Increased levels of estrogen cause tendons and ligaments to become lax, potentially increasing the risk of injury.
Earlier this year, when British tennis player Heather Watson was defeated in the first round of the Australian Open, she attributed her performance to "girl things," causing her to experience dizziness, nausea and fatigue as she attempted to play.
Annabel Croft, a former tennis player, told the BBC that Watson's openness was "brave" and that "women do suffer in silence on this subject. It has always been a taboo subject."
Croft considers the impact of the menstrual cycle on sporting performance to be "the last taboo" in sports, yet others downplay its influence. British runner Paula Radcliffe currently holds the world record for the women's marathon and she broke the existing record at the start of her period.
"I broke the world record so it can't be that much of a hindrance," she told the BBC, "but undoubtedly that's why I had a cramped stomach in the final third of the race and didn't feel as comfortable as I could've done."
In this Spotlight, we investigate to what extent the menstrual cycle can affect sporting performance, as well as examining strategies for mitigating against its draining effects.
What symptoms are caused by menstruation?
Firstly, a brief recap of what the menstrual cycle involves. The cycle is a series of changes that a woman's body goes through each month preparing her for the possibility of pregnancy. An egg is released from the ovary and the lining of the uterus thickens (the luteal phase). If the egg is not fertilized before the end of the cycle, the lining of the uterus is shed through the vagina.
Alongside these changes, women can also be affected by premenstrual syndrome (PMS) manifesting in emotional, behavioral and physical symptoms. The American College of Obstetricians and Gynecologists believe that around 85% of menstruating women experience at least one symptom of PMS as part of their monthly cycle.
These symptoms have a lot of potential to disrupt a sportswoman's performance. In addition to the cramping that Radcliffe referred to, women can experience physical symptoms such as joint and muscle pain, headaches, weight gain and low energy levels.
The emotional and behavioral symptoms caused by PMS also appear disruptive to physical activity, especially at elite levels of competition when even the smallest margins can prove decisive. These include insomnia, poor concentration, irritability and appetite changes.
Currently, experts are unsure what causes PMS, but it is believed that changes in hormone levels and the neurotransmitter serotonin could play roles in the development of symptoms.
There is also a severe form of PMS known as premenstrual dysphoric disorder (PMDD) that has many disabling symptoms, such as panic attacks, feelings of despair, binge eating and a lack of interest in daily activities, alongside the physical symptoms of PMS.
But to what extent do menstruation and its associated symptoms have an effect on women's ability to participate in sporting activities? It is well documented that, for some women, PMS symptoms can be severe enough to force them to miss days of work, and so it stands to reason that they could also impair women's capacity for exercise.
However, getting regular exercise is often recommended as a step that women can take to alleviate PMS symptoms. Does this mean that sportswomen should be protected from the full extent of the condition?
Evidence of menstruation affecting performance
Exercise physiologist Jason Karp, PhD, believes that fluctuating levels of the hormones progesterone and estrogen lead to physiological changes in the body during menstruation and that these changes are exacerbated by exercise - particularly if it is intense.
PMS can cause dizziness, nausea and muscle cramps, which could hinder some women's athletic performance.
Changes to the body during the luteal phase of the menstrual cycle also include increases in breathing and body temperature. "A higher body temperature during the luteal phase makes it harder to run in the heat, because you don't begin sweating to dissipate heat until you have reached a higher body temperature," Karp explains.
Increased breathing during the luteal phase also means that less oxygen is available for the muscles involved in exercise, he adds, as more oxygen is required by the muscles responsible for breathing.
In 2011, however, the New York Times ran an article on the menstrual cycle and athletic performance, citing a series of studies examining female rowers as proof that women should not be concerned with where they are in their cycle when it comes to sporting performance.
The researchers concluded that "normally menstruating female rowers and female rowers taking [oral contraceptive] pills should not be concerned about the timing of their menstrual cycle with regard to optimized sport-specific endurance performance."
Although the studies examined the performance of both competitive athletes and women that rowed for fun, their results are severely limited by the number of participants that were studied. One study involved a total of 15 rowers, the other just 11.
These studies are indicative of a lack of quality research in this area, meaning that experts are unable to speak with certainty about the full impact of menstruation on sport.
Dr. Susan White, the chief medical officer for Netball Australia, says that it is a difficult area to research:
"The things that some women associate with the menstrual cycle, like fatigue or bloating or general lethargy, are hard to measure. And even if we could measure them, it's then difficult to say that it's just one or a combination of those symptoms and other internal or external factors that may affect performance."
She states that while world's best performances have been recorded at all stages of the menstrual cycle, one study conducted in Italy indicates that female soccer players may be more at risk from injury before and during their menstrual periods. "It is unclear whether it was because of physiological or psychological factors or a combination of them," she adds.
A silent psychological battle
Although there is a lack of certainty from researchers as to the effects of the menstrual cycle, since Heather Watson raised the subject there have been plenty of other female athletes coming forward to share their experiences and describe how the menstrual cycle has affected their performances.
In a news conference, Czech tennis player Petra Kvitova agreed that "it's quite tough" to play at the start of the menstrual cycle. Former world number one Martina Navratilova also stated that her playing had been affected.
"You don't want to use it as an excuse," she told the BBC, "but it can affect some players in a big way. I never talked about it but it certainly was there."
Paula Radcliffe was able to set a world record while on her period. For Andu Bobby George, India's long jump champion, however, menstruation prevented her from succeeding.
Some sports require competitors to wear a particular uniform that could increase the psychological impact of menstruation.
"I was in top form in every other way, but the period made me feel weaker and there was nothing I could do about it," George told Scroll.in. "After the events, many people criticized my performance but this is not something I could ever tell them."
In India, menstruation is considered to be even more of a taboo than in the UK and the US. Some consider menstrual blood to be impure, some girls are not permitted to enter kitchens or sleep on mattresses during their period and it is estimated that 10% of girls believe that menstruation is a disease.
The fact that menstruation is a taboo subject can make participating in sport an anxious occasion, particularly when there is the potential for it to come into conflict with the rules of specific games. Some sporting uniforms such as the traditional whites of tennis and the tight trousers of horse-riding can leave women anxious about the possibility of "leaking," as Annabel Croft puts it.
Being a member of a sports team can certainly help with these concerns. Having colleagues with which to share worries who are affected by the same things can help erode the feeling of taboo that has a hold over most of society.
In fact, some teams such as the British Olympic hockey team monitor the menstrual cycles of their players. "It's something we didn't want to take chances on," coach Ben Rosenblatt told The Guardian. "You get to the final of an Olympics, you want to control every aspect of your performance."
Team member Hannah Macleod states the biggest comfort of this team monitoring is that team members do not have to suffer the menstrual cycle in silence.
The conversation continues
Aside from the social support being in a team provides, there are other options available to sportswomen to lessen the effects of menstruation if they are particularly affected by it.
Oral contraceptive pills and injections are taken by some athletes to either control when their periods occur or to stop them completely. However, some forms of medication are known to affect water retention and some contain ingredients that are banned, considered to be performance enhancing.
Ultimately, medication adds a further level of complexity to the already complicated world of elite level sports.
And just as women's sporting performance is affected differently by menstruation, the opinions of women on the subject vary just as much. Many agree that menstruation can affect performance, but that it should not be used to explain occasions when athletes are unsuccessful.
"It's personal to every athlete and by no means should it ever be used as an excuse but, at the same time, it does have an effect," says Anne Keovathong, a former British tennis player. Her career was marked by several knee injuries sustained during - and attributed by Keovathong to - menstruation.
Professional cyclist Inga Thompson told CNN that there was a risk of undermining women's sporting abilities through openness. "I feel very protective of our sport," she said. "You don't want to pull the 'girl card,' because we've fought so hard for equal representation."
It is clear that the taboo around menstruation and the battle for greater equality place sportswomen in a difficult position. There is plenty of anecdotal evidence now that menstruation affects performance, but a lack of clinical data to back it up and lend it authority.
Annabel Croft believes that Heather Watson has opened up a world debate about menstruation, making it easier for athletes to talk about and seek help with any problems they have in the future. Many will hope that this debate will extend to more robust clinical research, addressing the limitations that currently exist in elite sports.