The relationship between two menstrual cycle phases and cardio respiratory fitness in athletes on oral
contraceptives and not on oral contraceptives was assessed in a pilot study. Twelve endurance-trained college cross
country runners underwent maximal oxygen consumption treadmill testing, during the late follicular/ovulatory phase and
late luteal/premenstrual phase of their menstrual cycle. No significant differences were detected in maximal oxygen
consumption between the oral contraceptive group and non-oral contraceptive group or between the two phases. There
was a non-significant phase effect in the non-oral contraceptive group with maximal ventilation averaging 90.5±14.6
L/min during the late follicular/ovulatory phase and decreasing to 79.1±9.8 L/min during the late luteal/premenstrual
phase (p=0.102). Maximal ventilation was significantly lower by 15.6% between oral contraceptive and non-oral
contraceptive users during the late luteal/premenstrual phase (93.7+7.2 L/min vs 79.1+9.8 L/min, p=0.014, respectively).
There was no significant phase effect in the oral contraceptive group for maximal ventilation. While oral contraceptive use
was associated with an attenuation of the negative effect of the late luteal/premenstrual phase on ventilator performance,
there was no effect on maximal oxygen consumption.