An ex-con opened a prison-themed fitness boot camp in NYC - and people love it

Coss Marte began to take his health seriously while behind bars. Convicted on a drug kingpin charge, Marte, now 30, had been told by prison doctors that his cholesterol levels were dangerously high - and that he'd likely die before his seven-year sentence was completed.

"I said I was not going to die, and I went right back to my prison cell and started doing whatever exercises I knew, with the space I was given," Marte told INSIDER.

After six months of continuous planks, jumping jacks, dips and push-ups, he had lost 70 pounds, and was healthier than ever.

Marte began leading workouts in prison to help the other inmates get in shape, too. And, after his release in 2013, he formally started his prison-style boot camp company, ConBody.

"I came home and began doing it in a local park, and from there started going to studios, and now I'm here," Marte said.

ConBody opened its first studio in the Lower East Side of Manhattan - the neighborhood where Marte was born and raised - in January. The studio is designed to look like a prison cell, with metal bars and white cement block walls.

The workout is solely composed of exercises that can be done in prison, which means there's an emphasis on body weight training and cardio, and absolutely no exercise equipment - aside from pull-up bars that are made to emulate the bars of a prison cell.

ConBody has already built a huge following since the studio opened. More than 6,000 classes have been sold, and Marte noted that the studio has seen a 70% retention rate with its clients.

"No one really works out like we work out," Marte said. "What I mean by that is basically the camaraderie we build in our workout, and we joke around with the whole prison theme. Also, it's part of a larger social movement."

In addition to trying to provide people with effective body-weight workouts, Marte is on a mission to provide opportunities to those who had been previously incarcerated like himself. Every employee of ConBody - from the trainers to the janitors - has at one point been in prison.

The ConBody boss also recently entered into a contract with Rikers Island Prison in New York, to train inmates and motivate them to take better care of themselves. "We hire people that come out of prison to work the front desk," he said.