-month season of competitive collegiate tennis. Of particular interest is the lack of a significant change in strength despite the rigorous training and volumes of upper extremity exertion that are inherent in competitive tennis play. This lack of change in strength over a 4-month period of heavy use supports the need for rotational strength training as an adjunct to tennis-specific training and competition. It appears from this study that a 4-month period of repetitive tennis play alone does not result in significant changes in rotator cuff strength, and does not change range-of-motion patterning in the upper extremity of elite female players. This finding is in contrast to traditional schools of thought stating that per-

Table 3. Pre- and postseason glenohumeral joint internal and external rotation strength from the elite female tennis players.*

Motion/Parameter Preseason ER PT 90 ER PT 210 ER PT 300 ER SRW 90 ER SRW 210 ER SRW 300 IR PT 90 IR PT 210 IR PT 300 IR SRW 90 IR SRW 210 IR SRW 300 Postseason ER PT 90 ER PT 210 ER PT 300 ER SRW 90 ER SRW 210 ER SRW 300 IR PT 90 IR PT 210 IR PT 300 IR SRW 90 IR SRW 210 IR SRW 300

Dominant arm

Nondominant arm

Mean 6 SD

Mean 6 SD

13.45 11.73 10.09 27.18 22.09 17.18 19.36 15.73 14.00 39.91 30.09 24.18

6 6 6 6 6 6 6 6 6 6 6 6

2.94 2.49 2.88 7.44 6.07 5.86 4.30 2.94 3.41 9.77 7.02 7.81

14.73 12.00 11.09 29.18 23.64 20.55 14.18 11.09 10.27 26.55 19.27 16.64

6 6 6 6 6 6 6 6 6 6 6 6

2.28 2.41 3.27 5.53 5.66 6.31 4.09 3.86 4.20 9.44 8.04 8.05

13.27 10.91 9.82 25.09 20.64 15.82 17.36 14.27 13.00 36.82 27.55 22.18

6 6 6 6 6 6 6 6 6 6 6 6

2.45 2.74 2.79 6.69 6.22 6.21 5.12 4.61 4.02 12.16 9.38 9.26

14.00 12.27 10.45 27.09 23.27 17.36 12.91 10.55 8.45 23.64 18.64 13.09

6 6 6 6 6 6 6 6 6 6 6 6

3.41 3.07 3.24 7.98 7.18 6.79 3.59 2.81 3.17 8.66 6.44 6.91

* IR 5 internal rotation, ER 5 external rotation, PT 5 peak torque, SRW 5 single repetition work, 90, 210, and 300 5 isokinetic testing speed in degrees per second. Note: All measures expressed in foot-pounds.

forming a repetitive upper extremity sport movement pattern during practice or competition alone would lead to substantial gains in muscular strength. The primary finding in this research study does not support this recommendation. Therefore, on the basis of the finding of a lack of muscular strength development during a 4-month college tennis season, supplemental exercises to promote strength and endurance of the rotator cuff appear warranted.

Glenohumeral Joint Changes in Tennis Players 95

Table 4. Pre- and post season external/internal rotation ratios from the elite female tennis players.*

Motion/Parameter Preseason ER/IR PT 90 ER/IR PT 210 ER/IR PT 300 ER/IR SRW 90 ER/IR SRW 210 ER/IR SRW 300 Postseason ER/IR PT 90 ER/IR PT 210 ER/IR PT 300 ER/IR SRW 90 ER/IR SRW 210 ER/IR SRW 300

Dominant arm

Nondominant arm

Mean 6 SD

Mean 6 SD

70.27 74.55 71.45 68.27 73.00 71.64

6 6 6 6 6 6

12.51 10.36 9.05 11.21 9.32 13.26

109.45 117.91 116.55 120.45 135.18 137.00

6 6 6 6 6 6

29.10 33.82 33.68 44.16 45.86 46.53

79.55 79.53 77.82 70.73 79.00 74.64

6 6 6 6 6 6

16.31 16.21 18.11 14.88 19.90 21.61

111.91 117.91 127.82 121.36 132.82 142.55

6 6 6 6 6 6

31.34 33.82 36.06 44.65 51.23 45.35

* IR 5 internal rotation, ER 5 external rotation, PT 5 peak torque, SRW 5 single repetition work, 90, 210, and 300 5 isokinetic testing speed in degrees per second. Note: All measures expressed in %.

It was hypothesized initially that external rotation strength would decrease over the 4-month season of competitive tennis. Repeated eccentric loading, which occurs during the follow-through phase of the tennis serve, subjects the muscle tendon unit to large inherent stresses and is a proposed cause of shoulder injury in overhead athletes (12). Examination of the descriptive data in Table 3 shows external rotation peak torque and work values to decrease over the course of the research; however, these decreases were not statistically significant. Changes in internal rotation strength were also not significant. The concentric internal rotation required during the acceleration phase of the serve and forehand is thought to provide a stimulus for strength development of the glenohumeral joint internal rotators (3, 4, 7, 17, 19). Despite the repeated tennis practices and competitions that occurred during the 4-month season, concentric improvements in internal rotation strength did not occur. Table 4 displays the external/internal rotation ratios from the 11 subjects in this study. Normal external/internal rotation ratios range between 66 and 70% in healthy, uninjured shoulders (2, 5, 9). Selective development of the internal rotators from chronic tennis play is a commonly measured characteristic reported in descriptive isokinetic studies in elite junior and adult tennis players (1, 3, 4). This selective development of the internal rotators, without similar development of the external rotators, leads to a lowering of the external/internal rotation ratio on the dominant arm in elite tennis players (1, 3, 4). Alteration of the

external/internal rotation ratio has been described in individuals with glenohumeral joint impingement and instability, and is thought to characterize an important muscular imbalance that can lead to injury (5, 21). Eleven subjects examined in this study had external/ internal rotation ratios between 66 and 70% both before and immediately after the 4-month season of competitive collegiate tennis play. Ratios on the dominant arm are lower than on the nondominant extremity, indicating a greater internal rotation bias on the dominant extremity in these elite tennis players. Similar to the glenohumeral joint rotational strength measurements, rotational range of motion did not statistically change over the 4-month period. The range of motion measured in these elite players is similar to previous research in elite tennis players that found reduced dominant arm internal rotation, and either no difference or slightly greater dominant arm external rotation (6, 10). Total rotation range-of-motion measurements generated in this study also did not change significantly during the testing period. Total rotation range of motion was approximately 68 less on the dominant arm both before and after the season of competitive tennis. Dominant/nondominant differences in total rotation range of motion have been reported as high as 248 among elite female tennis players (10). The 4-month time period of study in this investigation most likely was too short in length for significant range-of-motion alterations to occur. The chronic musculoskeletal range of motion adaptations reported in the dominant arm of elite tennis players that lead to reduced dominant arm internal rotation and total rotation range of motion are considered to have implications for shoulder injury (5, 8, 10). Tightness of the posterior capsule of the glenohumeral joint, as well as muscular tightness of the external rotator muscles, coupled with osseous adaptations such as humeral retrotorsion, have all been cited as probable mechanisms for the typical and unique range of motion patterns seen in unilaterally dominant overhead athletes (10, 14). The lack of significant changes in rotational range of motion and strength in this study is not thought to diminish its importance. Rather, these findings support and highlight the importance of the use and intervention of supplemental resistive exercise for the rotator cuff in elite tennis players. The short 4-month season studied in this investigation may not have been long enough to ultimately see measurable differences in range of motion or strength. Further variables to be considered are the high relative level of training and prestudy preparation by the female tennis players, small homogenous subject population, and adaptation to the stresses inherent in a truly year-round sport such as tennis. Future research is needed on longer pre–post testing time periods, as well as longitudinal assessment of strength and range of motion.

96 Ellenbecker and Roetert

Practical Applications The results of this study support the use of supplemental exercises for the rotator cuff in elite tennis players. A 4-month season of tennis play did not significantly change internal or external rotation strength or range of motion. Muscular imbalance of the shoulder, as well as limitation of glenohumeral joint rotational range of motion, are variables thought to increase the risk of injury. Supplemental exercises to promote muscular strength and endurance of the rotator cuff (5, 19), as well as stretching for the posterior capsule and external rotators, are recommended for unilaterally dominant upper extremity overhead athletes such as those studied in this research.

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Address correspondence to Todd S. Ellenbecker, [email protected].
Effects of a 4-Month Season on Glenohumeral

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