Originally Posted by Artmo

I ride with a bunch of oldies, age range 65-79, at 16-19 mph, 3x 25-35 miles per week. (I'm 72) About half use HRMs, including myself. Three of us have intermittent a-fib, so it's useful to know when this occurs, so we ease off the pace. It happened to me this morning: my wife and I on our tandem were pulling the group at 18+mph, with my HR around 135, when it suddenly shot up to 185. We dropped off the paceline, and after a few minutes it was back to 135.

As mentioned above, a HRM is also very useful for training and for measuring performance improvement.