Scientists explain secret of Bolt's speed
Scientists looking at the technique of 100m and 200m world record holder Usain Bolt have explained his success is not down to moving his legs faster than his rivals.
Bolt has revolutionised sprinting with some electric performances which make him the current Olympic and World Champion, setting best times far away beyond those of his peers.
However, as scientists in America have realised, leg speed is not a differentiating factor in being quick.
More than 10 years ago, Peter Weyand of the Southern Methodist University first identified that athletes and non-athletes had similar leg speeds.
"The amount of time to pick up a leg and put it down is very similar," said Weyand. "It surprised us when we first figured it out."
The difference between the ordinary and the elite comes down to the pressure applied as the foot comes down, and how long the foot touches the ground.
Whereas the average step of a casual runner can propel someone forward with around 500-600 pounds of force, an Olympic sprinter manages more than 1,000.
And when the foot touches the ground during a stride it is on the ground for about 0.12 seconds in the case of average runners - but the elite sprinter can be 33% more efficient by moving off in just 0.08 seconds.
"The amount of time [one's legs are] in the air is 0.12, regardless if you're fast or slow," Weyand theorised. "An elite sprinter gets the aerial time they need with less time on the ground to generate that lift - or to get back up in the air - because they can hit harder."
Where Bolt gets an advantage over his rivals, then, is his ability to get those same advantages from a larger frame.
The Jamaican covers a 100m sprint in 41 strides, whereas the majority of his rivals will do so in 44.
Taller sprinters have traditionally struggled to work as efficiently, however, as the discipline also requires balance and control as well as power. The shorter build, such as that of Bolt's closest rival, Tyson Gay, who stands at five foot 11 inches, has been seen in the past as the ideal size. Bolt, by contrast, is six inches taller.
"He has a very unusual combination of being extremely tall and relatively massive and being able to accelerate well. Those things are at odds with each other," said Dr Mike Young, a strength and speed coach.
"He accelerates better than all but one guy in the world - behind [compatriot] Asafa Powell - but because he's so massive, he takes fewer strides. If you're that large, once you're moving, you stay moving."
And as Dan Pfaff, who coached 1996 100m Olympic champion Donovan Bailey puts it, "Would you rather take 44 steps to your car or 41?"
Scientists have also debated how far the record can be broken if the still relatively inexperienced Bolt can make further improvements.
Bolt has previously told the BBC he believes a realistic target is to run the 100m quicker than 9.50 seconds, explaining :"That's where I think the record will probably never be beaten."