Why is my resting heart rate going up?


When I first got my Fitbit tracker, back when I first began seriously training as an endurance runner, it initially showed my resting heart rate’s (RHR) beats per minute (BPM) in the high 60’s.

As I continued training, my resting heart rate came down and settled around the high 50’s. Sometimes it would drift up, but often it came back down to around that number.

I noticed that generally it would increase during times of substantial stress, and that it would decrease with proper rest and exercise.

Suddenly, during the late summer and early fall, my resting heart rate started slowly climbing. Suddenly it settled into the mid 60’s and nothing I thought to do could bring it down. Resting more didn’t help. Eating more or less or better didn’t help. Exercising more or less didn’t seem to help.

At some point, not at the same time as last year, it began to come down again and settled around the high 50’s, low 60’s.

And now my resting heart rate’s risen again. It had settled around 65 for several weeks, and nothing I’ve done has gotten it to move. Now suddenly it’s climbed to 68… but at the same time I think I realized what has caused it to increase.

It’s not a lack of rest: I’ve actually slept rather well, and I haven’t trained at anywhere near the volume I’ve trained before. Outside of residual soreness from workouts and Sunday’s cross country race I haven’t been all that sore, tired or hurting. My energy levels by and large have been great.

It’s not a lack of exercise. I’ve now ramped back up to about 25-30 miles per week, and I’ve done multiple speedwork sessions as well as some long runs. The only difference from my last training cycle is I’ve taken days off and not held myself to much of a strict training schedule.

It’s not even post-marathon weight gain. I’ve had my RHR go lower even after gaining weight, and I’ve had it rise after losing weight. There’s not much correlation between my resting heart rate and my current weight.

It’s not illness. I haven’t been sick and I’m not sick right now. I don’t feel any passive symptoms like unusual tiredness or soreness. I’m in good health on that front.

It’s two things.

1) I’ve let my diet slip a bit. I’ve taken an extended victory tour when it comes to fried and fast food following my marathon effort. I still largely eat clean, but I’ve had stretches where I’m subsisting more on processed food than is probably necessary.

Sometimes, intermittent fasting can offset this by helping the body’s hormonal functions reset during the fasted state. But to be honest, while my lunch efforts to eat clean have been solid (and I generally skip breakfast by intermittent fasting), there’s been a few too many dinners of something like pizza, and I even had McDonald’s as a treat a couple times.

This can affect the function of your organs and increase the viscosity of your blood, as it has to deal with an ingested excess of chemically processed crap. Your heart now has to pump harder to keep things moving, hence a higher resting heart rate.

It’s easy to fix and clean up. I just need to lean back onto daily habits and bake/boil dinner at home every night. My resting heart rate is telling me that I’ve overkilled lately and that it’s time to clean up. Flushing the processed waste with strict, cleaner eating can correct that.

2) Reduced water intake. Remember when I mentioned blood viscosity? Well, nothing increases blood viscosity faster than a reduction of hydration. I haven’t been particularly thirsty (thanks in no small part to Chicago getting cold), and so I haven’t put down as much water as before. I’m sure the overall water content of my blood has gone down, and now the heart’s had to work more to keep the thicker blood moving.

If I make sure to drink more water going forward, my RHR should go back down.

Of course, any of my positive contributing habits need to remain for this to be effective.

I need to continue balancing running and activity with sufficient rest. I need to eat sufficient protein and other nutrients. Fasting in lieu of breakfast remains a good idea.

If I make sure to end the post-marathon honeymoon with my diet and clean it up, plus drink more water every day, my heart rate should come back down to the high 50’s in a couple weeks.

At least now I have a better idea of what insidious factors cause my resting heart rate to go up, as well as what else I can do to help bring it back down.

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