Mechanisms for the age-related increase in fatigability of the elbow flexor muscles in healthy adults

The mechanisms for the age-related increase in fatigability of the elbow flexor muscles during dynamic contractions are unknown. The purpose of this study was to determine the contribution of supraspinal and contractile mechanisms for the age-related increase in fatigability of the elbow flexor muscles. Twenty-eight young (23.2 ± 2.6 years; 14 females) and 32 older adults (72.6 ± 5.6 years; 15 females) performed 80 maximal velocity contractions at 20% of maximal isometric strength. Voluntary activation and muscle contractile properties were assessed before and immediately following the fatiguing exercise using transcranial magnetic stimulation (TMS) and electrical stimulation. Fatigability (% reduction in power) was greater in older (49.2%) than in young adults (37.6%; p = 0.01) with no differences between males and females (p = 0.36). Reductions in voluntary activation following exercise did not differ between young and older adults (p = 0.96). Reductions in peak rates of torque relaxation induced by TMS were greater in older (44.4%) than in young adults (22.8%; p < 0.001) and were associated with fatigability (r = 0.51, p < 0.001). These data suggest that the age-related increase in fatigability of the elbow flexors is due primarily to mechanisms that impair muscle contractile function.