Sex Differences in Rotator Cuff Muscles' Response to Various Work-Related Factors

Background: Baseline strength, endurance, perceived exertion, and muscle activity data are essential to characterize sex-specific responses of the rotator cuff muscles to the workplace tasks to minimize risk of injury due to overexertion. Purpose: This study was conducted to measure sex differences in strength, endurance time, activity, fatigue, and perceived exertion for the rotator cuff muscles. Method: Muscle-specific maximum voluntary contractions (MVCs) were used to measure the maximum torque for the supraspinatus, infraspinatus, and teres minor muscles among 10 male and 10 female participants. Four submaximal exertions (15, 30, 45, and 60% MVC) were used to measure differences in endurance time, muscle activation, fatigue, and perceived exertion between sexes. Surface electromyography was used to measure muscle activity and fatigue. Results: Strength was the highest for the infraspinatus followed by teres minor and supraspinatus regardless of sex. Strengths for females were 70, 50, and 48% that of males for the infraspinatus, supraspinatus, and teres minor muscles, respectively. Muscle activity was significantly higher for females than males during the sub-maximal exertions. Among males, muscles with higher activity developed fatigue faster. Females exhibited lower endurance during all sub-maximal exertions. Perceived exertion ratings showed an increasing trend with %MVC, and females exceeded an acceptable limit at lower %MVC levels compared to males. Conclusions: Sex differences observed in this study suggest that a safe level of %MVC level for females is approximately 15% lower compared to males.