Supraspinal Fatigue After A Low- Force Fatiguing Contraction In Men And Women

Abstract

Supraspinal fatigue contributes to neuromuscular fatigue during a low-force fatiguing contraction; however, the influence of the sex of the individual is not understood. PURPOSE: The purpose was to quantify supraspinal fatigue of men and women before and after performance of a low - force isometric fatiguing contraction. METHODS: Thirteen young men and women (5 men [21.20 ± 2.39 yrs], 8 women [20.4 ± 4.2 yrs]) attended one experimental session after a familiarization session. Subjects performed a low-force isometric fatiguing contraction at 20% of maximum voluntary contraction (MVC) force with the elbow flexor muscles until task failure. Voluntary activation was quantified using the force of a superimposed twitch evoked with transcranial magnetic stimulation during MVC's performed before and after the fatiguing contraction. RESULTS: Men had greater MVC torque compared with women (90.6 ± 19.4 Nm vs. 36.9 ± 5.5 Nm, P < 0.05). There was a significant reduction in MVC torque at termination of the task for both men and women (P < 0.05); however, men had a greater reduction in strength than women (47% vs. 37% respectively, P < 0.05). Women had a longer time to task failure for the fatiguing contraction when compared with men (12.3 ± 5.5 min vs. 7.0 ± 1.3 min P < 0.05). The amplitude of the superimposed twitch (%MVC) increased significantly after the fatiguing contraction (P < 0.05), with no difference between men and women (P > 0.05). Consequently, voluntary activation was similar for men and women before the fatiguing contraction (P > 0.05) and decreased similarly for both sexes after the fatiguing contraction (94 ± 4% before to 70 ± 21% after, P < 0.05). Force fluctuations (coefficient of variation of force, CV) during the fatiguing contraction increased at a similar rate for both men and women (1.6 ± 0.5 % at the start vs. 4.8 ± 1.7 % at task failure, P < 0.05). CONCLUSION: Supraspinal fatigue during a low-force fatiguing contraction with the elbow flexor muscles was not influenced by the sex of the individual.