The Big Question: As the 100m world record falls again, how much faster can humans run?

Why are we asking this now?

Because Usain Bolt, a 21-year-old Jamaican, smashed the world 100-metres record in a race in New York at the weekend, clocking 9.72 seconds, two hundredths of a second faster than the previous best, set by his compatriot Asafa Powell in September last year. It was the 17th time the record had been legally broken since an American called Don Lippincott ran 10.6 seconds in 1912, and the eighth new 100 metres record set since 1991. The 10-second barrier was broken in 1968, the 9.90 barrier in 1991, and the 9.80 barrier in 1999. Now the 9.70 barrier is in sight.

Who is Usain Bolt?

He is a quietly spoken, 6ft 5in student at Jamaica's University of Technology who has long been expected to reach the top in athletics, having run the outstanding 200 metres time of 19.93 sec as a 17-year-old. He won the silver medal in the 200 metres in last year's world championships but then surprised everyone a month ago when he produced the second-fastest 100 metres of all time – 9.76 sec – in what was only his third serious race at the distance.

Bolt's coach, Glen Mills, wanted him to run 400 metres rather than 100-metre races this year in preparation for the Olympic 200-metre event in Beijing, but Bolt hates the longer distance, and when Mills said he could run 100 metres if he beat the Jamaican 200-metre record, his athlete duly obliged.

Does Bolt's height give him an edge?

It's not that simple in sprinting. "The smaller you are, the more force you can generate to body mass," says Peter Weyand, an assistant professor in the department of kinesiology at Rice University, in Houston, Texas. Weyand, who watched Bolt's world-record race, believes all the runners were moving their legs at about the same speed, and touching the ground for less than one-tenth of a second with each stride. But Bolt was able to deliver more force to the ground relative to his body weight.

Tyson Gay, the world 100-metres champion whom Bolt beat into second place, backed this up anecdotally, lamenting that Bolt's stride pattern was not quicker, but bigger. "He was covering a lot more ground than I was," he said.

Could Bolt run even faster in the future?

Certainly. Although his size tells against him in the start – it's too big a frame to get out of the blocks smoothly – he can certainly improve upon it with practice, and will be even better if he sprints right to the end of his races rather than slowing down to see how well he has done on the clock, as he did when he ran 9.76 sec, or slowing down and raising both arms in the air as he did in celebrating his victory on Saturday night. The wet conditions in New York were also far from ideal.

So what is the fastest a human can run?

Broadly speaking, the average man can manage about 15mph for short periods, while the best sprinters are running, albeit briefly, at about 26-27mph. Not very efficient compared with a cheetah, which can reach speeds of three times that. Dogs and ostriches can also put us to shame.

The title of "fastest man in the world" is traditionally held by the 100-metre world record holder, but one scientific form of reckoning bestows that title on the former 200-metre runner Michael Johnson, whose performance in setting the world record of 19.32 sec at the 1996 Olympics produced an average speed of 23.15mph (compared with Bolt's 23.02mph on Saturday). In terms of peak speed, Canada's Donovan Bailey is credited with the record, hitting 27.07mph in winning the 100m title at the 1996 Olympics in a then world record of 9.84 sec.

So will the record go again soon?

The days when 100-metre runners used to knock a tenth of a second off the world record – as Jesse Owens did in running 10.2 sec in 1936 – are long gone. The record has been creeping down in hundredths of second since Jim Hines became the first man to break 10 seconds in 1968, winning the Olympic title in 9.95 sec. Bolt looks the obvious candidate to take it down further, but he will have strong competition from both Gay and Powell.

Athletics statisticians claimed in the wake of Bolt's run that even though it was faster than Powell's, the latter's was intrinsically superior, by one-hundredth of a second, once the different wind speeds had been factored in. Powell ran in virtually dead-still conditions, while Bolt had a 1.7 metres-per-second following wind. There might be a further challenge from the 2004 Olympic champion, Justin Gatlin, if the American can get his doping ban halved by the Court of Arbitration for Sport this week.

What part might doping play in man going even faster?

Ben Johnson was infamously stripped of his 1988 Olympic 100-metre title – and world record of 9.79 sec with it – for taking banned steroids. It took another 11 years for another man to equal that time – Maurice Greene, who retired last year after winning world and Olympic titles, but recently had to deny accusations that he had been supplied with and paid for drugs.

With all the bad publicity over Gatlin, Greene and Britain's Dwain Chambers, who served a two-year doping ban, the world of athletics is desperate for genuine sprint performances.

Meanwhile, Bolt responded to the obvious question that followed his world record by saying that he had never taken any performance-enhancing drugs, and had already been tested five times this year.

What legal aids might help sprinters?

Improvements in track surfaces and running shoes have certainly helped athletes go faster in the last 20 years, as have advances in training methods and nutrition. Nevertheless, it is generally agreed that 30mph is the likely limit for humans as things stand. "We're very close to the edge," says Weyand. What might yet push human beings beyond that edge, however, is gene therapy. As recent experiments with mice have vividly demonstrated, this rapidly growing technology can produce profound improvements in strength, speed and endurance. It's scary stuff.

Is the fastest really the best?

Had Jesse Owens been able to take advantage of the advances in physiology, nutrition, training, footwear and track surfaces, you fancy he would have been a contender in today's sprinting scene. And while Maurice Greene, self-styled Greatest Of All Time, according to his tattoo, may have run faster than Carl Lewis ever did, many observers would say the latter's consistency and elegance gave him a claim to be regarded as the best ever.

Can athletes keep going faster in the 100 metres?

Yes...

*Usain Bolt could shave some hundredths of a second off his time by running through the line and not raising his arms

*If the race starts being measured in thousandths of a second, even slight improvements will count as a new record

*A course of gene therapy could give athletes a new edge, boosting human capabilities yet further

No...

*We're already reaching our top speed. Scientists believe man cannot run faster than 30mph, with the best at about 27mph

*We have certain physiological handicaps that will always hinder us. We'll never resemble a cheetah, which can reach 70mph

*There must be some point at which the record will never be broken – we'll surely never see the 100 metres run in five seconds