The following is an excerpt from UP TO SPEED: The Groundbreaking Science of Women Athletes by Christine Yu.

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Up to Speed: The Groundbreaking Science of Women Athletes

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In 2016, mountain biker Kate Courtney neared the end of her under‑23 career and was ready to make the leap to the next level. She started working with coach Jim Miller, then the director of high performance at USA Cycling and now the organization’s chief of sport performance. Miller knows a thing or two about what it takes to develop Olympians and world champions. In the last two decades, his athletes have won fourteen Olympic medals and multiple world championship titles. Together, they built a plan not only to prep Courtney for what was supposed to be the 2020 Summer Olympics in Tokyo but to set her up for a long-term career at the next stage of elite competition.

To succeed in cross-­country mountain biking, Courtney needs different tools in her arsenal—explosiveness to get off the starting line quickly; technical skills to navigate tight, single-­track turns and through rock gardens; power to churn up steep climbs; vision to spot fast lines; mental calm to handle unexpected situations; and endurance to gut out a ninety-­minute race that she describes as “sprinting a marathon.” There are a number of levers Courtney and her team can play with to optimize her performance potential. Given her laser focus on being the best athlete, it’s not surprising to learn that Courtney’s a data nerd who wants to understand how the human body works. (She was a human biology major at Stanford University, after all.) It suits her sport, where there is no shortage of numbers, statistics, and trends to mull over and analyze. She has worked meticulously to dial in her nutrition and training—lung-­searing intervals on picturesque trails across the Golden State, gym sessions that involve a mind-­boggling mix of box jumps and Olympic lifts, and yoga for recovery—all of which has helped her climb the competitive ranks, both in the United States and internationally.

But the world champion and Olympian isn’t one to blindly go by the numbers or apply prescriptive exercise and nutrition guidelines. She looks at research studies to understand the why behind the recommendations and determine if they make sense for her as an athlete and a person. “I’m always trying to look at the underlying picture and make sure I’m applying the right thing to my training and to myself individually,” she told me. Except that when she started looking into the sports science studies, she quickly realized that the vast majority were based on men, and it wasn’t entirely clear whether the findings held true for women too.

The process of conducting scientific research is like putting together a jigsaw puzzle. You work with thousands of disparate data points that, at first glance, don’t seem to fit together. Just like you’d sort puzzle pieces by edge, color, and pattern, you start with the most basic re‑ search questions and work on those in small batches before moving on to thornier questions. As different pieces begin to match up, the accumulated data points resolve to form a clearer picture of what’s going on.

In sports science research, scientists have studied men for more than a hundred years. It’s like they’ve completed multiple sections of the puzzle—cardiovascular response, muscle adaptation, endurance, and biomechanics—and have started fitting them into a larger framework. We have a pretty good idea of what exercise means for active men and their bodies. Courtney’s male mountain bike peers are working with a base of research that offers them more nuance to tailor their training and nutrition protocols to their physiology. It gives them a leg up on improving their health, well-­being, and athletic performance.

Scientists didn’t begin to study women athletes in earnest until the 1980s and 1990s. It’s like they’ve just dumped out all the puzzle pieces and assembled the border, without a photo of the finished puzzle to guide them. Once all the pieces are connected, will it be the same picture as the men’s puzzle or something else entirely? Courtney realized that the advice she’d read in books or received from others was based on either mixed evidence or one or two small studies on women. For a world-­class athlete, that’s a pretty rickety foundation to rely on.

Courtney shared her concerns on Instagram, writing, “Throughout my career, it has often been hard to see myself in sports science research. In many cases, women aren’t included in the data at all or treated as a poorly understood ‘special case.’ What does it look like to train sustainability, fuel well, pursue longevity and stay healthy, happy and strong as a female athlete?” Right now, we don’t have the answers.

Sex and gender bias have long been baked into the DNA of both athletics and exercise science. Modern sports developed in the late nineteenth century at a time fraught with change. The Industrial Revolution and urbanization ushered in massive disruptions to the way people lived and worked. People moved from the country to overcrowded cities, where gambling and drinking were common. Jobs required less hard labor, spurring concerns that men would become physically weak and “effeminate,” Jaime Schultz, a professor who studies the history and culture of sports, told me. And weakness was perceived as a sign of a lack of moral character.

From UP TO SPEED: The Groundbreaking Science of Women Athletes by Christine Yu, to be published May 16th, 2023 by Riverhead, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2023 by Christine Yu.