Running During Pregnancy: Monitoring Exertion

*Note: I am NOT a healthcare professional.  This post is in response to many questions I have received in regards to my running pace during pregnancy.  The below information is what I have learned from my current OB-GYN as well as research on this topic.  Before you engage in physical activity during pregnancy, talk to your doctor about his/her recommendations and guidelines.   

Over the last few months, I have received a number of emails, comments, and tweets regarding running during pregnancy – with the number one question being whether or not I track my heart rate (HR) as a measure of exertion during my runs.

During pregnancy #1, my Dr advised me to keep my HR below 140 bpm during my runs and any other physical activity I was engaging in (biking, elliptical, etc).  For the first few months, I ran with my heart rate monitor and was a SLAVE to that number.  I would freak out if it was even slightly over 140.  It was extremely frustrating because it forced me to run extremely slow – sometimes I even had to walk to get my heart rate under that magic number.  It seemed that my HR jumped to 140 without almost no effort the first few months.  As my pregnancy continued, I became a little more relaxed when it came to that number – I would check my HRM (heart rate monitor) every few minutes to ensure it was within reason.  But I was still pretty cautious to keep it close to 140 bpm.

I just completed a course to certify me as a pre / post-natal exercise specialist (hoping to find out if I passed the exam in the next few weeks).  During my training, I learned an enormous amount about exercising during pregnancy – things I WISH I knew the first time around.  But the most startling was that keeping your heart rate under 140 bpm is severely outdated guidance.  

In 1985, the American Congress of Obstetricians and Gynecologists (ACOG) came out with guidelines for exercise and pregnancy which included:

  • Maternal heart rate should not exceed 140 beats per minute
  • Maternal core temperature should not exceed 38 degrees C (100.4 degrees F)
  • Strenuous activities should  not exceed fifteen minutes in duration

    Factors affecting heart rate (Source: Dr. Clapp)

However, since 1985, there have been numerous guidelines released by the ACOG that retracted the aforementioned tips.  The most recent ACOG guidelines (published in 2002 and reaffirmed again in 2009)  completely removed the first two aspects and adjusted the third to:
  • Thirty minutes or more of moderate exericse on most, if not all, days of the week is acceptable for pregnant women without medical complications.

Why the change?

The biggest reason is because studies had shown that a woman’s heart rate response varies considerably during pregnancy.  It increases in early pregnancy, then falls gradually but continually throughout the latter trimesters. (Source: How to Exercise When You’re Expecting by Lindsay Brinn).

    • Exercise heart rate at one’s usual intensity will be extremely high during the first trimester because there is not enough blood in the system for the heart to pump the usual amount of blood each beat.  Therefore, it must pump more often to supply the same amount of blood to the exercising muscles. (Note: This pregnancy effect is so common that women who exercise regularly will often recognize they are pregnant because suddenly their exercise heart rate is sky-high and way of proportion to how they feel)
    • As pregnancy proceeds, the blood volume rapidly expands to fill the dilated arteries and veins, and the amount of blood pumped by the heart each beat rises.  So exercise heart rate gradually falls.
    • By midpregnancy, the relationship between heart rate and exercise intensity is usually similar to before conception. 
    • In late pregnancy, the combined effects of regular exercise and pregnancy appear to expand blood volume further. This probably increases the amount of blood the heart pumps each beat during exercise because, in the last 10 weeks of pregnancy, many fit women complain that they can’t get their heart rate up to what they think it should be without working very, very hard.

(Source: Exercising Through Your Pregnancy by James F. Clapp III. M.D)

If you try to hit one target heart rate (for example: 140 bpm) during the 9 months of your pregnancy, you can easily underwork in the early trimesters when your heart rate increases rapidly and overwork in the later months when your blood volume has increased and brought your heart rate response down.

How a pregnant women FEELS before, during and after a workout appears to be a BETTER index of her health, safety, and quality of the workout then her heart rate response.
Source: Dr. Clapp 

Borg Rating of Perceived Exertion (Borg RPE)

Most health professionals now recommend using the Borg Rating of Perceived Exertion to monitor effort during pregnancy:

A few examples:

  • 6: No activity (in bed or sitting) 
  • 11: Light Activity (such as walking)
  • 20:  All out-effort (almost ready to pass out)

Pregnant women (in good physical condition) are typically advised to stay within the 12-15 range (considered to be moderately hard to hard).  Note: some articles I read recommended 12-14.

Running during my second pregnancy has been different – partially due to my new-found knowledge.  My previous OB-GYN retired soon after my son was born and I am now being seen by a midwife for baby #2.  During my first visit, she instructed me to stay within the 12-15 window.

What does this all mean?

  • A person’s exertion rating may provide a fairly good estimate of the actual heart rate during activity.  And actually, a high correlation exists between a person’s perceived exertion rating times 10 and the actual heart rate during physical activity (Borg, 1998).
  • However, it’s not one single number that every pregnant woman needs to stay below.
  • Lindsay Brin (author of How to Exercise When You’re Expecting) defines the recommended range as the feeling you get when rushing out the door to  slightly tiring exercise but still able to speak full sentences. 
  • I have interpreted the guidelines to mean that I can be slightly winded but not to the extent where I am out of breath or breathing hard on my daily runs.
  • My pre-pregnancy “easy pace” was 8:00-8:15.  It’s currently around 8:45.  But, I don’t run the same pace every day. Some days I feel great and find that my pace is closer to 8:30 while other days 9:00+ feels more comfortable.
  • I head out on most of my runs without my Garmin so I can be more in tune with my body and my breathing without concerning myself about pace.  I am able to determine my average pace when I return from my run (I have certain routes pre-mapped so I know the distance).
What guidelines or advice has your healthcare professional given you?  Did you keep to the 140 bpm while you were pregnant? 

*Note: I am NOT a healthcare professional.  This post is in response to many questions I have received in regards to my running pace during pregnancy.  The below information is what I have learned from my current OB-GYN as well as research on this topic.  Before you engage in physical activity during pregnancy, talk to your doctor about his/her recommendations and guidelines.   

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    56 thoughts on “Running During Pregnancy: Monitoring Exertion

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    2. I am so happy I found this post! I just found out I am pregnant and this morning while doing an Orange Theory workout my HR was in the red (180+ bpm) and I was barely at an 8:30min pace! (I typically do an 8-8:10). I got really worried and slowed my pace down into the 9’s but felt fine! Reading this paragraph makes what I saw this morning w/ my HR total sense:

      Exercise heart rate at one’s usual intensity will be extremely high during the first trimester because there is not enough blood in the system for the heart to pump the usual amount of blood each beat. Therefore, it must pump more often to supply the same amount of blood to the exercising muscles. (Note: This pregnancy effect is so common that women who exercise regularly will often recognize they are pregnant because suddenly their exercise heart rate is sky-high and way of proportion to how they feel)

      I’m meeting with my doctor today but being a runner, I think I need to focus more on how I’m feeling and breathing vs. solely on my HR.

    3. Can you further explain the Borg Index? Did I miss how to actually make the measurement? Is that BPM? I just don’t understand the unit of measure. Eleven what? Stay between 12-15 whats? Thanks!

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    5. Hi, I’m really glad I found this. I’ve been finding it tough to get relatable and current information for athletic mamas! My first pregnancy I ran through the first 8 months.. and now my 2nd pregnancy I feel totally different. I was the slave to the 140 bpm in the gym and hated it. But I never wear a HRM when running. This 2nd time around I am boggled by the incredibly increased heart rate (I’m at 10 wks).. It will stay elevated even 30 min after I’ve finished my morning 6 miler. Its reassuring to know this is a first trimester side effect! Thank you. It keps to keep things in perspective as I continue through and go by how I feel. Thank you again.

      • Hi Karen! Thanks so much for your comment and letting me know that the post has helped/is helping you!! =)
        Congrats on your pregnancy!! Hope you have a safe, healthy, happy pregnancy and that you can run as long as possible =)
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    7. You are a God send! I’m 12 weeks, and I have been struggling with trying to keep myself around 150bpm, but two nights ago my heart rate skyrocketed to 235!! I stopped, walked, brought it down to 170, then started up again and WHAM it was up to 245 this time! I thought my monitor was broken, since I didn’t feel even winded yet. I will definitely be letting my midwife know about this, but reading your blog has made me feel a little less concerned. There’s a very good reason for a higher heart rate, and now that I know what it is I’ll head out on my run today with this in mind.

      …I think it was so cold (-35 with the windchill) that I just really really wanted to run and not walk too…so maybe I was at about a 17 on the scale, probably could have taken it down a notch!

      Thanks for everything, you are a fantastic resource for running mamas! I can see you writing thee game-changing book on exercise and running for pregnant women!
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        • Hey! Thanks for checking in! I’m doing great, actually! I have finally gotten into a running every other day routine and am building up my mileage slowly again. Pace is out the window but that’s ok, I just love the fresh air. I feel so much BETTER after a good run. 5k Winterman race this weekend, and the half marathon in May – fully intend to finish (and RUN) that one at 30 weeks!

          Thanks again for checking back, very sweet! :)

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    10. So glad to have come across this!!!!! I am 11 weeks, and I have only experienced random bouts of fatigue (thank god!). I have been running 5-6 miles a few times a week when I have had the energy really. The first couple of times I would check my coratid pulse for a few seconds…. Knew within seconds I was well beyond 140. I have always been one to push myself running, now I really just listen to myself and slowdown if I feel like I’m pushing it. I can’t imagine how that lil peanut is not loving the surge :). I feel a little better now about continuing to run, hopefully soon the fatigue will be replaced with a surge of energy! Happy Running!!!!

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    12. Great post! I expected my doctor to be more current on this topic – he’s an avid cyclist and exercise advocate – so I was surprised when he told me at my 12 week appointment to keep my HR under 140. I told him my aerobic zone is usually 145-155 and I asked if that was okay. He said I should really aim to keep it under 140. So frustrating! In addition to my summer triathlons (which are out for sure), I run two half marathons a year – one in May and one in November. I continue to train for my May race as I always do – slow and steady – and am walking more to make sure my HR doesn’t creep past 155. I feel GREAT. The thought that my doctor is outdated on this pretty important topic makes me wonder what else he is missing! I am definitely going to check out Clapp’s book and the Runner’s World resource. Thank you!

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    15. This is the method i use as soon as i found out i was pregnant i rushed out to get Exercising through your pregnanancy by Dr Clapp as well as Runners world guide to running while pregnant by Chris Lundgren. Both were sooooo beneficial.

      I luckily also have a very liberal doctor and she uses the Borg method and basically said i can do anything i want exercise wise as long as i listen to my body and can still hold a conversation and stay between 12-15 as well. I also find warming up 5 min with a walk before i start running helps too and then cooling down with a walk for 5 min. Which really is something most of us should be doing anyways especially if we are sitting at a desk all day,…hello tight hip flexors! My physio and chiro have always said walk before…but i only did about 2 min and then was so antsy to run!

      I have had a few people ask me whether or not it was ok for the baby to run…they haven’t full out been mean about it but were very questioning as to whether it was ok…but i dont let that get me down. I will keep running as long as my body and baby are ok with it.

      I also have maintained my biking, yoga and weight lifting circuit training as well. I am feeling great and energized:)

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    17. I really like this post. I am always worried about my exercise these days. My doctor is like if you feel good after 3 miles keep going if you want. She has been pretty liberal with it. I appreciate that. I have noticed in the past week and a half that I am able to exercise with much more ease. Today I did 3 miles. It was a speed workout for sure for me. I was winded and sweaty for sure but felt good at the end – never any weird pains and recovered in a minute of walking. Then some days forget I don’t even try. But I never know if what I am doing is ok or not or what. everyone is always saying somethign different it seems to me.
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    18. No offense to doctors but as someone who deals with them daily for my work in Cardiac Rehab, the majority of them don’t know much about exercise. They consult the outdated books and see 140 bpm for pregnancy. The RPE scale is much better for gauging exertion. The real key is listening to your body.
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      • Agree x 100. The 140 bpm is severely outdated information – over 25 years! I’m astounded at the number of emails and comments I have gotten recently that indicated doctors still recommending that #. And I agree – your body will tell you when it’s too much or too fast.

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    20. What a really great post for future mamas! Very informative and filled with a lot of good resources. A lot of people get “funny” about pregnant women doing things sometimes, but at least we’ve come a long way in the Western world from the olden ways of being “in confinement”. You go girl!
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      • Oh I agree!! Thankfully I haven’t gotten too much flack about running during pregnancy. During my first, I directed people to Kara Goucher and Paula Radcliffe – they had the best doctors monitoring them so obviously if it was unsafe, they would have stopped!! =) And thank you for your sweet comment!
        nycrunningmama recently posted..Running During Pregnancy: Monitoring ExertionMy Profile

    21. An interesting read….my sister is scheduled for a c-section tomorrow (is at full term) and just jogged 3 miles today! She has run almost daily throughout her pregnancy (maintaining a slow pace and not in great heat) so I’m going to send this to her. I think she’ll have a lot to say on the matter after having gone through it as well!
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      • Congrats, again, to your sister!! I hope the c-section went well today =) And kudos to your sis for running the day before she had her c-section! That is awesome.

    22. Great post! I feel like so much information out there is antiquated in regards to exercise during pregnancy. Nice to see there is some new info popping up:-)
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    23. Thank you for this post!! I am currently 9 weeks, and I feel like my heart rate is crazy high compared to my exertion! I just read Chris Lundgren’s book, and i found the information regarding exertion sooo helpful. I wasn’t in this good of shape with babies #1 and #2, and I run about 25-30 miles a week now. I feel my pace has slipped about 30 sec/mile..but i feel great on my runs. I get out of breath running up steep hills, so now i just walk if i need to. I thank you sincerely for getting this type of information out there:)

      • Oh I’m so glad that this may help you!! The first trimester is/was always the toughest for me in regards to running. Some days I stopped after 1/2 mile b/c my HR was out of control. I just didn’t feel right. But running in the 2nd trimester is awesome – you’ll love it. You don’t even feel like you are pregnant for most of it =)

        • I’m reading all the reader comments and your comment about running in the 2nd trimester is awesome got me excited! I won’t hit that until late January but it’s something to look forward to!

      • It’s crazy that it was changed over 25 years ago and it’s still being used. When my dr told me, I didn’t think twice. He has been around for over 35 years and I trusted him implicitly. I probably should have done a bit more research but felt comfortable with what he prescribed. You live, you learn, right? =)

    24. This is going in my bookmarks for when baby #3 happens! I think the most important part of being a fit pregnant woman is listening to your body. It’s really great at telling you when you should chill or when you can push a little harder. There are a lot of outdated guidelines out there…and they’re usually passed down from mom to mom. Thanks for sharing this since we’re surrounded by so many pregnant fit mommas recently!
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      • Agree, Melissa!! Our bodies let us know when we are pushing too much. There’s just that feeling we get that we need to pull back. Can’t wait to follow your running when you get pregnant =) =)

    25. I also had a doc who used the 140 rule, then did my own research. When I learned it was outdated way back to 1985, I was pretty angry, honestly. Get with it, docs! I took that info to him and then just went by perceived exertion. I was also really cautious about heat in the 1st trimester especially. One thing is for sure–it is constantly evolving and we have to stay on top of it ourselves, not count on the doctors to do the homework for us.
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      • I was so mad at myself when I found all of this out b/c it was after AJ was born. I definitely should have done more research during pregnancy #1. I did a ton on running while pregnant but didn’t pay much attention to the HR rule.

    26. Thanks for going to all the trouble to put all this helpful information out there!! I knew that the info was outdated from the old 140bpm time period, but I really had nothing new to go on and felt that from going through other pregnancies I would recognize when it was time for me to slow down or stop. Having some better guidelines is very helpful to a lot of people I am sure! I am pretty close to the end now – due in 2 1/2 weeks – so I’m just trying to still get out there for a run, and even 12 minute pace is starting to feel tough!! :)
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      • Oh girl, everything feels tough at the end! LOL. You’ve got a watermelon in there! But you are still out there running and that is what matters =)
        So excited for you!!! I’m happy to start the 3rd trimester tomorrow – yay!!! The end is getting near! LOL

    27. I LOVE this post! What you explained is how I exercised during pregnancy. While I stopped running (had to take a 5 month break because I was SO DANG SICK) I continued weight lifting and interval training until the day I delivered. I think seeing how science has evolved is fascinating. You go mama!
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      • YES!! Me too =) I spent most of the 1st trimester with my 1st child doing a run/walk b/c I couldn’t keep my HR under 140!!! You live, you learn =)
        I hope you are feeling great – and congrats on continuing to run !!! You go, mama!

    28. This is a really interesting post. Although I am not pregnant (and likely won’t be for a few more years) my cardio team LOVES to talk about pregnancy when I come in for 6 month appt. There have been lots of talks about how active I will be able to be while pregnant, if I will require bed rest, if I will need a scheduled C-section, etc. The list is long and there are lots of unknowns for me in that department, b/c every woman’s body is different and we really know how my heart will react to those changes until it happens. This is all great info to have because I would love to be at least moderately active if and when the time comes!
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    29. great post! I wore a heart rate monitor once at the beginning of my pregnancy and quickly realized that that couldn’t possibly be correct. After doing some reading I figured out what you basically just posted. I just go with how I’m feeling. I don’t push myself to the extreme, I just try to enjoy my runs!
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