Back in my youth (late 20's) I was in my best condition ever. I would ride my bike 3 days a week to a workout class at the junior college, then run a 5K, workout, and ride home. The ride was from sea level to the top of a hill in Redwood City up a very steep street. My highest heart rate was maybe 172. Later in life as a mailman, I walked well over 50,000 miles, and my resting heart rate was in low 40's, sometimes high 30's. Then a cardiologist found that my heart stopped for up to 4 seconds at a time while resting and put me on a pacemaker. After a while I convinced them to raise my max ceiling up to 150 to aid in riding my bike. A couple of days ago I did the Kilo track race in my Wahoo Systm trial and my heart got to 156.