Metabolic responses to energetic stimuli in female athletes using or not hormonal contraceptives during a high training load period.

Background: Despite growing interest in women's physiology in exercise sciences, the understanding of female athletes' energy metabolism remains limited. This study aimed to analyze substrate oxidation in response to energetic stimuli in female athletes using or not hormonal contraceptives, and to determine the influence of the estradiol-to-progesterone ratio fluctuations on energy metabolism.

Methods: Body composition (dual-energy X-ray absorptiometry), energy expenditure and substrate oxidation rates (resting, low-intensity walking exercise (4 km/h), and postprandial conditions; indirect calorimetry) were assessed among 32 athletes (23±3 years) during a high-training load period, in athletes using or not hormonal contraceptives (nine and 23, respectively). Athletes not using hormonal contraceptives were tested during high and low estradiol-to-progesterone (salivary samples) ratio conditions.

Results: No significant differences in energy metabolism at rest, whether fasting or postprandial, were observed between groups. During low-intensity exercise, a significantly higher net energy cost was observed in athletes using hormonal contraceptives (vs. high [P=0.01] and low [P=0.02] estradiol-to-progesterone ratio conditions). Higher carbohydrate (P=0.001) and lower lipid (P=0.005) oxidation rates were observed in the low estradiol-to-progesterone ratio condition compared with the high one in women not using hormonal contraceptives.

Conclusions: Thus, endogenous and exogenous ovarian hormones may influence energy metabolism during low-intensity exercise in female athletes under high-training loads.