Growth hormone responses to continuous and intermittent exercise in females under oral contraceptive therapy

In this study we investigated the effect of oral contraceptive (OC) use (OC U) and non-use (OCNU) on growth hormone (GH) responses to exercise in the s ame females (n = 7, age 22-31 years) during the normal course of OC therapy . Continuous (60% maximum oxygen consumption, (V) over dotO(2max) for 20 mi n) and intermittent exercise (> 80% (V) over dotO(2max)) protocols of equal total duration, and similar external work were performed during phases of OCNU (days 3-5 of the menstrual cycle) and OCU (days 7-11). Levels of GH, l actate, 17 beta-estradiol, and progesterone were measured. Lactate response s were significantly greater (P < 0.05) during intermittent than continuous exercise, with no effect of OC use. However, significantly greater GH resp onses were found during the OCU phase than the OCNU phase in both the conti nuous (+ 94%) and intermittent (+ 250%) exercise protocols. Estradiol and p rogesterone levels increased significantly during exercise in all four cond itions. We suggest that the increased GH responses observed during the OCU- phase were potentiated by the elevated levels levels of total estrogens (en dogenous 17 beta-estradiol and exogenous ethinyl estradiol). It is suggeste d that training programs for female athletes could be timed in accordance w ith the menstrual cycle to benefit from an increased GH response to exercis e during phases of OC use or the luteal phase of women not on OC therapy.