Peripheral fatigue in young and old females and males
Yacyshyn AF, Gelinas JC, Brunton N, Eves ND and McNeil CJ
School of Health and Exercise Sciences and Centre for Heart, Lung and Vascular Health, University of British Columbia – Okanagan Campus, Kelowna, BC, Canada
Physical activity-induced muscle fatigue is a common experience that can limit daily tasks in many populations. This fatigue is task-dependent and evidence suggests both sex and age play critical roles. However, data are scant on sex differences for non-volitional contractions, which assess intrinsic fatigability of muscle while limiting spinal and supraspinal adaptations to mitigate fatigue. The purpose of this study was to assess the effects of sex and age on fatigability during isometric contractions induced by electrical stimulation at a physiological frequency. It was hypothesized that young females would fatigue less than males, but old adults would fatigue similarly. To date, data have been collected from 8 young females, 8 young males, 6 old females and 8 old males (24±3, 24±3, 64±3 and 67±3 years, respectively). The quadriceps of the dominant leg were fatigued by 3min of intermittent transcutaneous muscle belly stimulation (10 pulses at 15Hz; 1.25s between train onsets) at the intensity which initially evoked 25% of maximal voluntary force. Preliminary data support the hypothesis that young females fatigue less than young males (end-task force = 57±11 vs. 50±10% baseline, respectively). Interestingly, in contrast to the hypothesis, old females may fatigue more than old males (end-task force = 46±12 vs. 54±15% baseline, respectively). This suggests an interactive effect of sex and aging, wherein old females undergo intrinsic contractile changes that increase susceptibility to fatigue compared to old males. If true, old females may be more successful at using central nervous system adaptations to mitigate muscle fatigue during voluntary tasks.