Relationship Between Isokinetic Rotational Shoulder Strength and Scapular Dyskinesia in Division III Overhead Athletes

Abstract

Sports specific movements of overhead athletes require dynamic stabilization of the glenohumeral joint to maintain humeral head congruency, concentric strength of internal rotators, and eccentric strength of external rotator cuff muscles. The balance between shoulder external rotator and internal rotator strength is hypothesized to be related to clinical symptoms of shoulder dyskinesia. However, the relationship between the isokinetic strength profile and shoulder dyskinesia remains less understood. PURPOSE: To examine the isokinetic strength of shoulder internal rotation (IR) and external rotation (ER) in Division III overhead athletes, and its correlation to the outcome of Kibler's lateral scapular slide test (both at 45° and 90°). METHODS: A total of twenty eight NCAA Division III overhead athletes (12 female volleyball players [18.5±0.67 yrs, 70.79±9.29 kg, 173.25±6.65 cm] and 16 male baseball players[19.4±1.2 yrs, 83.84±13.03 kg, 182.25±7.62 cm]) performed maximal isokinetic concentric shoulder ER and IR (60°/sec) testing, and Kibler's lateral scapular slide test (LSST). RESULTS: The isokinetic strength ratio of ER to IR was shown to be 80.6% in the male athletes' dominant shoulders, 94.9% in the female athletes' dominant shoulders, 82.2% in the male athletes' non-dominant shoulders, and 102% in female athletes' non-dominant shoulders. The results also showed significant gender differences on peak torque values (p<0.005 for dominant and non-dominant ER and IR). When compared to Kibler's LSST results, the athletes who showed a positive sign at 90° had an increased dominant ER time to peak torque (p<0.001). CONCLUSION: These results suggest that males produce greater ER and IR peak torque per kg of bodyweight in both dominant and non-dominant shoulders. The significant correlation found between shoulder asymmetry and dominant ER time to peak torque could be considered a potential factor contributing to the dysfunction of the shoulder.