Elliott, N., Senefeld, J., Pereira, J., Yoon, T., Harmer, A. R., & Hunter, S. K. (2013). Sex differences and supraspinal fatigue of the knee extensor muscles in young adults. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 467.

This study assessed supraspinal and peripheral fatigue in young males (N = 8) and females (N = 6) during and following a sustained maximal isometric voluntary contraction (MVC) of the knee-extensors. Ss performed a 60-second sustained maximal isometric voluntary contraction of the knee-extensor muscles while seated at 90° of hip and knee flexion. Supraspinal fatigue was assessed as the amplitude of the superimposed twitch elicited from transcranial magnetic stimulation before, during, and after the fatiguing contractions. Electrical stimulation was also used to assess contractile properties of the quadriceps muscle before and after the sustained maximal isometric voluntary contraction.

Males were stronger than females at the beginning and throughout the fatiguing contraction. Males and females experienced a similar decrease in maximal isometric voluntary contraction force by the end of the 60-second fatiguing contraction. Maximal isometric voluntary contraction force recovered more slowly in males than females, especially immediately after fatigue. There was no gender difference in peak rate of relaxation and resting twitch amplitude decreased similarly for both males and females from control values by the end of the fatiguing contraction. The superimposed twitch elicited by transcranial magnetic stimulation increased more for males than females during the 60-second fatiguing contraction. The average superimposed twitch correlated significantly with the decline (%) in maximal isometric voluntary contraction force in early recovery (those who had greater decrements in maximal isometric voluntary contraction immediately after the sustained contraction had greater superimposed twitch amplitude during the fatigue task.

Implication. Males and females experienced a similar reduction in superimposed twitch force during the fatiguing contraction but males remained more fatigued during recovery. The slower recovery in males was associated with greater supraspinal fatigue during the sustained fatiguing contraction.

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