The yoga craze has been burning for years now and shows no signs of slowing down. In fact, yoga has sparked interest in a few groups you wouldn’t expect.

Yoga offers a number of health benefits including relaxation, mindfulness, and increased flexibility, but many people are still reluctant to try yoga for themselves. Today, 36.7 million Americans practice yoga, but here are three groups whose love for yoga may surprise you.

Jail inmates

That’s right: inmates in a Norfolk, VA jail have officially graduated from their first yoga class as of August 15.

Through The Prison Yoga Project, inmates are taught yoga to promote mindfulness while encouraging better impulse control. As of now, the program is headed by Christine Harrell at only one location, but Harrell hopes to expand the program throughout Virginia. When up to 95% of current inmates will return to society, it’s important to teach them skills that will follow them into the future. The Norfolk Sheriff’s Office hopes that yoga will help inmates become less likely to commit crimes once they get out.

Nama-slay, Metal-heads

This rough-and-tough group is the last type of person you’d expect to relax. Metal enthusiasts of Massachusetts, however, have opted to attend yoga classes with the relaxing soundtrack of blaring guitar solos and heavy drums to carry them through their workout.

Metal fan and middle school teacher, Angela Fontaine, curates each playlist for her metal yoga classes. She sees the practice as a way to give back to the music that has done so much for her while helping friends in the community get into shape.

Most of her clientele are a little older and not as flexible as they used to be. In fact, 22% of accidents caused by a slip and fall can cause an adult to miss up to a month of work. As they heal, they might not be as limber as before the accident. Now, an aversion to Peruvian flute music won’t be a barrier to attending your first yoga class.

“I don’t need someone to throw out a guttural roar when we should be in shavasana. I’ve got it timed down to a science. There are metal songs that are very melodic, and there are others that, when you’re in the warrior pose, make you feel like a warrior, she said in an interview with the Daily Hampshire Gazette.