Overview

Exercise during pregnancy is evidence-based to reduce the risk of certain complications, support healthy weight gain, alleviate common pregnancy discomforts, and improve mental well-being. Despite these well-documented benefits, confusion remains about which exercises are safe and which should be avoided. Guidelines from organizations like ACOG tend to be broad and overly cautious, which may not always align with your fitness level or lifestyle. While prioritizing safety is important, finding a balanced approach that works for you is key. In this episode, we answer a listener’s questions about working out during pregnancy, including cardio, HIIT, and strength training. Learn about the research, how to assess your comfort level, and how to make informed decisions about staying active during pregnancy.

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Hi Vanessa,

I’m currently pregnant and really want to keep up with my workouts, but I have so many questions and concerns. I’d love it if you could do a Q&A episode on exercising during pregnancy. I have always been really active with a mix of strength training, cardio, and high-intensity workouts. Now that my belly is showing, I feel like I’m getting weird looks at the gym, and I’ve even had people ask if it’s safe for me to be exercising. I know staying active is supposed to be good for me and the baby, but I don’t want to do anything that could be dangerous.

I keep hearing mixed messages about pregnancy and exercise. Some people say I should take it easy and avoid anything strenuous, while others say I can do almost anything I was doing before. I still feel good doing HIIT and strength training, but I’m not sure if I should be adjusting my routine. Should I be lowering the weight I lift? Cutting out certain movements? Are there warning signs that I should stop or modify my workout?

I remember hearing that pregnant women should keep their heart rate below 140 bpm, but then I’ve also heard that’s outdated advice. Should I be using a heart rate monitor to gauge intensity, or is there a better way to tell if I’m overdoing it? I’d love to hear about some research on these topics. Thanks again for all the amazing work you do. I always feel more confident making decisions after listening to your podcast.

-Kayla

Kayla, thank you so much for your email. I love that the podcast helps you feel more confident in your decisions. You mentioned that now that your belly is showing, you feel like I’m getting weird looks at the gym. It also sounds like some people have approached you and asked if it is safe for you to exercise during pregnancy. I am sure that is frustrating. Hopefully, as we discuss some of your questions, you can feel more confident in the workouts regardless of other people’s opinions. You should also know that many expecting moms would applaud you for continuing to work out; I certainly do.

Physical Changes During Pregnancy that Can Impact Your Exercise

Many physical changes can impact your workouts. These are the mechanisms on which most safety precautions are based.

Your blood volume increases by 50% during pregnancy, and the additional blood requires your heart to work harder. Plus, your heart rate already tends to be higher during pregnancy. That may mean that you reach an increase in heart rate more quickly than usual during exercise.

Your growing belly can shift your center of gravity as your pregnancy progresses. This could make you more susceptible to falling if you lose your balance. Your growing belly also pushes your other organs up, decreasing your lung capacity. This can make you short of breath or make breathing more challenging, especially during cardio workouts.

As your uterus grows, it also puts more pressure on your vena cava. Your vena cava is the main artery that carries unoxygenated blood from the lower half of your body back to your heart. When you lay on your back it puts additional pressure on this vein. The concern is that exercise positions where you lay on your back could decrease blood flow, ultimately reducing your oxygen and oxygen going to your baby.

During pregnancy, an increase in a hormone called relaxin relaxes your ligaments. Your ligaments are the connective tissues that help keep bones, joints, and organs in place. Unfortunately, relaxin doesn’t only concentrate its effects on your pelvis and hips before birth. The downside is that it can also loosen other ligaments, putting you at a higher risk of injury. If your ligaments are looser, you have less stability in your joints, and it is easier to overstretch your ligaments, which can cause pain or injury.

Recommendations for Exercise During Pregnancy

Given the physical changes during pregnancy, there are official guidelines for exercising while pregnant. The American College of Obstetricians and Gynecologists recommends that pregnant women get at least 150 minutes of moderate-intensity aerobic activity weekly. They define moderate aerobic activity as one in which you move large muscles of the body in a rhythmic way enough to raise your heart rate and start sweating. You still can talk normally, but you cannot sing. Moderate-intensity aerobic activity could mean anything from a brisk walk to general gardening like raking, weeding, or digging.

ACOG’s guidelines tend to err on the side of caution and recommend you avoid anything with even the slightest risk. For example, ACOG recommends a stationary bike over a standard bicycle during pregnancy due to the risk of falling. Of course, a stationary bike is always safer than a standard bicycle. Your decisions about your activity must also consider your experience and comfort level. While the conservative approach may be the safest, it is not always realistic.

ACOG cautions against specific activities when pregnant and specifically names activities with a risk of getting hit in the abdomen, like ice hockey, boxing, soccer, and basketball. They warn against participating in activities that can result in a fall, like downhill snow skiing, water skiing, surfing, off-road cycling, gymnastics, and horseback riding. They also list activities that can cause you to overheat, like hot yoga or hot pilates. ACOG also recommends against activities above 6,000 feet (if you do not already live at a high altitude), skydiving, and scuba diving.

ACOG does note some conditions or complications that make exercise unsafe. Their list includes certain types of lung or heart diseases, cerclage, a multiples pregnancy with risk factors for preterm labor, placenta previa after 26 weeks, preterm labor or ruptured membranes, preeclampsia, pregnancy-induced high blood pressure, and severe anemia.

Cardio

Different modes of exercise involve different considerations. First, let’s examine cardio. Your cardiovascular system includes your heart and your blood vessels. Cardio is any workout in which you elevate your heart rate. Many exercises fall under the umbrella of cardio, including walking, hiking, running, biking, using a rowing or elliptical machine, dancing, playing sports, or HIIT (high-intensity interval training). Even activities like jumping jacks, burpees, and jumping rope are cardio workouts.

How Cardio Affects Your Baby

During a cardio workout, your body redirects blood towards working muscles, and the theoretical concern is that this could reduce blood flow to your baby. Reduced blood flow to a baby in utero could result in a baby who is small for gestational age, low birth weight, and premature. Many studies examining cardio in pregnancy specifically look at these outcomes to determine safety. A meta-analysis examined vigorous-intensity exercise completed into the third trimester and found it safe for most healthy pregnancies.

Measuring Heart Rate

One way to quantify cardio level is by measuring heart rate. The normal resting heart rate range for most adults is between 60 and 100 bpm. A resting heart rate on the lower end is ideal because your heart is not working as hard. Individuals who regularly exercise tend to have a lower resting heart rate. Research shows that pregnancy increases heart rate by 7-8 beats per minute. The easiest way to measure heart rate is with a fitness tracker like an Apple Watch, Fitbit, or Oura ring. You can also use the tips of your first two fingers and press lightly over the artery on the inside of the wrist of the opposite hand. Count your pulse for 30 seconds and multiply by two to find your beats per minute.

Maximum Heart Rate

Your maximum heart rate is the maximum number of times your heart should beat per minute during exercise. The most accepted way to estimate your maximum heart rate is by subtracting your age from 220. The American Heart Association recommends that the target heart rate zone for exercise is 50-85% of your maximum heart rate. For a 30-year-old, the average max heart rate is 190 bpm, and your target would be 95-162 bpm.

In the 1980s, ACOG guidelines recommended that your heart rate should not exceed 140 bpm during pregnancy. It is unclear how they came up with this figure, and over the years, they removed this recommendation. However, it does appear again in the guidelines updated in 2020. ACOG states, “Although an upper level of safe exercise intensity has not been established, women who were regular exercisers before pregnancy and who have uncomplicated, healthy pregnancies should be able to engage in high-intensity exercise programs, such as jogging and aerobics, with no adverse effects.” The same guidelines also state, “Intensity should be less than 60-80% of age-predicted maximum maternal heart rate, usually not exceeding 140 bpm.”

To make things even more confusing, there are different recommendations from other organizations and questions about the accuracy of heart rate to measure exertion. An excellent paper breaks down the recommendations from ACOG and the evidence on heart rate during pregnancy. Researchers suggest that for pregnant women, a combination of both heart rate and perceived exertion may be the current best way to monitor exercise intensity to account for their prior level of training. Monitoring intensity during regular exercise consistently can help pregnant women identify when a change happens and if there might be a reason to lower their intensity.

ACOG releases blanket guidelines that apply to nearly everyone and often cannot account for individual circumstances. It is much easier to recommend that a heart rate remains below 140 bpm than to break down different circumstances to define your optimal max heart rate during pregnancy. Plus, we don’t have clear research to define what that would be. The result is a more conservative and conservative guideline.

Monitoring Your Heart Rate

You don’t need to start if you do not already monitor your heart rate. Like anything, it is easy to overthink this. Please keep it simple and pay attention to how your body feels. A straightforward method that involves no math is the talk test. If you’re doing a moderate-intensity activity (50-70% of maximum heart rate), you can talk but not sing. If you are doing a vigorous activity (70-85% of max heart rate), you cannot say more than a few words without pausing for a breath. If you feel like your heart rate is too high, slow down. If you can easily talk and are comfortable increasing your activity, you can.

Recommendations for Strength Training

The American College of Obstetricians and Gynecologists along with the National Institute of Occupational Safety and Health have specific guidelines on lifting heavy objects during pregnancy. ACOG states that lifting, in particular, poses a risk of musculoskeletal injury and low back pain. The recommendations are specifically for pregnant workers and vary based on your trimester, the height of the lift, the distance from your body the item is, and how often you are lifting. The weight limits are relatively low, especially for lifting from below your waist. However, lifting a heavy box that you have to hold away from your body differs from lifting weight like a dumbbell, kettlebell, or using a resistance band.

Unfortunately, it really doesn’t work to extrapolate these guidelines to weight lifting or strength training.

ACOG recognizes that there is sparse literature on strength training during pregnancy. They attribute the lack of literature to resistance training not being considered a safe activity in early guidelines for exercise during pregnancy. This was due to potential injury and possible fetal heart decelerations.

In the past, one of the reasons doctors advised against strength training during pregnancy was due to concerns that the Valsalva maneuver during pregnancy reduced blood and oxygen flow to your baby, creating fetal heart decelerations. The Valsalva maneuver is a breathing technique used when lifting heavy weights that creates pressure in your abdominal and thoracic cavities, which reduces the load on your spine. More recent research using a 3-D Doppler ultrasound shows that placental blood flow does not decrease during the Valsalva maneuver.

The Research on Strength Training During Pregnancy

While there is a lot of research on exercise during pregnancy, few studies specifically examine strength training. A small study showed that low-to-moderate strength training is safe during pregnancy. A study with 160 women found that light-intensity resistance training and toning exercises performed over the second and third trimesters of pregnancy do not have a negative impact on the newborn’s body size or overall health. A study of 92 women found moderate to vigorous resistance exercise safe in pregnancy. This study used a modified version of BODYPUMP workouts, which used high repetitions of lightweight barbells. Sessions were one hour, including warm-up and wind-down. To modify the workouts for pregnancy, squat jumps were exchanged for heel raises, the squats were less deep, and the abdominal training was exchanged for pelvic-lift and static-abdominal training.

Tips for Strength Training

Kayla, you asked if you should lower the weight you lift or cut out certain movements. Ultimately, this is up to you. Proper techniques will maximize the results for the muscles you work on and help prevent injuries. Pregnancy is probably not the best time to break any of your personal weight-lifting records.

Remember that you can always modify any exercise. You may want to try switching out free weights for bands. You can always decrease your weight and increase repetitions.

In regards to cutting out specific movements. If you are concerned about performing any exercises while lying on your back, a systematic review concluded that supine exercise is not associated with adverse pregnancy outcomes. There is a difference between spending several hours on your back and lying on your back for a few minutes to complete an exercise. You can also modify some positions to be in more of an incline position rather than flat on your back. Or, if you are planning several exercises or reps in a supine position, mix up your routine to alternate positions so you have breaks between sets that require you to be on your back.

Do You Need to Adjust Your Workout Routine During Pregnancy?

A study looked at women who were long-distance runners before becoming pregnant. On average, the participants reduced the intensity of their running during their pregnancy, including cutting their intensity by half. This shows that even competitive runners understand that their running practice may need to slow down a bit to accommodate all the changes that happen to your body when you are pregnant. Although with decreasing the intensity, they did maintain running while pregnant. This aligns with a lot of research showing that expecting mothers voluntarily scale back on exercise. If you still feel good doing HIIT and strength training, you may not need to adjust anything. You may feel differently as your pregnancy progresses.

Warning Signs to Stop Exercising

There are warning signs that you should stop or modify your workout, and most are obvious. The list from ACOG includes regular, painful contractions of the uterus, bleeding, fluid gushing, or leaking from the vagina. Other warning signs include feeling dizzy or faint, shortness of breath before starting exercise, chest pain, headache, muscle weakness, calf pain, or swelling.

Paying attention to your body and how you feel is the key to keeping your workouts within safe limits. It is safe to exercise during pregnancy for the majority of expecting mothers. If your body is too far outside its comfort zone and you feel overly winded or exhausted, slow down. Listen to your body, and if you feel like you may be overdoing it, you probably are.

Experience Level Matters

There is a difference between someone new to exercise and someone who already has an active lifestyle. Your experience and comfort level with cardio, strength training, HIIT, or any other form of exercise will affect how comfortable you are continuing these exercises during your pregnancy. ACOG states that if you were very active before pregnancy, you could keep doing the same workouts with your ob-gyn’s approval.

Talk to Your Doctor or Midwife

Your doctor or midwife is an excellent resource for questions about what is safe during your pregnancy. Like ACOG, they will almost always err on the side of caution. One study found that more than one-half of the physicians trained in the United States received no formal education in physical activity. Even for medical professionals knowledgeable about exercise, it is challenging to have an in-depth discussion in a prenatal appointment that lasts fifteen minutes or less. You should discuss your exercise and activity with your doctor or midwife in the context of your level of experience and the particulars of your pregnancy. If your care provider has reservations about workouts you feel comfortable doing, please talk through their concerns. Whether you are an athlete or are just beginning, almost any activity can be modified so that you can feel empowered to exercise during your pregnancy.

Additional Resources

• Tips for Getting Your Body Back After Baby
• Exercise During Pregnancy, Recommendations and What to Avoid
• Cardio Exercise During Pregnancy (Running, Walking, Swimming, and more)
• Strength Training and Lifting Weights During Pregnancy
• Prenatal Yoga, Recommendations and What to Avoid

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