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Is It Safe to Exercise During Pregnancy?

Pregnancy Workouts: Is It Safe to Exercise?
Pregnancy Workouts: Is It Safe to Exercise?
pregnant woman holding exercise ball

The first thing that most newly pregnant exercisers worry about is miscarriage -- thanks to age-old myths that have women believe that a bout of strenuous exercise can harm the baby. "There is no real evidence that exercise is linked to miscarriage," says Bruce K. Young, MD, coauthor of Miscarriage, Medicine & Miracles (Bantam) and professor of obstetrics and gynecology at New York University School of Medicine. Heavy exercise isn't going to hurt your baby, but it will tire you more quickly than it did prepregnancy. The amount of blood a woman has increases during pregnancy by about 50 percent, and her heart needs to work harder to push all that blood around -- including circulating it through the placenta, an extra organ. "That means the stress on your heart will be 50 percent greater for the same exercise that you were doing before pregnancy," Dr. Young says. So you can work just as hard doing less than you did before you were pregnant.

Pregnancy isn't the time to push yourself to the max, but it's also okay -- and good for you -- to get your heart rate up with cardiovascular exercise. Although a target heart rate of 140 is a number that's often cited, there's no precise number to shoot for. When prenatal trainer Erinn Mikeska, owner of Delivering Fitness, in Dallas, works with pregnant women, she has them monitor their rate of perceived exertion (RPE) -- how hard they feel they're working, on a scale from 1 to 10. "You probably want to stay around 5 or 6," she says. In the first trimester, when you're not any bigger and don't yet have balance issues, you may be able to exert yourself more if you're not too tired.

Pregnant women often notice that they feel out of breath more quickly than they used to. You may assume this is a sign that you're out of shape. In fact, during pregnancy you're breathing 20 to 25 percent more air because you need to get rid of the carbon dioxide levels in your own blood -- and in your baby's. (Babies in utero aren't breathing on their own, but they're still producing carbon dioxide, which transfers to the mother's blood. She needs to breathe more so she can get rid of it.) "So breathing more doesn't mean you're any less fit," explains Dennis Jensen, PhD, lead researcher on a Queen's University study of exercise and respiratory discomfort during pregnancy. It simply means that your body is adapting exactly as it should.

Jensen's research found that when pregnant women exercised to fatigue on a stationary bike at 20, 28, and 36 weeks, their maximal aerobic capacity (how hard they could work) was well preserved, even though they were breathing more.

For women who are already in top shape, exercising during pregnancy is about maintaining their fitness, not about making fitness gains, Pivarnik says. "Even if I had tried to take it to a new level, my body wouldn't have let me," Amy Hyland says. Before Hyland got pregnant with her first son four years ago, she was a triathlete who had completed an Ironman, and she exercised six or seven days a week. She was determined to stay active during pregnancy and continued to run, swim, and even ride her bike. "For me, it was about maintaining fitness, not training hard," she says. Hyland even did a duathlon (a run/bike/run event) at five months. "My doctor just told me to stop if I had any pain." She finished just fine -- though certainly not in record time. For most pregnant women, the fear of working out too hard is likely a misplaced worry because the pregnant body has a way of both imposing its own limits and adapting.

While there are some things to avoid, such as scuba diving, horseback riding, or any contact sport that could cause blunt-force trauma to the abdomen, there's relatively little that pregnant women can't do. Even the longstanding prohibition against exercising on your back is somewhat of a myth, Dr. Young says. It's true that lying flat on your back late in your pregnancy can cause your growing uterus to push down on the veins whose job it is to deliver blood, leading to decreased blood flow. "Blood can get shunted away from the uterus, and you might feel light-headed," Dr. Young says. But performing exercises on your back for a short period (such as a series of Pilates moves) is not likely to do any harm, and you would feel uncomfortable long before your blood flow was compromised, he explains.

Hyland didn't just exercise to stay in shape; it also helped lift her mood. "I was so happy to be able to get outside and jog for 45 minutes," she says. In fact, exercise keeps your endorphins (your body's natural "happy" chemicals) flowing, Mikeska says. That's a crucial benefit, especially since we now know that there are more mood disturbances during pregnancy than postpartum, due to the massive influx of extra estrogen and progesterone (hormones linked closely to mood), says Melanie Poudevigne, PhD, health and fitness management program coordinator at Clayton State University, in Morrow, Georgia.

Psychologically speaking, pregnancy can also be stressful because it's full of so many unknowns. "That perceived lack of control makes pregnant women very vulnerable to mood disturbances," Poudevigne says. She and her colleagues recently conducted a study where they led sedentary pregnant women with lower-back pain through a moderate-intensity weight-training program. It not only curbed the pain, it also lifted the women's moods, Poudevigne says. They learned how to monitor their discomfort levels, and came to feel that they were more in control of their own bodies.

Pivarnik suggests that pregnant women who exercise monitor signs of potential problems, keeping in mind that if there's something wrong with the pregnancy, it's not caused by exercise. Rather, exercise might provide that extra bit of stress that brings the problem to the forefront. "Don't ignore these symptoms (see below), especially if they keep happening when you exercise," Pivarnik says. Stop exercising and consult your doctor if you have:

  • Vaginal bleeding
  • Abdominal cramping
  • Light-headedness
  • Excessive nausea
  • Extreme headaches

First Trimester Tips

  • You can pretty much continue doing exactly what you were doing before pregnancy (including lifting the same amount of weight).
  • Now is a smart time to get involved in a prenatal yoga or Pilates class; it's a great habit to carry throughout your pregnancy (plus, you'll get to be around other pregnant women).
  • If you feel sluggish, try decreasing either the intensity or the duration of your workout rather than skipping the workout altogether (example: drop your jogging pace by 30 seconds a mile, or cut your bike ride a few miles short).

Second Trimester Tips

  • Your heart is starting to work harder to circulate all the blood you built up during the first three months. Cut back your cardio intensity by 20 to 30 percent, says Dr. Young. You'll still feel as if you're working just as hard.
  • Avoid inversions (such as Downward Dog in yoga) if you feel at all light-headed.
  • If you're a cyclist, consider switching to the stationary bike or to a Spinning class; your growing belly can make balancing on a bicycle tricky.

Third Trimester Tips

  • Your joints are more vulnerable, so beware of heavy (15 pounds or more) weights; opt instead for more repetitions, says Pivarnik.
  • Do free-weight exercises seated, if possible, because you'll want your back supported (plus it's hard to balance while standing up).
  • You can continue with your cardio right up until you deliver, but don't be surprised if you can walk faster than you can jog. Many pregnant women find that supporting their belly (with something like the Belly Band) during cardio helps take the pressure off.
  • Now is a great time to try swimming: You'll feel wonderfully weightless in the water, and it won't stress your joints.

Originally published in American Baby magazine.

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