Examination Of Sex-differences In Fatigability And Semg Spectral Shifts During Sustained, Isometric Leg Extensions

PURPOSE: This study investigated sex-differences in fatigability and shifts in the frequency components of the surface electromyographic (sEMG) signal of the vastus lateralis during sustained, maximal, unilateral isometric leg extensions. METHODS: Twenty men (n = 10) and women (n = 10) performed a sustained, maximal, unilateral isometric leg extension with the dominant limb until a 50% reduction in peak force was achieved. sEMG signals were recorded from the exercised limb’s vastus lateralis and were decomposed using a wavelet-based analysis, producing 11 center frequencies spanning 6.90-395.46 Hz. To quantify changes in signal content, changes in the intensity (Ij,k) within each domain were calculated for each sample point (j). Specifically, the rate of change was calculated during the time-to-task failure trial as the slope of the linear fit of log Ik plotted as a function of trial duration (0 to 1, representing the start and end of the trial). This describes the exponential change, expressed as the percentage change of Ik per trial. Independent samples t-tests were used to compare time-to-task failure between men and women, and linear mixed effect models with fixed effects, and interactions thereof, for sex and wavelet domain were used to compare the relative change in wavelet intensities. RESULTS: The women demonstrated a greater time-to-task failure than the men (Mean difference [CI95%] = -17.3 sec [-32.4, -2.08]; p = 0.028). There was no two-way interaction between sex and wavelet domain (p = 0.434) or main effect for sex (p = 0.694). There was, however, a main effect of wavelet domain (p < 0.001), which indicated parallel decreases in spectral intensity for men and women, with greater relative changes for the higher frequency domains compared to lower, as indicated by the negative model coefficient (β [CI95%] = -2.63e-05 arbitrary units [-4.47e-05, -7.98e-06]). CONCLUSION: The patterns of spectral changes suggested a greater rate of fatigue induced responses for higher than lower threshold motor units. However, despite significant differences in time-to-task failure between men and women, changes in spectral intensity did not depend on sex. Thus, it is possible that sex differences in exercise performance can occur independent of any electrophysiological differences, or lack thereof, during exercise.