On the upper-body days, they’d hit a mix of push and pull exercises, covering chest, back, shoulders, biceps, and triceps in each session. They also alternated between horizontal and vertical movements from one workout to the next, allowing them to work the muscles along different planes of motion. “We’d do a flat dumbbell bench press, and then the next upper-body day we’d do it at an incline,” Stump recalls. “Or if we did a chest-supported row one day, we’d do pull-ups the next time.”
Sessions would begin with a main lift, like a bench press or row, followed by accessory work, such as cable flies or landmine presses, to isolate the smaller (albeit highly photogenic) muscles that would end up getting the most screen time in the film. Stump had Damon doing three or four sets per exercise across the board, with 8 to 10 reps for the main lifts and 12 to 15 for the subsequent accessory work. “The general idea was to do higher volume,” Stump says. “Lots of sets, versus really intense strength work.”
Lower-body days followed the same formula. “We had a trap bar, so our big leg lift was the trap bar deadlift,” Stump says. “That’s where we would go the heaviest.” But in the absence of basic leg-day equipment, like, say, a squat rack, the duo had to get creative. “We had a regular barbell, but no rack,” Stump says, “so we did landmine [squat] variations, and different kinds of hip thrusts.”
The cardiometabolic day was less structured, concedes Stump, who notes that Damon isn’t particularly fond of cardio. (“He hates doing cardio. But who doesn’t, right?”) Instead, these sessions served as a miscellaneous catch-all for any kind of beneficial non-strength work. Some weeks that meant intervals on the Versaclimber or a HIIT circuit consisting of medicine ball slams, kettlebell swings, and jump rope, while other weeks the pair would simply focus on mobility or steady-state cardio. “Let’s say we’d had a couple of hard workouts during the week and we needed something that was lower intensity,” Stump says. “So I’d just say, ‘Alright, throw on the weight vest, put your headphones in, and walk uphill for 45 minutes. It doesn’t have to be super fast; just get a good sweat going and then come home.’”
“The power of a sacrifice is in the cost to the person making it”
At the end of the day, regardless of how hard or how often he worked out, Damon’s ability to drop 15 pounds of fat would come down to his diet. “I told him at the outset that this is a diet and nutrition goal,” Stump says. “Anytime you’re talking about losing body fat, that’s a calories-in thing. You’re not going to control that by exercising more.”
Fortunately, this came as no surprise to Damon, who knows his way around a Hollywood transformation. “My big thing was just making sure he’s getting enough protein to support the muscle mass that he has, but the truth is that he didn’t really need that much help with his diet, and I think that’s because he’s done this so many times before,” says Stump, who notes that staying away from alcohol, gluten, and processed sugar went a long way in helping Damon cut his caloric intake while training for the role.
According to Stump, it was ultimately Damon’s commitment to the process—both in the gym and in his diet—that allowed the actor to achieve blockbuster results in such a short time. “In terms of his training, I would say the most impressive thing about him is his consistency,” Stump says. “He’s really a guy that will show up, day in and day out, and put in the work. And I think that’s probably what comes through the most in terms of how he looks in the movie.”
A version of this story originally appeared in British GQ.