Olympians get boost from 'legal doping'
Many athletes at the Athens Olympics will use performance-enhancing substances with no fear of failing a dope test.
"Legal doping" involves taking supplements to boost the levels of substances that occur naturally in the body.
"If you think of an athlete's body as being like a car, things like carbohydrate or creatine are like changing the oil," said Paul Greenhaff, professor of muscle metabolism at the University of Nottingham.
"On the other hand, anabolic steroids are like changing the architecture of the engine - the muscle."
Although the effectiveness of some nutritional supplements is far from proven, the evidence for creatine, caffeine and carbohydrate supplements working to an athlete's advantage is good.
"It's well known in the sports science literature that these things can be effective," said Mike Gleeson, professor of exercise biochemistry at Loughborough University.
"Creatine, for example, is very popular with power athletes, sprinters, weightlifters, that sort of thing. There are no figures for usage, but I would expect it to be a rather large percentage."
Creatine is an amino acid which occurs naturally in the body and increases the amount of work done by the muscles during short duration, maximum effort exercise.
Athletes have been using it since the 1930s and it has a controversial reputation. Creatine is not on anti-doping agency WADA's list of banned drugs but its use is outlawed by some federations and many coaches believe it should be banned.
Caffeine, used in a variety of sports including short-distance sprinting events, was only last year taken off the banned list. Anti-doping experts said its presence in the body could vary greatly depending on an individual's metabolism.
Tea, coffee and cola
"Caffeine definitely has some effect in improving endurance. It has a stimulating effect on the brain and may affect perception of effort," Gleeson said.
"You wouldn't have to drink much tea, coffee or cola to acquire the dose you'd need for increased performance."
Some evidence suggests that sodium bicarbonate can boost performance in intensely active sports.
"It's only effective if you take it one or two hours in advance. It can improve performance in high intensity exercise where the big problem is build-up of lactic acid," he said.
By reducing the acidity of the blood, sodium bicarbonate can lead to more lactic acid being drawn out of the muscle cells, possibly delaying the onset of fatigue.
However, it can also cause bloating, Gleeson said.
Athletes have tried various methods to increase the number of red cells in their blood, so boosting the amount of oxygen that can be carried to their muscles. This is often done through illegal "blood doping."
"People would have blood taken out of them," said Gleeson. "It would be stored for a month or so, their red count would recover and then they'd have their own blood put back into them."
Blood doping can also involve using other people's blood and the blood-boosting agent erythropoietin (EPO). However, there are other legal ways that might produce the same effect.
Training at altitude, where there is less oxygen also boosts the number of red cells in the blood. Gleeson warns the jury is still out on whether mountain training works.
"You have to be at altitude for two or three weeks or more if you want to see any real benefit," he said. "But then you can't train as hard as you do at sea level. You might effectively be 'detraining."'
An easier option is sleeping in an oxygen tent which mimics the lack of air at altitude, boosting the blood's red count and allowing athletes to train harder during the day.
Several top flight athletes, including marathon world record holder Paula Radcliffe, have tried a hypoxic tent.
"The idea is to train low and to sleep high," says Gleeson. "But there isn't enough evidence it works."