Laird, M. D., Bergeron, M. F., Marinik, L. L., Brenner, J. S., Lou, M., & Waller, J. L. (2007). Physiological strain and perceptual differences during repeated-bout exercise in the heat. ACSM Annual Meeting New Orleans, Presentation Number 1842.

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This study tested the hypothesis that young athletes will experience an increase in physiological strain and related ratings of perceptual discomfort during a second identical exercise bout (compared to the first) in the heat, with a one-hour recovery period (21C) in between bouts. Young soccer players (M = 12; F = 12) completed two 80-minute intermittent exercise sessions (treadmill: 60% VO2max; cycle ergometer: 40% VO2max) in the heat (33C) on the same day.

Sweat loss during each exercise was similar within each age group. Core body temperature, physiological strain index, and thermal sensation did not differ for any age/gender sub-group or for all Ss combined. However, rating of perceived exertion for all Ss combined was higher during the second exercise bout, with the biggest difference shown in older boys. Notably, four Ss experienced a consistently higher core temperature and physiological strain index throughout the second exercise compared to the first.

Implication. For fit young athletes, one hour of cool-down and rehydration, following 80 minutes of exercise in the heat, is insufficient time to avert greater perception of effort, and for some, greater physiological strain, during a subsequent identical exercise bout.

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