Gender-based differences in substrate use during exercise at a self-selected pace

The aim of this study was to investigate gender-based differences in substrate use during exercise at a self-selected pace. Seventeen men and 17 women performed a maximal exercise test and a 20-minute bout of self-paced treadmill walking to determine carbohydrate and fat 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 using fat oxidation rate (gmin21) vs. exercise intensity (percentage of maximal oxygen uptake, % _ VO2max). Each individual curve was used to obtain the following variables: maximal fat oxidation (MFO), the peak rate of fat oxidation measured over the entire range of exercise intensities; fatmax, the exercise intensity at which the MFO was observed; and fatmax zone, range of exercise intensities with fat oxidation rates within 10% of fat oxidation rates at fatmax. Although the MFO was similar between genders, fatmax was lower in men than in women. Similarly, the ‘‘low’’ and ‘‘high’’ borders of the fatmax zone were lower in men than in women. During exercise at a self-selected pace, carbohydrate oxidation rates were greater in men than in women, despite no gender-based differences in fat oxidation rates. However, fat oxidation contribution to total energy expenditure (EE) was greater in women than in men, despite no gender-based differences in the exercise intensity. In conclusion, although both genders self-selected a similar exercise intensity, the contribution of fat oxidation to EE is greater in women than in men. Interestingly, both genders selfselected an exercise intensity that falls within the fatmax zone.