At a prison about three hours drive from Sao Paulo in Brazil, inmates are taking part in an innovative and voluntary new programme - spending their time pedalling on stationary bikes.
But it is not just about the exercise.
For every pedal, prisoners charge car batteries attached to the bikes. And at night, these batteries power the lights at a local park that previously did not have electricity.
Al Jazeera's Gabriel Elizondo reports from Santa Rita do Sapucaí.