Low dosage monophasic oral contraceptive use and intermittent exercise performance and metabolism in humans

Nine untrained women using low dosage monophasic oral contraceptives (OC) p erformed an intermittent treadmill test on two different occasions within o ne pill-cycle to determine the effect of OC on performance and some commonl y used metabolic markers. The first test was performed after 5-8 days of re suming the OC agents after menstrual bleeding while the other test was perf ormed after 19-21 days. Performance time on the final exhausting run of six intermittent high intensity 20 s runs was no different between trials [mea n days 5-8: 22.3 (SEM 1.2) s vs days 19-21: 27.7 (SEM 1.1) sf. There was no difference in heart rate [peak heart rate days 5-8. 183 (SEM 3) beats(.)mi n(-1) vs days 19-21: 186 (SEM 2) beatsmin(-1)], oxygen consumption during a ny run [run 5 of days 5-8: 1,397 (SEM 51) ml(.)min(-1) vs run 5 of days 19- 21: 1,493 (SEM 3) ml(.)min(-1)] or in any of the metabolic variables measur ed at any time in venous blood [peak blood lactate concentration days 5-8: 8.4 (SEM 0.3) mmol(.)l(-1) vs days 19-21: 8.1 (SEM 0.5) mmol(.)l(-1) peak b lood glycerol concentration days 5-8: 0.39 (SEM 0.02) mmol(.)l(-1) vs days 19-21: 0.38 (SEM 0.02) mmol(.)l(-1); resting free fatty acids concentration days 5-8: 0.25 (SEM 0.05) mmol(.)l(-1) vs days 19-21: 0.29 (SEM 0.07) mmol (.)l(-1) peak blood glucose concentration days 5-8: 6.7 (SEM 0.5) mmol(.)l( -1) vs days 19-21: 6.6 (SEM 0.2) mmol(.)l(-1) peak capillary blood ammonia concentration days 5-8: 139 (SEM 18.3) mu mol(.)l(-1) vs days 19-21: 170 (S EM 18.0) mu mol(.)l(-1)]. These results suggest neither intermittent high i ntensity exercise performance nor energy metabolism change between days 5-8 and days 19-21 of a low dosage monophasic OC pill during one pill-cycle.