Far from calming its inmates, Ringerike jail found yoga was making them more aggressive.

An excerpt from the BBC story:

Prison warden Sigbjoern Hagen said some of the inmates became more irritable and agitated and had trouble sleeping.

He said the prison did not have the resources to treat emotions unleashed by the deep breathing exercises.

The yoga group expressed surprise at the prison's findings.

It said the project had been tested successfully on some 100,000 prisoners in around 15 countries, the AFP news agency reported.

"The reactions we received from the prisoners who participated in the classes were very varied, ranging from completely positive to completely negative," Mr Hagen reportedly wrote in a letter to the group.

On the negative side, the yoga had provoked "strong reactions: agitation, aggression, irritability, trouble sleeping and mental confusion", he said.