A woman’s hormones are forever changing and, according to at least one expert, those changes can affect how well she adapts and responds to intense exercise.
Jason Karp, an award-winning personal trainer and co-author of “Running for Women” (Human Kinetics, 2012), said the phases of the menstrual cycle affect a female runner’s hormones, and the fluctuations in estrogen and progesterone can influence her performance.
As a result, for example, female runners may have more difficulty in the days following ovulation, known as the luteal phase of the menstrual cycle.
In the book, Karp and co-author Carolyn Smith explain how oxygen consumption, body temperature and metabolism are affected by the menstrual cycle during training.
“Progesterone stimulates ventilation independent of the intensity of the run,” Karp said in a press release, “which can increase the perception of effort, since runners typically link their perception of effort to how much they’re breathing,”
Since progesterone concentration is highest during the luteal phase, or later stages, of the cycle, that can cause women to feel more winded during luteal-phase workouts, Karp said, compared with workouts during the follicular phase, or first half of the menstrual cycle.
During the luteal phase, the muscles that aid breathing demand additional oxygen, which, in turn, means less oxygen is available for the leg muscles used in running.
Body temperatures also change throughout the menstrual cycle, peaking during the luteal phase in response to the increased progesterone, according to the authors.
“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 said in the press release. “Women also have a decreased ability to dilate the small blood vessels under the skin, which compromises their ability to release heat to the environment.”
That means that long, intense workouts in the heat can be more difficult during the luteal phase.
Metabolism is also affected by the menstrual cycle, according to Karp and Smith. The ratio of estrogen to progesterone appears to be a key factor.
Research suggests that estrogen — most abundant in the follicular stage, according to the Women in Balance website — may improve endurance by altering carbohydrate, fat and protein metabolism, according to the Karp/Smith press release; estrogen also affects glucose in a way that provides fuel during short-duration exercise.
The Karp/Smith press release describes progesterone as often acting “antagonistically” to estrogen.
The website of Women in Balance, a national nonprofit association of women, doctors and health-care professionals and organizations, describes progesterone as the hormone that works in the body to balance the effects of estrogen. It is often referred to as the “relaxing hormone,” according to the website.
Dr. Steve Scharmann, assistant director of the residency program at McKay-Dee Hospital and team physician at Weber State University, said there have been suggestions that women are more susceptible to concussions in sports, and there may be a hormonal influence involved.
He said studies have suggested women may be more wobbly during the menstrual cycle, causing injuries to the hip, knee and foot.
“Estrogen tends to loosen your ligaments, which is very natural during pregnancy,” Scharmann said. “The same thing happens to a mild degree during ovulation.”
Scharmann said he would not suggest women stop exercising because of changes in their menstrual cycles. Instead, he said, taking preventive measures such as strengthening the muscles and ligaments is a good idea.
“Are injuries influenced by the menstrual cycle? Maybe, but I think it’s a good idea for most people to be active,” he said. “If you’re in a high-risk sport such as soccer, taking precautions to avoid injury is wise. Do everything you can do to become strong. If you want to scale back a little during the cycle, that’s fine, too, but I wouldn’t use it as an excuse not to exercise.”
“Running for Women” includes guidelines for tailoring training to the menstrual cycle, as well as determining the best times to be involved in various types of training during all stages of life, including pregnancy, menopause and postmenopause.