I used to go to an elementary school in Tacoma by the name of Christensen. There was a track around the playground. Christensen promoted health and fitness by creating a Track program. A mile would consists of 12 laps. A student would be enforced positively by running a certain amount of miles during recess. There were awards like a pencil (10 miles), pizza party (75 miles), name in the gym (125), medal (200), etc. And the great thing about this was that it was voluntary.
Students were being reinforced positively by being rewarded for staying active during recess.