Repeated-bout exercise in the heat in young athletes: physiological strain and perceptual responses

Abstract

A short recovery period between same-day competitions is common practice in organized youth sports. We hypothesized that young athletes will experience an increase in physiological strain and perceptual discomfort during a second identical exercise bout in the heat, with 1 h (21°C) between bouts, even with ample hydration. Twenty-four athletes (6 boys and 6 girls: 12-13 yr old, 47.7 Ϯ 8.3 kg; 6 boys and 6 girls: 16 -17 yr old, 61.0 Ϯ 8.6 kg) completed two 80-min intermittent exercise bouts (treadmill 60%, cycle 40% peak oxygen uptake) in the heat (33°C, 48.9 Ϯ 6.1% relative humidity). Sweat loss during each bout was similar within each age group (12-13 yr old: bout 1, 943.6 Ϯ 237.1 ml; bout 2, 955.5 Ϯ 250.3 ml; 16 -17 yr old: bout 1, 1,382.2 Ϯ 480.7 ml; bout 2, 1,373.1 Ϯ 472.2 ml). Area under the curve (AUC) was not statistically different (P Ͼ 0.05) between bouts for core body temperature (12-13 yr old: bout 1 peak, 38.6 Ϯ 0.4°C; bout 2, 38.4 Ϯ 0.2°C; 16 -17 yr old: bout 1 peak, 38.8 Ϯ 0.7°C; bout 2, 38.7 Ϯ 0.6°C), physiological strain index (12-13 yr old: bout 1 peak, 7.9 Ϯ 0.9; bout 2, 7.5 Ϯ 0.7; 16 -17 yr old: bout 1 peak, 8.1 Ϯ 1.5; bout 2, 7.9 Ϯ 1.4), or thermal sensation for any age/sex subgroup or for all subjects combined. However, rating of perceived exertion AUC and peak were higher (P ϭ 0.0090 and 0.0004, respectively) during bout 2 in the older age group. Notably, four subjects experienced consistently higher responses throughout bout 2. With these healthy, fit, young athletes, 1 h of complete rest, cool down, and rehydration following 80 min of strenuous exercise in the heat was generally effective in eliminating any apparent carryover effects that would have resulted in greater thermal and cardiovascular strain during a subsequent identical exercise bout. hydration; recovery; risk management; thermoregulation; youth sports A SHORT RECOVERY PERIOD between same-day rounds of tournament competition is common practice in organized youth sports. With the additional effects imposed by a hot environment on cardiovascular and thermal strain, performance, and exertional heat injury risk (1,2,4,8,9,14,21,22,24,25,45,47,48), the ability to perform safely and effectively through multiple strenuous same-day competition bouts in the heat can be challenging for young athletes (8, 16). The apparent cumulative demands can often result in poor performance or complete withdrawal from play. Wallace et al. (58) found that exertional heat illness risk was more strongly associated with the combined effects of previous-day wet bulb globe temperature (WBGT) and current-day heat exposure than with either measure alone, suggesting a cumulative effect on thermal strain during exercise in the field. With same-day exercise, Ronsen et al. (46) found that a longer recovery period between bouts (6 vs. 3 h) attenuated the degree of increased metabolic stress and cardiovascular and thermal strain in the second exercise bout for elite endurance athletes, demonstrating how the extent of residual or carryover effects from a previous ...

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