Heart Rate Zones For Exercise For Pregnant Women

Even during healthy, problem-free pregnancies, most women experience common pregnancy-related symptoms, such as lower back pain and decreased energy. Regular exercise can help alleviate such aches, boost mood, improve circulation and help maintain posture as your belly expands. Overexertion during exercise, however, can lead to dehydration, overheating, or even deprive your fetus of oxygen. Before beginning or continuing an exercise program during pregnancy, check with your midwife or obstetrician.

Previous Guidelines

The American Congress of Obstetricians and Gynecologists, or ACOG, sets comprehensive pregnancy guidelines, which include exercise and heart rate guidelines. Before 1985, ACOG recommended that pregnant women keep their heart rate at or below 140 BPM, or beats per minute, and limit the duration of each workout to no more than 20 minutes. While these recommendations may have sufficed for a certain population of pregnant exercisers, including previously sedentary women, they didn’t take highly fit, or even fit, pregnant women into account.

Current Guidelines

Current ACOG guidelines do not set heart rate limits. Rather, the guidelines state that if you’re able to “talk normally” while exercising, your heart rate isn’t too high. The thinking behind this recommendation loosely corresponds to heart rate training zones, which are divided into three main categories: aerobic, a combination of aerobic and anaerobic, and anaerobic. In the aerobic heart rate zone, your muscles receive all the oxygen they need for the demands you’re placing upon them. When you work out aerobically, you should be able to speak in full sentences without pausing to breathe or gasping for air. Once you cross the anaerobic threshold, it's harder to carry on a conversation — a signal that you're working too hard.

Rate of Perceived Exertion

In accordance with current ACOG heart rate guidelines, you don’t need to use a heart rate monitor to make sure you’re not overexerting yourself during exercise. Instead, use Borg’s RPE, or rate of perceived exertion, scale. Borg’s scale is based on the idea that how you feel when you’re working out indicates how hard you’re working in comparison to your capacity. The scale ranges from 6, or “no exertion,” to 20, or “maximal exertion.” Pregnant women should exercise between 12 and 15 on the scale, which is in the “somewhat hard” range. For an unconditioned pregnant woman, a 12 on the RPE scale could correspond to a heart rate of 140 BPM, while for a fit pregnant woman, it might correspond to a heart rate of 155 BPM.

Considerations

In a survey conducted by the American College of Sports Medicine and published in the “Journal of Women’s Health” in late 2010, more than half of physicians, certified nurse midwives and doctors of osteopathy surveyed weren’t aware of current prenatal exercise and heart rate guidelines. While the majority of those surveyed acknowledged the benefits of prenatal exercise, they also referenced outdated guidelines when advising their patients. In light of this disconnect, it’s important for you to understand how to gauge your level of exertion during your doctor-approved prenatal workouts.