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 a 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 stimulate 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).
Anterior Cruciate Ligament (ACL) Laxity
The results of research by Heitz (1999) demonstrate that female ACL laxity significantly increases in conjunction with surging levels of estrogen and progesterone during the normal menstrual cycle.
Research by Slauterbeck (2002) found a significantly greater number of ACL injuries occurred on days 1 and 2 of the menstrual cycle.
A systematic review by Belanger (2013) of 13 clinical trials investigating the effect of the menstrual cycle on ACL laxity found that there is evidence to support the hypothesis that the ACL changes throughout the menstrual cycle, with it becoming laxer during the pre-ovulatory (luteal) phase. Overall, these reviews found statistically significant differences for variation in ACL laxity and injury throughout the menstrual cycle, especially during the pre-ovulatory phase. Female athletes may need to take precautions in order to reduce the likelihood of ACL injury.
Impact on Resting Heart Rate
Research indicates that the menstrual cycle has an impact on an individual's resting heart rate. Moran (2000) and her team found that resting heart rates (RHRs) show distinct values for the four phases of the menstrual cycle. RHR was significantly higher in both ovulatory and luteal phase (the second part of the cycle) when compared to menstruation and the follicular phase (the first part of the cycle). Shiliah (2017) and her team found that during a woman's fertile window, the period of about six days when a woman can become pregnant, her resting heart rate increases by about 2 beats per minute, on average, compared with her heart rate during menstruation.
The following graph is an example of an individual's resting heart rate, periods and ovulation over a period of nine months:
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