He begins by testing himself in a centrifuge – a machine that can make fighter pilots and astronauts break out in a cold sweat. He wants to find out what would happen to his body when it is subjected to high forces.
As he reached 4.4 g – he passed out:
"There was no doubt that I’d clearly reached my limit. The blood was forced from my head to my feet and I passed out."
He then tries out anti-g trousers, and manages to get to 5.4 g without passing out.
Next stop is New York where James meets a group of athletes that have pushed their bodies to the limit to get extraordinary results. These elite sportsmen and women have each lost a leg – but are able to run long distances at high speed thanks to hi-tech prosthetic replacements.
They are now winning against able-bodied competitors, a success which has brought the remarkable complaint that the disabled athletes may have a competitive advantage because of their artificial limbs.
Back in the UK James is invited to watch open heart surgery - and sees a man’s heart come to a complete stop during the operation. But James’ biggest surprise came when he looked at one of the 20th century’s greatest medical breakthroughs – the discovery of DNA. He had his DNA tested: "To be honest I’m so English that I’m assuming I’m descended from a piece of fruit cake and cricket bat, but let’s see."
The results, however, were not at all what he expected.
First broadcast: Tuesday 10 Jul 2007 on BBC TWO