Responses of Lean and Obese Boys to Repeated Summer Exercise in the Heat Bouts

DOUGHERTY, K. A., M. CHOW, and W. L. KENNEY, Responses of Lean and Obese Boys to Repeated Summer Exercise in the I-feat Bouts. Med. Sci. Sports Exerc., Vol. 41, No. 2, pp. 279-289, 2009. Purpose: To determine the degree of natural acclimatization and artificially induced acclimation-related changes during repeated exercise in the heat bouts in seven]can and seven obese 9- to 12-yr-old boys during summer months. Methods: Beginning at random times during the summer, subjects underwent a 70-min exercise (30% VO2max) in the heat exposure (38 degrees C, 50% relative humidity) on six separate days. Results: On day 1, obese children were less naturally acclimatized as indicated by significantly higher baseline core temperatures (T-c) (obese = 37.62 +/- 0.06 vs lean = 37.41 +/- 0.06; P < 0.004). By day 6 versus day 1, significant reductions in baseline T, were evident in both groups (obese = 37.41 +/- 0.04 vs lean -37.18 +/- 0.04; both P < 0.05). Baseline T-c in obese subjects by day 6 was similar to that of lean subjects on day 1. Daily reductions in exercise T-c were evident in both groups (final exercising T-c day 1 vs day 6: obese = 38.15 +/- 0.05 vs 37.89 +/- 0.05; lean 38.17 +/- 0.09 vs 37.72 +/- 0.06 degrees C; both P < 0.001), occurring at a significantly slower rate in obese Subjects (final exercise T, day 6 day 1: obese vs lean -0.26 +/- 0.04 vs -0.45 +/- 0.08 degrees C; P < 0.05). Significant reductions in exercising heart rate (HR) occurred in the lean but not the obese subjects by day 6 (final exercising HR day 1 vs day 6: obese = 132 +/- 3 vs 131 +/- 3, P > 0.05; lean = 138 +/- 3 vs 127 +/- 3 bpm; P < 0.001). Conclusions: During summer months, obese children are less naturally heat-acclimatized and Subsequently acclimate at a slower rate.