Substrate utilization during exercise in postmenopausal women on hormone replacement therapy.

It has been suggested that due to the slight direct or indirect effect of estrogen on lipolytic activity, the age-related decrease in production associated with the menopause may heighten the risk of cardiovascular and metabolic disease in women. While hormone replacement therapy (HRT) alone may have little or no effect on body mass in postmenopausal women, data suggest it can alter the shift toward abdominal adiposity. Furthermore, estrogen may have a synergistic effect on exercise-induced reduction in fat mass. Accordingly, the purpose of this investigation was to examine the potential influence of HRT on substrate utilization during 30 min of treadmill exercise at approximately 80% maximal oxygen uptake (VO(2max)) in postmenopausal women. Eight women were receiving HRT and nine women were not (NHRT). No significant differences between the HRT and NHRT groups were noted for age, body mass, body fat, VO(2max) or the percentage of VO(2max) maintained during exercise. Expired gas samples were analyzed every 30 s to determine respiratory exchange ratio (R) and % VO(2max). The R, total energy expended and percentage contributions from fats and carbohydrate were averaged over three periods during the exercise (min 1-10, 11-20, and 21-30). There was no effect of HRT on R, total energy expended or substrate contribution. Thus, treatment of postmenopausal women using HRT (primarily conjugated equine estrogens in doses of 0.625-1.25 mg x day(-1)) did not appear to affect the percentages of fat and carbohydrate utilized during 30 min of treadmill exercise at 80% of VO(2max). However, the exercise responses in this group of menopausal women were consistent with a duration-dependent increased reliance on fat as an energy source during exercise of moderate to vigorous intensity as has been demonstrated in younger populations.