Exercise and Postexercise Substrate Oxidation in Young Women Resulting from Exercise Bouts of Different Intensities 255

Abstract

Some practitioners have suggested that high intensity exercise is less effective than low intensity exercise in promoting fat loss. However, this notion fails to account for the impact of exercise intensity on postexercise energy expenditure and substrate oxidation rates. Thus, we studied the effects of low and high intensity exercise, of similar energy output, on exercise and post-exercise energy expenditure and substrate oxidation in eight active, eumenorrheic females (aged 22-31). Continuous indirect calorimetry was performed during and for 3 h following three separate conditions administered in random order: 1) low intensity cycle ergometry exercise (LIE: 500 [email protected] 50% VO2 max); and 2) high intensity cycle ergometry exercise (HIE: 500 calories @ 75% VO2 max); and 3) a no-exercise control condition (C) of quiet sitting. Mean excess postexercise oxygen consumption (EPOC) for the three hours of recovery for HIE (9.0±1.7L) was greater (p<0.05) than EPOC for LIE (4.8±1.6 L). Recovery VO2 following HIE, but not LIE remained elevated at the end of the 3-h post-exercise period. Total carbohydrate oxidation (exercise plus postexercise period) was significantly higher for HIE (116±8.6 g) compared to LIE (85.0 ± 5.2 g). Total fat oxidation was lower for HIE (27.7±3.3 g) compared to LIE(36.9±3.0 g), but this difference was not significant. The rate of fat oxidation at the end of the measured 3-h recovery period remained higher for HIE compared to LIE. These data indicate that the recovery period should also be considered when determining the impact of different exercise intensities on total energy expenditure and fat and carbohydrate utilization.