A female athlete's performance may depend on the phase of the menstrual cycle she is in. The menstrual cycle ranges from 24 to 35 days and comprises of three phases: menstrual phase (menses), preovulatory phase and the postovulatory phase. The menstrual phase is the periodic discharge of 25 to 65ml of blood, tissue fluid etc. and lasts for approximately 3 to 7 days.
Example of the phases of 28 day menstrual cycle:
The effect of sport
Physically active women increase their chances of changes to their menstrual cycle. These include irregular cycles (oligomenorrhea) or complete cessation of the cycle (amenorrhea). In the general population, amenorrhea occurs in 2 to 5% of women of reproductive age, whereas for women participating in sport it can be as high as 40%.
All women need to be aware that exercise is not the only factor that can result in oligomenorrhea or amenorrhea. The other factors are a high stress level, body weight and body composition (% body fat level below 20%).
Athletes are prime candidates for oligomenorrhea or amenorrhea as they are likely to experience:
Amenorrhea reduces the body's capacity to absorb calcium, decreases bone density and increases the risk of musculoskeletal injury in vigorous exercise.
Impact on training
The hardest time to race efficiently, for athletes experiencing a menstrual cycle, is during the week before menstruation and a week after ovulation (Williams 1997). At these times increased levels of progesterone simulate the brain's respiratory centre increasing ventilation rates (progesterone is also linked to the mood swings). Athletes use breathing rate as an indicator of exercise intensity so exercise can tend to feel harder at these times.
The time of maximum efficiency for athletes experiencing a 28 day menstrual cycle might be pre-ovulation (days 9 to 12) or post-ovulation (days 17 to 20).
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