How much is too much?

Doctors say pregnant women may be able to work out more vigorously than once thought.

We all know it’s important to stay active while pregnant, but when 27-year-old Amber Miller recently completed the Chicago Marathon measuring a full nine months, it got a lot of people thinking: When it comes to working out during pregnancy, how hardcore can you really (safely) be? According to new recommendations, while you may not want to run 26.2 miles (Miller half-ran, half-walked), it’s okay to sweat a little harder than you might think.

Official guidelines from the American College of Obstetricians and Gynecologists (ACOG) were released in 2002, suggesting a minimum of 30 minutes per day of moderate-intensity exercise, so long as the pregnancy was without complications. But a recent review of studies in Obstetrics and Gynecology offers a new perspective, giving pregnant women the green light to do vigorous cardio — the equivalent of about 5 hours of intense cycling per week.

Do you have to worry about your heart rate? "There’s no mention of that," says Equinox Health Advisory Board member Jacques Moritz, M.D., an ob/gyn and director of gynecology at St. Luke’s Roosevelt Hospital in New York. "The key is that you should be able to hold a conversation. If you can’t get a word out, you’re working too hard."

According to the study, "vigorous" means a perceived physical exertion of 15 to 16 out of 20. Bonus: Women who achieved this for about 5 hours a week during pregnancy reduced their risk of gestational diabetes by 33 percent.

The paper also gives the go-ahead for strength training, the perfect recipe being 8 to 10 resistance moves twice a week on nonconsecutive days. But because the pregnancy hormone relaxin loosens your joints, it’s important to down the weight and up the reps (say, 8 pounds and 20 reps instead of 15 pounds and 12 reps) to avoid strain. "And steer clear of walking lunges, which can put too much pressure on the pelvis," Moritz says. When lifting, you also want to be sure not to bear down without exhaling, which can decrease oxygen to the baby.

Perhaps the most surprising recommendation of all is that the abs aren’t off-limits. (Just use an incline bench, since lying flat on your back can press on main arteries, reducing the baby’s oxygen supply). Moritz offers a helpful hint: straight crunches could exacerbate pain from diastasis (when the abdominal muscle separates during pregnancy); if that’s you, focus on the obliques.

What are the warning signs that you’re taking "vigorous" too far? "In pregnancy, there is no 'no pain, no gain,'" Moritz says. "If you feel any kind of pain, stop. But there’s no reason to lose strength while pregnant."