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

Abstract

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).