Sex-Specific Links in Motor and Sensory Adaptations to Repetitive Motion-Induced Fatigue

The objectives of this study were to assess the sex-specific relationships between motor and sensory adaptations to repetitive arm motion-induced neck/shoulder fatigue, and to measure how additional sensory stimulation affects these adaptations. Twenty-three participants performed two sessions of a repetitive pointing task until scoring 8 on the Borg CR10 scale for neck/shoulder exertion or for a maximum of 45 min, with and without sensory stimulation (i.e., light touch) applied on the fatiguing shoulder. Just before reaching the task termination criteria, all participants showed changes in mean and variability of arm joint angles and experienced a fivefold increase in anterior deltoid sensory threshold in the stimulus-present condition. Women with the greatest increases in anterior deltoid sensory thresholds demonstrated the greatest increases in shoulder variability (r = .66), whereas men with the greatest increases in upper-trapezius sensory thresholds demonstrated the greatest changes in shoulder angle (r = -.60) and coordination (r = .65) variability. Thus, sensory stimulation had no influence on time to termination but affected how men and women differently adapted, suggesting sex differences in sensorimotor fatigue response mechanisms.