Overview

Cardio is any workout in which you elevate your heart rate. Many exercises fall under the umbrella of cardio. This includes walking, hiking, running, biking, rowing or elliptical machines, dancing, playing sports, or HIIT (high-intensity interval training). Activities like jumping jacks, burpees, and jumping rope are also cardio workouts. A large body of evidence supports cardiovascular exercise for nearly all aspects of your health. Cardio allows you to improve the health of your cardiovascular and respiratory systems while building muscle and burning calories. As with any exercise during pregnancy, physical changes can require you to modify your cardio to ensure your workouts are safe for you and your baby.

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Exercise in Pregnancy

There is a separate episode with an overview of exercise during pregnancy. This includes general recommendations and safety tips to keep your workouts healthy for you and your baby. Plus, a breakdown of the physical changes and common pregnancy symptoms that can affect your workouts. I recommend you listen to that episode before diving into this article on cardio.

Cardio

Cardio is short for cardiovascular training. Your cardiovascular system includes your heart and your blood vessels. In terms of exercise, cardio means a workout in which you elevate your heart rate. Many exercises fall under the umbrella of cardio. This includes 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 allows you to improve the health of your cardiovascular and respiratory systems while building muscle and burning calories. As with the research on physical activity, cardio improves physical and mental health. Exercise can improve your mood in the short term. It can delay brain aging and degenerative brain diseases like Alzheimer’s in the long term.

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.

Defining Levels of Cardio

Categories of exercise are typically light, moderate, vigorous, or high. While guidelines have been proposed, no universally agreed-upon definitions exist for these terms. This makes comparing different studies challenging and can cause confusion for following exercise guidelines. Cardio exercise intensity can be quantified by heart rate and oxygen intensity.

Heart Rate

To understand how to use heart rate to quantify activity level, 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 between 60 and 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. When you regularly exercise, you will have a lower resting heart rate. Someone very active may have a resting heart rate of 40, much lower than the normal range for adults.

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.

You may hear about cardio measured in zones as a percentage of maximum heart rate. Zone 1 is 50-60%, zone 2 60-70%, zone 3 70-80%, zone 4 80-90%, and zone 5 90%+.

Measuring Heart Rate

The easiest way to measure heart rate is with a fitness tracker because the device does it for you. You can manually check your heart rate if you don’t use a fitness tracker. 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.

Subjective Measures of Heart Rate and Intensity

There are also subjective measures you can use 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 a score of six, indicating no exertion, up to 20, signifying 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 straightforward method that involves no math is the talk test. If you’re doing a moderate-intensity activity, you can talk but not sing. If you are doing a vigorous activity, you cannot say more than a few words without pausing for a breath. If you do not already monitor your heart rate, you don’t need to start. Like anything, it is easy to overthink this. Please keep it simple and pay attention to how your body feels. 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.

How Cardio Affects 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 that you reach an increase in 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.

Your baby’s blood supply is reliant on yours. 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 prematurity. 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. We need further research on vigorous-intensity exercise in the first and second trimesters and exercise intensity exceeding 90% of the maximum heart rate.

Warm-Up and Cool Down

Many precautions anyone should take for a cardio workout also apply during pregnancy. This includes a 5-10 minute warm-up to gradually increase blood flow to your muscles, increase your heart rate, and loosen up your joints. When pregnant, the hormone relaxin relaxes your ligaments, and your muscles are under extra strain from physical changes. After cardio, you should also take 5-10 minutes to cool down. This involves slowing down your workout for the last five to ten minutes. If you go for a run, walk for the last five to ten minutes. Take it extra easy for the last 5 minutes if you are on a walk.

Stretching should be a component towards the end of your warm-up and 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 apparent. 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 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 are that you burn calories, strengthen your heart, lower your blood sugar, improve your immune system, increase your energy, improve your mood, and increase your longevity, so you live longer. It can even help your creativity and give you some space to think. ACOG states that brisk walking gives a total body workout and is easy on the joints and muscles.

A review on walking during pregnancy found only 14-23% of pregnant mothers are meeting 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 extra challenging to work out. The second trimester is usually the period you feel the best. Fatigue tends to kick in again in the third trimester, and your growing belly makes exercising more challenging.

Evidence shows that walking during pregnancy decreases the risk for gestational diabetes, and glucose levels are 4%–21% lower after a 25-40 minute low-intensity walk. Walking is also associated with a 33% decrease in risk for preeclampsia. Another benefit is that walking is associated with a 29-44% decrease in excess weight gain during pregnancy. The distance and time walked affected the decline in the risk of weight gain. Plus, there is some evidence 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 has all the same benefits as walking, and you burn more calories. The downside is that running also has a higher risk for injury and can be harder on your joints. According to the American College of Obstetricians and Gynecologists, if you are healthy and your pregnancy is normal, continuing or starting regular physical activity is safe. Physical activity does not increase your risk of miscarriage, low birth weight, or early delivery. However, discussing exercise with your obstetrician or another healthcare team member during your early prenatal visits is essential. If your healthcare professional gives you the okay to exercise, you can discuss what activities you can do safely. Having an open dialogue with your doctor or midwife is always great because you can get their feedback on any particulars of your pregnancy.

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’ weights at birth. This was independent of the stage or trimester of pregnancy and the distances participants ran. This is great news for runners because running was thought to affect preterm birth rates and your baby’s weight at birth.

There is a difference between an experienced runner and someone who isn’t. If your body is accustomed to running, it will be easier for you 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 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. Even with decreasing the intensity, they did maintain 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

Another excellent cardio activity is swimming. Physical changes in pregnancy can exert pressure on your cardiovascular system, joints, and spine. Being in water can be a great workout, relaxing and therapeutic. Floating on the water’s surface 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.

If you look at swimming solely for exercise, the evidence shows it is safe during pregnancy. If you are considering water aerobics, they may not yield significant results. 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. Swimming is good if you are specifically looking for an outdoor activity that does not strain your joints. One study found that exercise in a pool helped reduce swelling.

Chemicals in Pools and Hot Tubs

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 from 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, as you would find in 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 due to the risk of falling. This is a perfect example of how the 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 have a Peloton you enjoy using. 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 need to involve your experience and comfort level. You can always bring any questions to your doctor or midwife.

Other Cardio

Cardio is any workout in which you are elevating your heart rate. Gyms have a lot of machines you can use for cardio, like rowing machines, elliptical machines, or treadmills. Most gyms also offer group classes for HIIT (high-intensity interval training) or other aerobic workouts. Working out indoors can be nice if 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 does caution against sports that have a risk of you getting 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. This could range from basic fitness moves like jumping jacks, burpees, or jumping rope to dancing and kickboxing.

Making Cardio Enjoyable

If you habitually get cardio workouts in regularly and enjoy them, that is fantastic. Unfortunately, not everyone enjoys cardio workouts. They can be especially dreadful for someone who is just starting.

Your options are limitless for making your cardio workouts entertaining or productive. You can combine cardio workouts and connect with other people. You can meet up with a friend for a run or cardio workout. If you are going on a walk, you can 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 what life will look like 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 get outside your neighborhood to a different park for some cardio.

The key to exercise and cardio is finding activities you enjoy doing. 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 do 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 be helpful to keep track of 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. Even an iPhone will track activity reasonably well with the 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 walk often and continue that 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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