The surface EMG-force relationship during isometric dorsiflexion in males and females

This study compared the tibialis anterior (TA) surface electromyographic (sEMG) to force relationship for males and females. One-hundred participants (50 males and 50 females) performed three isometric contractions at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC) in an apparatus designed to isolate the action of the dorsiflexors. The sEMG signal was amplified (1000x), band-pass filtered (10-500 Hz), and sampled at 2048 Hz. The load cell signal was low-pass filtered at 100 Hz and sampled at the same rate. Males were stronger than females (p < 0.05). However, there was no significant difference in the root-mean-square (RMS) amplitude of the sEMG signal between males and females (p < 0.05). Both groups exhibited a quadratic increase in the RMS across force levels (p < 0.05). The mean power frequency (MNF) of the sEMG signal for males was greater than for females (p < 0.05). Males and females exhibited a linear increase in MNF means up to 80% of MVC (p < 0.05). Between 80 and 100% MVC, the frequency values for the females plateaued while males showed a decrease (p < 0.05). The magnitude of the difference in MNF between males and females was consistent with the observation that males have greater type II muscle fiber diameters. In general, the pattern of means for RMS and MNF between males and females revealed no differences between groups in the sEMG-force relationship. We therefore conclude that there are no differences between males and females in the gradation of muscle force.