Pregnancy Exercise Myths

Despite overwhelming evidence to the contrary, I still hear people (mostly those same know-it-alls I talked about in my last post) spout off these pregnancy exercise myths as reasons to avoid working out during pregnancy or at least not working too hard.  The truth is that women’s bodies are capable of amazing things.  During pregnancy, women can do most of the same activities they could before they got pregnant including exercise.  Pregnant women are not delicate little flowers; they are strong, powerful goddesses capable of accomplishing many great things in addition to growing a tiny human being! Working out while pregnant is both safe and beneficial to mother and child.  So, lets put to rest some of the most common myths being thrown around lately….

7 Pregnancy Exercise Myths

1. Exercising during pregnancy pulls oxygen, nutrients, resources, etc. away from the baby.

Most medical and safety issues about exercise during pregnancy are based on the concern that increase in body temperature, reduced oxygen/nutrient delivery to the placenta, stress, or trauma may result harm to the baby or to the mother.  The data do not support these concerns.  Functional adaptations as a result of exercise either compensate for or complement the changes due to pregnancy and vice versa.  Let me say that another way: changes caused by pregnancy and changes caused by exercise interact in such a way that not only extends the margin of safety for both mother and child during the cardiovascular, metabolic, thermal, and mechanical stresses of exercise but these adaptations also protect mother and child from these types of stresses should any unanticipated medical problems arise during pregnancy, labor, or delivery.  So, not only does exercising while pregnant help the body learn how to meet the added demands of exercising during pregnancy but the combination of exercise and being pregnant can actually help protect mother and baby from the very safety issues that people are concerned about in the first place…yes, your mind has just been blown.

2. While exercising, you need to keep your heart rate below 140 beats per minute.

In 1985, the ACOG (American College of Obstetrics and Gynecology) published its first guidelines for exercise during pregnancy.  These guidelines were very conservative but they were at least a starting point for women who wanted to continue to exercise during pregnancy and provided guidelines for healthcare providers.  These 1985 guidelines detailed very specific exercise heart rate and duration cutoffs of 140 bpm and 15 minutes respectively.  Many women and fitness professionals found the guidelines to be too restrictive.  In the years after this first set of guidelines was published, the attitudes of healthcare providers began to shift and more research emerged in favor of more liberal guidelines.

In 1994, the ACOG published a new set of guidelines that were a little more lax and removed specific limitations but still cautioned against exercising to exhaustion.  However, as the body of research on exercise during pregnancy continued to grow, it was discovered that heart rate is not a reliable indicator of how hard a woman is working during pregnancy.  The most recent guidelines published by the ACOG in 2002 removed the heart rate recommendation and upped their exercise duration recommendation to 30 minutes or more of moderate exercise on most if not all days of the week.   I’ll provide more info in a later post about why heart rate is not a good measure of the safety, health or fitness level of a pregnant woman but the Borg Rating of Perceived Exertion (RPE) scale is accepted as the best indicator for determining exercise intensity.  A range of 12-14 (moderate intensity to somewhat hard) on the Borg RPE scale (scale goes from 1-20) is considered  safe for pregnant women.  The Borg scale uses how an individual feels an a measure of how hard he/she is working relative to their maximum capacity.  There are many reasons that heart rate is not an effective or accurate measure of exercise safety or intensity but using the RPE scale normalizes all the individual variations in heart rate and variations due to eating, hydration, sleep, stress, and pregnancy so that all women can train at a level that is appropriate for them.

3. You shouldn’t do any sit-ups, crunches, or any abdominal work while you are pregnant…it will squish the baby.

Not only are abdominal exercises safe (with a few modifications) but  core workouts can provide many benefits.  Working out the entire core including all four abdominal muscle groups, the back, and pelvic floor will help improve posture and help prevent/relieve back pain and strain on the abdomen which are common complaints during pregnancy. Strengthening the core can also help prepare the body for the physical challenge of labor and delivery in addition to making recovery faster and easier.

Sit-ups and crunches are ok during the first trimester, but during the second and third trimester women should avoid performing any movements that are performed lying flat on the back.  Sit-ups and crunches can be replaced with plank holds, pelvic tilts, belly breathing exercises etc.

4. Lifting weights while pregnant is too stressful on the joints.

Weight-training is a very important part of any well-balanced fitness program.  Weight-training can actually off-set the effects of the hormone relaxin on joint and ligament laxity (which is commonly used as a reason to avoid resistance training) during pregnancy.  Data suggests that the exercise-induced injury rate in pregnant women is less than the injury rate seen in a control group just from the routine activities of everyday life.

Women who continue to exercise during pregnancy also experience fewer common pregnancy-related discomforts and symptoms such as low-back, leg, or pelvic pain.  Weight-training during pregnancy can also help maintain or increase lean muscle mass and reduce fat deposition.  Finally, weight-training can help women prepare for labor and delivery and for the demands of caring for and lifting/carrying a newborn baby.

5. Running while pregnant isn’t safe for the baby.

Baby is well protected in the fluid-filled amniotic sac.  If you enjoy running and it isn’t causing you too much discomfort there is no reason why running can not be a part of your pregnancy fitness routine! As with all exercise during pregnancy, keep a moderate pace.  You should be able to talk but not sing during your workouts.

6. Pregnant women should only do prenatal yoga for exercise.

Prenatal yoga is great for maintaining flexibility and easing stress during pregnancy but its not enough.  A balanced exercise program should include endurance, strength and flexibility components and that goes for all fitness programs not just for pregnant women.  Yoga is wonderful for stretching and maintaining flexibility but it does not challenge the cardiovascular system and except for certain types of yoga classes it does not include enough resistance/strength-training movements.

Cardiovascular exercise increases blood volume and vascular activity which improves the ability to dissipate heat and in the delivery of nutrients and oxygen to both the working muscle tissues and the fetus.  “Cardio” also  improves gas transfer and oxygen availability even when blood flow to the placenta falls by as much as 50%.  This type of exercise also increases metabolic capacity, insulin sensitivity, and use of fat stores to supply the mother’s energy requirements leaving energy-rich sugars for the baby’s growth.

Strength training improves skeletal muscle function and its effect on bone density is enhanced by pregnancy hormones.  Weight-lifting during pregnancy can help increase strength and lean muscle mass above pre-pregnancy levels.  This increase in strength can alleviate the mechanical stress on the back, pelvis, hips, and legs caused by the growing abdomen.  In addition, these improvements in body composition and strength will help the mom-to-be return to her pre-pregnancy weight more quickly and will help prepare her for the physical demands of labor and of lifting and carrying her new baby.

7. If you weren’t working out before you got pregnant, you shouldn’t start now.

It is never too late to start exercising.  There are so many important benefits to mother and baby that can still be achieved even if you were not exercising before becoming pregnant.  Working out can help combat pregnancy fatigue and improve your sleep!  Starting a moderate-intensity exercise program during pregnancy will also help limit weight gain and fat deposition but only if exercise duration totals more than 3 hours a week.  This is more than the minimum required for women who were already exercising before pregnancy to achieve the same benefits because they just need to maintain their fitness.  Part of the reason for the need for longer duration  for women who are just beginning exercise while pregnant is that they need to start slow.  So, since the intensity is lower the duration of exercise has to be longer to produce the same effects as it does for the more exercise-experienced women. This doesn’t mean that you have to do it all in one chunk.  You should aim to exercise all or most days of the week but you can split up the exercise throughout the day into 10-15 minutes bouts if that is easier for you.  You can start with just one 10 minute session a day and work your way up from there!

I highly recommend working with a trainer if you are pregnant  and want to begin an exercise program.  Women with exercise experience will have a little bit of an easier time figuring out what modifications to make to their normal routine as their pregnancy progresses but, if you are new to exercise, I believe it is better to ere on the side of caution.  So talk to your doctor and find a fitness professional who is knowledgeable about prenatal fitness.  I offer prenatal personal training in the Orange County area and I am also open to answering questions or providing consultations to help you address any pregnancy fitness concerns!

2 thoughts on “Pregnancy Exercise Myths

  1. Kristi says:

    Great summary. I completely agree that exercise is important but also women should pay attention to how they are feeling because everyone has different symptoms during their pregnancy. I always thought I would be able to keep up working out even while pregnant no matter what. I am almost through my first trimester and the nausea has been so overwhelming all day and all night to the point I did not feel comfortable working out and had to take several weeks off. I can’t wait for the nausea to go away so I can go back to exercising and staying fit and healthy for me and the baby.

    • Absolutely, listening to your body is the best way to determine appropriate exercise intensity, frequency, duration, safety, etc. In addition to of course listening to your doctor’s recommendations and the recommendations of any fitness professional, I would always advocate that women pay attention to what their body is telling them. Often, despite the best of intentions, morning (or evening, or all day) sickness can derail exercise plans…and that’s okay. If you can push through and find a window to fit in some exercise at a time when you aren’t feeling queasy, exercise can actually help alleviate some of the yucky symptoms of early pregnancy. But, if you have exhausted all the natural, home remedies and still no luck do not beat yourself up. The second trimester usually brings relief from the nausea and more energy and you can begin to resume a more regular exercise routine.

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