Solution to Overpopulated Prisons and Energy Crisis

It has occurred to me that the media keep harking on about:

Overcrowded Prisons - too many folk locked up

Obesity Crisis - we're all eating too much cake

Energy Shortage - either we need more batteries or a Nuclear Power Station or ten.

Now it seems to me the solution to all these problems is simple - get all the folk in the prisons on exercise bikes generating energy for the national grid - it will keep them slim and mean we don't need to start illegal wars for oil. Sorted.

Next time I'll sort out global warming...