Fuel Use In Boys And Girls During Prolonged Submaximal Exercise

Abstract

Some research has suggested that women may depend more on fat for energy during prolonged exercise compared to men. However, the extent to which this fuel use pattern exists in children is not as well understood. Specifically, the effect of sex on fuel use patterns in children during prolonged exercise is not well-understood. PURPOSE: This study examined fat and carbohydrate (CHO) metabolism during the latter half of a 40-minute bout of exercise in boys (n=9; 10.8±1.0 years, 148.5±6.7 cm, 46.6±17.2 kg) and girls (n=10; 10.6±1.2 years, 140.4±8.3 cm, 37.5±8.6 kg). It was hypothesized that there would be no difference between boys and girls with respect to fuel metabolism during exercise. METHODS: Participants reported to the laboratory for two separate visits. On the initial visit, body composition using dual x-ray absorptiometry and VO2max were assessed. On the experimental visit, participants completed two 20-minute exercise bouts separated by a 10-minute rest. Bout 1 consisted of 10 minutes at 50% VO2max and 10 minutes at 75% VO2max. Bout 2 consisted of 20 minutes at 50% VO2max. Fat oxidation rate (FOR) relative to fat-free mass [mg·kgFFM-1·min-1]) and carbohydrate oxidation rate (COR) relative to fat-free mass [mg·kgFFM-1·min-1]) were measured at 5, 10, 15, and 20 minutes of Bout 2 and averaged. RESULTS: There was no difference in VO2max between the boys (38.9±8.7 ml·kg-1·min-1) and the girls (37.1±5.6 ml·kg-1·min-1) nor were there any differences in the relative intensity (%VO2max) during exercise. FOR relative to FFM was 5.3±0.9 mg·kgFFM-1·min-1 in boys and 5.5±1.2 mg·kgFFM-1·min-1 in girls (p>0.05). Proportional fat use was 35.9±7.7% in boys and 37.9±8.4% in girls (p>0.05). COR relative to FFM was 24.1±4.9 mg·kgFFM-1·min-1) in boys and 23.0±4.2 mg·kgFFM-1·min-1 in girls (p>0.05). Proportional CHO use was 64.1±7.7% in boys and 62.1±8.4% in girls (p>0.05). CONCLUSION: In this age range, boys and girls do not display differences in fat and CHO metabolism relative to FFM during the latter half of a prolonged bout of exercise. Future research should investigate the influence of physical maturity on potential sex differences in metabolism. This study was supported by the Ball State University ASPiRE Graduate Student grant program.