Title: Substrate Oxidation And Energy Expenditure During And After Isocaloric Exercise Bouts Of Different Intensity
Abstract: Physical activity contributes to reductions in body weight and body fat. Determining the optimal exercise intensity for fat reduction is important in order to design effective physical activity programs that are attractive to overweight individuals. PURPOSE: To compare the effects of two different exercise intensities on fat and carbohydrate (CHO) contribution and total energy expenditure during and one hour after isocaloric exercise bouts in sedentary, healthy, overweight (BMI 25-29.9 kg/m2) males. METHODS: In a random order, fifteen males (mean ± SE; age: 24.9 ± 1.2 y; mass: 83.5 ± 2.4 kg; BMI: 27.2 ± 0.5 kg/m2; VO2max: 39.5 ± 1.3 ml/kg/min) volunteered to perform treadmill walking at 45% (moderate intensity) and 65% (high intensity) VO2max until they expended 300 kcal. On each occasion, exercise was followed by one hour of recovery in a seated, recumbent position. Expired gases were measured continuously during exercise and recovery, and substrate utilization was determined from the respiratory exchange ratio (RER). A two-way ANOVA with repeated measures was used to assess differences between trials and over time for both the exercise and recovery periods. RESULTS: Exercise RER was significantly lower (main effect of trial, P < 0.05) during the moderate (0.86 ± 0.01) than high intensity trial (0.92 ± 0.01). Recovery RER was similar between moderate and high intensity trials (0.85 ± 0.01 vs. 0.84 ± 0.01, respectively,:P > 0.05). Total energy expenditure during exercise was similar between trials. However, fat provided a greater energy contribution toward exercise on the moderate than high intensity trial (main effect of trial, P<0.05) while the reverse was true for CHO (main effect of trial, P<0.05). The energy contribution of fat and carbohydrate was similar during recovery, although the total energy expenditure was significantly higher during recovery from the high than moderate intensity exercise (391.2 ± 2.6 vs. 382.0 ± 2.5 kcal, respectively). CONCLUSION: Sedentary, overweight males expended more calories from fat during moderate than high intensity exercise. However, total energy expenditure was greater during recovery from high intensity exercise. Training studies are needed to determine if these findings translate into differences in body composition and weight loss with long term exercise.