Prisoners in a jail in Brazil will have a day shaved from their sentence for every 16 hours they spend pedalling on a stationary bike rigged up to a generator.
The generators power lightbulbs in Santa Rita do Sapucai prison.
According to a report in the Jornal Nacional, the city's judge instated the policy, but prison only has two bikes so far. The paper says that at the moment, a full day can power six lightbulbs, but doesn't say how long for.
Prisoners are so keen to sign up though, that the prison will install another eight bikes.
Judge Jose Henrique Mallmann told the paper that he got the idea from reading about a similar programme in Arizona on the Internet.
At Tent City Jail in Phoenix, female inmates could watch an hour of television from pedalling for an hour, under a system dubbed 'Pedal Vision'.
There are fringe benefits too; one prisoner in Santa Rita do Sapucai prison has reported losing 'about four pounds'.
After an unpromising start, having to be bribed by her parents to learn to ride without stabilisers, Sarah became rather keener on cycling in her university years, and was eventually persuaded to upgrade to proper road cycling by the prospect of a shiny red Italian bike, which she promptly destroyed by trapping a pair of knickers in the rear derailleur. Sarah writes about about cycling every weekend on road.cc.