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.