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

OCCUPATIONAL APPLICATIONS

Despite the frequency and cost of rotator cuff injuries among male and female workers, very little is known about the strength, endurance, and perceived exertion and electromyographic response of rotator cuff muscles to different exertion levels. In this study, sex differences were studied using muscle-specific maximal and submaximal exertions of the supraspinatus, infraspinatus, and teres minor muscles. Females showed lower strength and endurance, but higher muscle activity and perceived exertion compared to males. The baseline data presented in this paper can assist ergonomic practitioners in determining the worker capacity to ensure that physically-demanding shoulder exertions can be performed without incurring injurious stress. Such data is also essential to establish population norms for the better design of workplace tasks.

TECHNICAL ABSTRACT

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.

Keywords:

• Sex
• rotator cuff muscles
• strength
• fatigue
• electromyography

Conflict of Interest

None of the authors have any conflict of interest.

Additional information

Funding

Part of the funding required to complete the project was provided by the NIOSH training grant [grant number T03 OH008431-12].