"[Boxing] will keep you honest," Kitsch, 30, tells the April issue of Men's Health. "It's about pushing yourself and attempting to exceed those limits, and pushing the guy beside you."
David Paul, who runs the gym, oversees Kitsch's workout, which includes a series of abdominal sets with punches and stretches, bag drills and 27 rounds of "run and shoots" -- sprints alternating with jabs and uppercuts.
"You knock out both cardio and weights, really, in an hour and a half," Kitsch explains of the tough-as-nails exercise. "But you're drenched 99 percent of the time."
Kitsch, who often trains with his assistant, Trey, began boxing when he was first cast on Friday Night Lights; he prefers it to simply running and lifting weights.
"People hate cardio," Kitsch tells Men's Health. "I hate cardio. But pick the five top songs that you love. Do your cardio during these songs, and you're done. I'd say 95 percent of the time you don't even know you just did it."