Finally Some Research on Intense Exercise During Pregnancy!

pregnant fitness

Yoga IS great during pregnancy, but what about the more intense stuff? Is it safe for baby? Credit: lululemon athletica

I’m not even pregnant yet, and I’m already annoyed by how much misinformation there is about exercise during pregnancy. Obviously, you don’t want to play a contact sport or do crunches, but what about heavy weight-lifting? Running? Getting yourself good and sweaty and out of breath? Is that safe for the baby? And for how long into your pregnancy?

While there are a ton of anecdotal stories of woman who have been previously active and kept up their workouts throughout their whole pregnancy and gone on to have healthy, happy babies (off the top of my head I think of Charlotte from Sex and the City, and these two amazing runners), but there’s not a whole lot of research out there on it. Most doctors tell you to not let your heart rate get too high and everyone (us included!), tells you to listen to your body. But for many who do have the energy and desire to work out (’cause fatigue and exhaustion is a whole other ball of wax), they cut back on workouts because they’re scared. No one wants to hurt their unborn child, so everyone errs on the side of caution. Makes perfect sense to me. (And, let’s be honest, the mommy guilt starts early.)

So when I saw this new study published in the journal Obstetrics & Gynecology that found moderate- and high-intensity exercise in women who were active before they got pregnant to be safe during the third trimester, I was thrilled. In a nutshell, 20 minute of moderate exercise, like walking, three times or more a week or 20 minutes of vigorous exercise, like running, more than four days a week did not keep the baby from getting enough blood or oxygen. While the heart rate rose after the medium- and high-intensity workouts in the study, the heart rate, blood flow and biophysical profile stayed in the normal range, indicating that the baby was fine.

Sure, it’s just one study, but moms and moms-to-be need this kind of good scientific literature to be able to make informed decisions about our bodies and our lifestyles. As long as I don’t suffer from an achy breaky pelvis like FBM Erin did, I plan and hope to exercise and jog during my third trimester, whenever that may be. (And, yes, that is easy for me to say now, seeing as I’m not pregnant yet.)

Tell me, did you work out during your third trimester? How intensely? And was your doctor cool with it? —Jenn


  1. Abigail says

    I was a triathlete and runner before getting pregnant, and I ended up logging a workout on every single day of my pregnancy–either swimming with a Master’s group, biking with my bike set up on an indoor trainer, running (and luckily I had a pregnant friend to run with), or walking. Being in shape before getting pregnant allowed me to work out at moderate to harder intensities that were completely reasonable throughout my pregnancy. I would never have done anything that I felt endangered the baby, and yet I was still able to continue to comfortably work out at intensities that weren’t just a snail’s pace. With the running though, I never ran that long–maybe 30-40 min. max, 1 or 2 times per week, but was able to do so through my third trimester. For some reason I never experienced pelvic discomfort. I ran a respectable 5K at 30 weeks pregnant and then ran another 5K on my due date with my also-pregnant friend, at that point mainly because we were looking for something fun to do that would take our minds off how close we were to meeting our babies. And I’m not a ridiculously intense person when it comes to exercise, just consistent. I worked out throughout my pregnancy because it did so much for my mood and self-image, and studies also suggest the activity helps build a healthy placenta for the baby. It also felt like a bonding experience with my baby–I felt like we were doing these things together. My midwife (also a runner) was 100% supportive, provided I was gaining weight (which I was) and wasn’t doing crazy stuff (which I wasn’t). I ended up going into labor 2 days after my due date and delivered a healthy 7 lb. 12 oz. girl in a hospital waterbirth setting. I don’t think the exercise necessarily contributed to my relatively short labor (6 hours), but it certainly helped me get through it. I do think a lot of women are afraid to work out during pregnancy because of well-meaning advice from moms and grandmothers about it possibly harming the baby, but they grew up in different times and we know a lot more now about how moderate to intense exercise actually is a good thing when you’re pregnant.

  2. jenny says

    What I’m still confused about is how much is too much. I’m a fitness instructor and teach pretty intense boot camp like classes three, sometimes 4 a week. On the other days I do weight training and jogging at 6 mph so on those days my workouts are not as intense. I checked my heart rate after today’s class and the average was 150, but it got as high as 170. I am instructing at the same time so I have to talk on a regular basis and am able to do talk even with a higher heart rate. Is this safe? I have been researching like crazy, but the info is so conflicting I just don’t know what to do. I was extremely fit before I got pregnant and was doing 60-90 min of high intensity workouts most days of the week including Insanity (which I have quit).

  3. Atisheh says

    This is good to know. And I have to agree with Abigail: there is a lot of grandmotherly and motherly advice out there about not moving too much. In fact, my mom told me not even to go on walks during my first trimester. (Bad advice #124.) But then again, her experience of labour was on her back and miserable, so that tells you how much it’s worth.

  4. RK says

    Prior to getting pregnant, I had just spent 12 weeks getting into an awesome fitness routine led by an extremely knowledgable exercise expert. The routine was comprised of two days of strength training using machines at the gym and 3-4 days of cardio. I had just worked up to 45 minutes of running on the treadmill and was working on expanding from 3 to 4 days. My eventual goal was 5 days of cardio, as recommended by the aforementioned expert, who backed up everything he taught with scientific studies. This was an incredible acheivement for me, as at the start of the 12 weeks, I could barely do 15 minutes of fast walking on the treadmill.

    When I got pregnant, I switched from running to a mix of fast walking and cycling, and I stopped increasing the weight level on the weight machines, but otherwise kept my routine. As I got further into the pregnancy and the exercises felt more difficult, I dropped the weight a bit on some of them.

    My pregnancy was quite smooth and complication-free, and my daughter is very healthy. I did have trouble pushing her out during labor, but I doubt that’s because of exercise. I’m not even sure if it was necessarily a problem or if the doctor just had unrealistic ideas of how fast labor should be.

  5. April says

    You say you can’t do crunches, but in another article recommend pilates. Isn’t that just a lot of crunches and core/ab exercises. How is one okay and not the other?

  6. Jessica says

    Did the study say anything about the first and second trimesters? I read somewhere (don’t remember, so can’t say how reputable the source was), that the higher heart rate and temperature elevation were much more likely to be a risk for the baby early in the pregnancy. Of course, once I started getting morning sickness and pregnancy fatigue, my regular high intensity work outs pretty much stopped. I did continue a weights class until the week before I had my baby, and felt really good doing that. I also tried to get in some good walking and ellipticalling in my last trimester. Unfortunately I ended up having an emergency c-section at 36 weeks because my little one was in a breech position and my amniotic fluid had dropped to almost nothing. I keep wondering if the low amniotic fluid had to do with my exercise (like a tiny rupture of the sac of waters during a workout?), but there’s no way to know.

  7. Tatum says

    Jenn, I am so glad to see you writing this kind of post! I can SO relate. In fact, I share the exact frustration. So much so that I switched career paths many years ago and chose to focus on pre- and postnatal fitness full time.

    There is a ton of wrong information circulating based on old research and wives tales, it is great that there is now some real science! I don’t typically chime in, but if you don’t mind I wanted to add a couple things…

    1. You absolutely can and should do modified crunches, planks, and cat/cow type of exercises during your pregnancy to keep your core strong. I typically use the stability ball for crunches. Here is an example of what I mean:

    2. Listening to your body is the most important rule by far… what that means is, if it feels good do it. If it doesn’t back off. I usually tell woman, on a scale of 1 – 10, don’t go above an 8. You can get winded, but don’t get out of breath.

    I hope that helps! The benefits of exercise for both mom and baby are incredible. I am so glad the word is finally getting out that it is safe!

  8. Sara Haley says

    HI ladies. I totally understand your frustration, which is why I created Expecting More, my prenatal workout DVD program for fit & healthy moms-to-be. I was beyond frustrated when i got pregnant with the material that was out there. Please check it out at . Any woman who worked out prior to her pregnancy will love it!

  9. Jessica B says

    I am also a fitness instructor – I teach a high intensity boot camp style kickboxing class and run 4-5 miles/day on off days. I continued to teach my class (taking more breaks for myself than before I was pregnant) into my third trimester. When I got too tired to teach, I continued taking the same class up until 2 weeks before my due date (including kicking, planks, push-ups, burpees, etc). Of course I did move slower and take more breaks as I got bigger. I also continued to run through week 32. After that, I used the elliptical (~45 min/session) but kept the intensity up. In all of my workouts, I broke a heavy sweat, and my heart rate hit the 165-175 range at the high point (sometimes even 180 in the early months of pregnancy – when I pushed to that point, I always slowed down).

    I had a fairly quick and easy labor and gave birth to a very healthy 7lb, 12oz little girl. And the placenta was huge and also very healthy.

    Upon conception, my doctor was no help when I initially asked her advice on how much I could do. She recommended the standard max heart rate of 140 and didn’t want to make any allowances for the fact that I was already in great shape. In fact, she made me feel irresponsible for even asking about pushing beyond that threshold. I later found out that her clinic requires that policy to be recommended in order to avoid lawsuits.

    From what I could tell from online research, that 140 number was reached arbitrarily in the mid-1980′s by a doctor that has since recinded the limitation. I just listened to my body and never pushed it to the point of dizziness or exhaustion. I am so glad to see more studies coming out about this. I was shocked at the lack of research.

  10. Marisa Frank says

    I went to the gym 5 days a week with my first pregnancy up until week 36. I did aerobic classes 3 days and resistance training the other two. I had no morning sickness and felt great through the pregnancy. I never got back into shape after having that child and therefore did not work out with pregnancy #2 or #3. I had bad morning sickness and actually lost weight with #3 because I couldn’t keep anything down. It felt like the longest pregnancy ever. Then I got back into shape with P90X. I got pregnant with #4, which was a total surprise. I wasn’t planning on having any more kids. I had worked so hard to get back into shape and change my fitness habits I didn’t want to give up exercise. So I did P90X and Turbo Jam the entire 9 months. Of course I modified it. I took more breaks and some days I couldn’t finish the whole dvd. I just listened to my body. But I had more energy the days I worked out! I had zero morning sickness again. It was the easiest pregnancy and a very quick labor. I bounced back so much quicker with the 4th. I am not a doctor but I felt great with pregnancy 1 & 4 and those were the times I was exercising. Not only did I feel better physically but my whole attitude was better. I felt stronger and could get more things accomplished because I had energy after working out. My doctor just told me to be careful and not push myself too hard. I am glad more information is out there. I think the benefits for both Mom and baby are great.

  11. Crystal Best Labranche says

    I am 33 weeks pregnant with our first child… A little girl we are naming J’Adore :D

    I am a LES MILLS BODYPUMP instructor for GoodLife Fitness and I have continued to teaching my 3 classes a week, along with 2 cardios (ZUMBA & BODYATTACK) which are high intensity.

    During the first 3 months, I tonned it down and really listened to my body due to fatigue and nausea, backing off my weight selection as well. I have had to modify my workouts, due to my fitness goals are different than pre pregnancy… My goal has been to stay active, healthy and really listen to my body as I honor my temple.

    I have had an amazing pregnancy, continuing to work full time and teach and participate. I say… listen to your body. I do modified crunches, planks…still do jumping jacks, plyos etc….I’m still pumpin’ weights in PUMP class…and having a sweaty and awesome workout… that in turn keeps my mind, heart and body healthy.

    I wish there was more research for pregnancy fitness. I hope my labor, delivery and recovery is as amazing and easy as my pregnancy has been.

    Loving my workouts, looking forward to whippin’ back into shape after J’Adore arrives and loving MOMMYHOOD :D

  12. Kathryn L says

    I am currently 21 weeks pregnant and have, for the most part, have been able to keep up with my workouts. I am a competitive cross fitter, and the exercise guidelines I got from my midwife were simply to stay well hydrated and to not get exhausted. She is very open minded and has encouraged me to listen to my own body. As I’ve gotten bigger I am not able to workout as intensely, but my goal from this point forward is simply to facilitate a healthy pregnancy, labor and delivery. Oh, and getting back into shape quickly post baby with the work I am doing now will be the added bonus :-)
    There is an awesome site designed specifically for cross fit moms – – that has some great informative articles as well as a daily workout for beginners, intermediate, and advanced athletes. Give it a peek!

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