IRA FLATOW: This is Science Friday. I’m Ira Flatow.

KATHLEEN DAVIS: And I’m Kathleen Davis. This weekend, Spain and England face off in the Women’s World Cup finals in Sydney, Australia. Every four years, I am tuned in watching these amazing female athletes. So growing up playing sports, looking up to athletes like Mia Hamm, I was surprised to learn that the first Women’s World Cup wasn’t until 1991.

I was also surprised to learn that those games were only 80 minutes compared to the men who played for 90 minutes. Part of the rationale was that women just weren’t tough enough to play a full 90 minutes of soccer.

This idea of women as the quote unquote, “weaker sex” is everywhere in early scientific studies of athletic performance. Sports science was mainly concerned with men’s abilities. Even now, most participants in sports science research are men.

Luckily, things are changing. More girls and women are playing sports than ever before. And with that, there’s a little more research about women as well as those who fall outside of the gender binary. Here to talk about all of this is my guest, Christine Yu, health and sports journalist and author of Up To Speed, The Groundbreaking Science of Women Athletes. She’s based in Brooklyn, New York. Christine, Welcome to Science Friday.

CHRISTINE YU: Hi, Kathleen. Thank you so much for having me on the show.

KATHLEEN DAVIS: So let’s start by talking a little bit about the inspiration for this book. Can you tell me what made you decide to write about this topic?

CHRISTINE YU: Yeah. I think it was really the confluence of two different things. One was back in., I want to say, 2013 or 2014, I was at this women’s fitness magazine event. And there was a panel and a doctor talking about the female athlete triad.

So generally, when women lose their periods, because theoretically, they exercise too much. So it’s something that I had heard about since I was young but never really thought about. And this doctor was talking about how the menstrual cycle is so important, not just for fertility but in connection to bone health in particular.

And it was just one of those moments where I just sat there. And I was like, wait, why don’t I know this information about my own body? I feel like this was important information that I should have had when I was younger during adolescence, during these periods of time when your bone is growing. And it’s really important.

And then like you said, I report a lot on sports and science. And in my conversations with a lot of elite athletes as well as experts in the field, they all kept saying almost like as a side whisper, actually, we don’t really a lot about female physiology. And again, it was one of those moments where I was like, what do you mean? This was 2018, 2019.

And it just sent me down this rabbit hole really trying to understand why is it that we don’t study women to the same extent as we study men? And more importantly, what are the implications of this gender data gap in sports science research? And how does that affect not only the health and well-being as well as the performance of women who are athletic and performance-driven?

KATHLEEN DAVIS: I want to talk a little bit about injuries, which I think is something that a lot of female athletes are familiar with. ACL injuries, in particular, are more prevalent among female athletes than in men. There are about 20 players in the Women’s World Cup who are not playing right now because of ACL injuries. Why are women more susceptible to this type of injury?

CHRISTINE YU: Yeah, it’s absolutely wild when you think about it, the number of high-profile players who have been injured and who have been taken out of this really career-defining tournament. It’s one of the biggest moments in their career.

The thing with ACL injuries is we’ve known since the late ’80s and early ’90s that women tend to tear their ACLs more than men. Yet over these past 20, 30 years that prevalence rate hasn’t changed. Women still experience a much higher rate of tears compared to men. Yet for men, actually, the prevalence seems to have gone down a little bit. The traditional reasons why folks often point to is tied to the female body.

Because we have wider hips, there’s more stress that potentially goes through the knee. There are certain anatomical features of the knee that might make the ACL more prone to tear. There are also things like our fluctuating hormones that might make ligaments more lax. But a lot of those features, like I said, focus specifically on the female body in and of itself. And I can’t change the width of my hips. I can’t change my hormones really. It’s almost a very disempowering narrative. There’s nothing you can do.

So more recently, researchers have been pulling back the curtain a little bit and looking more at the factors that surround women. Like how we grow up playing sports, whether or not similar athletic resources are dedicated to boys versus girls. Do girls at a young age have the opportunity to play and really learn how to move their bodies in safe ways and develop those good biomechanics from a young age that matter as you get older?

And then I think when we look at the professional level, the game, especially women’s soccer, has grown so much, has intensified so much, the athleticism of these athletes is phenomenal. And they’re being asked to play a lot more games within a shorter period of time. But are we providing them with the same resources to help them deal with this higher training load, to recover from this training load, and really to keep them safe?

And so I think part of that is this research piece that we haven’t really looked into the factors specific to women athletes that could influence their injury rate and that could help potentially put them in a better place so that they don’t get injured.

KATHLEEN DAVIS: Another thing you write about in your book is concussions. And there’s this disparity between men and women. But the discrepancy is maybe a little more complicated than we may think. Can you tell me about the research that you found?

CHRISTINE YU: Yeah, so this is another one of these areas where we see that women may experience more concussion compared to men or may experience worse outcomes compared to men. And again, the traditional injury model kind of points to the female-specific factors, what makes women’s bodies different or deficient in comparison to men.

And so when researchers have dug into this a little bit more, they found that maybe those sex-specific factors aren’t the only reason. So there’s some research that’s been done, I believe, it was with high school athletes when they looked at boys and girls who had concussion– and again, you see those differences in terms of outcomes and prevalence. Yet when boys and girls actually saw doctors or specialists within the same period of time, those discrepancies disappeared.

So what this kind of suggested was that boys got to care faster or within a shorter time frame than girls. So again, it suggests that there might be something around resources or like outside of just those physiological or anatomical differences that might be playing a role here.

KATHLEEN DAVIS: One of the big issues that you touched on a little earlier here is athletes who miss their periods combined with not getting enough nutrition. And this can be especially harmful to young athletes. So can you tell me a little bit about what’s going on here and possible long-term health ramifications of this?

CHRISTINE YU: It’s a huge factor that, I think thankfully, I feel like some sports are starting to pay more attention to. But again, it’s this factor that we’ve long ignored or at least downplayed.

The narrative goes that when girls become more athletic, when you are fit, you lose your period. You have doctors telling girls this. You have parents kind of saying, oh, yeah, that’s normal. And you have girls and coaches saying this as well.

But really, what’s going on here is that it’s a sign that the body doesn’t have enough energy, that you’re under-fueling your body. And so our bodies are pretty smart. When it senses that it doesn’t have enough energy, it starts to shut down systems.

And so one of the first systems that it starts to shut down is the reproductive system. And so we see that in menstrual cycle dysfunction and irregularity and absence of menstrual cycle. And while that might not seem like it’s a big deal, those hormones that are associated with the cycle– so things like estrogen and progesterone– play an enormous role in the body’s health. The cycle is one of the body’s most important rhythms second to the circadian rhythm.

So it influences everything from bone health to cardiovascular health to immunity, gut health, pretty much every system in the body. And yet, we often only think about the menstrual cycle in terms of fertility. So I think that for, especially girls in adolescence, girls who are going through puberty as their cycle is just getting started, this is a really critical period for bone growth.

And so that’s why it’s really important that girls start their menstrual cycle and that they have regular menstrual cycles. Because you need that surge of estrogen to really lay down bone. Because you accumulate, I believe, it’s like around 80% of your adult bone mass by the time you’re early 20s.

KATHLEEN DAVIS: One of the central themes in your book is that historically, women were largely excluded from sports science. And still most sports science studies focus on men’s bodies. Why is there such a gap?

CHRISTINE YU: I think there are two big reasons. One is because sports in and of itself has always been developed for men by men. That’s who the ideal athlete was. That’s who was allowed to participate from the time of the ancient Greeks and Romans when scientists began to study athletics and exercise and thinking about how the body adapts and trains, that’s the population that they naturally looked to and wanted to study.

The other piece of it is science, the scientific research process in and of itself. Scientists in labs are, oftentimes when they’re conducting experiments, concerned with understanding a very specific, say, molecular mechanism or how a specific hormone works or chemical reaction. They’re trying to create almost a model to understand these complex biological processes.

So when you have something like a menstrual cycle where the hormones fluctuate up and down pretty unpredictably and not always on the same pattern, that complicates things. It throws a lot of noise into the data, which would mean that scientists would have to take the time and, frankly, money to account for a lot of these changes so that hormonal fluctuation doesn’t mess up their data, if you will.

So in a lot of ways, it was just easier to not include women. And I think it’s one of these oversights that we didn’t really think about the implications of what that might mean. We just assume that the findings will apply across the general population.

KATHLEEN DAVIS: In sports science research, in general, there is this binary, men versus women. And that’s not exclusive to science. That’s happening throughout society at large too. How can we study these physiological differences between bodies without reverting to this rigid way of thinking about sex and gender? Is there a way to do that, do you think?

CHRISTINE YU: I think that’s definitely one of the biggest challenges, both for sports and for science. Because both of these fields are predicated on the binary. I think that it is a challenge that a lot of the scientists are currently grappling with, because the tendency is to kind of put men or male bodies into a bucket and women and female bodies into another bucket and kind of keep them separate.

But I think what scientists are realizing more and more is that there actually is a lot of overlap more so than we acknowledge or give credit to. Because we’ve studied men for so long, we’ve really only studied a very small sliver of the human population. Because a lot of the sports science studies, not only are they men they tend to be pretty young, like college age men and pretty fit men.

Really, if we expand the diversity of the population that we’re studying– so that means including women, that also means including populations from non-western countries, again, because sports science research tends to take place in a lot of the westernized countries– we actually learn a lot more about the human population as a whole. So I think that’s where we start. We have to be studying a more diverse population, be able to understand a lot of the nuances that happen across the board.

KATHLEEN DAVIS: This is Science Friday from WNYC Studios. If you’re just joining us, I’m talking with Christine Yu, author of the book Up To Speed, The Groundbreaking Science of Women Athletes. You stress in your book that we should stop comparing women’s athletic results against men’s standings because that continues to suggest that women are quote, unquote, “less than men,” and only worthy of accolades if they’re living up to these male standards. What should we do instead?

CHRISTINE YU: I think we should be looking at women’s sports, women athletes, the women’s game as an entity in and of itself. Because sport has been created really with men in mind. Women have constantly been forced to almost like force-fit themselves right into this world that wasn’t designed or made for them.

So I think that being able to separate that out, consider the women’s game for what it is in and of itself, it gives women an opportunity to perform and to succeed and really see what’s possible without the weight of all of that expectations of what men have done in the past.

I feel like that’s not fair. Because the path that women might take might be the same as men. The trajectory of women’s sports and performance might be the same as men. But it could be really different. We just have never given women the opportunity to explore which path makes the most sense.

KATHLEEN DAVIS: And there are some sports where women actually show an advantage like in ultra-long distance running?

CHRISTINE YU: Yeah. So these ultra events, running events that are longer than a traditional marathon which is 26.2 miles, these folks are out there running 50 miles, 100 miles, 200 miles multiple days at a time. You have ultra distance cycling events too and marathon swimming events.

And what we’re seeing in these events is that women appear to do really well. The performance gap between men’s and women’s performances is smaller than it is in other sports. Women are winning these events outright.

And so I think it’s an area where it’s really interesting to see. And to explore what is possible. Because at these distances, some of the physiological factors that tend to give men advantages in traditional sports– so like speed and power– sort of wash out, frankly, over 100 miles. They play a little bit less of a role at that distance. So it’s really exciting to see what’s been going on in that world.

KATHLEEN DAVIS: Well, Christine, I could talk about this with you forever. But we have run out of time. So thank you for joining us.

CHRISTINE YU: Thank you so much for having me. I’ve really enjoyed this conversation.

KATHLEEN DAVIS: Christine Yu, health and sports journalist and author of Up To Speed, The Groundbreaking Science Of Women Athletes. She’s based in Brooklyn, New York. If you want to read more about the science of women athletes you can go to sciencefriday.com/uptospeed.

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