Effect of a synthetic progestin on the exercise status of sedentary young women.

CONTEXT

The impact of progestins on exercise performance in women has not been previously studied.

OBJECTIVE

The objective of this study was to examine the effect of a synthetic progestin on aspects of exercise status in young women. DESIGN, PATIENTS, SETTING: Twenty-three young, healthy, habitually sedentary women participated in a single-blind, randomized, counterbalanced, cross-over study in a university-based laboratory setting.

INTERVENTION

Two monophasic oral contraceptive pills (OCPs) were administered in which the dose of the synthetic progestin, norethisterone, was 2-fold different but the dose of the synthetic estrogen, ethinyl estradiol, was constant. During each month of OCP aspects of exercise status were assessed during incremental exercise to exhaustion and steady-state submaximal exercise and with a performance test.

MAIN OUTCOME MEASURES

The main outcome measures were peak oxygen uptake (VO(2peak)), respiratory exchange ratio (RER), time to exhaustion, lactate concentrations, and total work done.

RESULTS

Peak heart rates were approximately 95% of age-predicted values with both OCP preparations, whereas VO(2peak) was approximately 30% above age-predicted values. Peak postincremental exercise plasma lactate concentrations exceeded those reported for males and females, whereas the RER was below expected values throughout both incremental and steady-state exercise. The effects on VO(2peak) and RER were increased with the higher dose progestin OCP, as were exercise time to exhaustion and total work done.

CONCLUSION

Synthetic progestins in OCP formulations can have a significant effect on the exercise status of young, sedentary women, possibly through an effect on stroke volume and a shift in the principal energy substrate used during exercise from carbohydrate to lipid.