| Whole body lipid and carbohydrate utilization during moderate intensity exercise was examined in eumenorrheic women using oral contraceptive agents (OCA) (n = 10) compared to women who were not using OCA (n = 9) during the high and low hormone phases of the menstrual cycle. High hormone phases were considered to be the mid-luteal phase on non-OCA users, or the third week of active pill phase of OCA users. Low hormone phases were the placebo pill phase for OCA users or the early follicular phase of non-OCA users. Subjects were tested in an overnight fasted state. The two exercise trials consisted of cycling for one hour at 65% of peak oxygen consumption on an electronically braked cycle ergometer. Substrate utilization was assessed at rest and at 15 minute intervals during exercise using respiratory gas analysis and measurements of serum glycerol and free fatty acids and plasma glucose. Measurements of plasma estradiol, progesterone at rest and plasma insulin at rest, 30, and 60 minutes were also performed. The only significant differences notes in substrate utilization was a lower resting respiratory exchange ratio (RER), and consequentially lipid utilization, during the high hormone phases compared to the low hormone phases of the menstrual cycle for both OCA and non-OCA users. A main effect of ovarian hormones and insulin was also found, in that higher circulating insulin levels were noted in the high hormone phases when compared to the low hormone phases, regardless of OCA use. These findings suggest that there is no need to omit female subjects using OCA from studies examining energy substrate utilization during moderate intensity exercise. |
