Riding on the Queen Ka’ahumanu Highway during the 2002 Ironman World Championships in Kona, Stacy Sims felt off. With a low-grade headache and her body starting to swell, the then 29-year-old took a couple glucose and electrolyte tablets. Immediately, she had to pee. A lot. She later learned that the sodium levels in her blood were low and she was becoming hyponatremic, a serious condition that can be life threatening if not properly treated. Post-race, she found herself in the medical tent.
Sims, who at the time was working toward her PhD in environmental exercise physiology and nutrition science, was curious. Why did she have trouble with heat and hydration? Did she not taper correctly? Did her training partners experience similar issues during the race? After all, they followed the same nutrition, training, and heat-acclimation protocols. Was there another explanation? So she asked her female training partners and found that those who were about to get their periods were also borderline hyponatremic, while those at the beginning of their cycle had great races.
This wasn’t the first time Sims wondered if a woman’s menstrual cycle played a role in athletic performance. She says that as an undergraduate on her school’s crew team, it was taboo to discuss the subject with her teammates. “We had a joke that when we had our period, we performed worse,” she says. “But why is that? Is it because we can’t talk about our periods, or is there something else going on?”
When Sims returned home from Kona to the University of Otago in New Zealand, she decided she wanted to become a “biohacker for the female race.” She has devoted her research to understanding how hormones affect the way women regulate body temperature, use macronutrients, maintain hydration, perform, and recover. Since the passage of Title IX in 1972, the number of women participating in sports has skyrocketed, increasing 560 percent at the college level, yet women continue to be underrepresented in exercise science research—both as participants in general studies and as the specific subject of scientific inquiry—creating huge gaps in knowledge about female physiology and performance. For decades, scientists have worked under the misguided assumption that, with the exception of their reproductive organs, men’s and women’s bodies were essentially the same.
Sims, now a senior research fellow at the University of Waikato in New Zealand, has become one of the leading voices pushing for greater consideration of sex and gender in sports science. She co-founded Osmo, a hydration company that formulates products customized for men and women. In 2016, she published Roar, a training and nutrition guide aimed at women.
“I didn’t think I would be sitting here in 2018 still talking about how we need to have this conversation,” Sims says. “Women are not little men. When you look specifically at our physiology and genetic profile, and when you adjust our training and nutrition to account for those factors, we get better performance outcomes.”
Men have long been overrepresented in medical research for a few reasons. “Males were predominantly the ones conducting the research and in the position to make decisions about policy and research design,” says Audrey Bergouignan, a physiology researcher at the University of Colorado at Denver and the French National Center for Scientific Research. She recently studied an all-women trek to the North Pole to understand how the female body adapts to extreme environments. Decision-makers may also have been drawn to studying men because it was easier. With more men participating in sports in general compared to women, there were simply more males to choose from in the potential pool of research subjects.
There’s also the issue of funding. Exercise science is often supported by sports organizations like the NFL and the Union of European Football Associations (UEFA). “Women’s sports organizations don’t have as much money as male sports organizations,” says Dr. Kate Ackerman, director of the Female Athlete Program at Boston Children’s Hospital.
Then there are the logistical and methodological hurdles. It can be more expensive to study female athletes since women exhibit greater physiological variability due to fluctuating hormones. These chemical messengers have wide-reaching effects on temperature regulation, macronutrient metabolism, hydration, and central nervous system fatigue, in addition to the menstrual cycle. Those effects can create noise in the data that’s difficult, time-consuming, and expensive to control for in the research design.
When Bergouignan studies women, she has to pay attention to where a woman is in her menstrual cycle. That means that in addition to all the research parameters she must account for—recruitment, staff, equipment—Bergouignan must run additional tests to ensure that all her subjects are in the same phase of their cycles. “That all costs money, and you haven’t even run your study yet. And research budgets are limited,” Bergouignan says.
As a result, researchers across disciplines have frequently opted to exclude females from cell, animal, and human studies and assumed research findings from men could be applied across the board to both sexes, affecting everything from disease prevalence and risk factors to treatment and medication protocols. It’s the biomedical equivalent of “shrink it and pink it.”
The implications of this bias have far-reaching consequences across scientific and medical research. For example, women and men experience widely different heart attack symptoms. While doctors recognize crushing chest pain as a red flag in men, women tend to have more diffuse and vague symptoms that resemble the flu. As a result, doctors are more likely to misdiagnose women or dismiss their symptoms as “stress,” especially if they are under the age of 55. On the flip side, a handful of conditions like breast cancer, osteoporosis, and relative energy deficiency in sport (RED-S) disproportionately affect women. While men also suffer from these ailments, they are heavily investigated in the female population, Sims says, creating knowledge gaps in how to treat men.
The same risks apply to medication where dosage and treatment recommendations are based on the effects on men. A 2001 report from the Government Accountability Office found that eight of the ten prescription medications that were pulled from the market between 1997 and 2000 were removed because of adverse effects for women.
The absence of females is pervasive across all medical research. A review of 1,382 exercise medicine studies published between 2011 and 2013 found that women made up 39 percent of total study participants. A follow-up evaluation found that among 188 studies published in two academic journals in early 2015, women made up 42 percent of study subjects. The discrepancy is particularly pronounced in sport science. Among studies in that field, women accounted for only 3 percent of participants.
As Angela Colantonio, professor and director of the Rehabilitation Sciences Institute at the University of Toronto, put it, “If your science isn’t generalizable to half of the population, how good is your data?”
Despite this imbalance, there’s growing recognition that women experience training, injury, and recovery differently than men and would benefit from sex-specific research and guidelines.
Take concussions, for instance. When women and men play the same sports by the same rules and use the same equipment (say, in soccer), women have a 50 percent higher concussion rate, according to a 2015 study in JAMA Pediatrics. Women also suffer different concussion symptoms and take longer to recover than men do. A 2017 study in the British Journal of Sports Medicine found that, of 207 male and female athletes evaluated for concussion, women presented a greater number and severity of symptoms. While 34 percent of males completed concussion treatment within two months, only 12 percent of females were cleared in the same time frame, and approximately 35 percent of females still experienced concussion symptoms six-plus months post-injury. But there are no female-specific care protocols for women with brain injury. The 2017 Consensus Statement on Concussion in Sport mentions the word “sex” just once, and “gender” is included in one footnote.
“Women have long been the invisible patients in brain injury” says Katherine Snedaker, executive director and founder of PINK Concussions, a nonprofit focused on female brain injury. “When a woman judges her symptoms and recovery by the male experience, she may doubt herself when she’s not better by the time she and her doctor think she should be.”
A handful of variables may account for the differences between male and female concussion episodes. Physically, men have stronger necks on average compared to women, which may provide a measure of protection against head trauma. More likely, however, hormones are the main culprits. Snedaker says variations between male and female brain injury patterns emerge around puberty—premenstrual girls have similar outcomes to men—and a woman’s monthly cycle may also affect recovery and end results.
Still, there are few studies that explain why or how these differences occur in female athletes, which makes it difficult to create treatment recommendations tailored to women’s experiences. “You can’t have guidelines without data feeding into those guidelines. There’s not a lot of data to draw upon that’s sex-stratified,” Colantonio says.
In an effort to gather more data on brain injuries, the NCAA and Department of Defense teamed up to launch the Grand Alliance CARE Consortium. During the first two years, they enrolled more than 23,000 students, 35 percent of whom are female (on par with the gender breakdown in sport science research overall), to study brain injury in student athletes and cadets. Other groups, including PINK Concussions, are encouraging women to donate their brains to research after their death. U.S. National Soccer Team players, including Brandi Chastain, Megan Rapinoe, and Abby Wambach, are among the athletes who’ve committed to donating.
Sims sees the lack of data and understanding of female physiology as the missing piece to unlocking higher levels of female performance. She’s one of a handful of scientists studying the role of hormones. When hormones like estrogen and progesterone rise and fall during the month, female body systems fluctuate in a way that a man’s body doesn’t.
For example, when women start their periods, estrogen and progesterone drop, and they most resemble men hormonally. During this time, women can easily metabolize carbohydrates and experience less fatigue. “You can hit really hard training and get fantastic training adaptation during this time,” Sims says. As hormone levels increase, women generally don’t perform as well. In addition to cramps, GI issues, and bloating, core temperature rises and plasma levels drop, making it harder to stay cool. It’s also more difficult to metabolize stored carbohydrates and repair muscle during this high-hormone phase.
“Our menstrual cycle shouldn’t be a detriment,” Sims says, but women need information about how it affects their bodies so they can make adjustments to account for those changes.
Recently, the rallying cry for greater representation and inclusion of women in scientific research has grown louder. In June 2015, the National Institutes of Health (NIH) announced a new policy stating that scientists must include sex as a biological variable (just like age or weight) in the design, recruitment, analysis, and reporting of preclinical cell and animal research, in addition to human studies. If not, scientists must justify why it’s not included. (Canada began requiring all research grants to include sex and gender as a variable in 2010.) It’s a step up from the 1993 National Institutes of Health Revitalization Act, which required scientists to include women and minorities in NIH-funded clinical trials.
High-level journals are beginning to follow suit and now require reporting on sex and gender in published studies, which may hold researchers accountable to their research plan. Even if scientists don’t explicitly dig into sex differences in their work, it’s important to have the data available, segmented by sex, for future researchers who may want to compare results across multiple studies, explains Colantonio.
Beyond simply including women in research studies, some, like Ackerman, are championing female athlete–specific clinical practice. In 2013, Ackerman started the Female Athlete Program at Boston Children’s Hospital. “My vision was to have comprehensive care in one place to address the underlying issues female athletes face,” she says. The team of physicians, registered dietitians, and psychologists looks at the whole athlete in an interdisciplinary context, assessing exercise and training, hormone levels, nutrition, and mental health, not just injuries. That same year, Ackerman launched the Female Athlete Conference to increase collaboration in the field of sports medicine and science nationally and internationally. Proceeds from the conference go toward funding more research.
Others are putting the latest findings into the hands of female athletes so they can proactively use the information in their training. Last year, Orreco, a tech company that uses biomarkers and sports data to improve performance, launched FitrWoman, an app that helps women track their period and tailor their training and nutrition based on hormonal fluctuations. “People want to know why they feel the way they do and what they can do about it,” says Georgie Bruinvels, research associate at St. Mary’s University in London and lead scientist for FitrWoman. In July, FitrWoman announced a partnership with USA Swimming to provide educational workshops for coaches and athletes and to conduct research. Sims’ book Roar is a manual to help female athletes understand the inner workings of their body and home in on the best nutritional and training strategy to perform well.
More interdisciplinary groups working together could lead to more accurate information about exercise science and better clinical guidelines—including prevention, injury, and return-to-play protocols. While these efforts are a step in the right direction, questions about sex- and gender-based differences in sports remain. “The conversation is still muted,” Sims says.
Ultimately, looking at scientific research through a more inclusive lens benefits everyone. “It leads to better science across both sexes and genders, because you’re not just lumping everyone together,” Colantonio says.