"I kept saying to the stunt guys, 'I need to spin around and figure out how to maneuver that suit,'" the actor, 51, tells PEOPLE in this week's issue. "The thing weighed anywhere from 85 to 125 lbs. when I had full armor on it."
In the film, out June 6, Cruise and costar Emily Blunt don the massive metal suits for their roles as warriors trying to save the world – and in a Groundhog Day-type twist, every time they die trying, the day resets itself.
Blunt, 31, got herself into action-hero-worthy shape with a regimen of Krav Maga martial arts training, sprint training, gymnastics, yoga and weight training. But she still wasn't quite prepared for the rigors of the shoot.
"In my initiation to the action world, in stunt training I almost broke my nose," she says. "It wasn't even a cool story. I smacked myself in the face with my sword. Tom came into the trailer as I was sitting there with ice on my face and high-fived me and said, 'Welcome to the club.' I said, 'Dude, I'm in so much pain.' He said, 'Yeah!' "
Cruise also took some hits, including falling off a car during a scene.
"I was bleeding – I got slashed by the metal," he says. "But that stuff happens. The thing with Em was, we never compared bruises. Making an action movie everyone's in pain, so you just don't mention it."
Reporting by MARY GREEN
For more from the stars of summer's biggest blockbusters, pick up this week's issue of PEOPLE magazine