Isokinetic Profile of Shoulder Internal and external rotators by MLB Pitching

Journal of Strength and Conditioning Research, 2004, 18(4), 861–866 q 2004 National Strength & Conditioning Association

ISOKINETIC PROFILE OF SHOULDER INTERNAL EXTERNAL ROTATORS OF HIGH SCHOOL AGED BASEBALL PITCHERS IVAN J. MULLIGAN,1,2 WILLIAM B. BIDDINGTON,3 BRUCE D. BARNHART,4 TODD S. ELLENBECKER5

AND

Rocky Mountain University of Health Professions, Provo, Utah 84601; 2Vantage Physical Therapy and Rehabilitation, Johnstown, Pennsylvania 15905; 3Graduate Program in Athletic Training, California University of Pennsylvania, California, Pennsylvania 15419; 4Undergraduate Program in Athletic Training, California University of Pennsylvania, California, Pennsylvania 15419; 5Physiotherapy Associates, Scottsdale, Arizona 85258. 1

ABSTRACT. Mulligan, I.J., W.B. Biddington, B.D. Barnhart, and T.S. Ellenbecker. Isokinetic profile of shoulder internal and external rotators of high school aged baseball pitchers. J. Strength Cond. Res. 18(4):000–000. 2004.—The purpose of this descriptive study was to determine whether bilateral differences exist in concentric and eccentric shoulder internal and external rotation strength in high school aged baseball pitchers. Thirty-nine high school aged baseball pitchers were bilaterally tested for concentric and eccentric internal and external rotation muscle performance on a Kin-Com 500-H isokinetic dynamometer at 908·s21 and 1808·s21. Paired t-tests were used to test for differences among extremities, speed, and ratio of external rotation to internal rotation (ER/IR ratios). Concentric peak torque internal rotation at 908·s21 was significantly greater (p , 0.05) in the dominant arm compared with the nondominant arm. Statistically significant differences (p , 0.001) were found between the nondominant and dominant in concentric 908·s21. The nondominant arm demonstrated significantly greater eccentric strength (p , 0.05) compared with the dominant arm in ER/IR ratios at 908·s21 and 1808·s21. The nondominant arm demonstrated significantly greater eccentric strength (p , 0.05) than the dominant arm in ER/IR ratio at 1808·s21. Data demonstrated that muscular adaptations are consistent with previous research in this area. Also, muscular adaptations occur in the shoulder in the high school aged population. These data can serve as a guideline to be used by clinicians who rehabilitate shoulders in patients in this population. KEY WORDS. muscular strength, rotator cuff, pediatrics

INTRODUCTION sokinetic strength has been examined in various populations since the advent of isokinetic strength testing (10, 11, 13, 20, 21). Over the years, research has examined concentric and eccentric contractions in shoulder internal and external rotation in professional, college, and high school pitchers (1, 3, 9, 12, 14, 16, 18, 21, 23). Isokinetic strength testing assists in providing objective data to determine agonist and antagonist muscular strength surrounding the glenohumeral joint. Most sports use the shoulder joint in an open kinetic chain movement (11). These sports activities include volleyball spike, tennis serve, and the throwing motion. An isokinetic device can evaluate the shoulder in a more functional pattern. Although an isokinetic device cannot match the velocities the shoulder demonstrates during the act of overhead throwing, it provides information concerning agonist-an-

tagonist muscular activity, which is essential in evaluation and rehabilitation activities. Many variables in shoulder strength have been studied using isokinetic testing, specifically in baseball pitchers. Many advantages have been described in using isokinetic testing. Muscular performances that can be analyzed include peak torque, average power, total work, and fatigue indexes (11). Given the abundance of information that can be gathered, isokinetic testing has been used in various settings to examine strength in both nonathletic and athletic populations. Isokinetic data have been examined in many aspects of shoulder strength in various populations, including overhead athletes. Bilateral comparisons of shoulder internal rotation and external rotation have been described in various research studies. These studies examined internal and external rotation strength in the dominant and nondominant shoulders in all levels of baseball and tennis players (1, 3, 5, 11, 14, 23). Internal rotation strength has demonstrated significantly greater strength in the dominant arm vs. the nondominant arm in various levels of baseball pitchers (12). Internal rotation strength of the dominant arm was found to be significantly greater compared with the nondominant arm (5, 11, 12, 14). External rotation strength has also been examined in various groups of baseball players, and no significant difference was found between dominant and nondominant shoulders (12, 14, 23). It has been surmised that based on the findings of these studies muscular adaptation occurs and the shoulder internal rotators exhibit the greatest force during overhead activity (11). When attempting to determine muscle strength in the upper extremity, the ratio of external rotation to internal rotation (ER/IR ratio) has been reported to assess the strength balance of the shoulder (10). Various studies have been performed to examine this ratio, providing a wide range of results (0.53–0.78) (1, 7, 10, 14, 22). Based on these findings, an ER/IR ratio of 66% has been approximated as normal (11). It has been recommended that if this ratio were biased to favor external rotation, greater stability may be added in the glenohumeral joint in athletes performing overhead activity and shoulder injuries may possibly be prevented. Furthermore, increasing the ER/IR ratio to 76% has been specifically recommended (11). 861

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METHODS Experimental Approach to the Problem

This study was designed to accomplish 2 objectives. First, this study was to determine if a significant difference existed between dominant and nondominant shoulder external and internal rotation isokinetic strength in high school aged baseball pitchers. A second purpose of this study was to add to the population-specific data profile of peak torque and total work ratios and ER/IR ratios for concentric and eccentric strength on the Kin-Com isokinetic dynamometer (Chattecx Corp., Chattanooga, TN). The results were expected to be comparable to previous research in this area, which would enhance the normative data of isokinetic strength of high school aged baseball pitchers. Also, the isokinetic strength of the internal rotators of the dominant shoulder was expected to be greater than the nondominant arm. Finally, it was anticipated that the external rotation strength of the dominant arm would be less than the nondominant arm given the bias of the internal rotators of the dominant arm during the act of throwing. Subjects

High school baseball pitchers located in the western Pennsylvania region were recruited for this study. Subjects underwent approximately 1.5 hours of testing. Initially, the subjects and their parents or guardians reviewed the cover letter that explained the purpose of the study, and both the subjects and their parents or guardians signed the informed consent forms. The subjects were assigned a 3-digit number to allow for subject confidentiality and enable the researcher to share all results of the study with the respondents. All procedures were reviewed and approved by the Rocky Mountain University of Health Professions Institutional Review Board. Forty-six baseball pitchers, who played for their high school or in a summer league, volunteered to participate in the study. Six potential subjects were excluded from the study secondary to having an injury to their throwing shoulder or elbow in the 6 months before testing. Forty subjects were included in the study; however, 1 subject wished to stop testing and was eliminated from the data collection. Procedures

This study examined 39 high school baseball pitchers recruited in the western region of Pennsylvania who were recruited from local high schools. The investigator documented differences in physical characteristics and years pitching. Initially, a pretest questionnaire was used to examine demographic data (sex, age, high school, years pitching, dominant arm, pain during throwing, and preseason exercise routine). The variables collected by the questionnaire were analyzed using descriptive statistics to determine if trends existed. To allow for confidentiality of subjects, the subjects were assigned a 3-digit number, which was placed on all documentation from the subject in the upper right hand corner of all forms. Next, the subject’s height and weight were measured and recorded. The scale was a standard scale with counterweights. The scale was calibrated as per manufacturer’s recommendations before data collection. Before isokinetic testing was performed, the Kin-Com

TABLE 1. Warm-up procedure before isokinetic testing. Activity

Repetitions and time

Shoulder stretches (flexion, extension, abduction, internal and external rotation) Upper body ergometer (alternating forward and backward) Warm up on Kin-Com device

5 repetitions, 10 s 5 min 3 submaximal and 2 maximal repetitions

TABLE 2. Isokinetic protocol for testing internal and external rotation strength. No. of repetitions Concentric Eccentric Concentric Eccentric 908·s21 908·s21 1808·s21 1808·s21 Internal rotation External rotation

5 5

10 10

isokinetic dynamometer was calibrated as per manufacturer’s recommendations. Isokinetic testing was performed with the subject placed in the testing position as recommended by the manufacturer (6). This position had the subject sitting with the dynamometer at a 308 angle away from the side being tested, which placed the shoulder in the scapular plane. The subject’s arm that was being tested was strapped to the dynamometer. Stabilization belts were placed across the thoracic region and abdominal region to minimize compensatory movements. During the warm-up procedure, the subject performed 3 submaximal contractions through the available range of motion followed by 2 maximal contractions. The type of contraction during the warm-up procedure was consistent with the type of contraction for the testing procedure. For example, if a concentric contraction test was performed then the warm-up consisted of concentric contractions. The warm-up procedure has been described in the literature to effectively train the subject in the movement of the isokinetic device (10). The range of motion of the shoulder was standardized for 458 of internal rotation and 458 of external rotation. Next, the subject was asked to perform a series of shoulder stretches (flexion, extension, abduction, internal rotation, and external rotation). All stretches were performed 5 times, with the subject holding each stretch for 10 seconds. Next, the subjects were asked to pedal an upper body ergometer, forward and backward, for a total of 5 minutes. The upper body ergometer was set for 90 rpm for the intensity of the exercise. Finally, the subject completed the warm-up repetitions on the Kin-Com isokinetic dynamometer. Table 1 describes the warm-up procedure. Following the warm-up, the subject performed the isokinetic test at the speed selected and type of contraction. The protocol for testing is described in Table 2. There was a rest of 90 seconds between each bout of exercise. The isokinetic dynamometer measured total work, peak torque, and ER/IR ratio by software included with the testing system. The manufacturer has standardized this program. The above protocol was performed on both the dominant and the nondominant shoulders. Random selection was used to determine which shoulder was tested

ISOKINETIC PROFILE TABLE 3. Subject characteristics (N 5 39). Age (y) Height (cm) Weight (kg) Years pitching

Mean

Range

15.36 176.18 72.14 6.59

2.03 11.70 13.43 2.05

13.00–19.00 144.78–200.66 42.18–99.79 2.0–12.0

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ously examined. Dvir (10) stated that slower velocities should be tested first followed by the faster speeds. Other factors were discussed in producing enhanced reliability. First, 3–6 submaximal repetitions and 1–2 maximal repetitions should be performed. This not only enhances reliability but also allows the individual being tested to accommodate to the machine. A total of 4–6 total warm-up repetitions are acceptable to produce results indicative of the individual’s ability.

first. The protocol remained consistent for all subjects to ensure accurate data collection.

Statistical Analyses

Demographic data (age, height, weight, and years pitching) were analyzed by descriptive analysis (mean, SD, and range). Descriptive data were also used to analyze peak torque, total work, and ER/IR ratio. Paired t-tests were used to test if there was a significant difference in the means of peak torque, total work, and ER/IR ratio of the dominant and nondominant arm. The level of significance was set for all statistical analyses at p # 0.05. Statistical analysis was performed using Minitab statistical software package (State College, PA) on a Windows-compatible personal computer.

Reliability and Validity of Instruments

Various studies examined the reliability and validity of isokinetic testing. It has been suggested that isokinetic test results might vary between machines and possibly between tests during normal use. Therefore, it was necessary to calibrate the machine before data collection (10). Given this recommendation, the Kin-Com isokinetic device was calibrated the week before data collection. Intramodel reliability has been examined, and intertester reliability was found to be high, indicating sufficient reliability for these devices (4, 17). However, intermodel reliability cannot be assumed, since several studies have found that results cannot be generalized between different brands of isokinetic devices (20). The reciprocal concentric and eccentric cycle has been examined, and the results indicate that the interclass correlations were 0.79–0.88 (15). This finding indicated that performing isokinetic testing using a reciprocal cycle was acceptable. The order for testing velocities has also been previ-

RESULTS Table 3 contains the characteristics of the 39 individuals included in the study. Thirty-three were right handed and 6 were left handed. Comparisons of the mean peak torque in concentric contractions, eccentric contractions, and ER/IR ratio are given in Tables 4–6. Comparisons of the mean total work and ER/IR ratios of concentric and eccentric contractions are given in Tables 6–8.

TABLE 4. Mean peak torque in shoulder external and internal rotation concentric contraction between dominant and nondominant arms. Nondominant arm

Dominant arm Concentric Concentric Concentric Concentric

908·s internal rotation 908·s21 external rotation 1808·s21 internal rotation 1808·s21 external rotation

Mean

11.97 6.97 15.27 10.05

8.13 4.77 12.65 7.28

11.03 7.31 15.10 10.89

7.51 4.97 12.25 7.74

0.040* 0.338 0.868 0.347

* Significant at the 0.05 level. TABLE 5. Mean peak torque in shoulder external and internal rotation eccentric contraction between dominant and nondominant arms. Nondominant arm

Dominant arm Eccentric Eccentric Eccentric Eccentric

908·s21 internal rotation 908·s21 external rotation 1808·s21 internal rotation 1808·s21 external rotation

Mean

12.28 7.44 14.12 10.93

8.65 3.25 9.12 8.43

11.36 7.82 13.88 11.20

8.91 6.80 9.29 7.90

0.095 0.340 0.669 0.545

TABLE 6. Peak torque shoulder external rotation to internal rotation ratio between dominant and nondominant arms. Nondominant arm

Dominant arm 21

Concentric 908·s Eccentric 908·s21 Concentric 1808·s21 Eccentric 1808·s21 * Significant at the 0.01 level.

Mean

0.5764 0.6261 0.7070 0.7661

0.1620 0.1589 0.1836 0.1689

0.6779 0.6520 0.7556 0.8268

0.1545 0.2365 0.2029 0.1564

0.001* 0.548 0.210 0.061

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TABLE 7. Mean total work in shoulder external and internal rotation concentric contraction between dominant and nondominant arms. Nondominant arm

Dominant arm Concentric Concentric Concentric Concentric

908·s internal rotation 908·s21 external rotation 1808·s21 internal rotation 1808·s21 external rotation

Mean

16.56 9.26 151.6 74.10

10.84 6.44 110.4 53.27

15.54 9.74 139.8 76.07

10.39 6.70 93.2 50.97

0.073 0.328 0.084 0.528

TABLE 8. Mean total work in shoulder external and internal rotation eccentric contraction between dominant and nondominant arms. Nondominant arm

Dominant arm Eccentric Eccentric Eccentric Eccentric

908·s internal rotation 908·s21 external rotation 1808·s21 internal rotation 1808·s21 external rotation

Mean

15.95 10.08 117.9 83.15

11.07 7.26 83.4 61.04

15.36 10.92 112.2 90.5

11.72 9.51 78.2 64.5

0.427 0.185 0.263 0.065

TABLE 9. Total work shoulder external rotation to internal rotation ratio between dominant and nondominant arms. Nondominant arm

Dominant arm 21

Concentric 908·s Eccentric 908·s21 Concentric 1808·s21 Eccentric 1808·s21

Mean

0.5628 0.6506 0.5100 0.7243

0.1517 0.1439 0.1495 0.2008

0.6544 0.6827 0.5761 0.8261

0.1656 0.1776 0.1803 0.1762

0.000* 0.180 0.048** 0.012**

* Significant at the 0.001 level. ** Significant at the 0.05 level.

Table 4 demonstrates statistically significant (p , 0.05) dominant arm concentric internal rotation peak torque at the 908·s21 testing speed compared with the nondominant arm. No significant differences were found between the dominant and nondominant arms for concentric 908·s21 external rotation and both concentric 1808·s21 internal and external rotation tests. Table 5 gives the peak torque findings of eccentric contractions at the 908·s21 and 1808·s21 testing speeds for internal and external rotation. No significant differences were found between the dominant and nondominant arms for the eccentric contractions at the testing speeds for internal and external rotation. Table 6 presents the ER/IR strength ratio for peak torque in concentric and eccentric contractions at the 908·s21 and 1808·s21 testing speeds. Statistically significant (p , 0.001) differences were found between the nondominant and dominant arm concentric contraction at the 908·s21 testing speed. All other testing speeds and types of contractions were found to have no significant difference in the ER/IR ratio. Tables 7 and 8 examine the total work findings of concentric and eccentric contractions in dominant and nondominant arms at the 908·s21 and 1808·s21 testing speeds. No significant differences were found between dominant and nondominant arm in total work of concentric and eccentric contractions. Table 9 reports the total work ER/IR ratio at the concentric and eccentric contractions at the 908·s21 and 1808·s21 testing speeds. The nondominant arm demonstrated significantly greater strength (p , 0.05) compared

with the dominant arm in ER/IR ratio at the concentric 908·s21 and 1808·s21 testing speed. Also, the nondominant arm demonstrated significantly greater strength (p , 0.05) than the dominant arm in ER/IR ratio at the eccentric 1808·s21 testing speed. No significant difference was found for eccentric contraction at the 908·s21 testing speed.

DISCUSSION The results of this study are in agreement with previous research that found that the dominant arm demonstrated significantly greater internal rotation concentric muscle contraction at the 908·s21 testing speed (3, 12, 14, 19). The findings of this study demonstrate internal rotation concentric strength greater than external rotation at both testing speeds. These findings are also in agreement with previous research (3, 12, 14, 19). The results of this study regarding limited strength in eccentric external rotation are similar to previous research (16). The limitations noted in external rotation strength are of particular interest given the fact that the act of throwing relies on the external rotators as described in the literature that has examined throwing mechanics, especially during the arm deceleration phase (2). The posterior shoulder musculature reacts as the arm is attempting to rapidly decelerate. These muscles will contract eccentrically rather than concentrically (23). Therefore, it was initially expected that the peak torque and total work would demonstrate greater eccentric strength compared with the nondominant arm. However, this was not the finding;

ISOKINETIC PROFILE

in fact, the eccentric strength in external rotation mirrored the findings in concentric strength, where the external rotation of the dominant arm demonstrated less strength than the nondominant arm. Examining ER/IR strength ratios, the results of this study are similar to previous reports that describe this ratio to between 0.53 and 0.78 (1, 7, 10, 14, 22). This study found that in the dominant arm the ER/IR ratios in the 908·s21 and 1808·s21 testing speeds were 0.58 and 0.71, respectively. This study also found ER/IR ratios in the dominant arm to be 10% lower at 908·s21 and 5% lower in 1808·s21 concentric contractions. This has been found in various reported research, with a range of 4–11% (8, 12, 14, 23). This finding has been attributed to greater internal rotation in the dominant and nondominant arm (8, 12). This ratio can be explained given the fact that there is greater internal rotation strength and less external rotation in the dominant arm compared with the nondominant arm. This would lead to a lower ratio when comparing external rotation to internal rotation. The ER/IR ratio of eccentric and concentric strength of the dominant and nondominant arms was examined. The eccentric ER/IR ratio was greater than the concentric ER/IR ratios of 0.63 and 0.77 at the 908·s21 and 1808·s21 testing speeds, respectively. These findings are similar to previous research (16). The nondominant arm again demonstrated a greater ER/IR ratio compared with the dominant arm (3–6%). Increasing the concentric ER/IR ratio to 76% has been suggested as a goal (11). This study supports this recommendation. The lower ER/IR ratio in the dominant arm could be due to the selective internal strength development. The increase of external rotation could effectively bias this ratio and may add greater stability to the glenohumeral joint in athletes performing overhead activities and possibly prevent shoulder injuries. Given the limited published research examining eccentric external and internal rotation strength, no recommendations could be made effectively. Since this current study has found results similar to previous research, it can be recommended that the ER/IR ratio in eccentric strength should be increased to 80%. The results of this study are limited to high school baseball pitchers; however, the results confirm previous research findings and can assist in determining trends and strength ratios in isokinetic testing of shoulder internal and external rotation. Additional research should be undertaken to examine effective ways to increase external rotation in the shoulder concentrically and eccentrically. Examining a workout routine using isokinetic testing as a pretest and posttest may be the most effective approach.

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HIGH SCHOOL BASEBALL PITCHERS 865

muscular imbalance could affect performance during the season or be a precursor to injury to the shoulder. The implementation of a preseason strengthening program that emphasizes the posterior shoulder muscles, specifically the external rotators, may be beneficial in preventing injuries to the shoulder and possibly improving performance.

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PRACTICAL APPLICATIONS This study provides demographic data of isokinetic strength in high school aged baseball pitchers that are consistent with previous research. This study also provides the ER/IR ratios in the dominant and nondominant arms. The results found in this study demonstrate that the internal rotators of the throwing shoulder are significantly stronger than the nonthrowing arm. However, the results also show that the external rotators of the throwing shoulder are weaker than the nonthrowing shoulder. Given this result, the ER/IR ratio is decreased, which demonstrates a muscular imbalance at the shoulder. This

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Address correspondence mulligan@floodcity.net.

Dr.

Ivan

Mulligan,