Olympics: Radcliffe Defies Gravity in Quest for Glory

If Paula Radcliffe pulls off her comeback by winning a medal in next Sunday's Olympic marathon she will owe a big thank-you to US astronauts.

Radcliffe has spent most of the past three months preparing as though she was about to get ready for a trip to the moon rather than covering 26.2 miles through one of the world's most populous cities.

Unable to run on the road because of the stress fracture to her femur that doctors told her would prevent her competing in the Olympics, the world record holder has instead been hopping on board a machine designed by Nasa with information gathered from astronauts following their trips into space.

Called the G-trainer, it is a high-tech, anti-gravity treadmill that makes it as close as possible to run in zero gravity by effectively cutting the body's weight in half, lessening the stressful impact on Radcliffe's femur.

The G-trainer is surrounded by a dough nut-shaped inflatable plastic chamber, which encases the runner's body from waist to knee. 'It uses air pressure to lift up on the runner, taking a 150lb runner down to an effective weight of 75lb,' said Professor Rodger Kram from Colorado University.

Jemma Simpson, who will run in the 800 meters, has also been training on one at the UK Athletics Endurance Performance Center (the third machine in Europe is owned by AC Milan). 'It does feel as though you're flying,' she said.

So if Radcliffe wins she will not be so much over the moon, as feeling like she has run on it.