Adaptations to the cardiovascular, pulmonary and skeletal muscle systems allow endurance athletes to perform exercise for prolonged periods and delay the onset of fatigue. These adaptations explain why the current men's marathon world record holder can run 42.195 km (26.2 miles) in a little over 2 hours at an average speed of over 20 km/h. The adaptations which enable sustained endurance performance also offer protection against many chronic diseases and increase average lifespan. For example, former cyclists who competed in the Tour de France before 1964 demonstrated a 17% increase in average longevity compared with the general population 1 . Therefore studying the elite endurance athlete can give us clues as to how partaking in regular physical activity, or failure to do so, alters disease risk and life expectancy.