A fellow blogger has noted a correlation between enjoyment of exercise (or is it travel?) and the ability to measure it. I must admit that I have a hard time arranging to exercise, but I like to measure travel. I feel lost if my car’s clock or odometer are broken or somehow unreadable.
As for exercise, I find the most effective are swimming and downhill skiing: in both cases I put myself in a risky situation (drowning, falling down a steep hill) and I must exercise my way out of it!