Mark Ruffalo Did ‘500 Pushups a Day’ While Playing Dominick in ‘I Know This Much Is True,’ Director Says

“Mark is the kind of actor where he’ll do anything,” says Derek Cianfrance

Derek Cianfrance, Mark Ruffalo
Derek Cianfrance (Left) and Mark Ruffalo (Right) on set of HBO's "I Know This Much Is True"

Mark Ruffalo was willing to push himself to great lengths both physically and mentally in order to play the Birdsey twins in HBO’s limited series “I Know This Much Is True” — so much so that he was game to do “probably 500 pushups a day” while shooting the scenes as Dominic, said writer and director Derek Cianfrance.

Add that to the 1,000 calorie-a-day diet Ruffalo went on in order to lose the 20 pounds necessary to become the neurotypical brother, and you’ve got a recipe for the physical embodiment of “toxic masculinity,” Cianfrance told TheWrap ahead of Sunday’s series finale.

“I guess you could say he was always a little bit hangry. He was eating an egg white for breakfast and just starving. And he couldn’t eat for another 3 hours, and all he could eat then was a granola bar that had 120 calories or something, because he was on this strict diet. It created this guy Dominick who was just wiry and aggressive,” he said.

Ruffalo, who was also an executive producer, was in close contact with Cianfrance throughout the adaptation of the script from Wally Lamb’s novel. When it came time to start production, the pair agreed that they would spend 16 weeks shooting all of Ruffalo’s scenes as Dominick first — and then the actor would gain back 30 pounds play his twin brother, Thomas, who struggles with mental illness in the form of schizophrenia.

“My very first meeting with Mark, I told him that if we were going do something like this, I couldn’t imagine us shooting in the morning, breaking for lunch and having him putting on a wig or a fake goatee and playing the second half,” Cianfrance said.

But the extreme weight loss and gain was one aspect of the physical challenges Ruffalo would go through.

“I just had this instinct one day when we were doing a phone call scene… I asked Mark, I said, ‘Hey, could you do 50 pushups?’” Cianfrance said. “Mark is the kind of actor where he’ll do anything. So he dropped to the ground, he did about 35 pushups, he came up, and he did this phone call scene and… he was a little out of breath, you know? He was smoking these cigarettes and struggling for his breath a little bit, and his chest was puffed out, and I noticed the vein in his neck was engorged. We finished the scene and I was like, ‘Hey, let’s do another take. Can you do another 50 pushups?’”

At that point, Ruffalo questioned Cianfrance’s reasoning.

“I was like, ‘Well, you’re just becoming Dominick — this guy who’s just struggling for every breath. This guy with a barrel chest,’” Cianfrance said. “So we shot for 17 weeks and I would have Mark do push-ups — he was doing probably 500 pushups a day. All the time between takes, it was always our way to get Mark into the zone as Dominick.”

The sixth and final episode of “I Know This Much Is True” airs Sunday at 9 p.m. ET/PT on HBO.