The Effect of Shortening-induced Torque Depression on Fatigue-related Sex Differences

Residual torque depression (rTD) is the decrease in isometric (ISO) torque after active shortening of skeletal muscle compared with a purely ISO contraction performed at the same muscle length and level of activation. Performance fatigability is defined as any exercise-induced reduction in voluntary force or power, and females are typically more fatigue resistant than males at low-intensity ISO contractions. Purpose This study investigated performance fatigability in males and females during ISO contractions and ISO contractions after active shortening (rTD). Methods Fourteen females (22 +/- 2 yr) and 14 males (23 +/- 2 yr) performed three baseline maximal voluntary contractions (MVCs) of the dorsiflexors. The MVCs were used to determine a 30% submaximal torque target, which participants matched as steadily as possible until task failure. The ISO fatigue task was performed at 10 degrees plantar flexion. In the rTD session, the participants' ankle was rotated from 40 degrees to 10 degrees plantar flexion before performing the same fatigue task. MVCs were performed immediately after task failure, 30 s, and 1, 2, 3, 4, 5, 10, 20, and 30 min after task failure to track recovery. Results The baseline MVC torque amplitude for males (32.1 +/- 6.6 N center dot m) was 31% greater than that for females (22.3 +/- 3.1 N center dot m; P < 0.001, eta(2)(p) = 0.490). Females' time to task failure was 44% longer than that of males in the ISO state (P = 0.032, eta(2)(p) = 0.164). However, there was no sex difference in the rTD state (P = 0.142). Conclusion It seems that the sex differences in fatigue resistance observed in a low-intensity ISO task are abolished in the ISO state after an active shortening contraction.