BERLIN - Once the gun sounds, Usain Bolt seems to test the very limits of the race - the human race.
The Jamaican sprinting sensation put on another amazing performance at the world championships Sunday, shattering his own world record in the 100 metres by .11 seconds to take it down to an almost inhuman 9.58 seconds.
Maybe "inhuman" is a bit too strong, but the man is certainly on another level.
Sunday's result was the biggest improvement in the 100-metre record since electronic timing began in 1968.
Bolt's not done, either. On Tuesday, he cruised into the semifinals of the 200 metres, and he also figures to lead his country's 400-metre relay.
After that, who knows how low he can go? He's certainly willing to try.
"Personally, I think I have more work to do," Bolt said after winning the 100-metre title at the same Olympic Stadium where Jesse Owens won four gold medals at the 1936 Berlin Games.
Several researchers have done studies recently to predict how fast a man can run 100 metres. The latest, from Tilburg University in the Netherlands, predicts that someone will eventually be able break the tape at 9.51 seconds.
Bolt, who has set three records at the 100-metre distance with times of 9.72, 9.69 and Sunday's 9.58, is already looking to rip that theory apart.
"I said 9.4," Bolt said. "I think the world records will stop at 9.4."
British bookmakers are betting that Bolt will get there. As of Monday morning, Ladbrokes is giving 3-1 odds that the 22-year-old Bolt will run under 9.5 seconds by the end of September.
"You'd have to think he can't keep getting faster, but we wouldn't put it past him," Ladbrokes spokesman Robin Hutchison said in a statement.
Bolt became the premier runner in the world when he ran 9.72 in May 2008 - only 2 1/2 months before the Olympics, where he lowered the mark to 9.69. At the Bird's Nest in Beijing, he outdid himself, easing up at the end of the 100, mugging for the cameras even before he showboated across the finish line - and also setting records in the 200 and 400 relay.
"The world's fastest man" is a nickname traditionally given to the 100-metre record holder, and the first such record on the books was set in 1912, when American sprinter Donald Lippincott ran 10.6 seconds.
Charles Paddock, Percy Williams, Owens, Willie Williams and Armin Hary all set the record before Jim Hines finally broke the 10-second barrier June 20, 1968, with a time of 9.9.
A few months later, the American set the first electronically timed record of 9.95.
But since that day, it's been tougher and tougher to shave significant amounts of time off the world record. It took 23 years after Hines' 9.95 for Carl Lewis to get under 9.9, running 9.86 in 1991.
Another eight years came and went before Maurice Greene ran it in 9.79.
In this decade, with the record getting lower and exposure of races getting bigger, scientists have decided to weigh in on what they believe are the physical limits of humanity.
Some say Bolt's performance - during which he averaged 23.3 miles an hour - can be topped. But not by much.