Sex hormones and substrate metabolism during endurance exercise

Abstract

During endurance exercise, carbohydrates and fat are the main energy sources to ensure muscle contraction. Their relative contribution depends on the exercise modality (intensity and duration) and individual factors, such as age, sex, diet, training, nutritional and weight status. As research protocol standardization is difficult in women’s populations due to the frequent hormonal status changes throughout their life span, studies are predominantly conducted in men. Yet results are frequently extended also to women despite the sexual dimorphism in substrate metabolism during endurance exercise, mainly due to ovarian hormones. Animal and human studies demonstrated the influence of estrogen, and to a lesser extent of progesterone, on fuel mobilization and utilization. However, conflicting results have been obtained on the effect of natural hormone fluctuations during the different phases of the menstrual cycle. Similarly, the influence of oral contraceptives on fuel metabolism is not well understood, although recent formulations seem to favor lipolysis during endurance exercise. Finally, the decline in natural ovarian hormone concentrations observed with the menopause is associated with body composition and substrate metabolism changes. Hormone replacement therapy may also affect substrate metabolism during endurance exercise, but the available results are still contradictory. This chapter describes the sex differences and the effects of menstrual cycle, oral contraceptives, menopause and hormone replacement therapy on substrate metabolism during endurance exercise. Results are sometimes conflicting, mainly due to methodological discrepancies, and further studies are, therefore, needed.