Cyclists: the ultimate athletes

It is the most gruelling event in the sports calendar. Over the past three weeks, competitors in the Tour de France have covered almost 2,000 miles in arduous mountain terrain.

So, is Lance Armstrong, who won the race for the fifth time, the world's fittest human? We review the facts.

Energy levels: since they use up the liver's stores of glycogen - the fuel for exercise - very quickly, professional cyclists must eat 8,000 calories - four times more than the average person needs - just to ensure their energy reserves don't run out.

"Apart from eating a lot before they start and when they finish, they also need to eat while they are cycling," explains Louise Sutton, head of health and exercise science at Leeds Metropolitan University. Olympic gold medallist Chris Boardman, who has finished two Tour de France races, adds: "During the race I would be eating every 10 minutes. Just carbohydrate foods like slices of pizza."

Strength: cycling on hilly terrain requires immense strength as well as stamina; some stages of the Tour involved climbs and descents at almost eight per cent gradients. Air resistance or drag also makes cycling more challenging.

Stamina: unlike rugby and football, which involve periods of sprinting interspersed with slower recovery jogs, cycling demands non-stop aerobic effort. As with marathon runners, elite cyclists need highly tuned cardiovascular and respiratory systems simply to keep going. But Tour riders are doing 100 miles (four times the marathon distance) every day for three weeks. Studies show that they have the best aerobic capacity of all endurance athletes.

Fluid intake: Tour riders need to drink nine to 12 litres of fluid a day to compensate for fluid lost in sweat. Dehydration will increase the viscosity of the blood, disrupting oxygen flow to muscles and can increase the risk of heart attacks. Dr Roger Palfreeman, the British Tour team doctor, says: "On very hot stages, you are taking on 11 litres of liquid a day. This is physically very difficult to do but, if you don't, you can easily become dehydrated."