Background. More women suffer from musculoskeletal disorders (MSDs) in the neck-shoulder and hand-arm regions than men, even when they are performing similar jobs. Fatigue is a known predictor of MSDs, and gender differences in fatigue responses could help explain the difference in MSD occurrence. This study aimed to assess the extent to which genders differ in fatigability by examining muscle-activity responses when perform-ing a low-force, repetitive arm-task leading to muscle fatigue in the neck-shoulder region.

Methods. 108 healthy individuals (55 males, 53 females) repeatedly touched two targets placed at shoulder height in front of them. The targets were placed at 30% and 100% of arm’s length and touched at a rate established by a 1Hz metronome until the subjects reported a perceived exertion of 8 on the Borg CR-10 scale for the neck-shoulder region. Bipolar surface EMG was recorded from the upper trapezius, anterior deltoid, biceps and triceps. Task duration and EMG amplitude (average and cycle-to-cycle variability) during the first minute (baseline) and last minute (fatigue-terminal) were compared between men and women.

Results. There were no gender differences in task duration, EMG variability at baseline, or change in average EMG amplitude with fatigue. Change in EMG variability from baseline to fatigue-terminal was lower for women than men in the upper trapezius (7.2% vs. 30.6% increase, p=0.02), and higher for women than men in the biceps (11.8% increase vs. 23.2% decrease, p=0.0006).

Discussion.This is the first study to report gender differences in muscle-activity responses to a fatiguing, dynamic manual task relevant to working life based on a comprehensive sample of healthy individuals. Despite no differences in task duration, there may be gen-der differences in the physiological mechanisms behind fatigue adaptations: while women may use compensatory mechanisms mainly involving the elbow, men may use more shoulder-driven strategies. These gender differences in muscle-activity responses may contribute to explaining why women suffer more from neck-shoulder MSDs than men.