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

Baseline, postexercise (20 min 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 (13 min 50 s vs. 17 min 9 s) 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 (184 bpm vs. 179 bpm, p < .05).