I have been noticing recently with the Whoop 5.0 on my bicep while rowing indoors and outdoors, that the HR readings have been really variable compared to what I am getting on my Garmin on my wrist or what I was getting on my Coros bicep hr band.
During steady state, it would gradually follow my HR up to mid 140s and then jump to 170, stay there for a couple seconds that gradually work it way back down to like the low 120s and sit there for a couple minutes. This is all while I am keeping the same physical output on the water or on the erg.
What could be the issue for this. I do not think its a fit or placement issue since I tested with my Coros bicep hr band in the same sport during similar workouts, indoors and outside, and it has been pretty steady and consistent with what I am feeling and what I was seeing with my Polar H10 chest strap (+/- 1bpm).