Some hearts are just different from others. I took a stress test at the doctor's office some time ago. They kept me on the machine for 15 minutes adjusting the incline and speed bit by bit. The two technicians finally looked at each other and said "it's not going to happen." They were trying to push my heart rate to a certain point and it simply would not go. I have enjoyed cycling and the benefits of cycling without ever having measured my heart rate. I am not sure what I'd do with the numbers if I had them.