SAN QUENTIN (CBS NEWS) — Prisons can be described as many things, but “peaceful” is not usually one of them. For those convicted of crimes from robbery to murder, being locked up is a harsh way of life. But for those who plan on — or will one day be — returning to society, practicing yoga can help them learn to find peace before they are released.

Danny Plunkett is a prisoner at San Quentin State Prison — a notorious lockup on the San Francisco Bay. It’s not a place where one might expect to find hardened criminals resting in lotus or child’s pose. But Plunkett is three years into his yoga practice — and 26 years into a prison sentence for murder and robbery.

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“I spent a number of years in some pretty rough prisons, and you carry that with you, you carry that violence with you,” he told CBS News.

Twice a week, yoga instructor James Fox makes his way through the prison yard to lead a packed class. It’s not easy to get a spot because there’s always a wait list.

Fox started the non-profit organization The Prison Yoga Project at San Quentin in 2002. It’s since expanded, and now prisons and jails across the country are bringing in yoga instructors to help rehabilitate offenders through alternative means.

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“Violent offenders are going to return to society — what kind of person do you want to run into on the highway? On the subway?” Fox asked.

Fox has trained other volunteers, who are now teaching at more than 100 facilities across the country.

For Plunkett, who may be released as early as next year, the benefits of practicing yoga have been immeasurable. He said yoga has given him a new sense of self that will help him start a better life on the outside.

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“I’m not reacting and I can pause,” he said. “I live in a pause so to speak.”