Scarlett Johansson is always impressed by her The Avengers co-star Chris Evans' physique, because the actor appears to be able to drop and gain weight on a whim.

The actress admits she struggled to stay in tip-top shape for Captain America: The Winter Soldier, in which she reunited with Evans, but he makes it look easy.

She reveals, "The last time I saw him was for some reshoots that we did... and he was much smaller. I don't know how he bulks up like that! I can't imagine that he ever is not eating chicken. Like, 'How much chicken do you eat a day? Be honest. Do you just wake up with meat kabobs (kebabs)?' I don't know how he does it. He puts so much bulk on."

Of her own efforts to control her diet and work-out regime during filming, Johansson adds, "It's boring 5am work-outs and salad and chicken and nothing else, pretty much.

"It's that old tried and true 'work-out-like-a-dude-and-eat-like-a-rabbit' (plan)."