You should do it against the clock. Say you are going to do 30 laps in 15 minutes. Then you try to do it each day a little faster. That is putting demands on the body, and that is how you build up. You keep up your energy instead of going downhill.
Jack LaLanneIf you can't afford a half hour three or four times a week taking care of the most priceless possession, your body, you've got to be sick. You're stupid.
Jack LaLanne