Neuromuscular failure is unlikely to explain the early exercise cessation in hot ambient conditions

Baseline, postexercise (20min cycling) and postexhaustion (incremental test) neuromuscular function was assessed in control (24°C) and hot (40°C) conditions. Heat affects the plantar flexors and knee extensors differently, but most of the effects of heat (e.g., M-wave decrement) and fatigue (e.g., voluntary activation and H-reflex decrement) were independent of each other. However, peripheral fatigue of the knee extensors was lower at exhaustion in hot than neutral environment (peak twitch decrement from baseline to exhaustion: -19% vs. -33%, p<.05). In addition, heat had no negative effect on transcranial magnetic stimulation responses during cycling, and neuromuscular failure is unlikely to explain the early exercise cessation in the heat (13min 50s vs. 17min 9s) that occurred when participants reached maximal perceived exertion (19.2 vs. 19.1, ns) with higher core temperature (38.7°C vs. 38.2°C, p<.05) and heart rate (184bpm vs. 179bpm, p<.05).