The gym at Riverside Correctional Facility in Philadelphia is through the metal detector, two heavy doors and down the hall.
There's a basketball court like one you'd see at any high school, except there's a corrections officer on guard near the 3-point line.
Sixteen stationary bikes are set up in a half-circle in the corner. On bike No. 2, Lakiesha Montgomery, 32, from Philadelphia, is pedaling fast and singing along to the Nicki Minaj song "Fly."
"I didn't think I'd be able to keep up; I'm not the skinniest thing in the bunch," she says.