The Physiology of Speed

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The Physiology of Speed
(Photo by John Gichigi/Getty Images)

Usain Bolt, the triple Olympic gold medal sprinter from Jamaica, predicted last week that he could break his own world record of 9.69 seconds in the 100 meter sprint with a time as low as 9.54 seconds.

He claimed his coach told him its possible, so he believes him. His coach, Glen Mills, may have just finished reading some new research coming out of Duke University that showed sprinters and swimmers who are taller, heavier but more slender are the ones breaking world records.

At first glance, it may not make sense that bigger athletes would be faster. However, Jordan Charles, a recent engineering grad at Duke, plotted all of the world record holders in the 100 meter sprint and the 100 meter swim since 1900 against their height, weight and a measurement he called "slenderness."

World record sprinters have gained an average of 6.4 inches in height since 1900, while champion swimmers have shot up 4.5 inches, compared to the mere mortal average height gain of 1.9 inches.

During the same time, about 7/10 of a second have been shaved off of the 100-meter sprint while over 14 seconds have come off the 100-meter swim record.


What's going on

Charles applied the "constructural theory" he learned from his mentor Adrian Bejan, a mechanical engineering professor at Duke, that describes how objects move through their environment.

"Anything that moves, or anything that flows, must evolve so that it flows more and more easily," Bejan said.

"Nature wants to find a smoother path, to flow more easily, to find a path with less resistance," he said. "The animal design never gets there, but it tries to be the least imperfect that it can be."

Their research is reported in the current on-line edition of the Journal of Experimental Biology.

For locomotion, a human needs to overcome two forces, gravity and friction. First, an athlete would need to lift his foot off the ground or keep his body at the water line without sinking.

Second, air resistance for the sprinter and water resistance for the swimmer will limit speed.

So, the first step is actually weight lifting, which a bigger, stronger athlete will excel at. The second step is to move through the space with the least friction, which emphasizes the new slenderness factor.

By comparing height with a calculated "width" of the athlete, slenderness is a measurement of mass spread out over a long frame. The athlete that can build on more muscle mass over a aerodynamic frame will have the advantage.

The numbers

In swimming, legendary Hawaiian champion Duke Kahanamoku set the world record in 1912 with a time of 61.6 seconds with a calculated slenderness of 7.88.

Some 96 years later, Eamon Sullivan lowered the world mark to 47.05 seconds at a slenderness factor of 8.29.

As the athletes’ slenderness factor has risen over the years, the winning times have dropped. In 1929, Eddie Tolan's world-record 100 meter sprint of 10.4 seconds was achieved with a slenderness factor of 7.61.

When Usain Bolt ran 9.69 seconds in the 2008 Olympics, his slenderness was also 8.29 while also being the tallest champion in history at 6'5".

“The trends revealed by our analysis suggest that speed records will continue to be dominated by heavier and taller athletes,” said Charles. “We believe that this is due to the constructal rules of animal locomotion and not the contemporary increase in the average size of humans.”

So, how fast did the original Olympians run?

Charles used an anthropology finding for Greek and Roman body mass and plugged it into his formula.

“In antiquity, body weights were roughly 70 percent of what they are today,” Charles said. “Using our theory, a 100-meter dash that is won in 13 seconds would have taken about 14 seconds back then.”

Bolt puts his prediction to the test next month at the track and field world championships in Berlin.

One of his main competitors is Asafa Powell, the previous world record holder, who is shorter and has a slenderness factor of 7.85.

My money is on the Lightning Bolt.

Please read more sports science articles at Sports Are 80 Percent Mental

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