Measuring Exertion in Pregnancy! (Without Heart Rate)

When Measuring Exertion in Pregnancy, Heart Rate is NOT useful.

If you're a Pelvic Floored Pro, or VIP (Very Important Pelvis, Newsletter Subscriber), you may have seen my new post on Heart Rate Changes in Pregnancy. That gem went over WHY our heart rate is faster earlier in pregnancy, and slower later in pregnancy. If you're new, WELCOME!! That little gem is DEFINITELY worth a read sometime, if you have a few minutes :) 

That post explains that, due to a variety of reasons, as our pregnancy progresses, heart rate is no longer a reliable indicator of 'how hard' you are working out when pregnant, and we can't use it.

THIS POST explains that, luckily, there is another option besides using our heart rate, for figuring out how hard we should be exercising while pregnant. It's called the Relative Perceived Exertion, or Rating of Perceived Exertion, but the cool kids (that's YOU and ME!!) call it "the RPE scale."

Rating of Perceived Exertion

The Rating of Perceived Exertion Scale (RPE) is a way to monitor 'how hard' you are working out. The original scale was 0-20, but "science people" quickly figured out that using a 0-10 scale was easier for 'real people' to make sense of.  Here's what the numbers translate to:

1. No Exertion at all. You're dead, or resting fully.
2. Very Light
3. Light. We can carry on a normal conversation here.
4. Moderate. Think of '3 sets of 15-20' here, as long as you have a nice muscle burn at the end of them. If you don't have a nice burn at the end, those 3 sets of 15-20 might actually be light.
5. Somewhat Hard. Now we're breathing heavy, and starting to sweat. Talking is harder.
6. Hard. We can't talk while we are working out, or "doing the thing".
7-8. Very Hard. This is where most of us tend to self-limit our workouts. Not only can we not talk. We can't really think about anything else than the task at hand.
9. Very, Very, Hard. You are running for your life, or lifting a car off of an injured child.
10. Max Effort. You cannot maintain this for longer than 1-2 minutes.  You WILL start to throw up if you stay here for much longer.

But isn't this just 'my opinion' of how hard I'm working out?

Yes, and that's the beauty of it.

To quote Albus Dumbledore in Harry Potter "Just because it's in your head, doesn't mean it's not real."  Many Studies, including, Lea, et al, 2021 (full reference included at end of post),  have shown that RPE is a valid and reliable measure for assessing workout intensity, meaning that while it make take you 1-2 practice workouts to figure out what "medium intensity" really means to you... but after that, your "medium intensity" really will correlate to 60% intensity of your max heart rate, and a "medium intensity heart rate" exertion levels when you're not pregnant.  And more importantly, it helps you adjust your workout to what your body needs, and what is appropriate for your body, at any given stage of pregnancy (or life, to be honest).  And even more importantly, that "percentage relationship" will continue to be accurate as you travel through the second and third trimester...and even through the fourth trimester and beyond, so THE RPE SCALE is in fact THE PERFECT WAY to measure your exertion while exercising while pregnant!!

So, when we're pregnant, and can't use Heart Rate as a marker, we can use the RPE!

Now, in case you missed the last blog, here's a general explanation of how heart range response to exercise will change in pregnancy 

Early in Pregnancy, Heart Rates will be elevated, even with "easy" tasks.

Here, we might perceive even easy tasks (like walking around the house) as 'moderately hard' to 'hard.'  That's because the amount of blood in our body is increasing (to grow another human), and the the pliability (loosey-goosey-ness) of our blood vessels have increased (to grow another human) and our body doesn't yet know how to manage this...so our heart beats SUPER FAST...even with "easy" things....so "things we would have previously considered to be 'easy' now become hard".

We can help our heart here in early pregnancy by working out in water, if we have that available to us. The pressure of the water compensates for the looseness in the blood vessels, and helps our heart react more efficiently.

Need ideas for exercising early in pregnancy?  I've got you! Check out these options from my Instagram Account, @therealpelvicfloored. This water workout includes whole body, another option is mostly legs, and here's one that lets you 'play' with older kids WHILE you get a workout in! 

Later in Pregnancy, Heart Rates will be lower, even with hard tasks.

And here is where the RPE scale REALLY matters. Because if you were chained to your heart rate monitor to 'know' if you are working hard enough...no matter how hard you work, your heart rate might not increase to those target levels. And if you push, push, PUSH to try to get there, you might injury yourself.

But, by using RPE, you can easily decide when you are working out moderately hard to hard!!

There is no "percentage" that the heart rate will reduce vs pre-pregnancy. In fact, your actual heart rate at 'moderately hard to hard' exertions might vary significantly based on temperature, hydration levels.

Exercise Modifications for Later in Pregnancy

As the heart rate isn't so reliable here, I do LOVE strength training (all the time), but especially in mid to late pregnancy. You'll be lugging around beautiful baby in a car seat before too long, so let's get you ready for the challenge!  My IG account (& this blog) has lots of fun, free info, and while I did have a stand alone Pregnancy Weight Lifting course (that was featured on the Morning Chalk Up, if I'm allowed to brag a bit :), at one point, in 2025, In order to improve access to individuals of ALL socio-economic levels, I moved that course into "Dr. Kelly's Treasure Chest, which you can access for a monthly fee of just US$9.99/month.   As with all courses, it's streamable on your computer, and phone and tablet via the Kajabi App, so your workout (and my coaching) is never more than one click away!!  

And, of course, as pregnancy continues, we do want to ensure that our pelvic floor muscles remain RELAXED and HEALTHY, to optimize delivery. So while weight lifting is vital to a health pregnancy, please be sure to also make time for some pelvic floor relaxation ("down-training" is what we pelvic pros call it) every day.  Poke around the blog for other ideas, but here's one of my favorite pelvic floor awareness exercises are here, and if you are excited to do EVERYTHING possible to prepare for your best delivery, my world-famous Push Prep Course is just one-click away.  (And YES, friends, I will eventually get it bundled in the Treasure Chest, too...but I'm trying to figure out how to set a price point that gets this info to as many pelvises as possible, while working and being a mom, so I appreciate your patients with me :). As always, I'm imperfect and ever so grateful that you are here with me, and that I get to be a part of your story and journey.  

I hope this post has given you more confidence in how to exercise safely in pregnancy, for a healthier YOU and healthier baby.  THANK YOU FOR BEING here.  If this was helpful to you at all, please consider sharing it with your circle, either via email, or on your socials, as the more people we have spreading this information, the better.  If it wasn't helpful, I would honestly sincerely like to hear from you as to why--was it too science-y?  Too long?  Too short??  Not enough boob shots?  Had you heard it before? Let me know, as it's my mission to help and entertain people, so your feedback is ever-so-important to me. 

XOXO

Dr. Kelly 

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Fellow Geeks, It's True, You Can Look it Up, Or Better Yet, Make Your OWN Blog on Your Website or Socials!!! Spread the Word About Good Science!!

Lea JWD, O'Driscoll JM, Coleman DA, Wiles JD. Validity and reliability of RPE as a measure of intensity during isometric wall squat exercise. J Clin Transl Res. 2021 Mar 24;7(2):248-256. PMID: 34104828; PMCID: PMC8177844. link here