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Dalhousie, S S. Cheung1

Medicine & Science in Sports & Exercise: May 2003 - Volume 35 - Issue 5 - p S30
A-15O Free Communication/Poster Heat Stress and Dehydration

1University, Halifax, N.S

(Sponsor: Alan M. Batterham, FACSM)

Hyperthermia is well-established as a limiting factor in exercise performance. Pre-cooling of the body prior to submaximal endurance exercise in the heat has been demonstrated to be effective in improving performance by reducing heat storage, cardiovascular strain, and perception of effort.

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To investigate the effects of upper-body pre-cooling prior to intermittent sprinting exercise in a temperate environment.

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Over two experimental sessions, ten male or female competitive cyclists performed 30 min of cycling exercise at 50% VO2max. At t = 0, 5, 10, 15, 20, 25, and 30 min, they performed a 10 s Wingate cycling sprint with a resistive load of 0.09 kp/kg. In the control (CON) session, subjects rested for 30 min prior to exercise. In the pre-cooling (PC) session, subjects wore the hood and the upper body segment of a liquid cooling garment circulating 5°C coolant for either 75 min or until core temperature decreased by 0.5°C. No warmup occurred during the 5 min transition between the resting/cooling phase and the exercise phase.

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Rectal temperature at the start of exercise was 36.49 ± 0.32°C with PC and 36.97 ± 0.47°C with CON, remaining approximately 0.40°C lower throughout exercise. Skin temperature (unweighted mean of chest, arm, thigh, and calf) at the start of exercise was significantly lower with PC (28.75 ± 2.25°C) than with NC (32.02 ± 1.04°C), but this difference disappeared by 5 min into exercise. Subjective thermal sensation with PC was significantly lower from the start through 10 min of exercise. Heart rate during submaximal exercise were similar between PC and NC, though peak heart rate following the Wingate sprints were lower with PC. With PC, peak power (909 ± 161 W) and mean power output (797 ± 154 W) were similar to CON sprints (peak 921 ± 163 W, mean 806 ± 156 W), with no differences in the subjective ratings of perceived exertion.

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Mild upper-body pre-cooling was able to decrease subjective ratings of heat stress, but did not provide any benefit to intermittent sprinting exercise in a temperate environment.

©2003The American College of Sports Medicine