Originally Posted by Moishe

I (68) ran regularly for 40 years and stopped completely a few years ago. I now bike about 4,500 miles a year. The difference between the two activities is this: I really enjoy cycling while I'm doing it, for hours on end. I explain why I've run for so many years with the classic joke about the guy who goes to the doctor and complains that he keeps banging his head against the wall; when asked why he keeps banging his head against the wall, the man says "Because it feels so good when I stop." Credit to Billymc above for telling this joke with extreme efficiency. I ran for 40 years because it always felt good to have finished a good cardio workout even though it sucked while I was running.