When I started working out again, one of my first questions was related to intensity. How hard could I work out while still taking care of my unborn child? A number I often ran across in online articles and discussion groups was 140 bpm for maximum heart rate. Not having anything else to base my workouts on, I started there. The problem was that I needed a way higher heart rate to feel like I was getting a workout, even pregnant.
This became obvious to me when I subbed for a Zumba class around my 18th week, dutifully wearing my heart rate monitor. My goal was to stay under, or at least around 140. I did fine for the first few songs, and then I was up in the 160s and low 170s. A quick self-check of all my vital systems told me I was doing just fine, so I carried on, making sure to drink plenty of water. After that I decided I needed to find out more about this bpm limit.
Turns out 140 is a number quite literally pulled out of thin air with no real scientific basis. It’s obviously hard to recommend a single number for a population of people who share the fact that they are pregnant but very little else. Each pregnant woman’s pre-pregnancy training status and pregnancy story are different, and both need to be respected.
A much better way to monitor your effort during pregnancy, and one supported by the American College of Obstetricians and Gynecologists (ACOG), is with Borg’s Rate of Perceived Exertion (RPE) scale. The key word is “perceived,” meaning the scale accounts for not only differences between people but also for differences between one person’s fitness level from day to day. The scale gives you a way to self-assess the intensity of your activity, independent of heart rate, ranging from the amount of effort it takes to sit around (6) all the way up to your maximum effort (20). When pregnant, and depending on your pre-pregnancy level of fitness, you should mostly be working out at a ‘moderate’ to ‘hard’ level ( 12-14 on the scale of 6-20) that allows for some conversation with some effort. For me, if I can still sing all the words to my favorite song on my playlist, I need to step it up.
What’s really interesting is that due to some crazy changes a pregnant body goes through, you most likely won’t have to work out as hard to reach the same intensity levels as pre-pregnancy. The following result in the heart having to work harder to pump blood around the body, hence influencing your perceived exertion:
- blood volume increases by 40-50%
- heart rate increases by about 15 bpm
- stroke volume and cardiac output (basically how much blood your heart pumps with each beat) increase
Workout intensity is an important consideration since you shouldn’t be working out so hard that the baby starts suffering. This is why it’s beyond important to listen to your body. Really listen. If something feels good, it probably is good. If something feels bad, drop it. And if you’re not sure, call it quits and ask your doctor.
Some days I like to push it. Other days it just feels better to take it easy, and so I do. I never forget that pregnancy is the time to be kind to myself – I am, after all, baking another human being in that lovely belly of mine!