Paula Radcliffe won the 2007 New York City Marathon less than a year after giving birth to her daughter. At the 2011 Boston Marathon—and just seven months after her son was born—two-time Olympian Kara Goucher recorded her personal best time at the distance.
The idea of a post-pregnancy performance bump gets passed around among elite female runners. And Goucher and Radcliffe’s marathon performances lend the idea some anecdotal evidence. But does it really exist?
“Yes, there are some women who feel their performance is enhanced after pregnancy,” says Michelle Mottola, director of the R. Samuel McLaughlin Foundation Exercise and Pregnancy Lab at the University of Western Ontario. “I wouldn’t say that it happens for everyone, and I don’t think there’s a simple explanation for this—it’s multifactorial—but I do think pregnancy can have a training effect on the body.”
Other running experts agree. “The response varies widely among women and depends on numerous factors,” says Jennifer Copeland, an associate professor of kinesiology and physical education at the University of Lethbridge in Canada. But she doesn’t doubt that, for some women, the post-baby performance boost is legit.
What might explain it? “There are changes to a woman’s cardiovascular system to account for the increase in blood volume during pregnancy,” Mottola says, “and the heart of a pregnant woman is remodeled to accommodate this increase." Pregnancy actually enlarges the heart and increases its blood volume in ways similar to exercise, according to a 2014 study in the journal Cardiovascular Research. She adds that a woman’s rib cage also expands during pregnancy, and research has shown this may increase a pregnant woman's lung capacity. (Drugs that increase the amount of oxygen carried to the muscles are banned as performance-enhancing substances.)
Increased blood volume and lung capacity can both play a role in increasing VO2 max—a standard measurement of exercise ability that relates to the maximum amount of oxygen someone utilizes while working out. These anatomical and physiological adaptations could—for some women—lead to performance improvements.
There are other potential explanations, too: Mottola says postpartum hormonal changes could play a role. Some research has found increased levels of the “feel-good” neurotransmitters oxytocin and dopamine among new moms. It’s possible that these hormonal shifts could increase a woman’s pain threshold—and therefore her ability to push through the fatigue and agony of an endurance event.
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It’s also possible that taking an extended break from running—something women are forced to do following labor—could have a rejuvenating effect, Cooper says. Rest and recovery are crucial for running performance. And even though they understand that overtraining can hurt performance, some runners find it difficult to take a break from their favorite form of physical activity. “In some cases with elite runners, it is likely that any real or perceived performance boost is coming from a period of relative rest—both physical and mental—from intense training and competing,” she says.
Both Mottola and Cooper are quick to add that pregnancy, labor, and post-partum recovery are unpredictable. The specifics of the delivery—C-section or vaginal? Infections or tearing?—will determine how quickly a woman can return to training. Ditto the amount of sleep and rest a new mom is getting, or how much time and energy she has to train.
“Even if a woman had, for example, a hormone profile that could provide some short-term performance benefit, that is not likely going to be enough to override the effects of a prolonged period of dealing with nausea or insomnia, or a physically traumatic delivery, or a baby that doesn't like to sleep more than an hour at a stretch,” Cooper says.
Another important factor, she says, is a woman’s psychological response to having a baby. “There is a lot of variation there in terms of mood, energy, and stress,” she says.
To sum all this up, experts agree that a post-baby athletic boost is possible, and that there are some legitimate physiological or chemical shifts linked to pregnancy that could explain it. But it’s all unpredictable and dependent on the person.
Mottola says women who continue to stay physically active during pregnancy are more likely to bounce back quickly and completely after labor. But she also warns against hurrying back into a training routine. “I always want to caution athletes about ignoring their pain threshold, and doing too much too soon,” she says. “I always say, start slow and listen to your body.”
In the weeks following labor, a woman could try walking or “walk-jogging,” she says. And if that feels all right, she could slowly increase the intensity. But Mottola recommends waiting at least six to eight weeks—and getting clearance from a doctor—before resuming regular training.
“Enjoy motherhood and don’t worry about getting back to improved performance,” she adds. “I can’t stress that enough.”
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