"I twisted my knee," the 22-year-old reveals. "I try to just fight through it. There's so many people standing around waiting for you to do your thing. You feel sort of obligated not to let everyone down."
According to Hemsworth, who plays heroine Katniss Everdeen's trusted pal Gale Hawthorne, "There's a bunch more action in this one. All of the characters have more action than they did in the first one."
Hemsworth, who asked Miley Cyrus, 19, to be his wife in June, says he's also been trying to "lose some weight" for the role. "It's The Hunger Games," he explains. "My character needs to look hungry. A little bit."
Prior to reporting to set for The Hunger Games: Catching Fire, the actor filmed two other movies in 2012: Empire State and Paranoia. "I haven't had a break in about a year. I've kind of shot one film to the other. And have had to prepare for each while shooting another," Hemsworth tells USA Today. "It's been a tremendous workload. But I feel so lucky to be where I am. I'm so thankful."
The Hunger Games: Catching Fire hits theaters November 22, 2013.