PGA Tour star Justin Thomas leveled-up in the 2017 season, winning four tournaments including his first-career major at the PGA Championship.

After dealing with some injuries, Thomas overhauled his training program—putting an intense focus on core-strengthening workouts, mobility exercises, and routines to boost flexibility, which helped him play some of the best golf of his career.

“I wasn't always someone who loved working out,” Thomas tells Men’s Fitness. “But now, it’s a major part of my life. It's important for my body to feel how it needs to feel to play the best I can. It's something I take very seriously. I probably put on a good 15-20lbs last year.”

That added strength helped Thomas put more speed on his swings and gain confidence on the course. Thomas and his trainer prioritized core and mobility work to strengthen the stabilizing muscles in his abdomen, back, hips, and glutes.

“We’ll always work on something core-related and we do a lot of split-stance [work],” Thomas says. “We rarely do something that's working only one aspect. It's nice to be big and strong, but let's be real: Golfers don't need to be throwing weight around. We need to stay flexible.”

How Thomas trains in the off-season

When Thomas isn’t playing in a tournament, he’ll usually hit the gym Monday and Tuesday, rest Wednesday, return Thursday, rest Friday, then train again on either Saturday or Sunday. Thomas’ workouts usually last between 60 and 90 minutes, with 10 minutes of stretching before and after to keep his body loose.

Thomas also begins every routine with some glutes activation by loading his hips to make sure those muscles are firing.

“If they don't, that kind of misaligns everything else and you can feel it," he says. He'll do lunges, anti-rotation work with bands, pull and push exercises, and unilateral movements to work on balance.

How Thomas preps during PGA tournaments

When he’s in a tournament week, though, Thomas’ workouts are a bit different.

“During those weeks, I'll workout maybe two times,” Thomas says. “It depends on if I have a morning or afternoon tee time. We have a physio guy that's out with us on tour and I’ll see him everyday—in the morning to stretch me out and 30 minutes after I play or practice for deep-tissue work to keep me loose and moving. We're doing so much walking on the course for a five-hour round, so you can’t drain yourself with a workout every day."

His efforts have clearly been working. In 2017, Thomas finished as the highest-earning golfer on the PGA Tour, and he brought home the PGA Tour Player of the Year award for his accomplishments. Thomas plans to keep that momentum rolling into 2018.

"All I can do is get myself as prepared as possible, and try to play the best I can," Thomas says. "With training, it’s really just making sure you're being functional and not overdoing it."

Want to train like a PGA Tour champ? Here’s a core-centric workout, and a strength- and muscle-boosting routine, inspired by the training that helped Thomas dominate the green.

How to do Thomas' golf workouts

Complete as straight sets: Perform one set of the first exercise, then repeat for recommended number of sets. Once complete, move on to the next exercise in the workout.