Although there is little empirical research on the upper limit of exercise intensity, athletes who are accustomed to high-intensity training before pregnancy and have an uncomplicated pregnancy can safely assume no adverse effects of maintaining that intensity once they’re expecting. Women have been physically active and making babies since the beginning of time. As long as you don’t get overzealous with a new program or try to prove any points about what you can pull off with your exertion when you’re expecting, your body knows how to manage exercise and grow a baby quite well and will let you know if you need to pull back.
If you are already engaging in vigorous activity, you can keep your workouts at that level during pregnancy, but be aware that you may need to make changes in your workout intensity based on your body’s cues and responses to exercise. A fit pregnancy really can’t accommodate dogged, disciplined severity with exercise. As long as you adjust your mind-set and don’t try to push through fatigue, which is a common trait in endurance athletes, it’s fine to maintain the status quo in your training intensity because your body is used to it.
Fit & Healthy Pregnancy can help you cultivate peace of mind when it comes to changes in your body’s tolerance for various types and levels of exercise. Just remember that you’re exercising for two, and your passenger will have a say in what you do.
That said, if you signed up for a race before pregnancy, you’re probably okay to complete it, depending on how far you got in mileage in training. A veteran marathoner might be able to complete a marathon in the first trimester if her pre-pregnancy fitness level and experience with the distance mean she won’t be taking her body to new and unfamiliar territory. She’ll probably have to lower her level of exertion in training and perhaps switch to a walk-run plan for both prep and the race, but pregnancy doesn’t necessarily mean she must sit it out. The safety and sensibility of running a marathon or completing a similar long endurance event will vary from woman to woman. Every woman is different and needs to talk about her situation and background with her doctor before they decide together if she can safely do her race. While running a marathon in your third trimester might get you a lot of attention, it doesn’t mean it’s the right achievement for you, and of course pregnancy is not the time to make statements about your endurance. Athletes who push their workout intensity to 90 percent of max heart rate may endanger fetal well-being, so it’s critical to stay cognizant of your exertion.
If you’ve been a vigorous athlete, use Borg’s scale to direct your exertion to a safe zone rather than striving for a percentage of max heart rate. There is simply too much variability in the max heart rate across a pregnancy and too much individual variation between women to say that a specific percentage of target heart rate should direct your exertion. ACOG states that because of the variability in a woman’s heart rate during exercise throughout pregnancy, target heart rates are an unreliable measure of intensity. Borg’s scale is a more useful assessment of your cardiovascular output, and how you feel is a better measure of your physiological response to exercise.
Keeping your pre-pregnancy level of exercise intensity is a great goal, but if your body tells you it’s exhausted or your joints start to bother you as your weight increases, you need to make a change in activity (and perhaps in nutrition). Have your doctor monitor your risk for anemia, since increases in your blood volume mean you need to generate a higher red-bloodcell count to prevent anemia. The risk of anemia is greater for competitive (versus recreational) athletes who want to continue with high-intensity training, so stay on top of your iron intake and ask your health care provider to closely monitor your risk for anemia. If you exercise throughout pregnancy, you will sustain an elevated blood volume, and your red-cell volume and total red blood cells will increase to match that volume.
Fit & Healthy Pregnancy is a friendly, comprehensive guide to exercising during pregnancy from athlete-moms Kristina Pinto and Rachel Kramer, MD.
Find Fit and Healthy Pregnancy in your local bookstore or online and learn safe ways to exercise for two!
- Amazon – Fit & Healthy Pregnancy
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- Chapters/Indigo – Fit & Healthy Pregnancy
Please consult your doctor before embarking on an exercise program during pregnancy.