Gender Differences in Shoulder Performance Fatiguability are Affected by Arm Position, Dominance and Muscle Group

Abstract

Background: Injury prevalence data, muscle strength, and fatiguability have shown differences between males and females. In addition, arm spatial orientation affects muscle activation and strength of the shoulder muscles, but little to no research has been conducted in relation to the shoulder rotator muscles comparing men and women. Therefore, the main aim of of this study was to perform a comparative investigation between two arm spatial orientations (45⁰ and 90⁰ of abduction in frontal plane) during a fatigue assessment of shoulder internal rotator (IR) and external rotator (ER) muscles. Secondly, the interaction of gender and dominance with muscular performance was assessed.Methods: Forty healthy sedentary participants, 20 males and 20 females took part in this study. Participants performed a fatigue resistance protocol consisting of 30 consecutive maximal concentric contractions of the IR and ER shoulder muscles in a supine position at a speed of 180⁰/s. The upper limb was abducted to an angle of 45⁰ or 90⁰ in frontal plane and each subject was tested on dominant and nom-dominant side, counterbalanced in order of administration. Performance measures of Induced Fatigue (IF), Cumulated Performance (C.Perf) and Best repetition (BR) were calculated and used for further analysis.Results: There was a significant difference in angle, with higher values observed in 90⁰ of abduction compared to 45⁰ of abduction for C.Perf by 6% and 7% for BR (P < 0.0005) in the ER. The dominant arm was significantly higher than the non-dominant arm for C.Perf with higher values of 9.7% at 90⁰ of abduction compared to 45⁰ of abduction (P = 0.017) and BR with higher values of 4.2% at 90⁰ of abduction compared to 45⁰ of abduction (P < 0.0005) in the ER in males. There was a significant difference in muscle group, with higher values observed in the IR for C.Perf (88.2%), BR (22.5%) and IF (36.9%); at 90⁰ of abduction compared to 45⁰ of abduction in males (P < 0.0005). Significantly higher values were observed for C.Perf in females between the dominant and non-dominant arm for the IR and ER (P < 0.0005). The females showed significantly lower values for C.Perf (47.74-55.10%) and BR (47.30-53.41%) in both muscle groups, both testing positions and in both limbs, when compared to males (P < 0.05)Discussion: It was established that an increase in the abduction angle will influence the strength of ER muscles in favour of the 90° angle without any differences observed in IR muscles. Males were found to produce approximately double the amount of work done compared to females, but the amount of induced fatigue was no different between both groups. Conclusion: Therefore, these findings are useful for clinicians throughout the monitoring of rehabilitation programs in sedentary individuals following shoulder injuries.