Exercise duration and thermoregulatory responses after whole body precooling

Whole body precooling was hypothesized to reduce thermoregulatory and metabolic responses, thereby enhancing running time. Fourteen male runners completed two high-intensity running tests consisting of resting in 24 degrees C (normothermic condition; NC) or 5 degrees C (hypothermic condition; HC) for 30 min followed by 10-16 min of rest at 24 degrees C and then an exercise bout (24 degrees C) at 82% maximal aeorbic capacity to exhaustion. Rectal temperature (T-re)before exercise was lower (by 0.37 degrees C; P < 0.005) and exercise duration was longer (by 121 +/- 24%; P < 0.05) in HC than in NC. T-re and mean skin ((T) over bar(sk)) and mean body ((T) over bar(b)) temperatures remained lower during HC (P < 0.01). Pre- and postexercise changes for (T) over bar(sk), (T) over bar(b), thermal gradient (T-re - (T) over bar(sk)), and heart rate (HR) were larger in HC than in NC (P < 0.05). Final T-re, T-re - (T) over bar(sk), HR, and blood lactate were similar between HC and NC. During exercise, heat storage was greater (P < 0.01) in HC than in NC (173 +/- 46 and 143 +/- 38 W/m(2), respectively) and subjects sweated more in NC than in HC (P < 0.01). O-2 consumption was lower initially in HC than in NC (P < 0.05), but O-2 pulse was not different. It was concluded that precooling results in greater exercise endurance with enhanced heat storage rate and less stress on metabolic and cardiovascular systems.