Scott mentioned above that he noticed his resting heart rate dropped upon returning to training following a layoff, which made me think about something I’ve noticed.
After a fairly short layoff (maybe about 1-2 weeks), I notice that my heart rate seems higher than usual for a given (low) intensity. After a few days, it seems to return to the levels that I’m used to seeing during training, or even lower.
For example, I recently had a few days off due to a cold and took about a week of easier recovery after that. (I had been kind of hanging it out there doing big days and racing for a few weeks in a row, so pushing overtraining wasn’t a huge surprise.) As mentioned, upon returning to training, my heart rate was high during workouts, but now, after a fairly big week (for me, ~14hrs, 60miles, 14k’) of mountain running, including a couple of higher intesity interval running and ME workouts (both mostly new territory for me), my heart rate is pretty low again. I’ve even noticed my HR is lower than it has been in the past on the same trails at the same speeds, or even slightly faster (during fully Z1 workouts). Feeling pretty good still, for what it’s worth.
I’ve introduced some intensity recently and I’m maintaining a high easy aerobic volume, similar to what Scott S. described, but I don’t track RHR for the reasons mentioned. Perhaps I digress, just thought I’d add an anecdote. This sounds like it could be a related adaptation?