The fashion designer told Stylist that it was an "incredible opportunity" to come up with the uniforms.
"It's never been done in the history of the summer games and I thought it was an honour and privilege to be asked," McCartney said.
"I started the process talking to the athletes themselves, asking them questions and getting into the psychological side of what they wear to compete."
She continued: "They all said they felt the way they looked did impact on how they performed.
"We all forget that athletes are normal people too and in the same way that you or I feel differently when we know we look good, so do they."
McCartney added: "The athletes know they've had someone looking closely at every single moment of the design and I hope that lifts their spirits and makes them feel special."
The designer went on to explain that "feminising the [women's] podium outfit" was part of her design, which she achieved with the removal of Aertex lining and the ability to cinch in the waist.
Photo gallery - London 2012 Olympics: