For the past three months, they have been taking regular doses of a substance called creatine which is found naturally in fresh meat and fish. One tablet, the size of an old 5p piece and dissolved in water, is thought to have the same effect on performance as the consumption of 8lb- 10lb of raw steak.
It was widely and legally used at the Barcelona Olympics. Wigan rugby league players have taken it. In Australia, it is given to racehorses and greyhounds.
But there is concern in sporting and scientific circles that the practice of supplementing athletes' diet with extra creatine is open to abuse.
Although it is not on the banned list issued by the International Amateur Athletics Federation, doping control officer Bryan Wotton said: 'That doesn't mean that the IAAF approves it.'
The former 5,000-metres world record holder Dave Moorcroft is also sceptical: 'It falls into an area between vitamin and iron supplements and a substance that aids performance.
'It's perfectly legal, so you can't blame anyone for taking it. But I think the authorities should look at banning it because it could be giving an unfair advantage to those who have taken it.'
A senior British Athletic Federation coach, Frank Horwill, recently circulated an article to members of the British Milers' Club which encouraged experimenting with up to 30 grams a day. 'That's terrible,' said Dr Roger Harris, a bio-chemist at the Animal Health Trust in Newbury, who has been researching the effects of creatine for over 20 years. 'The maximum recommended by the manufacturers is three grams three times a day for a maximum of 10 days, then dropping to one gram a day.'
Fear that athletes or coaches might be tempted to abuse the substance made him and his colleagues wary about publishing the results of their research six years ago. But since then a research programme in Estonia indicated an improvement in performance among athletes taking creatine. 'Now the genie is out of the bottle I don't think we can get it back in again,' said Dr Harris.
Creatine is manufactured by AMS, a Hull-based company, and marketed under the name Ergomex. A box with a month's supply costs just under pounds 40. Managing director Steve Jennings is a former professional cyclist who says he wants to help athletes get more out of their sport.
'Unlike a steroid,' he said, 'creatine won't alter the blueprint of your body. It enables the body to work at intensity for a fraction longer.'
Mr Jennings rejects the view that his product could provide one athlete with an unfair advantage over another. 'It's no different from using a state-of-the-art running shoe, doing altitude training or using a high-tech javelin. It's using technology to push sport forward and onward.'
Research into the effects of creatine is still going in at various universities, including Warwick, where Dr Dean Sewell has been carrying out tests at the nearby headquarters of Coventry's Godiva Harriers.
'I'm not interested in making athletes run faster,' he said. 'But as a physiologist I want to know what causes muscle fatigue. It could help the elderly person who can't climb a flight of stairs or the muscular dystrophy sufferer trying to pick up a pen.'
Like Dr Harris, he is concerned about some coaches encouraging athletes to use up to 30 grams of creatine at a time. 'I would not encourage any uncontrolled use,' he said, pointing out that little work has yet been carried out to examine the load placed on the kidneys.
His tests on the Godiva Harriers have so far proved inconclusive. But at least one of them, the current British Universities 400-metre champion Brian Darby, feels that he benefited from taking creatine before training.
'I felt I could do more without tiring so quickly,' he said. 'As long as it's not on a banned list and it's not harming me, I don't see any problem.'
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