Originally Posted by Random11

As a former runner who recently turned to cycling, I can assure you that running uses far more energy. As a runner, one of my goals was to run a marathon (I eventually did five), and when I picked up cycling, I viewed riding a century as a similar goal, which I accomplished last year. It is much easier to ride 100 miles than to run 26. It took me several weeks to recover from my marathons, but the day after my century I was riding as usual. Also relevant to the comparison, I ran my last marathon at age 40, and I was 70 when I rode my century last year.