BBC Future
Will We Ever?

# Will we ever… run 100m in under nine seconds?

To understand how fast a human can ultimately run, we need to go beyond the record books and understand how Usain Bolt's legs work.

In 2008, at the Beijing Olympic Games, Jamaican sprinter Usain Bolt ran the 100m in just 9.69 seconds, setting a new world record. A year later, Bolt surpassed his own feat with an astonishing 9.58-second run at the 2009 Berlin World Championships. With the 2012 Olympic Games set to begin in London, the sporting world hopes Bolt will overcome his recent hamstring problems and lead yet another victorious attack on the sprinting record. He is arguably the fastest man in history, but just how fast could be possibly go?

That’s a surprisingly difficult question to answer, and ploughing through the record books is of little help. “People have played with the statistical data so much and made so many predictions. I don’t think people who work on mechanics take them very seriously,” says John Hutchinson, who studies how animals move at the Royal Veterinary College in London, UK.

The problem is that the progression of sprinting records is characterised by tortoise-like lulls and hare-like… well… sprints. People are getting faster, but in an unpredictable way. From 1991 to 2007, eight athletes chipped 0.16 seconds off the record. Bolt did the same in just over one year. Before 2008, mathematician Reza Noubary calculated that “the ultimate time for [the] 100 meter dash is 9.44 seconds.” Following Bolt’s Beijing performance, he told Wired that the prediction “would probably go down a little bit”.

John Barrow from the University of Cambridge – another mathematician – has identified three ways in which Bolt could improve his speed: being quicker off the mark; running with a stronger tailwind; and running at higher altitudes where thinner air would exert less drag upon him. These tricks may work, but they’re also somewhat unsatisfying. We really want to know whether flexing muscles and bending joints could send a sprinter over the finish line in 9 seconds, without relying on environmental providence.

To answer that, we have to look at the physics of a sprinting leg. And that means running headfirst into a wall of ignorance. “It’s tougher to get a handle on sprinting mechanics than on feats of strength or endurance,” says Peter Weyand from Southern Methodist University, who has been studying the science of running for decades. By comparison, Weyand says that we can tweak a cyclist’s weight, position and aerodynamic shape, and predict how that will affect their performance in the Tour de France. “We know down to 1%, or maybe even smaller, what sort of performance bumps you’ll get,” he says. In sprinting, it’s a black hole. You don’t have those sorts of predictive relationships.”

Our ignorance is understandable. By their nature, sprints are very short, so scientists can only make measurements in a limited window of time. On top of that, the factors that govern running speed are anything but intuitive.

Sole power

Weyand divides each cycle of a runner’s leg into what happens when their foot is in the air, and what happens when it’s on the ground. The former is surprisingly irrelevant. Back in 2000, Weyand showed that, at top speed, every runner takes around a third of a second to pick their foot up and put it down again. “It’s the same from Usain Bolt to Grandma,” he says. “She can’t run as fast as him but at her top speed, she’s repositioning her foot at the same speed.”

That third of a second in the air – the swing time – is probably close to a biological limit. Weyand thinks that there is very little that people can do to improve on it, with a notable exception. Oscar Pistorius, the South African double-amputee, runs on artificial carbon-fibre legs that each weigh less than half of what a normal fleshy limb would do. With this lighter load, he can swing his legs around 20% faster than a runner with intact limbs, moving at the same speed.

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