Will we ever run the 100 metres in 9 seconds?

By Ed Yong | July 18, 2012 7:54 am

Here’s the ninth piece from my BBC column

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.

For most runners though, speed is largely determined by how much force they can apply when their foot is on the ground. They have two simple options for running faster: hit the ground harder, or exert the same force over a longer period.

The second option partly explains why greyhounds and cheetahs are so fast. They maximise their time on the ground using their bendy backbones. As their front feet land, their spines bend and collapse, so their back halves spend more time in the air before they have to come down. Then, their spines decompress, giving their front halves more time in the air and their back legs more time on the ground.

Such tricks aren’t available to us two-legged humans, but technology provides alternatives. In the 1990s, speed skaters started using a new breed of “clap skates” where the blade is hinged to the front of the boot, rather than firmly fixed. As the skaters pushed back, the new design kept their blades in longer contact with the ice, allowing them to exert the same force over more time. Speed records suddenly fell.

People have tried to duplicate the same effect with running shoes, but with little success. That’s because a running leg behaves a bit like a pogo stick. As it hits the ground, it compresses. As it steps off, it gets a bit of elastic rebound. Technologies that try to alter a runner’s gait tend to interfere with this rebound, and diminish the leg’s overall performance. “It’s hard to intervene in a similar manner to the clap-skates without buggering up the other mechanics of the limb,” says Weyand. (Again, Pistorius bucks the trend because his artificial legs are springier than natural ones, and give him around 10% longer on the ground than other runners.)

Ground force

For those with intact limbs, one option remains: exert more force on the ground. Put simply, fast people hit the ground more forcefully than slow people, relative to their body weight. But we know very little about what contributes to that force, and we are terrible at predicting it based on a runner’s physique or movements.

We know that champion male sprinters can hit the ground with a force that’s around 2.5 times their body weight (most people manage around two times). When Usain Bolt’s foot lands, it applies around 900 pounds (400kg) of force for a few milliseconds, and continues pushing for around 90 more.

Weyand likes to imagine a weightlifter trying to apply the same force in a one-legged squat – they would come nowhere close.  “What we know about force under static conditions under-predicts how hard sprinters hit by a factor of two,” he says. “We just don’t have the ability to go from the movements of the body to the force on the ground.” Even if a sprinter’s muscles were eventually boosted by gene doping techniques, we have no way of calculating how much faster their owners would run.

Studies are underway to fill in those gaps, and Weyand is hoping that we’ll be able to make better predictions in five or 10 years. Just a few months ago, Marcus Pandy from the University of Melbourne used computer simulations of sprinters to show that the calf muscles, more than any others, determine the amount of force that runners apply to the ground. At top speeds, the hip muscles become increasingly important too. “Maybe if you train a sprinter, you could potentially train them to have really strong calves,” says Hutchinson.

For the moment, however, any predictions about the ceilings of human speed are still ill-informed ones. The only way to work out if Bolt or some other sprinter will smash the existing record is to watch them.

Image by PhotoBobil

More from Will we ever?

1. I wonder what effect runners’ arms have. It seems that sprinters tend to have very muscular arms, while long distance runners tend to have quite small, weedy arms. It makes sense to have small arms to reduce one’s body mass, so presumably arm strength has a positive effect on sprinting.

2. Justin Tungate

@Peter: Arm swing has a strong correlation with stride length.

3. Georg

Who is “we”? Whoever, not I!

4. Rogier

John Brenkus in The perfection point argues that we’ll reach <9 seconds (actually, his calculations come out to 9.01, but he says we'll break the 9 because of the 'boundary' factor). I'm not sure I agree with all his calculations and assumptions, but it's an interesting read nonetheless!
He reiterates most of the data/suggestions from his book here:
http://sports.espn.go.com/espn/news/story?id=5349284
I'd be interested in your views on his ideas!

5. The clap skate effect is hard to apply to running, but maybe tuning the shoe bounce for individual runners is one way to improve their speeds (they may already do this in the olympics, I’m not sure). Harvard Prof. Thomas McMahon tuned a track there that increased running speeds and reduced injuries. See http://www.thecrimson.com/article/1999/2/19/prof-mcmahon-tuned-track-creator-dies/

6. Old Geezer

For decades the best scientific minds agreed that there would never be a sub-four minute mile. Then a fellow named Roger proved them wrong. Shortly thereafter it became somewhat of a habit to break the four minute barrier. At some point it will be shown that an even better human body will come along and break the 9 second barrier. Shortly thereafter….well, you know.

7. Melissa G

@Peter

Using arms when running counterbalances the legs. The natural motion when running or walking is to have the arm swing coincide with the opposite step. This is to keep things balanced and help enable you to move in a straight line. If a runner has poor upper body form, the lack of an arm swing can slow the legs because they are working harder and against the upper body. Having them balanced with the same intensity is the key to getting faster. The arms should start bent at the elbows at a 90-degree angle. The range of motion will largely depend on how fast the runner is going. Faster running calls for a higher knee raise while a distance runner who is going slower can afford to keep the hands low and have less arm swing. Though the arm motion will be fast and vigorous, it should be done with relaxed muscles and joints. A weak upper body will make it difficult to swing your arms aggressively enough to keep up with your legs, which causes you to work harder and tire sooner.

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