The pair team up in the new movie to play two astronauts facing a life-threatening crisis in outer space, and to simulate the zero gravity conditions a special device was used on set.
The actors were required to climb into a giant light box where they were suspended on a special harness so they appeared weightless, but the contraption took its toll on the two stars.
The shoot aggravated Clooney's ongoing back injury, but it was Bullock who came off worse - she suffered cuts, bruises, and a pelvis problem, and she had to undergo regular physiotherapy sessions, admitting, "(It was to) put me back together."
However, the actress had more sympathy for Clooney, telling British newspaper The Guardian, "He's always in an extreme amount of pain and he had to get into that rig every day. He was only there for three weeks, but George had a lot more to deal with than I did."