How Footsteps Reveal Speed

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Determining how fast someone is moving can be as simple as a walk on a beach.

For years, researchers relied on a formula that included leg length to determine the speed of humans from fossils. But when study authors tested an equation formulated by the British zoologist Robert McNeil Alexander in 1976, they were able to get more accurate results using stride length alone, according to a study published in the journal Ichnos.

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The researchers had 14 students from the Complutense University of Madrid run along a beach in Asturias (Spain) in order to measure their stride lengths from footprint to footprint.

Using Alexander’s formula, they were able to pinpoint speed with a margin of error of 10 to 15 percent. The former equation had a margin of error of 50 percent.

“The data fit with the equation very well,” study author Javier Ruiz said in a press release.  ”Alexander did a good job with very little statistical data but with a large mathematical basis and we have seen empirically that his equation is correct.”

After the present-day trial, the authors studied fossil tracks from the Pleistocene era to estimate the speed at which those humans moved. The formula appears to work for both walking and running.

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Ruiz cautioned that the equation should only be used statistically. Too many variables come into play to be able to use it as a precise measure of any one specific instance.

“Strangely, sometimes 400- and 100-meter athletes have the same stride length, but run at different speeds,” he said. “What the body does is try to optimize how energy is used at a given speed.”

Photo: iStockPhoto

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