Mine was actually getting a bit too low, and I was feeling sluggish much of the time, until I realized that this was a known effect of beta-blockers for BP medication. I saw my regular doctor about it and he was surprised -- said there was no reason I need to be on a beta blocker and he would not prescribe it to any of his more active patients (I'm a runner as well). He switched me to another combo of BP meds and now my HR acts more normally (still in the 50s at rest, but at least it speeds up when needed).