Neuromuscular responses to an isometric force and position task during passive hyperthermia
Mechanisms of central nervous system (CNS) impairment during hyperthermia are largely task-dependent. This thesis sought to compare neuromuscular responses of an isometric force and position task during passive hyperthermia, and the relative contributions of rectal (Tre) and skin (T ̅sk) temperature afferents. Surface electromyography (sEMG) was used to assess the electrical activity of the flexor carpi radialis (FCR) muscle during a force and position task. Twenty participants were passively heated from 37.1°C to 39.0°C Tre or thermal tolerance and then cooled back to 37.8°C using a liquid conditioning garment. Passive hyperthermia induced progressive increases in root-mean-square (RMS) amplitude, mean power frequency (MPF) and median power frequency (MDF) for the force task. No change was observed in the sEMG signal for the positon task with passive heating, yet RMS amplitude increased upon skin cooling. Discrepancies in the sEMG signal exist between isometric and dynamic tasks, and these changes are due to core and skin afferents, respectively.