Mark Ruffalo Did '500 Pushups a Day' to Play a Twin for HBO's I Know This Much Is True

Mark Ruffalo went all in for his latest role.

Ruffalo, 52, plays twins in HBO’s limited series I Know This Much Is True and did “probably 500 pushups a day” while shooting scenes as one of the twins, Dominic, writer and director Derek Cianfrance told The Wrap.

“I guess you could say he was always a little bit hangry,” Cianfrance said of Ruffalo’s diet which included 1,000 calories a day in order to lose 20 pounds for the role.

“He was eating an egg white for breakfast and just starving,” Cianfrance continued. “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.”

He added, “It created this guy Dominick who was just wiry and aggressive.”

I Know This Much Is True follows the story of twin brothers Dominick and Thomas, the latter of whom is schizophrenic and in an asylum that Dominick tries to get him out of through the course of the series.

At the TV Critics Association Winter Press Tour in January, Ruffalo revealed he gained 30 lbs. for his dual role. He filmed all his scenes as Dominick for the first 15 weeks, before taking five weeks off to transform into Thomas.

Due to Thomas’ years of dependency on medication for his schizophrenia, Ruffalo said he gained weight to accurately portray the effect medications and “mood stabilizers” can have on someone’s body.

"We didn’t want it to be like I run and throw a wig on and do the same scene in the same day, so we took six weeks off to really separate these two guys," Ruffalo explained. "And Thomas is on medication, mood stabilizers and anti-psychotics. A lot of people put on weight."

"Putting on the weight for Thomas was really challenging," he added. "I didn’t expect it to be. I thought I was going to have a fun time doing that, but when you’re force-feeding yourself, some of the romance of food sort of leaves."

Melissa Leo, Archie Panjabi, Imogen Poots, Juliette Lewis and Kathryn Hahn also star in the limited series.

The final episode of I Know This Much Is True airs on HBO Sunday at 9 p.m. ET.