I get asked all the time by expecting mamas about cardio: what’s appropriate, what’s not appropriate, what’s the right intensity, etc. So, I’ve decided to put together some guidelines that I recommend following during all of your prenatal workouts, but especially during your cardio workouts.
Cardio sessions can help improve your body’s ability to deliver oxygen to your working muscles. They can also help build an aerobic base, which helps you to recover faster between exercises and sets, lift heavier weights for more reps, promote better recovery between exercise sessions, and help you develop the aerobic endurance needed for labor and delivery.
Research has shown that steady-state, low- to moderate-intensity cardio is safe throughout your pregnancy regardless of a woman’s training state or previous body weight, meaning it is fine to start exercising in pregnancy as long as your intensity is appropriate, and you have been cleared by your doctor.
On the flip side, high-intensity cardio (including high-intensity interval training) can also have its place in your pregnancy, but to what extent is VERY individual. Listening to your body is paramount, and pregnancy should be viewed as a time to potentially maintain aerobic fitness levels, but not necessarily increase them, in already trained women.
What’s more, high-intensity cardio in pregnancy is generally only safe in women who have regularly exercised at high intensities prior to getting pregnant. That is because previously trained women have a higher cardiac output (the amount of blood that the heart can pump out per minute) as well as a higher VO2 max (the maximum amount of oxygen that can be taken up and used by the body’s tissues) during exercise. Regardless though, I tend to err on the side of caution with my coaching clients and program more conservative forms of aerobic exercise through pregnancy and postpartum for the sake of your core and pelvic floor and all that it will go through during pregnancy and postpartum.
In sum, pregnant women who have previously and routinely exercised at high intensities in the past can perform high-intensity exercise for short periods of time—keeping in mind that it will probably look a bit different in pregnancy than outside of pregnancy, especially as the belly grows. For that reason, it’s often beneficial to gauge your exercise intensity based on the RPE (Rate of Perceived Exertion) scale than on speed. So with that said, let’s talk about what it means to gauge your cardio workouts on an RPE scale.
Gauging Exercise Intensity
You’ve probably heard somewhere along the way to keep your heart rate lower than 140 BPM. While this way of measuring intensity can be helpful for some, it’s not exactly the most accurate measure of your exertion levels and exercise intensity (especially during pregnancy), and furthermore, unless you’re wearing a heart rate monitor, it’s not always convenient to stop and check your pulse.
Therefore, I like to use the Rate of Perceived Exertion (RPE) Scale ranging from 1-10 to monitor your effort and adjust the intensity of your cardio sessions.
1 Little or no activity, anything other than sleeping, like watching TV, reading, or riding in a car.
2-3 Light activity, easy and could be sustained for hours. It’s easy to carry on a conversation.
4-6 Moderate activity, feels like you could sustain it for hours, but you are breathing heavy, and it’s more difficult to hold a conversation.
7-8 Vigorous activity, on the verge of becoming uncomfortable. You can only speak a sentence or a few words at a time and can’t sustain the activity for long periods.
9 Very hard activity, very difficult to sustain. It feels like you can hardly breathe, and you can barely speak a word.
10 Maximal activity almost impossible to keep going. You can hardly breathe, and you can’t speak at all.
Now depending on what type of cardio you are performing, as well as how you are feeling in your pregnancy, your intensity levels will change and fluctuate which is perfectly normal.
If you are doing more moderate intensity cardio (where your heart rate stays between 120-140 beat per minute, and these sessions generally lasts between 20-40 minutes) then your effort should feel like a six-seven on the RPE scale, and you should be able to maintain that level throughout the entire session. In other words, your intensity for moderate cardio sessions should range between being able to speak a few sentences at a time to only being able to speak a sentence to a few words.
If you are performing HIIT (high intensity interval training that generally last between 5-20 minutes) sessions then your exercise intensity should feel more like a seven-eight on the RPE scale during your “work” intervals, and between four-six when resting. In other words, your intensity for your working sets should range between being able to speak a sentence at a time to only a few words at a time. Your intensity for your resting sets should be being able to hold a short conversation, but breathing somewhat heavy.
Body Temperature and Hydration Levels
My second rule is to not get overheated during your cardio workouts. Your body temperature is something you’ll want to be aware of especially during higher intensity interval training. There is concern that high body temperatures could cause birth defects, especially in the first trimester.
It’s recommended that you keep your body temperature under 100 degrees Fahrenheit or 38 degrees Celsius. Practice caution when exercising in extremely hot or humid climates, and opt for indoor cardio substitutions if you do live in areas with these types of climates.
Be sure you keep yourself well hydrated during your cardio sessions, and maintain your fluid intake between 16-32 ounces or 500 milliliters-1 Liter of fluids during your cardio workouts (especially during high intensity interval training). Also keep in mind that you do want to be sweating during exercise, but it’s not a good idea to be exercising to the point where you are pouring sweat.
First Trimester Pointers
Your first trimester may not be the best time to do interval training as part of your cardio workouts. This is because your body is going through so many changes right now like potential morning sickness, nausea, extreme fatigue, food aversion, as well as there being an increased concern of overheating during the first trimester. I usually recommend for my clients to stick to more moderate intensity cardio sessions when they feel up to it, so that way they are getting some solid aerobic conditioning without overly taxing their already fatigued bodies.
Second Trimester Pointers
The second trimester is usually a better time to introduce more interval type cardio sessions if you were already doing them pre-pregnancy. Many women tend to start feeling like they can handle higher intensity cardio sessions as they enter the second trimester because they are less fatigued, have more bursts of energy, and feel a little more like themselves again. You can obviously continue with your moderate intensity cardio sessions during this time, but if you feel ready and comfortable to ramp up the intensity by adding in some high intensity interval training then do so by slowly and gradually introducing this type of exercise into your program.
You can continue with high intensity interval training through your third trimester as long as you feel up for it, but you will probably find the need to start slowing down more as you progress further into your third trimester.
You will probably begin to feel more out of breath, so simply adjust the intensity of your cardio workouts and maybe even stick to more moderate intensity cardio sessions for these last three months (remember…you have nothing to prove to anyone about how hard you can work out right now, no pregnancy badge of honor necessary). And remember, your rate of perceived exertion is based on how you’re feeling right now in your third trimester, not a few weeks ago, or a few months ago.
What About Running…Should I…Shouldn’t I?
So…the next thing you’re probably wondering about is running. Is it okay to run during your pregnancy or not? While running isn’t directly dangerous to you or your baby, not dangerous and safe aren’t exactly the same. Don’t give up on me if you happen to be an avid runner, please just hear me out and keep an open mind about what I share with you! 🙂
As your pregnancy progresses and your baby grows bigger, your pelvic floor muscles have to work overtime in order to hold your abdominal and pelvic contents (mainly the bladder, uterus, and rectum) up and in the pelvic bowl. Much like a trampoline, these muscles need to be strong and taut in order to expand and recoil in response to pressure changes throughout your core, to prevent leaking of urine, fecal matter, or gas, and to keep your organs from literally falling out of your body (prolapse). The strength of these muscles is already compromised from the additional weight of your growing baby, and the repetitive pounding from running makes matters worse.
With every jarring foot strike, your muscles have to work even harder to keep everything where it should be. The repetitive pounding can also strain the hormone-loosened ligaments of your pelvis, which can also cause annoying back pain. There are other low-impact options to get your “cardio” fix like walking, cycling, swimming, rowing (as long as the belly allows for it), or metabolic strength training workouts.
And yes…you can opt to wear a support belt for your runs, but at some point I think you need to start asking yourself what the risks vs rewards are when it comes to running through your entire pregnancy. Maybe you will be fine running through the entirety of your pregnancy, but really pay attention to any aches, pains, discomfort, or dysfunction (leaking, or any feelings of bulging, dragging, heaviness, or extreme fatigue through the pelvic floor or vagina. These are all signs that running isn’t potentially the best activity for your body right now. There will be plenty of time for running again in the months following baby’s arrival, and by keeping your pelvic floor strong, you won’t have your runs interrupted by bathroom breaks. Provided you’ve carefully and thoroughly rehabbed your core and pelvic floor, that is.
So that’s it for now! Have more questions about working out during your pregnancy? Leave them in the comment section below, and don’t forget to grab your 3 free pregnancy workouts HERE.