Sex Comparisons for Relative Peak Torque and Electromyographic Mean Frequency During Fatigue

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 (M-age +/- SD=22 +/- 2 years) and 20 women (M-age +/- 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 greater than 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 the sexes. The vastus medialis was more fatigue-resistant than both the vastus lateralis and rectus femoris.