How low can he go: Usain Bolt keeps setting records, but is there a human speed limit?

As Bolt breaks another record, is he near a limit?

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 meters 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-meter record since electronic timing began in 1968.

Bolt’s not done, either. On Tuesday, he cruised into the semifinals of the 200, and he also figures to lead his nation’s 400-meter 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 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 meters. 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-meter 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 2½ 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-meter 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 on 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 mph — can be topped. But not by much.

Tilburg University said last month in its study that 9.51 was the “estimated ultimate world record.” But Tilburg’s Sander Smeets said Bolt’s performance on Sunday could push the statistical analysis to 9.50.

“He is really getting close now,” Smeets said in a telephone interview from the Netherlands. “It surely is happening all very fast.”

Late last year, Stanford University biology professor Mark Denny concluded in a study that male sprinters could eventually get the 100 record down to 9.48 seconds.

“An absolute speed limit is definable, and the current record (9.69 seconds) approaches that predicted maximum,” the 57-year-old Denny, an avid marathoner, wrote in his summary.

“My results … tell us that speed has limits, but not what accounts for these limits,” Denny wrote.

Howard Wainer, a distinguished research scientist at the National Board of Medical Examiners in Philadelphia, said the 100-meter record will get lower and lower as the world’s population increases and more and more people take up running.

“Even if the human race is not getting any better, because there’s more of us, the times will drop,” Wainer said. “It’s not just that there’s more of us. There’s more of us who are running.”

Statistically, however, it’s difficult to pinpoint exactly when someone better than Bolt will come along.

“It’s complicated because training and equipment get better,” said Dylan Small, a statistics professor at the University of Pennsylvania. “There may have been somebody sometime who, if they lived today, might have been as fast as (Bolt).”

Kenny McDaniel, who has a degree in kinesiology and coaches track at Arizona State, said the key to going faster was simply nutrition and training, and that the better you take care of your body, the faster you’ll be able to make it move.

“There’s no limit. Speed has no limit,” McDaniel said Tuesday. “I truly believe that 30 years from now, we’ll see a 9.30.”

While science uses data to produce its findings, Bolt uses his long legs to motor down the track and blow away the competition.

And unlike scientists, many sprinters won’t even hazard a guess as to what Bolt can do in the future.

“I think the sky is the limit,” American Allyson Felix said. “He’s doing things we’ve never seen before, so, I don’t think you can put a time on it.”

Bolt is also left wondering just how fast he can go.

“You never know,” Bolt said. “I’ll just keep on working.”

AP Sports Writer Raf Casert contributed to this report.