Impact Of Gender On Substrate Utilization During Treadmill Walking At A Self-selected Pace

Abstract

PURPOSE: To determine the impact of gender on substrate utilization during exercise at a self-selected pace. METHODS: Healthy male (n = 17) and female (n = 17) subjects performed a maximal exercise grade test and a 20-min bout of treadmill walking at a preferred pace in order to determine fat and carbohydrate (CHO) oxidation rates. Gas exchange measurements were performed throughout the tests and stoichiometric equations were used to calculate substrate oxidation rates. For each individual, a best-fit polynomial curve was constructed of fat oxidation rate (g·min-1) vs exercise intensity (%VO2max) and used to obtain the following variables: (a) the maximal rate of fat oxidation (MFO) measured over the entire range of exercise intensities; (b) the exercise intensity at which the MFO was observed (Fatmax); and (c) Fatmax zone, a range of exercise intensities with fat oxidation rates equal to ± 10% of Fatmax. Independent t-tests were used to examine gender differences in substrate oxidation rates during the maximal exercise test and 20-min bout of walking at a preferred pace. RESULTS: The MFO was similar between men (0.41 ± 0.22 g·min-1) and women (0.39 ± 0.14 g·min-1). However, the Fatmax was lower (P < 0.01) in men (36.7 ± 6.5%VO2max) than in women (44.5 ± 5.4%VO2max). Similarly, the "low" (28.4 ± 5.2 and 33.3 ± 3.6%VO2max) and "high" (45.1 ± 8.2 and 56.0 ± 7.5%VO2max for men and women, respectively) borders of the Fatmax zone were lower (P < 0.05) in men than in women. During treadmill walking at a preferred pace, the CHO oxidation rates were greater (P < 0.01) in men (1.40 ± 0.65 g·min-1) than in women (0.87 ± 0.51 g·min-1), but there were no gender differences in the fat oxidation rates (0.24 ± 0.13 and 0.24 ± 0.08 g·min-1 for men and women, respectively). However, the contribution of fat oxidation to total energy expenditure (EE) was greater (P < 0.05) in women (45.5 ± 12.6%) than in men (32.7 ± 16.4%), despite no differences in the relative exercise intensity between the men (37.5 ± 10.7%VO2max) and women (and 40.3 ± 7.2%VO2max). CONCLUSION: Although men and women self-selected similar relative exercise intensity, the contribution of fat oxidation to total EE is significantly greater in women than in men. Interestingly, both genders self-selected an exercise intensity that falls within the Fatmax zone.