Originally Posted by huffman
I have a Polar S150 that registered a max HR of 216 while mountain biking yesterday.
My S210 regularly gives whack-o readings like this. So much so that the Max Heart Rate function is useless. It really annoys me... I'd like to know my MHR from the attack on the climb when I had other things to do besides check my HRM. Instead... 233. BULL*****!!! Sorry. I had to vent a little.
Almost all of the previous posters reasons are causes for me to. Power lines are the most common. It's much worse if the battery in the transmitter is weak. Or if it's particularly cold out (maybe the battery gets cold, weakening it, or maybe it's because of the associated dry air and increased static electricity). The strap has to be good and snug, and using the transmitter strap jelly helps... if the signal from your heart is weak the HRM seems more susceptible to picking up BS signals.