This year I noticed my avg HR during my rides was from 150's to 175 bpm (this was the average for the ride) and spiking as high as 206. I'll be 70 next month, and in the past years I would occasionally check my HR and it would be in the 120bpm range average for my rides.
Long story short, went to the DR and turned out I have afib. They did a cardioversion and now my HR is back to normal. My ride avg HR now is back in the 110-120 range. Resting HR now in the 40bpm range.
Al