Twenty years ago, Gary Roberts was a 187-lb. Marine. Today, he’s roughly 270 lb. and starting to believe he’s destined for an early heart attack or open-heart surgery.

Join Roberts—and CrossFit HQ filmmaker Sevan Matossian—on the 16-week journey to “kill the fat man” at Oceanside CrossFit in California.

“Fit, to me, is the ability to do everyday things that I used to do when I was in shape and can no longer do,” Roberts says. “It’s about time I stopped looking at other people, looked at myself and said, ‘Hey, let’s change your habits.’”

For his first WOD at Oceanside, he does a short chipper involving a row, squats, sit-ups, push-ups and pull-ups.

“Bam, that’s it,” says trainer Laura Patefield.

After struggling through his band-assisted pull-ups, Roberts says he feels good.

“Things are burnin’ I haven’t even known existed,” he says. “There’s … places I don’t think I’ve flexed in a long time.”

Patefield responds, “It’s going to change your life.”

Watch episodes below: