Exercise duration and thermoregulatory responses after whole body precooling.

Abstract

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 aerobic capacity to exhaustion. Rectal temperature (Tre) 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. Tre and mean skin (Tsk) and mean body (Tb) temperatures remained lower during HC (P < 0.01). Pre- and postexercise changes for Tsk, Tb, thermal gradient (Tre-Tsk), and heart rate (HR) were larger in HC than in NC (P < 0.05). Final Tre, Tre-Tsk, 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/m2, respectively) and subjects sweated more in NC than in HC (P < 0.01). O2 consumption was lower initially in HC than in NC (P < 0.05), but O2 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.