Sex differences in kinematic adaptations to muscle fatigue induced by repetitive upper limb movements

Abstract

Background: Muscle fatigue induced by repetitive movements contributes to the development of musculoskeletal disorders. Men and women respond differently to muscle fatigue during isometric single-joint efforts, but sex differences during dynamic multi-joint tasks have not been clearly identified. Moreover, most studies comparing men and women during fatigue development assessed endurance time. However, none evaluated sex differences in kinematic adaptations to fatigue during multi-joint dynamic tasks. The objective of the study was to compare how men and women adapt their upper body kinematics during a fatiguing repetitive pointing task.

Methods: Forty men and 41 women performed repetitive pointing movements (one per second) between two targets while maintaining their elbow elevated at shoulder height. The task ended when participants rated a perceived level of fatigue of 8/10. Trunk, humerothoracic, and elbow angles were compared between the first and last 30 s of the experiment and between men and women. Linear positions of the index finger (distance from the target) and the elbow (arm elevation) as well as movement timing were documented as task performance measures.

Results: Men (7.4 ± 3.2 min) and women (8.3 ± 4.5 min) performed the repetitive pointing task for a similar duration. For both sex groups, trunk range of motion increased with fatigue while shoulder's and elbow's decreased. Moreover, participants modified their trunk posture to compensate for the decreased humerothoracic elevation. Movements at all joints also became more variable with fatigue. However, of the 24 joint angle variables assessed, only two Sex × Fatigue interactions were observed. Although average humerothoracic elevation angle decreased in both subgroups, this decrease was greater in men (standardized response mean [SRM] - 1.63) than in women (SRM - 1.44). Moreover, the movement-to-movement variability of humerothoracic elevation angle increased only in women (SRM 0.42).

Conclusion: Despite many similarities between men's and women's response to fatigue induced by repetitive pointing movements, some sex differences were observed. Those subtle differences may indicate that men's shoulder muscles were more fatigued than women's despite a similar level of perceived exertion. They may also indicate that men and women do not adapt the exact same way to a similar fatigue.

Keywords: Adaptation; Fatigue; Gender; Kinematics; Musculoskeletal disorders; Sex differences; Shoulder; Upper limb.

Fig. 1

Model used to analyze kinematic data. Joint coordinate systems are presented for the trunk-global, humerothoracic, and elbow joints. Wrist and hand joints are not presented here for clarity. The transformation orders (degrees of freedom, DoF) are presented for each joint. Transformations written in bold characters and presented with their name in the table represent the degrees of freedom reported in the “Results” section. Note that elbow pronation-supination (Ry) occurs at the radioulnar (ru) joint. T, translation; R, rotation

Fig. 2

Effects of Sex and Fatigue on task performance variables. F (main effect of Fatigue), S (main effect of Sex), S×F (Sex × Fatigue interaction)

Fig. 3

Effects of Sex and Fatigue on mean kinematic behavior. Left panel—men’s (blue) and women’s (red) mean joint angle time histories during Non-Fatigue (full lines) and Fatigue Terminal (dashed lines) movements. Center panel—mean average angle for each DoF. Right panel—mean range of motion for each DoF. F (main effect of Fatigue), S (main effect of Sex), S×F (Sex × Fatigue interaction). *Post hoc analysis showing differences between men and women. HT, humerothoracic

Fig. 4

Effects of Sex and Fatigue on kinematic behavior movement-to-movement variability. Left panel—men’s (blue) and women’s (red) joint angle standard deviation time histories during non-fatigue (full lines) and Fatigue Terminal (dashed lines) movements. Center panel—standard deviation of average angle for each DoF. Right panel—standard deviation of the range of motion for each DoF. F (main effect of Fatigue), S (main effect of Sex), S×F (Sex × Fatigue interaction). *Post hoc analysis showing differences between men and women. HT, humerothoracic

Fig. 5

Summary of results. Fatigue-related effect size for men (blue) and women (red) for all computed joint angle variables. Standardized response mean (SRM). Gray symbols indicate non-significant effect. *Sex × Fatigue interactions. HT, humerothoracic