On bit of a heads up: I use a polar HR monitor with a chest strap ( they apparently are more accurate than the wrist sensor ones). I too need to worry about HR spikes. Early this spring (cold=no sweat) was riding on the road and a couple times when was going 20-25+ mph the HR suddenly spiked at like 200...freaked me out.
Long story short. If it's low humidity and you are wearing a synthetic shirt and the wind is moving it around you can get a static situation which will screw up the HR reading ( I found this the fine print on the Polar web site.) The solution is to put a bit on water on the shirt over the chest band....or sweat
and you may want to read this:
https://www.mdedge.com/cardiology/ar...y-high-af-risk
may be a reason to use HR monitor