Health / running / Women

A Primer on Physical Activity During Pregnancy

I get asked lot of questions about exercise during pregnancy. Yes, I’m a woman, and I’m physically active, and I have 2 kids, so I’m probably a little biased as to the interest on this issue.  However, my instinct and experience tell me that this is a topic about which people have a lot of questions and relatively little information. So here’s a quick primer on the 4 most common questions I’ve received: Is exercise during pregnancy safe? There are substantial health benefits to being physically active during pregnancy, including reductions in the incidence of gestational diabetes, hypertension, and excessive maternal and fetal weight gain. However, only about 15% of pregnant women meet the American College of Obstetricians and Gynecologists (ACOG) recommendation of 150 minutes of moderate intensity aerobic activity per week during pregnancy. One study in 2005 followed 41 fit women through pregnancy as they participated in either high-volume (8.5 hours/week of exercise) or moderate volume (6 hours/week of exercise) training. Maternal and fetal safety and adverse outcomes were not different between the two groups. Moreover, analysis of data from 1647 women showed that vigorous activity during pregnancy (> 4 sessions/week) was associated with longer gestation and reduced odds of preterm birth. So, the answer is a resounding yes: for most women, exercise during pregnancy is very safe.

2. What about during the summer? Is exercise in the heat dangerous? Available data suggest that pregnant women are safely able to exercise outside without large increases in core body temperature. For example, an interesting study looked at the core temperature response to exercise in 14 women before, 5 times during, and after pregnancy. Authors found that the thermal response to exercise declined continuously from pre-conception to post-partum, suggesting that the body protects the fetus well during exercise. Other studies have shown that pregnant women tend to spontaneously decrease exercise intensity in the heat in order to instinctively avoid dangerous increases in core body temperature.  Moreover, pregnant women demonstrate several adaptations— faster onset of sweating, greater dilation of blood vessels in the skin– that promote effective cooling during exercise in the heat. So, again the answer is a resounding yes: there appear to be maternal adaptations, both self-selected and physiological, that contribute to body temperature regulation during exercise in the heat.

3. What about competing during pregnancy? Is that safe? Marathoners Paula Radcliffe and Kara Goucher maintained very high levels of training through their pregnancies, and as profiled in NPR’s All Things Considered, U.S. Olympic discus thrower Aretha Thurmond competed in the U.S. National Championships two weeks after her son was born. There are also case reports of pregnant endurance runners who maintain training exceeding 60 miles/week of running without any adverse outcomes and relatively few decrements in performance. By contrast, though, a more recent study of 6 pregnant elite Olympic-level athletes 23-29 weeks pregnant revealed that endurance exercise bouts at > 90% maximal heart rate evoked reductions in uterine artery blood flow and fetal heart rate, indicating a potential risk to fetal well-being at very high intensity exercise. The answer is that there just aren’t sufficient data on athletes who compete during pregnancy to make broad conclusions about safety. However, with more than 40% of Olympic athletes in the most recent Olympiads comprising women, there will no doubt be continued investigation on the safety of competing during pregnancy.

 Picture taken from www.theguardian.com4. Will I look the same after pregnancy? Ahh, this is the loaded question. Multiple studies demonstrate that exercise during pregnancy prevents excessive maternal weight gain.  One of the greatest predictors of post-partum weight retention is the amount of weight gained during pregnancy, especially in the first trimester.  Since active women gain less weight during pregnancy than inactive women, exercise during pregnancy plays a pivotal role in a woman’s likelihood of returning to pre-pregnancy body weight after giving birth. In fact, a longitudinal followup of women who voluntarily exercised during pregnancy showed that these women continued to exercise regularly over the 20 years following pregnancy, gaining less weight and depositing less body fat over time as well. However…certain anthropometric changes with pregnancy (e.g., changes in hip width and body fat distribution) are more permanent. Moreover, exercise in the post-partum period is influenced by breastfeeding, sleep deprivation, less time for recreation, and potential injury risk from changing hormones, so exercise patterns themself tend to fluctuate before, during and after pregnancy. To this question, therefore, I might answer: You may not look the same, but you also won’t be the same. You’ll be better.


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