"He isn't your kind of Wolverine-six-pack superhero. He's kind of brain over brawn," said Brad Bose, the creator of the so-called "Iron Man Workout."
"We don't want that beefy six-pack kind of look."
In "Iron Man," Downey needed to put on about 20 pounds of muscle and wear an extra 40 in his costume. Since the suit was made well in advance and could not be altered, he couldn't afford to get hulky.
So longtime trainer Brad Bose used cardio equipment called "Jacobs Ladder" that uses the arms, legs, back and buns for a killer calorie-thrashing routine.
Most importantly, Bose incorporated new technology called "The Vortex" to create a lean and mean Iron Man.
"There's literally no angle we can't have on the machine," Bose said. "We can hook you up by your legs and by your arms. You can do pull ups and you can hang upside down."
In six months, Bose had Downey creating strength without size.
What Bose did for Downey is a plus for women: make them strong yet lean. Women's center of gravity is below the belt, right in the hip area. Combine that with a weak upper body and you get a real workout.
"Everything uses your muscles so intensely, you can just feel it whittling away," actress Kit Pequin said.
Pequin knows her body is her calling card. Like other women, she wants to be buff, not big.
"To have a workout that you can really depend on to give you a body that's feminine, but also strong and ready to get into motion. It's great," she said.
Bose finished the program with a vibration and compression machine known as the "Pineapple" that thoroughly exhausts muscles.
"You're supposed to do them to failure, because that's what gets the body response," Bose said. "So things like the Pineapple actually get you to failure which is success in our business."
Click here for more information on Brad Bose's "Iron Man Workout"