This episode takes a deep dive into cardio exercise during pregnancy, including walking, running, swimming, cycling, and more. Cardio is a broad category that includes any activity that raises your heart rate. During pregnancy, normal changes to your cardiovascular system mean your heart is working differently, which often raises questions about safety for you and your baby. Find out how pregnancy-related changes can affect cardio workouts. Learn how current guidelines define safe exercise, and why intensity matters more than the specific activity you choose. This episode also covers practical ways to gauge effort using heart rate or simple body cues, along with clear guidance on when to slow down or stop.

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Exercise in Pregnancy

There is a separate episode that provides an overview of exercise during pregnancy. That episode covers general recommendations, safety considerations, and how pregnancy-related changes and common symptoms can affect your workouts. It lays the foundation for understanding how to approach exercise during pregnancy, so I recommend listening to it first before diving into this episode on cardio.

Cardio

Cardio is short for cardiovascular training. Your cardiovascular system includes your heart and your blood vessels. In exercise, cardio refers to a workout that elevates your heart rate. Many exercises fall under the umbrella of cardio. These include 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.

Benefits of Cardio Workouts

A large body of evidence supports cardiovascular exercise for nearly all aspects of your health. Cardio helps improve the health of your cardiovascular and respiratory systems while building muscle and burning calories. As with the research on physical activity, cardio improves both physical and mental health. In the short term, exercise can improve your mood. In the long term, it can delay brain aging and degenerative brain diseases like Alzheimer’s. 

Recommendations for Cardio During Pregnancy

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.

Cardio Intensity and Heart Rate

When we talk about cardio recommendations during pregnancy, intensity matters more than the specific activity you choose. Most guidelines describe exercise as light, moderate, vigorous or high. While these terms are commonly used, and guidelines have been proposed, there is no universally agreed-upon definition. Without clear universal definitions, recommendations can feel confusing. There are a few practical ways to think about intensity, and you can use whichever makes the most sense for you.

Tracking Heart Rate

If you like numbers or use a fitness tracker, heart rate is one way to quantify intensity. Without a fitness tracker, you can manually check your heart rate by using the tips of your first two fingers and pressing 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.

To understand quantifying exertion with heart rate, you must understand your resting and maximum heart rate. Your resting heart rate is the number of times your heart beats per minute at rest. The normal range for most adults is 60-100 bpm. One meta-analysis found that pregnancy increased heart rate by 7-8 beats per minute. A resting heart rate on the lower end is better because your heart isn’t working as hard. A lower resting heart rate generally reflects better cardiovascular fitness, and regular exercise tends to lower it over time.

Your maximum heart rate is the maximum number of times your heart should beat per minute during exercise. You can estimate your maximum heart rate by subtracting your age from 220. The American Heart Association recommends that your target heart rate zone for exercise is 50-85% of your maximum heart rate. The AHA classifies moderate-intensity activities as about 50-70% of maximum heart rate and vigorous-intensity as 70-85%. For a 30-year-old, the average max heart rate is 190 bpm, and your target would be 95-162 bpm.

Some fitness trackers also divide heart rate into zones, which are simply ranges based on percentages of your maximum heart rate. These can be helpful, but they are estimates and not exact targets.

• Zone 1 is 50-60%
• Zone 2 60-70%
• Zone 3 70-80%
• Zone 4 80-90%
• Zone 5 90%

Subjective Measures of Heart Rate and Intensity

If you do not track your heart rate, or you do not want to think about numbers, you do not need to. You can also use subjective measures to determine your activity level. One method researchers use to quantify exercise is the Borg Rating of Perceived Exertion (RPE) scale, which measures how hard it feels the body is working. This includes heart rate, breathing rate, sweating, and muscle fatigue. The scale ranges from 6 (no exertion) to 20 (maximal exertion). Each number corresponds to the heart rate. A six corresponds to a heart rate of 60 beats per minute, 12 to 120 beats per minute, etc.

A simpler version of this is the talk test. During moderate-intensity exercise, you should be able to talk but not sing. During vigorous exercise, you may only be able to say a few words at a time.

The most important takeaway is that you do not need to overthink intensity. Pay attention to how your body feels. If you feel overly winded, uncomfortable, or like your heart rate is too high, slow down. If you feel comfortable and can carry on a conversation, you are likely within a safe range.

How Cardio Affects You and Your Baby

Your blood volume increases 50% during pregnancy to support your growing baby and placenta. The additional blood requires your heart to work harder. That may mean you reach a higher heart rate more quickly than normal during exercise. As you get further into your pregnancy and your belly grows, it 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.

In addition to cardiovascular changes, you also experience an increase in relaxin, a hormone that relaxes your ligaments. Ligaments provide joint stability, and increased laxity can raise the risk of injury. In relation to cardio, be mindful of movements that involve rapid direction changes or deep stretching.

Your baby’s blood supply is reliant on yours. During a cardio workout, your body redirects blood towards working muscles. 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 prematurity. Many studies examining cardio in pregnancy focus specifically on these outcomes to assess safety. A meta-analysis examined vigorous-intensity exercise completed in the third trimester and found it safe for most healthy pregnancies. We need further research on vigorous-intensity exercise in the first and second trimesters and exercise intensity exceeding 90% of the maximum heart rate. The important takeaway is that the overall body of evidence supports cardio exercise as safe and beneficial for most pregnancies.

Warm-Up and Cool Down

Many precautions anyone should take for a cardio workout also apply during pregnancy. Because pregnancy-related changes increase joint laxity and strain, warming up and cooling down become especially important. This includes a 5-10 minute warm-up to gradually increase blood flow to your muscles and increase your heart rate. After a cardio workout, you should also cool down. This involves slowing down your workout for the last five to ten minutes. For example, if you go for a run, walk for the last five to ten minutes.

Stretching should be a component at the end of your warm-up and during your cool-down. There is some controversy as to whether stretching is effective at preventing injuries. Stretching will improve your flexibility and range of motion and reduce muscle soreness. Since your ligaments tend to be looser during pregnancy, take it easy on the stretching. If it hurts, scale it back. Stretching should feel good; it should not be painful.

Warning Signs to Stop Exercising

Most of the warning signs that indicate you should stop exercising are obvious. The list from ACOG includesregular, 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 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. If your body is too far outside its comfort zone and you feel especially tired, overly winded, or exhausted, slow down. Listen to your body, and if you feel like you may be overdoing it, you probably are.

Walking

Walking is one of the most accessible forms of cardio. The benefits of walking include burning calories, strengthening your heart, lowering your blood sugar, improving your immune system, increasing your energy, improving your mood, and increasing your longevity, so you live longer. It can even help your creativity and give you space to think. ACOG states that brisk walking gives a total-body workout and is easy on the joints and muscles.

A review of walking during pregnancy found that only 14-23% of pregnant women meet recommended levels of physical activity during their pregnancy. Physical activity increased from the first through the second trimester and decreased in the third. This makes sense because you may be dealing with morning sickness and fatigue in the first trimester, making it especially challenging to work out. The second trimester is usually when you feel the best. Fatigue tends to return in the third trimester, and your growing belly makes exercising more challenging.

Evidence shows that walking during pregnancy reduces the risk of gestational diabetes, and glucose levels are 4%–21% lower after a 25-40-minute low-intensity walk. Walking is also associated with a 33% lower risk of preeclampsia. Another benefit is that walking is associated with a 29-44% lower risk of excess weight gain during pregnancy. The distance and time walked affect the magnitude of this risk reduction. Plus, there is some evidence that it can also lead to a healthier birth weight for your baby and reduce the risk of preterm birth. Walking is an activity that nearly everyone can do. Even a daily walk around your block can be a good start to exercise.

Running

Running offers the same benefits as walking, and you burn more calories. The downside is that running carries a higher risk of injury and can be harder on your joints. One study of nearly 1,300 participants included expecting mothers in running groups across the U.S. It is important to know that these people had a running practice before becoming pregnant. There were two groups of participants: those who continued to run during their pregnancy and those who did not. They found no difference in gestational age at delivery, meaning running did not contribute to premature delivery. There was also no statistical significance in the babies’ birth weights. This was independent of the stage or trimester of pregnancy and the distances participants ran. This is great news for runners, as running was previously thought to affect preterm birth rates and your baby’s birth weight.

There is a difference between an experienced runner and someone who isn’t. If your body is accustomed to running, it will be easier during pregnancy than for someone new to running.

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 it by half. This shows that even competitive runners understand that their running practice may need to slow down a bit to accommodate the changes that occur in their bodies when they are pregnant. Even with the reduced intensity, they maintained running while pregnant. Of all women in this study, 3.9% sustained an injury during pregnancy. These were competitive long-distance runners, not people going for a casual jog around their neighborhood. Injury is always a risk with running, and you are more prone to injury during pregnancy due to the effects of relaxin.

Swimming

When people talk about swimming during pregnancy, they may mean different things. Some people are swimming laps at a pace that raises their heart rate, while others are referring to water aerobics or gentle movement in a pool. Physical changes during pregnancy can put pressure on your cardiovascular system, joints, and spine. Being in water can take pressure off your body and joints. ACOG supports swimming and water workouts because they use many of the body’s muscles, and the water supports your weight to avoid injury and muscle strain. In addition, some research suggests that swimming in a pool can help reduce swelling, which is very common, especially in the third trimester.

Swimming and water aerobics can feel very different in terms of intensity. Swimming laps or moving continuously in the water at an intensity that raises your heart rate is a great form of cardio. Water aerobics serves a different purpose. While it may feel good and provide gentle movement, it may not make a significant difference in your health. One study of 71 low-risk, sedentary pregnant women randomly allocated half of the group to water aerobics and the other half to no physical exercise. They found no significant differences in any outcome measured, including weight gain, BMI, preterm birth, blood pressure, or heart rate.

Pool Chemicals and Safety

A theoretical risk of swimming or spending time in pools is the chemicals used to clean or treat the water. Your baby is more susceptible to chemicals in the earlier stages of pregnancy. One study examined mothers who swam during early and mid-pregnancy and found no adverse outcomes. The researchers noted that pool chemicals might be toxic at higher exposure levels. There were no adverse effects, and even fewer preterm births, in the swimming group in this study.

Many pools use saltwater systems instead of chlorine to keep pools clean. It is a common misconception that saltwater pools are chlorine-free. Saltwater systems still use chlorine, but in lower amounts. The salt content is about 1/10 that of the ocean. See this episode for more information on the benefits of water during pregnancy, including swimming pools, hot tubs, baths, and float tanks.

Cycling

ACOG recommends a stationary bike over a standard bicycle during pregnancy because of the risk of falling. This is a clear example of how recommendations tend to be conservative. A stationary bike is always safer than a standard bicycle at any stage of your life. This is excellent news if you enjoy using a Peloton. If you like to go on bike rides in your neighborhood or are an avid cyclist, this may not be what you want to hear. Remember, recommendations will always err on the side of caution. Your personal decisions about your activity should reflect your experience and comfort level. You can always bring any questions to your doctor or midwife.

Other Cardio Options

Remember, cardio is any workout that elevates your heart rate. Gyms have many cardio machines, such as rowing machines, elliptical trainers, and treadmills. Most gyms also offer group classes for HIIT (high-intensity interval training) or other aerobic workouts. Working out indoors can be nice when the weather is too hot or too cold. Almost all sports involve cardio. You could join a local league to play a team sport. ACOG cautions against sports that carry a risk of being hit in the abdomen with a ball, including soccer and basketball. If you prefer to exercise solo or even in your living room, there are endless YouTube videos of solo home workouts you could do. These can range from basic fitness moves like jumping jacks, burpees, or jumping rope to dancing and kickboxing.

Making Cardio Enjoyable

If you enjoy cardio workouts, that is fantastic. Unfortunately, cardio can be especially dreadful for someone just starting to incorporate exercise. Thankfully, there are many ways to make your cardio workouts more enjoyable or productive. You can combine cardio workouts with social time. Meet up with a friend for a run or a cardio workout. If you are going on a walk, schedule a call to catch up with a friend or family member. Go for a walk with your partner. This is a great time to reconnect and discuss your plans for your birth or for life with a new baby.

Aside from swimming, you can do any cardio with headphones. You can listen to podcasts, enjoy music, or even stand-up comedy with headphones. Sometimes, switching up your surroundings can make a workout more enjoyable. You may be able to find a new hike or walking trail in your area. You can ride a bike to explore a different part of your town. Or even take a drive and head to a different park outside your neighborhood for some exercise.

The key to cardio or any form of exercise is finding activities you enjoy. You have nothing to lose by trying something new. In the worst-case scenario, you try something and don’t love it. You will still have physical activity for that day, and you can try something different the next time. Cardio workouts are so diverse. If you move your body and elevate your heart rate, it counts as cardio. You don’t need to log your workouts or track your heart rate; you just need to move.

Gear and Clothing for Cardio

The only thing you need for cardio is comfortable clothing and shoes. Clothing should be loose-fitting and comfortable for the temperature or climate.

Shoes should be comfortable and have good arch support. Relaxin can also relax the ligaments in your feet, permanently changing your foot’s shape and structure. Relaxin can contribute to your arch collapsing and over-pronation. This can lead to your feet increasing a shoe size, developing bunions, and stress and inflammation on the tissue along the bottom of your feet. I am a big fan of the Mommy Steps insoles designed to support your foot during pregnancy. (You can save 20% off Mommy Steps and Form Insoles with the promo code FEET.)

Fitness trackers like an Apple Watch or Fitbit can help track metrics, including heart rate. My favorite fitness tracker is the Oura ring, a fantastic sleep-tracking tool. You may want to consider an app on your phone for tracking your distance, pace, and time. Many free apps are available in the Apple App Store and the Google Play Store. They will store your exercises so you can see your progress and track your activity over time. Any phone will track activity reasonably well with a pre-installed Health app.

Your breasts also go through many changes throughout your pregnancy. You will likely need to go up a bra size and may require a bra with additional support. Later in your pregnancy, a belly support belt may reduce discomfort while walking or running. A belly support can help support some of the weight of your belly and take some pressure off your lower back.

Strollers for Running and Walking

If you are a runner or walker and plan to continue after your baby arrives, consider a stroller designed for jogging or walking. Some strollers will be more challenging to run or walk with than others. Strollers or joggers designed for this typically have two larger wheels in the back and one wheel in the front. I was gifted a Bob stroller when I was pregnant with my son (thanks to a very generous person who bought it off my baby registry). It is a big stroller that isn’t cheap but fantastic for running and walking. I used it every day with both of my children. Taking your baby out for a walk gets them fresh air and exposes them to new sights, smells, and sounds while you get all the benefits of being active.

Talk to Your Doctor or Midwife

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. If you are not very active and your care provider encourages you to start exercising, start with just a few minutes a day. 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.

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