I’ve got lots of hills around me in the Seattle area. One of my favorites for training is over 1.5 miles long and 6% grade with a good bike path shoulder. Depending on how hard I go on it, I can get most any heart rate zone or power zone I’m looking to achieve, including max rates. From my experience, wrist based HR sensors aren’t good enough. I have a Garmin chest HR sensor that I’ve never had dropouts or wild fluctuations that I’ve seen with wrist sensors.

Mark