Fat Oxidation Rate Curves and Exercise Intensity in Pre-Pubertal Males

1491 Evidence exists that, compared to adults, children utilize more fat and less carbohydrate during endurance exercise performed at similar relative intensities. Recently, a protocol has been published that standardizes the measurement of fat oxidation rates during a range of exercise intensities using elite male cyclists (Achten et al., 2001). PURPOSE: We determined fat oxidation rates over a range of exercise intensities in healthy, untrained, pre-pubertal males. METHODS: Five subjects, ages 11–12 yrs, underwent an incremental cycle ergometry test (12.5 Watts increments, 3 min intervals) to volitional exhaustion with measurements of breath-by-breath gas exchange and heart rate. Fat oxidation rate curves were determined from indirect calorimetry during the final 30 seconds of each stage as described previously (Achten et al., 2001) and expressed per kilogram lean body mass (LBM). Body composition was estimated from triceps and mid-calf skinfold measurements. RESULTS: Fat oxidation rates are shown in the figure below. Maximal fat oxidation rates were 0.818 ± 0.072 × 10−2 g/min/kg LBM, which occurred at 56 ± 1.3 % of peak VO2. High rates of fat oxidation (within 20% of maximum value) occurred between 33 ± 1.4 and 78 ± 1.8 %VO2 max. CONCLUSIONS: The observed fat oxidation rates are very similar to those published for elite male cyclists. We conclude that this protocol is highly suited for examining fat oxidation rates in pre-pubertal males and that in this population, fat oxidation is maximized throughout a wide range of exercise intensities.