Wham, bam thank you yam! What's the secret of Jamaica's sprinting success?

Then, it was the United States. Now it is a tiny island with a population one hundredth the size of its massive northern neighbour. So should we be suspicious?

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In truth, there is nothing new in good Jamaican sprinters. Their first Olympic gold was won by Arthur Wint at 400m in 1948,

Merlene Ottey took eight Olympic sprint medals for them and the country had 43 coming into Beijing, all but two of them in sprinting.

There are a host of reasons. Aunt Lilly of Miss Lilly's Bar and Shop in Trelawney, the parish that has produced most of the country's great sprinters, told Time magazine it is the yellow yams they eat.

The latest theory, put forward by Dr William Aiken, head of urology at the University Hospital of the West Indies, is a high level of testosterone in Jamaicans. He says it produces great sprinting but also the highest incidence of prostate cancer in the world, a high rate of traffic accidents and a high crime rate.

Nurture may be as important as nature. In 1910 the British started an annual Boys' and Girls' Championships, now known as Champs, which remains the biggest single annual sports event on the island.

More than 2,000 compete over three days every Easter, largely in sprints, watched by crowds of more than 30,000.

Kayron Raynor, athletics writer on the Jamaican Observer, says  kids are as likely to race on scrubland as play cricket. Premier League football and NBA are the main attractions on television but sprinting is what comes naturally when they get off their backsides.

What has changed in Beijing is not Jamaican ability to sprint but their dominance, helped by the fact that the United States is going through a bad patch, in part because it set up an independent anti-doping agency.

Its cheats have been tracked with a vengeance. Marion Jones, Tim Montgomery and Justin Gatlin, all world record holders or Olympic champions, were caught and banned. Others who were cheating have been deterred and the performance of the United States has declined.

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It is rare for their men to break 10secs and their women 11secs for 100m. So the Jamaicans who were always clipping their heels have moved into the void.

Another factor is that America no longer find it easy to lure Jamaican sprinters to their college system by offering sports scholarships.

Herb Elliott, a Jamaican member of the IAAF Medical and Anti-Doping Commission, said: 'National Collegiate Athletic Association scouts came to us in droves to recruit but our athletes often came back tired and mediocre.'

Jamaicans were used unsparingly in college competition by coaches unconcerned about how that would affect them in international competition. When a young Asafa Powell turned them down, the tide turned. Raynor said: 'When Asafa stayed home, coaches could point to him and his success to interest young athletes in staying home. Once Asafa stayed, others did.'

UTECH, Jamaica's technology university, helped by awarding its own scholarships. There are now 280 athlete students on its books.

There will be those who suspect doping after Jamaica declined to join the Caribbean Regional Anti-Doping Organisation and chairman Dr Adrian Lorde said: 'I don't have any suspicions but if you don't test you don't know.'

The IAAF target Jamaica's elite because of the absence of a national agency. Only the United States, Russia, Greece and Kenya have been tested more in the past 12 months. In the seven days before track competition started in Beijing, 32 Jamaicans were tested - Powell four times.

Not one Jamaican athlete training primarily in their own island has tested positive, a record they are proud of. And it would be a foolhardy Jamaican who ended that record.

As sprinter Michael Frater said: 'The country is so small if you take that record away, you would be embarrassed. In the States, it's big so you can move around but here you can't move.'

Only at incredible speed, it seems.