Purpose: This study compared the relative peak torque and normalized electromyographic (EMG) mean frequency (MNF) responses during fatiguing isokinetic muscle actions for men versus women.
Method: Twenty men (Mage +/- SD = 22 +/- 2 years) and 20 women (Mage +/- SD = 22 +/- 1 years) performed 50 maximal concentric isokinetic muscle actions of the leg extensors at a velocity of 180 degrees/s while surface EMG signals were detected from the vastus lateralis, rectus femoris, and vastus medialis. The dependent variables were initial, final, and average peak torque; percent decline; the estimated percentage of fast-twitch fibers for the vastus lateralis; and the linear slope coefficients and y-intercepts for normalized EMG MNF versus repetition number. The data were analyzed with independent-samples t tests and 2-way mixed-factorial analyses of variance.
Results: The mean initial, final, and average peak torque values for men were greaterthan those for women. There were no mean differences for percent decline and the estimated percentage of fast-twitch fibers for the vastus lateralis. There were also no sex differences for the linear slope coefficients, but there were differences among the muscles (vastus medialis > vastus lateralis > rectus femoris). The mean y-intercept for the vastus lateralis for men was greater than that for women.
Conclusions: Men demonstrated greater peak torque values than those for women, but the declines in peak torque and normalized EMG MNF were similar between thesexes. The vastus medialis was more fatigue-resistant than both the vastus lateralis and rectus femoris.