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Energy Expenditure During Acute Periods Of Sitting, Standing, And Walking: 608 Board #7 June 1, 1: 00 PM - 3: 00 PM.

Previous studies have shown individual differences in the energy intake (EI) response to exercise, but homeostatic or cognitive mechanisms underlying these differences are unclear, particularly in youth. Fat-free mass is a known predictor of daily EI in adolescents and adults, predominantly through its effects on resting metabolic rate and total energy expenditure. In addition, studies in adults have shown that increased perceived difficulty of exercise is associated with caloric over-compensation through greater EI. However, the influence of these biological and psychological factors in children is unknown. PURPOSE: To examine the predictors of post-exercise EI in children. METHODS: Healthy-weight children ages 9-12 years (n = 18) reported to the laboratory for 1 baseline and 2 experimental visits (EX = exercise, SED = sedentary) each separated by 1 week in a randomized crossover design. Percent body fat (bioelectrical impedance analysis), weight (kg), and height (m) were used to calculate fat-mass index (FMI) and fat-free mass index (FFMI; kg/m 2 ). On the EX day, children exercised at 70% estimated VO2peak for 30 minutes on a cycle ergometer and gave ratings of perceived exertion (RPE). Objective EI (kcal) was measured at identical meals on the EX and SED days: standard breakfast and ad libitum lunch, snack, and dinner. Paired t-tests, Pearson’s correlations, and multiple linear regressions were performed using SPSS. RESULTS: Total EI was not statistically different between the EX and SED days (t = 0.47, p = 0.64). However, FFMI was positively associated with EI on the EX day (r = 0.50, p < 0.05), but not the SED day (p = 0.25). RPE was also positively associated with EI on the EX day (r = 0.78, p < 0.01). Together, FFMI and RPE explained 71% of the variability in EI on the EX day (F(2,15) = 17.14, p < 0.01). CONCLUSIONS: Fat-free mass was associated with EI on the EX day but not the SED day, suggesting better homeostatic regulation of EI with imposed exercise. Despite experiencing the same 70% relative exercise intensity, children varied in their perceived difficulty of the exercise. Increased perceived difficulty predicted greater EI on the EX day. These findings demonstrate a role for both homeostatic and cognitive factors in post-exercise EI regulation in children.