“I’ve been working with Milo for roughly eight years now,” his trainer Jason Walsh, founder of Rise Nation, tells PEOPLE. “We meet anywhere between three to five times a week, depending on how busy he is.”
A typical workout moves through a variety of strength-building exercises.
“We get right to work, usually listening to Deftones or Nine Inch Nails,” says Walsh.
To tone up Ventimiglia’s butt, Walsh says the best exercises are single leg squats, barbell deadlifts, heavy sled pulls and pushes, and front squats.
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Because Ventimiglia, 39, has been working out regularly for years, he did not need to dramatically alter his workouts to get ready for his clothing-free television scenes.
“We really didn’t change much, we just kept doing our normal routine,” says Walsh. “Milo has always been dedicated to his workouts. Consistency is key. It’s the best method because as an actor, you don’t have to stress about taking your clothes off if that time comes. You just know you’re good to go.”