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!! Check out that post first (it's a quick read), then come back!

Due to those changes, heart rate is no longer a reliable indicator of 'how hard' you are working out when pregnant, and we can't use it.

Luckily there is another option for measuring exertion when working out while pregnant. It's called the Relative Perceived Exertion, or Rating of Perceived Exertion, but the cool kids 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 found out that 0-10 was easier for 'real people' to make sense of--and I 100% concur--I can figure out how hard 5 is working vs 0 and 10...but not 8 vs 17....

In essence, The Rating of Perceived Exertion Scale (RPE Scale) is a scale of 0-10, and my Pelvic Floored Verbiage, explaining what each number means, follows:

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 have shown that RPE is a valid and reliable measure for assessing workout intensity. Non-geeks, skip these next few blocks and get to how you adjust your workouts. For my fellow Geeks, here's a fun read for your spare time Lea, et al, 2021. 

The long and short of it is that, yes, it make take you 1-2 practices to guage your RPE, but after that, your RPE does indeed correspond to heart rates of those exertion levels when we'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)

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.'

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? Check out these options from my Instagram Account, @therealpelvicfloored. This water workout includes whole body, another option is mostly legs, this one is mostly arms, 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 those arms and legs ready for the challenge! Pelvic Floored's Pregnancy Course (formerly, Your RAD Pregnancy) includes full workouts for each trimester, with rationale for why we do (or don't) modify a particular exercise as your beautiful body changes.  It also includes a handy "exercise substitution" segment where you can pick a substitution exercise easily if your programmed workout (or class) is doing something you don't want to do.  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 down training here (but if you're preggers, you'll have to do the down training from a sitting position :).  And of course, my world-famous Push Prep Course teaches you all this AND MORE.

K--I hope this gives you more confidence in how to exercise safely in pregnancy, for a healthier YOU and healthier baby.  THANK YOU FOR BEING here.  I am grateful that I get to be a part of your journey

xoxo, Dr. Kelly 😊

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References

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