Women have approximately 457 menstrual cycles in their lifetime, corresponding to around 35 years of menstrual activity, writes Dr Jacky Forsyth – who works in the centre for Sport, Health and Exercise Research at Staffordshire University.
For a woman, therefore, the menstrual cycle pervades their reproductive life. And for the exercising female, the menstrual cycle may affect aspects of their exercise performance. This could be because of blood flow and severe abdominal cramps interfering with engagement in certain activities, or because excessive exercise and dietary restriction lead to a complete absence of the menstrual cycle.
Menstruation is often still considered taboo, and something that is mocked, or considered frivolous (Kissling, 2006). It is important, however, to keep talking about and researching about how the menstrual cycle affects the exercising female, so that we can better understand how to ensure that women can perform and exercise optimally.
Phases of the menstrual cycle
The menstrual cycle works as a series of feedback loops, involving the hypothalamus, the anterior pituitary gland, the ovaries and the corpus luteum (the tissue that develops in the ovary after the egg has been released). The first part of the menstrual cycle (day 1 to 14 in a normal 28-day cycle) is termed the follicular phase, since it reflects the growth of the follicle in the ovary. The second phase is termed the luteal phase, usually day 14 to 28 of a normal cycle, so called because it involves corpus luteum activity. At the beginning of the follicular phase (the first part of the cycle), increasing levels of gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus stimulate the anterior pituitary to produce and release follicle-stimulating hormone (FSH) and luteinising hormone (LH). Increased release of both these hormones stimulate follicle growth and maturation.
As the follicle increases in size, oestrogen is secreted, and eventually exerts positive feedback on the hypothalamus and pituitary; a burst of LH secretion occurs, which leads to the rupture of the follicle. This LH surge usually occurs on around the 14th day of a 28-day cycle and is termed ovulation. The remainder of the follicle cell, through stimulation of LH, increases in size forming the corpus luteum, which produces progesterone and oestrogen. With a decline in LH, and if fertilisation does not occur, the stimulus for corpus luteum activity stops. The corpus luteum degenerates and blood ovarian hormone levels decline, leading to menstruation.
In earlier decades, it was believed that menstrual cycle could adversely affect sports performance. Based on findings from 729 Hungarian female athletes, it was found that 51% of those questioned reported a reduction in their performance during menstruation (Erdelyi, 1962). It was also thought that because the menstrual cycle led to a number of menstrual cycle irregularities (Bullen et al., 1985), exercise should be avoided if fertility was to be maintained. Following decades of research, it is currently understood that although there are physiological changes that occur because of changes in sex steroid hormones that occur across the menstrual cycle, this does not mean that exercise should be avoided.
It is possible to win gold medals and set records at all phases of the menstrual cycle. Whether the menstrual cycle can affect performance directly is still, however, a matter of debate.
Stay hydrated and keep cool
One of the known changes that occurs across the menstrual cycle is a change in body temperature. A higher core temperature, which also persists with exercise, is associated with the luteal phase (second half) of the menstrual cycle (Pivarnik, Marichal, Spillman, & Morrow, 1992), owing to the thermogenic effect of progesterone. A delay in sweating response, and a decrease in skin blood flow, also contribute to this increase in temperature (Grucza, Pekkarinen, Titov, Kononoff, & Hänninen, 1993). There is, therefore, some concern that this increase in body temperature and the reduction in sweating response could make women more susceptible to the development of heat illness in the second part of their cycle, and could have subsequent effects on performance (Marsh & Jenkins, 2002). Being aware of this temperature shift is, therefore, important, so that women can make sure they hydrate and keep cool in the latter part of their menstrual cycle when exercising.
A change in body mass is another factor that is commonly reported as a result of variations in ovarian hormones that occur across the menstrual cycle. An increase in body mass is common prior to menstruation, due to water retention, alterations in electrolyte balance and glycogen storage; these minor alterations in body mass may have some impact on performance, especially in sports where weight is important. The fact that body mass can increase in the latter part of the cycle is important to be aware of, especially if on a weight-controlled exercise and dietary programme.
As a result of the increase in core body temperature in the second half of the cycle, ventilation (rate and depth of breathing) also increases (Schoene, Robertson, Pierson, & Peterson, 1981), as does heart rate, the latter increasing by as much as 10 beats/min, and persisting throughout exercise (Pivarnik et al., 1992). It is, therefore, important that exercise intensities based on perceptions of effort (the exercise often feels harder when breathing is deeper and faster) and heart rate are modified in the second half of the menstrual cycle. In other words, heart rate and breathing rate may well be higher because of hormonal changes, not because of the exercise stimulus.
There are advantages and disadvantages…
There is a higher incidence of musculoskeletal injuries, especially anterior cruciate ligament (ACL) injuries during physical activity in the follicular phase (the first part of the cycle), or around ovulation when oestrogen levels are elevated (Balachandar, 2017; Herzberg et al., 2017). This increased incidence is thought to be a result of lower rates of tendon collagen synthesis following exercise and increased joint laxity at ovulation. On a more positive note, oestrogen may protect against exercise-induced muscle damage, and may enable women to return to exercise sooner after muscle damage (Sipavičienė, Daniusevičiutė, Klizienė, Kamandulis, & Skurvydas, 2013; Tiidus, 2000). Oestrogen, being elevated in the first part of the cycle and around ovulation may, therefore, exert its influence by increasing the risk of injury, at the same time as protecting delayed onset of muscle soreness (DOMS).
In the second half of the menstrual cycle, there is a shift in substrate use, from carbohydrate to fat (Oosthuyse & Bosch, 2012), owing to the increase in oestrogen that occurs at this time. In theory, this change in metabolism should mean that less lactate is produced (Forsyth & Reilly, 2005), and performance is prolonged, although research to support this effect is lacking.
In fact, research on whether menstrual cycle can positively or negatively affect actual exercise performance is mixed. For instance, some researchers have reported no change in endurance performance (Forsyth & Reilly, 2008; Gordon et al., 2017), short-term, strength and power performance (e.g., Elliott, Cable, Reilly, & Diver, 2003), but others have (Gordon et al., 2013; Pallavi, 2017).
One of the issues or reasons for these mixed findings is because of the different methods used to pinpoint menstrual cycle phase. Often just body temperature is used, but it is important to measure levels of oestrogen and progesterone. But, even if these hormones are measured, they still may differ within the same individual over different cycles, and, of course may also differ between women. Another key reason is that the hormone progesterone antagonises the effect of oestrogen. For instance, although endurance performance, in theory, should be better in the latter part of the menstrual cycle owing to oestrogen increasing fat use and sparing carbohydrate, progesterone, which is also elevated during this time could negatively affect the body, due to increases in temperature and body mass. So, although it might be possible that women could perform better in the luteal phase (in terms of ultradistance events), or at ovulation (in terms of strength), individual differences in fitness, diet and hormonal status, as well as environmental factors (e.g., time of day, temperature) may mean that differences are not always apparent. In addition, improved performance may be offset by weight gain, injury, and the antagonising effect of progesterone.
Women in Sport and Exercise Conference
In this article, only the effects of a normal menstrual cycle on exercise performance have been discussed. Consideration has not been given to the use of hormonal contraceptives, or to a situation where severe exercise and insufficient energy intake results in menstrual irregularities, the most severe of which is a complete absence of menstruation or amenorrhoea.
Balancing exercise so that symptoms of the female athlete triad (osteoporosis, relative energy deficit and menstrual disturbances) are avoided, and monitoring how hormonal-based contraception influences performance are important issues for the exercising female. Such issues are being discussed at this year’s “Women in Sport and Exercise Conference: Blood, Sweat and Fears”, being held on 13th and 14th June, a preview of which can be read here.
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