Why Your Heart Rate Varies

This will be an interesting week with running. It’s gonna be hot and humid and I’m sure my heart rate will skyrocket! Or will it? Does it even matter?

Maybe it doesn’t; some of my research said it really doesn’t. I just like to understand things. I have a curious mind. Definitely still no expert, but I found a few interesting things.

Heat increases HR
Hardly shocking, right? According to this post here:

You can plan to add 2-4 beats per minute when the temperatures rise from 60-75* and another 10 beats per minute when temperatures soar from 75-90

This does not explain my recent HR variations.

Another nugget from the same post:

As you become dehydrated, blood volume decreases and less blood is pumped with each stroke.

A fluid loss of as little as 1% can cause your heart rate to raise 7 beats per minute.

I am a thirsty runner. I hydrate before my run, I’ll do Nuun the day before hot runs — I used to do Nuun before on the day of hot runs — this may be another thing for me to explore.

Cardiac Drift/Creep
I actually am aware of this one, I mentioned it recently. From this post here:

However, exercise research has shown that it is common to see heart rate “drift” upward during an easy or threshold run, even with no increase in pace of effort – sometimes by as much as 10-20 beats per minute over a 30 minute period.

Hmmm. Now we’re getting closer, maybe. That post goes on to say within 30 minutes your HR might increase 20 beats, but if you slow down you won’t get the best bang for your exercise buck — if you catch my drift (pun intended).

What’s a hot runner to do?
I also found this post here:

 Studies have shown that when the temperature rises above 65 degrees, your heartrate will also rise by about 10 beats per minute and performances will slow. If the humidity is also high, add another 10 or so beats to that number. My own experience tells me that under these types of conditions, my average pace will often be off by 10 to 20 seconds per mile at the same effort level. What does this mean? In short, slow down.

He actually goes on to write:

If your average heartrate on a typical tempo run performed under near-ideal conditions is in the range of 165 to 170 beats per minute, on a hot, humid day, trying to maintain that type of effort will yield a number in the neighborhood of 190. While you do everything in your power to stay “on pace,” you’ll also be working dangerously close to your max heartrate and exerting yourself at an effort level that’s much greater than it should be for that given workout–or is even safe, for that matter.

The interesting thing (to me, anyway) was that I gave myself some leeway and assumed my HR would be higher than normal. I ended my last run feeling just fine, too (and with a decent pace for the last mile when I just sorta let er rip)>

Other reasons your heart rate might be higher than normal
Heat and humidity aren’t the only things that drive your heart rate up. Other things that may effect it:

  • Caffeine
  • Stress
  • Dehydration
  • Lack of sleep
  • Anemia
  • Thyroid problems

There’s even a few more reason in this post here.

Final Thoughts
I’m not worried, but I am still curious! I don’t feel the need to see a doctor. I also looked back at some of my runs from July and August last year. There were several where I also had a high heart rate, but for the most part they were pretty normal for me. I haven’t really come to any conclusions yet!

The interesting thing is it’s been one year since my mom broke her hip — so there absolutely was lots of stress in my life last Summer! I am running more monthly miles this year — simply by running longer long runs. Definitely not racking up a lot of miles, though.

What makes you go hmmm about running?

Do you want to know why it happens?


Linking up with Zenaida Arroyo and Kim @ Kookyrunner

This week I am also joining up with the new Runners’ Roundup linkup.


23 thoughts on “Why Your Heart Rate Varies

  1. This is interesting, Judy! I like how you dig into things.

    I had similar questions about my resting heart rate.
    Kai and I both wear out watches 24/7, so it’s easy to read the resting heart rate over a 7-day period. Kai’s is about 10 beats higher than mine, although we have very similar habits.

    When Kai had a routine appointment with the cardiologist, I asked the doctor about it. He said that that is quite normal – people’s resting heart rates differ from each other and it’s no reason to worry.
    I still think it’s a bit weird, though!

    Liked by 1 person

    1. I don’t really worry about mine unless there’s a big jump (resting heart rate that is). I does go up & down — but you can see it with the vaccine & boosters, for instance. They’d make me really sick & my RHR would go up more than 10 beats overnight. I knew why though!

      Liked by 1 person

  2. My Garmin doesn’t read heart rate. My Apple Watch does but I don’t like to track my runs. And I barely have time to breathe most days and don’t have time to analyze stats on all my runs. But many runners do.

    I’m not saying heart rate isn’t important. I mean a guy just died during a 5k I ran.

    I’ve always had a high resting heart rate. And my hubby very low. As Catrina says that’s normal. Not worried!

    Liked by 1 person

    1. My RHR is higher than some runners, but I just know what’s normal for me. So I don’t really worry much about it unless I see a really big jump. Almost never happens, but it has with the vaccines, as I wrote to Catrina — so it’s a good thing for me to watch. Not saying that anyone else has to!


  3. Interesting! I have a HR-related tidbit you’ll like. My 16-year-old (a long-distance runner) has a super-low resting heart rate (I’ve seen it dip briefly as low as 38 when she was in the hospital hooked up to a HR monitor). They’ve done 2 EKG’s and both were normal. She just has a very efficient heart!

    Liked by 1 person

    1. My WW leader also has a very low RHR — although not as low as your daughter’s! Truly I think it’s all about what’s normal for you.

      I did have one aunt who had a very bad heart attack in her mid 80s, and an uncle who died young from a massive heart attack — both smokers, though. Obviously my parents are/were long lived!

      Liked by 1 person

  4. I’ve noticed that my heart rate spikes quickly when I’m running during my OTF classes. After reading your blog, I think this mainly due to dehydration (since I take class fasted) and because I’m still wearing a mask which makes me hot. This is really good information to know. Thanks!

    Liked by 1 person

  5. I had an issue with my heart rate being way higher than normal during my runs back in… February maybe? The only reason I checked it was because I was feeling like i was working way too hard, so something was definitely wrong. I decided it was dehydration, but then later I read about some runners having a high heart rate after having Covid…. and I had Covid in December. So, who knows? It eventually returned to normal. At least I assume it’s normal- I’m not checking it, but I feel fine.

    Liked by 1 person

  6. I don’t always wear my chest strap, so I don’t pay too much attention to my HR. I guess i just expect it to be higher in the heat. But this is interesting stuff to read about!

    Liked by 1 person

  7. I’ve had some weird fluctuations in my heart rate over the past year–that race in Georgia really threw me! I think the heat had something to do with it, but it sure was odd. I chalk it up to old age and just monitor it when I’m running. In fact, I have my Garmin set up to show my HR on the face.

    Liked by 1 person

  8. I noticed my new Garmin has a LOT of stats when I scroll through the settings, etc. Someday, I’m hoping to look at the heart rate stuff a little closer…there’s probably some valuable info there that I should be aware of.

    Liked by 1 person

    1. Well, if it ain’t broke . . . I’m not at all suggesting that everyone pay attention to HR, although I really do think it’s a good metric to see if you’ve really recovered or not.

      Wouldn’t mean not running but running easier. You seem pretty in touch with your body, Kim!


  9. I look at my heart rate stats after my run, and I think it is normal? Someone else wrote about this topic before and I said I was going to start wearing my watch 24/7 to get more information about my heart rate. I still haven’t. It is a habit I have that when I come home after my run, I take it off.

    Liked by 1 person

  10. Very interesting topic, Judy! Although my running Garmin has a heart rate monitor I just recently started looking at the stats, mainly because my husband was talking about it a lot and I wanted to compare notes. I just ordered a heart rate monitor for my bike Garmin that’s supposed to be delivered this evening. It will be interesting to track it a little more closely.

    Liked by 1 person

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s