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Harvard Commentaries
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Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Exercise and Your Menstrual Cycle: Does Time of the Month Matter?

October 23, 2012

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Healthy Lifestyle
Medical Myths
Exercise and Your Menstrual Cycle: Does Time of the Month Matter?
Exercise and Your Menstrual Cycle: Does Time of the Month Matter?
Years ago, women were often advised to "take it easy" during the first few days of their period, and women continue to ask about it. Is there cause for concern?
Harvard Medical School Commentary

Some exercise authorities — coaches, trainers, and popular fitness magazines — apparently recommend that a woman adjust or avoid certain athletic activities if she is having her period. This is based on some evidence that injuries may be more common (and performance poorer) if competitive athletics are pursued during certain parts of the menstrual cycle, and because some injuries (most notably, ligament injuries of the knee) are more common in female than male athletes. Years ago, women were often advised to "take it easy" during the first few days of their period, and women continue to ask about it.

This was not something I had learned during my medical training and, perhaps because of my gender, I had never heard it from my coaches or teammates on our high school basketball team. So, are the risks of exercising during menstruation little known but important? Or, are they part of medical myth and folklore? Other questions come to mind:

  • How good is the evidence that the menstrual cycle alters risk of injury during exercise?
  • How does menstruation alter one's risk of injury? Can increased risk be reversed by a particular treatment or a change in training?
  • Are all injuries, or only certain types, more likely during menstruation?
  • If menstruation affects the risk of injury or performance, what part of the cycle matters most? And what if the cycle is not regular?
  • What changes should be made based on the available evidence? For example, should certain activities be avoided altogether during menstruation?

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The Evidence Regarding Injuries and Menstruation

Some, though not all, studies have found an increased risk of injury during certain parts of the menstrual cycle. For example, in a study from Sweden published in 1989, researchers interviewed 84 female soccer players about their periods and injuries they had experienced. They reported an increased susceptibility to traumatic injury during the premenstrual and menstrual period, especially among those with premenstrual symptoms (such as irritability or breast discomfort).

A study from Michigan, published in 1998, analyzed consecutive ligament injuries in 40 women and found that more seemed to occur during the ovulatory phase — that is, the middle of the cycle — than during other phases. An even more recent study of runners found longer interruptions in training due to musculoskeletal injuries among those with menstrual disorders, though no specific part of the cycle was associated with injuries.

Similarly, a 2009 study found that the laxity (or looseness) in the knee varied for different women over the course of a menstrual cycle, but no consistent effect was seen for any particular part of the cycle. For example, some women had increased laxity and others had decreased laxity during the period prior to ovulation.

A 2009 review combining multiple prior studies concluded that injuries of the anterior cruciate ligament (a ligament that provides stability of the knee during stress) seem to be more common during the first half of the menstrual cycle. A 2012 study found that when estrogen levels were highest (during midcycle) there were slight differences in how women landed when hopping — their legs were "more wobbly" and the arches of their feet collapsed a bit more than during other points of their cycles.

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Why Is There No Answer?

Each of these studies found an effect of the menstrual cycle on injuries, but with different or inconsistent conclusions. Part of this could be because relatively few women have been included in these studies, and because they used different methods of investigation: Some were based on surveys of healthy women, while others started out with injured athletes. In addition, methods of verifying the phase of the menstrual cycle or the presence of an injury also differed between studies.

Further complicating the matter is that there are so many variables involved. For example, the type of exercise, intensity of exercise, and type of injury each could have an effect that makes it difficult to draw firm conclusions or make specific recommendations.

Consider the example of an athlete who exercises intensely on a regular basis. She might have fewer injuries by improving coordination and increasing the strength of muscles and bones. Yet that same exercise routine — through weight loss and reduction of body fat — might also lead to cessation of periods, a condition that may, in turn, lead to reduced estrogen levels and reduced bone strength (also known as osteoporosis). As a result, more injuries, such as stress fractures, could follow.

Several theories have been proposed to explain the relationship among exercise, injuries and the menstrual cycle. One suggests that the rise and fall of certain hormones affects the strength or flexibility of muscles, ligaments and tendons, but no proof of this or any other theory exists to help make sense of the observations.

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Athletic Performance and the Menstrual Cycle

Again, the studies find inconsistent effects of uncertain importance. In one study, a group of swimmers was found to have poorer performance just before menstruation and faster swim times during menstruation, yet cross-country skiers were best just after menstruation and after ovulation (which occurs mid-cycle). In yet another study, strength of handgrip and standing long jump distance were best during menstruation as compared with other phases of the cycle.

According to a 1994 review on the subject, for most women there is no significant effect — "medals have been won and world records set in any phase of the menstrual cycle." More recent studies concur. A 2012 study of rowers found no impact of the menstrual cycle (whether "natural"or regulated by birth control pills) on athletic performance.

In addition, moderate exercise is often recommended for premenstrual symptoms and there are small studies finding benefit in this approach.

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The Bottom Line

Our current understanding regarding the effect of the menstrual cycle on athletic injuries or athletic performance is inadequate to make clear recommendations. Individual factors, including overall health, type of exercise, degree of conditioning, and nutritional status may matter more than the phase of the menstrual cycle.

Clearly, there are women with premenstrual or menstrual symptoms who simply do not feel like exercising. Whether to exercise or not during one's period is an individual decision, but should not be made because the risk of injury is supposedly higher then.

Even as research continues to improve our understanding, women will wonder whether it is safe or advisable to exercise during certain times of the month. This uncertainty must be balanced against the wealth of well-established benefits (and fun) associated with athletic pursuits. In addition, the dangers of excessive exercise — which may lead to cessation of periods altogether and an increased risk of osteoporosis — must be kept in mind as well.

There is no compelling evidence that exercise or athletic activities should be avoided or altered based only on the phase of the menstrual cycle. Promising research suggests that muscle strengthening may prevent ligament injuries, and this may reduce risk more than trying to synchronize exercise around one's periods.


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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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