Differences in Muscle Fatigability of Vastus Medialis between Sexes Using Surface Electromyographic Power Spectral Analysis in Healthy Adults.

Objectives: With a relatively high percentage of type I fibers in the vastus medialis (VM), its fatigability may be more sensitive to the effects of muscle activity in the quadriceps. However, sex-related differences in the muscle fatigability of the VM remain unknown. The purpose of the present study was to assess the differences in fatigability of the VM between healthy adult men and women. Methods: Surface electromyographic (EMG) activities of VM oblique (VMO) and VM long (VML) were recorded during sustained isometric contraction on a leg press machine. The results of EMG power spectral analysis were compared between healthy adult men and women. The decline in the median frequency (MF), defined as MF slope, was calculated using spectrum analysis after fast Fourier transform of the raw EMG signals of VMO and VML. Results: The endurance time and the MF slopes of the VMO and VML were significantly longer and lower, respectively, in women than in men. The present results demonstrated that both VMO and VML are more fatigue-resistant in women than in men. Conclusions: Understanding the sex differences in fatigability could help to design more effective exercise regimens for VMO and VML in healthy individuals. A similar approach should be considered when prescribing practical exercise regimens for patients with muscle atrophy.