INTRODUCTION: The majority of available literature on excess post-exercise oxygen consumption (EPOC) focuses on the adult population. No study has quantified EPOC in children after exercise lasting more just a few minutes. Previous research has shown fat oxidation, measured by respiratory exchange ratio (RER), to be greater in children than in adults at rest and during exercise. Few studies have investigated substrate utilization post-exercise in children. PURPOSE: To examine young adult-child differences in EPOC and substrate utilization following moderate and vigorous intensity exercise performed on the cycle ergometer. METHODS: 19 children (7 to 9 years old) and 22 young adults (20 to 23 years old) visited our laboratory on three separate occasions and completed an exercise trial each time: VO2max test, moderate exercise (MOD), and vigorous exercise (VIG). Maximum power output (MaxPO) during the VO2max test was used to determine workload for MOD (35% MaxPO) and VIG (70% MaxPO) exercise. MOD and VIG trials were randomized and counterbalanced. Participants rested for 30 minutes (min) prior to exercise; the last 20 min were used for baseline VO2 measures. Tests were 2-min square-wave intervals lasting 1 hour for the MOD trial and 30 min for the VIG trial. Expired gases were captured 10 min prior to the cessation of exercise and for 20 minutes post-exercise. EPOC was examined using ANOVA and repeated measures ANCOVA to control for sex, fitness, body composition, and caloric intake. Substrate utilization was examined using multivariate analysis of variance (ANOVA) for RER at minutes 1, 5, 10, 15, and 20 post-exercise. Another ANOVA model statistically controlling for sex, fitness, body composition, and caloric intake was also performed. RESULTS: After MOD and VIG, children had significantly lower volume of EPOC when compared to young adults (0.30 + 0.13 vs. 1.18 + 0.38 L; F = 19.609, p < 0.001, d = 0.31 for MOD and 0.71 + 0.26 vs. 2.46 + 0.95 L; F = 59.73, p < 0.001, d = 2.44 for VIG exercise). Children returned to baseline significantly faster than the young adults after both MOD (240 + 105 vs. 552 + 325 seconds, respectively; F = 16.413, p < 0.001, d = 1.30) and VIG (424 + 345 vs. 925 + 340 seconds, respectively; F = 21.912, p < 0.001, d = 1.50). Children's RER was significantly lower than young adults at 1, 5, and 10 min (0.84 + 0.05 vs. 0.90 + 0.05; 0.93 + 0.05 vs. 1.00 + 0.08; and 0.86 + 0.03 vs. 0.91 + 0.05, respectively; all p < 0.01; effect sizes of 0.61, 0.26, and 0.29, post MOD respectively). After VIG, RER was similar in children and young adults at min 1 and 10; however, children's RER in min 5 was significantly lower than adults (1.02 + 0.06 vs. 1.15 + 0.11, p = 0.001; effect size of 0.60). Children's RER in min 15 and 20 was significantly higher than adults' (0.83 + 0.05 vs. 0.77 + 0.06; 0.83 + 0.05 vs. 0.75 + 0.06, respectively; p ≤ 0.001; effect sizes of 1.66 and 2.12, respectively). CONCLUSIONS: Children had lower EPOC and recovered faster than young adults after both MOD and VIG. Children had lower RER than young adults after MOD, but higher RER 15 and 20 min after VIG. Children relied more on fat oxidation at rest and during exercise than young adults. This study observed children to utilize a greater proportion of carbohydrates than young adults after VIG. Funded by Michigan State University College of Education
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