Overtraining or dodgy heart rate monitor - lower than usual exercise heart rate

Could this simply be increasing fitness? Five months is certainly long enough to see a gradual drop in both resting heart rate and exercise heart rate at the same level of intensity/perceived exertion. Of course it's not going to be an across the board, every day drop, but if on average it is lower, my guess is that it is fitness-related.

If not, and it's associated on those days with going slower, feeling tired, etc. then could be a fatigue issue. In that case the solution is obvious--back off a little; take regular rest days.

Another possibility is that something random is going on that you're not aware of. In particular, temperature, hydration, and caffeine intake (or lack thereof) can affect heart rate, definitely as much as the difference you describe. I usually train in pretty extreme heat/humidity in Vietnam; on the rare cool morning there, or at home in Oregon, my HR will easily be 10-20 beats lower at the same pace. Also, if you normally have coffee before a morning workout and you didn't on some days, that could make your exercise HR lower than usual--probably not a matter of 10-25 BPM though, unless you're really sensitive to the stuff. Dehydration can also jack up HR. Maybe on the low HR days, you are better hydrated? It would make a difference of 10-25 BPM in my case over a longer workout (2 hours plus) when training in the tropics; don't know about elsewhere.

ETA If it were a HR monitor issue it probably wouldn't be consistent across two monitors. When there's an issue, it typically involves random spikes and dips in heart rate which aren't related to changes in workout intensity or feelings of well-being. For example, when one of my old monitors was on the blink (dying sensor battery), it would sometimes spike to 212 (when I'd never gotten over 190 before, and that was toward the end of a hard tempo run in 100+ degree heat when I was almost hit by a motorbike!) and then declare me clinically dead for up to 5 minutes (HR=0). All the while I'm just tooling along at a moderate pace feeling perfectly fine. Those issues can be caused by electrical interference (from high-tension lines, electronics on people passing by, or even static from quick-dry shirts), battery problems, etc.

Edited by Hot Runner 2016-02-20 5:08 AM

Sounds to me like you're getting fit. Since you're using garmin devices, check your trending on garminconnect to see your heart rate has been trending downward over the last five months. I'd be willing to bet it has. . If you feel it's overtraining, take four days off and see if things change. From the info you've provided, it sounds like your aerobic base is improving. And as always, check with your doc if you still feel uneasy about it..

Edited by mdg2003 2016-02-20 12:49 PM