LONDON -- The greatest sprinter of all time will reach the finish line of his career at the upcoming World Championships.

Usain Bolt, nearing 31 years old, predicts one last victory in the 100 meters. Unbeaten in three Olympics, many wonder how Bolt has stayed at the front of the pack for so long.

At his peak, Usain "Lightning" Bolt clocked over 27 miles per hour.

"He's one of those people, one of those athletes that's just freakishly talented," said U.S. champion sprinter Michael Johnson. "He was just probably born with, you know, a unique blend of speed and power that most people -- even most world class sprinters --aren't born with."

But Bolt was also born with scoliosis -- a curvature of the spine that makes his right leg about a half an inch shorter than the left. That should have slowed him down.

Dallas researchers recently discovered Bolt's left foot strikes the track with 13 percent less force than his right. That uneven gait should have slowed him down.

And at 6-foot-5, so should his height. But the triple world-record holder seemed unaware of these handicaps.

"Usain Bolt is sort of energy spilling out in a lot of different places, but he can afford to get away with that," Johnson said. "He absolutely could have been faster."

And remember Beijing 2008 when he cruised to the finish line once victory was his?

"When you have the world record, I never really think I should have run faster," Bolt said. "I think my coach said that once that I underperformed, didn't he?"

Performance has always been a big part of Bolt's appeal -- regular fans to royalty have struck his lightning bolt pose. They're unlikely to complain that the world's fastest man might have been faster still.