The effect of sex steroid hormones on substrate oxidation during prolongedsubmaximal exercise in women

In animals, female sex steroid hormones (SS, estrogens-progesterone) influe nce the energy substrate that is metabolized. Human research on this issue is controversial. This study examined whether changes in circulating SS hor mone levels affected the carbohydrate-lipid metabolism during submaximal pr olonged (60 min) exercise. Young, physically active females were studied, F our were classified as anovulatory-oligomenorrheic and four were classified as ovulatory-eumenorrheic. Subject responses were pooled to form one group (n=8) and then their responses under low (L) and high (H) pharmaceutically manipulated SS hormone conditions were examined. During exercise, the mean oxygen consumption levels were 1.70+/-0.10/.min(-1) for L-SS and 1.75+/-0. 11/.min(-1) for H-SS (p= 0.07), respectively. The respiratory exchange rati o (RER) responses were significantly different during exercise between the conditions: 0.93+/-0.04 for L-SS and 0.90+/-0.04 for H-SS (p<0.05), respect ively. RER responses were utilized to calculate substrate oxidation. Signif icantly less carbohydrate oxidation was found in the H-SS condition as comp ared to the L-SS condition (p<0.05). Lipid oxidation was also significantly different, but for this measure, the levels of oxidation were greater in t he H-SS than in the L-SS condition (p<0.05). Finally, total energy expendit ure for the 60 min of exercise was not significantly different between the hormonal conditions. Results suggest that sex steroid hormones have an impa ct upon substrate oxidation in women during exercise. Specifically, high ci rculating concentrations of the SS hormones result in an enhanced reliance upon the oxidation of lipid as an energy substrate and consequently induce a reduction in carbohydrate oxidation. The mechanism inducing this "metabol ism shift" appears due to sex steroid hormones directly and indirectly incr easing lipid mobilization and lipolysis.