More than 50% of women quit sports following puberty, and women leave sports at twice the rate of men. These drop-out rates likely have long-term consequences for women, including fewer exercise benefits, less representation in sports, and weaker exercise performance. Yet, very little is known about why women leave sports at such high rates during puberty.
Enter Jessica Freemas, a graduate student in the Department of Kinesiology-Exercise Physiology at Indiana University. Her research, conducted under Dr. Zac Schlader, focuses on human exercise performance and cardiopulmonary function. While working in the lab, Jessica noticed that nearly all studies of exercise performance used only men and that the findings of these all-male studies were oftentimes generalized to women. This gap in the scientific literature is largely due to a vestige of a historical emphasis on male athletes as well as perceived complications in study design associated with studying women. “There are many physiological reasons why generalizing findings from men to women in this context might be disadvantageous to women in terms of their participation and experiences with exercise,” says Jessica. Determined to highlight the benefits of conducting female-specific studies of exercise performance, Jessica finds herself at the forefront of research on sex differences.
Jessica has spent most of her life around athletes and noticed that the menstrual cycle has traditionally been regarded as a burden, though its implications for human performance are not well understood. Swimmers, for instance, are notoriously pressured to select contraceptives that eliminate the monthly period because they want to mask natural hormonal fluctuations and their potential consequences for athletic performance. Yet, there is no strong evidence that leads to the belief that the menstrual cycle inherently disadvantages female athletes. It could, on the more positive side, be advantageous.
The Research. Jessica’s research puts a positive spin on the interactions between exercise performance and the menstrual cycle, and her findings have the potential to transform the menstrual cycle from a burden into a benefit for female athletes. Jessica hopes to show that the physiological changes associated with the menstrual cycle can be used to schedule workouts in ways that lead to: (1) more positive exercise experiences, and (2) better overall health. Specifically, she hypothesizes that women experience more feelings of fatigue during the progesterone phase of the menstrual cycle than during the estrogen phase (Figure 1) and, in turn, do not push themselves as hard during the progesterone phase as they would during the estrogen phase. She hypothesizes, further, that low intensity workouts during the progesterone phase can reduce the associated tension and fatigue (i.e., premenstrual syndrome). Thus, high intensity workouts may be most effective during the estrogen phase for increasing performance, while lower intensity workouts may be most beneficial during the progesterone phase to improve mood and avoid discouragement to exercise.
Societal Impact. Jessica’s findings have many implications for women’s health. Her research provides insight into methods aimed at improving mental health and increasing exercise adherence (i.e., how well a patient that is medically prescribed exercises sticks to their regimen). Jessica’s research also helps increase training effectiveness in women athletes by suggesting that high intensity workouts might be more effective during the estrogen phase. Scheduling training and competitions based on natural hormonal variations during the menstrual cycle can also improve reproductive health and reduce the risk of injury development. Last month, for example, the Women’s U.S. soccer team won the 2019 FIFA World Cup and has since been making headlines about the ingenious approach their trainer is taking: using natural variations in the menstrual cycle to gain a competitive edge.
Jessica’s research builds on our understanding of the contexts in which sex differences matter and the potential implications of these sex differences on human physiology. For example, a book, called “Invisible Women,” was recently published that identifies several important contexts where overlooking sex differences could cause safety and health concerns (e.g., Women are 47% more likely to be severly injured in a car accident because crash test dummies are based on male physiology), and similar discussions are occuring in animal research. Jessica hopes that her research “will encourage others to pay attention to the differences between men and women, so that research performed on males will not be inappropriately generalized to females (and vice versa). I also hope that my research will stimulate curiosity and more research about female physiology.”
If you’re interested in Jessica’s work and would like to know more, feel free to comment below, or contact her directly at firstname.lastname@example.org.