LONDON - Usain Bolt's stunning world record in the Olympic 100-meter final is still a long way from how fast the human body can go, according to a study by a U.S. professor.

Shortly after Bolt ran 9.69 seconds in Beijing, Stanford University biology professor Mark Denny set about to estimate just how fast humans will be able to run. He concluded that male sprinters could eventually get the 100 record down to 9.48 seconds and women could run the distance in 10.39.

"My results ... tell us that speed has limits, but not what accounts for these limits,'' writes Denny, whose conclusions were published last week in the Journal of Experimental Biology.

Bolt surely could have gone faster at the Olympics in August. The tall Jamaican slowed down over the final meters and even banged his fist off his chest in celebration before crossing the line three hundredths of a second faster than the record he had set a few months earlier.

In September, Norwegian physicist Hans Eriksen analyzed TV footage of the Olympic final and estimated that Bolt could have run 9.55 seconds if he had not slowed down.

The women's record in the 100 is 10.49, set by the late Florence Griffith-Joyner in 1988. But Denny used 10.61 seconds in his study because of "compelling evidence that the (10.49) race was wind aided.''

Denny used historical records dating back to the 19th century to track the progress of speed in humans, horses and dogs. He found that speeds in horses and dogs at the major races in the United States and Britain peaked, mostly in 1970s but some earlier, while most of the human races had not.

"In each case, an absolute speed limit is definable, and the current record approaches that predicted maximum,'' the 57-year-old Denny says in his summary.

But while Denny, like other experts in the past, concludes that speed has limits, he says it is impossible to know what those limitations are. He writes that it is unlikely that athletes' speeds are constrained by a single physiological or mechanical factor.

Denny, an avid marathoner, says the pattern of these limitations on speed could help scientists figure out how to break them.

At the Olympics, Bolt followed up his record in the 100 with another in the 200, running 19.30. Denny predicts that record could be lowered to a staggering 18.63.

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In the marathon, where Haile Gebrselassie holds the men's record of 2:03:59, Denny's study says that time can be lowered by more than three minutes to 2:00:47. According to the research, the women's record of 2:15:25 set by Paula Radcliffe could be trimmed to 2:14:97.

"Predicted maximum speeds for women are 9.3 percent to 13.4 percent slower than those for men,'' Denny writes. "The present gender gap between men and women will never be closed between 100 meters and the marathon.''

Denny also mentions performance-enhancing drugs and their ability to make a human, or animal, go faster.

"For present purposes, let us define a greyhound, thoroughbred or human (male or female) as an individual performing without drug or genetic enhancement,'' Denny writes. "If drugs have contributed to the winning speeds in the races used here, speeds in the absence of these drugs would presumably have been slower.''

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