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.