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PÉR1ARD. JD. C. CAILLAUD. and MW THOMPSON. Central and Peripheral Fatigue during Passive and Exercise-induced Hyperthermia. Med. Sei. Sports Exere., Vol. 43, No. 9, pp. 1657-1665, 201 i. Hyperthermia was induced during prolonged exercise (ExH) and passive heating (PaH) to isolate the influence of exercise on neuromuscular function during a maximal voluntary isometric contraction (MVC) of the quadriceps under heat stress. The influence of cardiovascular strain in limiting endurance performance in the heat was also examined. IVIethods: On separate days, eight males cycled to exhaustion at 60% maximal oxygen uptake or were immersed in a water bath {~ 41 C) until rectal temperature (r „) increased to 39.5 C. The ExH and PaH interventions were performed in ambient conditions of 38 C and 60% relative humidity with T „reaehing 39.8 C during exercise. Before (controi) and after each intervention, voluntary activation and force production capacity were evaluated by superimposing an electrically stimulated tetanus during a 45-s MVC. Force production decreased immediately after PaH and ExH compared with control, with the magnitude of decline being more pronounced after ExH (P< 0.01). Mean voluntary activation was also significantly depressed after both interventions (P< 0.01 vs control). However, the extent of decline in voluntary activation was maintained at-90% during both PaH and ExH MVC. This decline accounted for 41.5%(PaH) and 33.1%(ExH) of the decrease in force production. In addition, exhaustion coincided with a marked increase in HR (-96% of maximum) and a decline in stroke volume (25 …