Actor Robert Downey, Jr. worked out extensively and put on 20 pounds of muscle to play Tony Stark in the first Iron Man. He trained even harder for his follow-up role as the title character in Guy Ritchie's Sherlock Holmes, an experience that gave him a taste for doing some of his own stunt work.
In a recent interview with Empire, Downey, Jr. said that he enjoyed the physicality of the Holmes shoot so much that he wanted to bring that feeling to the set of Iron Man 2.
The action's certainly got bigger [in Iron Man 2]. But I went and did Sherlock Holmes, which was a real balls-to-the-wall, get-your-fists-grazed adventure. Coming back into this I really challenged our stunt team to get our hands dirty a little more, because I was still kind of into that. I love it so much! There is no better day that I can have than one where I beat people up or get thrown around. I just love it. It's supposed to be safe, but it's a little more than acting, so it's really fun.