McClain, 31, and his wife, Keisha, also 31, are majority owners of the franchise, which opened two weeks ago.
The 18,000-square foot gym features 108 pieces of equipment, including 54 cardio machines and weights up to 120 pounds, with 150-pound weights on the way.
The gym also has a 25-yard indoor turf field, a group fitness room for classes, such as indoor cycling or Zumba, and a cardio theater for more private workouts. When the weather gets warmer, the gym will have outdoor elements, as well.
The former Ravens linebacker spent six seasons of his seven-year career with the team, from 2008-13. He last played for the New York Giants in 2014.
In retirement, McClain said he has focused his efforts on giving back and said starting a gym would be a good next step in his and his wife's careers. He continues to be involved with the NFL Players Association and the Baltimore Ravens Media Team; his 53 Families Foundation, a nonprofit that supports Baltimore families; Newfit Kids, which provides after school sports opportunities for inner city elementary and middle schoolers and real estate ventures in Philadelphia.
"Physically, people have a feeling within themselves that they want to improve themselves," he said. "We wanted to give this opportunity too."
The McClains chose Retro Fitness because of how the company promotes a team atmosphere.
"We love the model, we love to give back to Baltimore and provide jobs," Jameel McClain said. "It's everything we needed."
Catonsville was chosen because the space used to be home to a fitness center — a L.A. Fitness at the location closed in 2015 — and it's accessible to Baltimore City and Baltimore and Howard counties, Keisha McClain said.
"Catonsville is kind of like the center of everything," she said.
The McClains partnered with Momentum Advisors, a New York City-based investment advisory and financial planning firm, to open the franchise. The McClains own 85 percent of the franchise, said Tiffany Hawkins, vice president for private equity and franchising for the firm.
Retro Fitness is comparable to other big box gyms, such as Planet Fitness, Hawkins said. Monthly membership options include $19.99 for a basic package; $29.99 for unlimited access to amenities such as group classes, child sitting, tanning and discounts for smoothies and merchandise; $79.99 for team training and access to a team training room and $399.99 for one-on-one personal training.
Jameel McClain said he plans to teach team training and one-on-one classes.
Start-up costs were about $1.8 million; construction took about three months.
Hawkins said 400 members signed up before the gym's opening and the first-year projections are about $1 million in revenue.
"We're on track to be extremely successful," she said.
The gym, on Baltimore National Pike, is open from 5 a.m. to 11 p.m. on weekdays and 7 a.m. to 7 p.m. on weekends.
"We want people to walk in one way, walk out transformed," said Allan Boomer, managing partner for Momentum Advisors. "Over time, of course."