Effects Of Exercise Duration On Substrate Utilization In High-fat And Low-fat Healthy Females

Abstract

PURPOSE: To investigate the effects of exercise duration on carbohydrate and fat utilization in women of high (>25%, HF) and low (<25%, LF) body fat percentage. METHODS: Healthy, physically active females (n = 14, age 19 to 23 y) were tested on 4 occasions. During session 1 air displacement plethysmography (BodPod) was used to determine percent body fat (%FAT), fat-free mass (FFM), and fat mass (FM), and a graded exercise test was used to determine maximal aerobic power (VO2max). HF women were 30.9 ± 3.7% fat with a VO2max of 63.6±11.8 ml/kgFFM/min and LF women were 21.6±2.6% fat with a VO2max 62.2±5.9 ml/kgFFM/min. Following an overnight 10 h fast, subjects participated in 2 exercise conditions lasting 30 and 60 minutes in duration. During the exercise conditions, subjects performed treadmill exercise at 55% of their VO2max. Expired gases were collected to determine non-protein fat (FAT) and carbohydrate (CHO) oxidation rates. A group x treatment ANOVA was used to determine significant differences with p<0.05. RESULTS: There were no significant differences for CHO and FAT oxidation rates (mg/kg FFM/min) between the HF and LF groups for either the 30 or 60 minute exercise conditions. The HF group had lower CHO oxidation % and higher FAT oxidation % during the 60 minute exercise condition compared to the 30 minute exercise condition. This effect was not observed in the LF group. The CHO and FAT oxidation percentages of the total energy expenditure are shown below:TABLECONCLUSIONS: Exercise duration may have an effect on the percentage of CHO and FAT oxidized in women with elevated levels of body fat that is different from women with lower body fat.