M-wave normalization of EMG signal to investigate heat stress and fatigue

Objectives We examined the extent to which peripheral changes affect EMG signal adjustments during repeated sprinting in temperate and hot conditions. Design Randomised, crossover study. Methods Ten males performed 10 × 6-s ‘all-out’ cycling sprints (recovery = 30 s) in either a temperate (24 °C/30%rH) or a hot (35 °C/40%rH) environment with concomitant surface EMG recordings of the vastus lateralis (VL) and rectus femoris (RF). In addition, peak-to-peak M-wave amplitudes were obtained for each muscle after each sprint (i.e., 15 s into recovery). Results For both the VL and RF muscles RMS decreased across sprint repetitions (P 0.621). M-wave-normalised RMS for the RF muscle was lower in the heat (P 0.240). Conclusions Controlling for changes in maximal M-wave amplitude of the quadriceps muscles after each bout of a repeated cycling exercise in hot and temperate conditions allows researchers to account for fatigue- and/or heat-induced neural and peripheral adjustments