The former MLB star "showed amazing commitment" to the intensive 54-day program at 54D gym, owner Rodrigo Garduño tells PEOPLE
Alex Rodriguez/Instagram
Alex Rodriguez
| Credit: Alex Rodriguez/Instagram

Alex Rodriguez set a goal for 2021 — to ditch his "dad bod" and refocus on his fitness. And the former Yankees superstar did just that by committing to an intensive 54-day fitness program at 54D gym in Miami.

Rodriguez, 45, shared two photos on Instagram on Tuesday, one of him in December and the other from April, showing his slimmed-down shape.

"Left the Dad-bod in 2020 💪🏽," he captioned the post. "Anyone else determined to stick with their fitness goals this year? I've been consistent with my workouts and finally put down the chips."

The newly-single Rodriguez, whose engagement to ex-fiancée Jennifer Lopez ended earlier this month, had joined 54D in January on the recommendation of fellow former Yankee Jorge Posada. The nine-week-long program is unique — rather than signing up at any time and coming to classes when you wish, members pay $4,000 and start the 54-day cycle together.

Alex Rodriguez
54D Gym
| Credit: Alex Rodriguez/Instagram

Members are asked to abstain from alcohol during the program and get nutrition advice to change up their diet. And classes are a mix of weightlifting, boxing and functional training, all run by former professional soccer player Rodrigo Garduño.

"When I retired, I had two or three months of big depression. That's the only thing you know how to do and then you're done," Garduño tells PEOPLE. Searching for something to do, he started thinking about "what I can do to help people."

With his background in soccer, Garduño decided that fitness coaching was the way to go and researched how long it takes to make significant mental and physical changes, settling on the 54 days that gives the gym its name.

"The objective is a change in mindset about the way they think about themselves and how they confront life," he says. The program, though "isn't for everyone."

Alex Rodriguez
Rodrigo Garduño
| Credit: Alex Rodriguez/Instagram

"It's very demanding and very disciplined," he says. "It's a very strict program, and if you fail to come to class or in other parts of [the program], we kick you out."

That seemed like a problem for Rodriguez when he first arrived, Garduño says.

"When [Rodriguez] showed up, he asked for private sessions, and we don't do that," he says. "I thought that this wouldn't be for him, because I can understand that it's difficult when you're a big star and you need to be in the room with 30 more people and you're going to be treated the same as others. And if you're not willing to commit and be like anyone else in there it's going to be difficult for you to come in every day."

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Plus, the attendance policy is strict.

"We have a lot of rules," Garduño says. "One rule that is very important for us is that if you fail three classes, we take you out. It doesn't matter who you are. We give you your money back and we kick you off. Because you need to understand that we are here to give results."

But Rodriguez "showed amazing commitment."

"He was always there on time, no matter how busy his day was," says. "One thing that was amazing was I saw him on TV when he went to President Biden's inauguration, and I was 100% sure that he would miss class because he was in D.C. It was a 6 p.m. class. And to my surprise he was there in class like everybody else."

Rodriguez loved the program so much that he signed up again, this time bringing seven of his family members — including his sister — and his staff along, and is now in the midst of another 54-day cycle.

"We are very happy that he feels proud with his results and that he's sharing them with the world," Garduño says.