Adam Walker is not your everyday record-breaking sportsman. He took on arguably the toughest extreme sport on the planet - to swim non-stop across seven of the world's deadliest oceans wearing only swim trunks, cap and goggles. It is not a test for the faint-hearted: swimmers face freezing temperatures, huge swells and treacherous currents, potentially deadly marine life (from sharks to Portuguese men o' war), vomiting and burning off a week's calories in a single swim.