How Pregnancy Affects Your Marathon Time

A few years ago, Nike-sponsored runners Alysia Montaño and Kara Goucher publicly revealed the extent to which their pay had been slashed when they got pregnant. Allyson Felix followed up with the story of how Nike had offered her a contract with a 70 percent reduction in pay after she got pregnant. “Getting pregnant,” former Nike runner Phoebe Wright said, “is the kiss of death for a female athlete.”

There are some basic questions of right and wrong here. But there are also some physiological questions. Is it correct to assume that, once a woman gets pregnant, her best athletic days are behind her? After all, some researchers consider carrying a baby to term to be an arduous feat of endurance that bumps up against ultimate human limits. Or, conversely, might it be that female athletes actually have an advantage after giving birth? That’s what other experts propose, pointing to lasting changes in cardiovascular abilities such as the amount of blood the heart can pump and potential increases in pain tolerance.

What we need is data, and that’s what a new study in the European Journal of Sport Science supplies. A research team led by Nicolas Forstmann of the Institute for Research in bioMedicine and Epidemiology of Sport and the National Institute of Sports Expertise and Performance, in France, analyzes the career trajectories of the fastest female marathoners in history—and concludes that giving birth doesn’t really make a difference either way.

The analysis included the 150 fastest female marathoners of all time, based on the lists maintained by World Athletics. Searching through official records, news reports, and personal websites, they identified 37 of these runners who had given birth to children during their elite athletics career, meaning that they had at least one elite-level performance in the World Athletics database at distances between 1,500 meters and the marathon both before and after childbirth. Of these 37 athletes, 23 had one child during their career, at an average age of 28.3; the other 14 had two children, at average ages of 24.7 and 32.6.

Overall, 26 of the 37 runners ran their fastest times (2:21 on average) after their first kid. If you break it down in more detail, in the one-child group eight runners ran their best time before kids and 15 ran their best times afterwards. In the two-child group, three ran their best time before kids, five between kids, and six after the second kid. On the surface, that looks pretty good.

The big confounder here is age. On average, the athletes were absent from the World Athletics database for 23 months surrounding childbirth, with a range from 9 months (wow!) to 94 months (also wow!). Time waits for no woman, so it’s difficult to know whether a post-pregnancy drop in performance is because you’re a year or two older—or conversely, for a relatively young mother, whether a post-pregnancy increase in performance is simply the result of additional training and experience.

To account for the effects of age, Forstmann and his colleagues use mathematical modeling to plot the typical career trajectory for female marathoners. For the 37 women in the study, that relationship looks like the graph below, with a gradual increase in performance up to a peak age of 31.7, followed by a gradual decrease in performance:

The timing of pregnancy had no observable effect on this curve. Women who had their first child before the age of 31.7 tended to get better post-pregnancy; those who gave birth after that age tended to get worse. Having kids didn’t seem to fundamentally alter anyone’s trajectory.

There’s a big gap in the dataset, though. What about hypothetical runners whose careers were derailed by pregnancy? Maybe they ran 2:21 pre-kid, and then never managed to return to world-class level and so disappeared from the World Athletics database entirely? They wouldn’t be included in the study at all, since they didn’t return to top-level competition, so we have no way of knowing whether this happens to anyone. This is a totally made-up scenario, but it’s worth acknowledging that pregnancy and childbirth do present real challenges to elite-level training. Lax ligaments can alter running mechanics, torn abdominal muscles compromise stability, the metabolic demands of breastfeeding might leave you calorie depleted and vulnerable to stress fractures. All these issues are common among athletes who rush back to full training after childbirth. Patience—the kind you can only have when your employer isn’t tying your next paycheck to your immediate return to competition—is key.

Despite that blind spot, I think the new data is reassuring. Women who are able to successfully return to training and competition after giving birth seem to pick up pretty much where they left off, with allowance for the passage of time. Since Montaño, Goucher, and Felix spoke out, Nike and other companies have made public commitments to protect athlete compensation during and after pregnancy. I suspect that athletes are still nervous about telling their sponsors that they want to have a family, but hopefully this data will give them some useful ammunition for the conversation.

For more Sweat Science, join me on Twitter and Facebook, sign up for the email newsletter, and check out my book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance.