Study: When it comes to animal speed size matters

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It’s not quite E=mc2, but scientists unveiled a powerful formula Monday that explains why some animals run, fly and swim faster than others.

Call it the "speed rule": Strength alone does not determine top velocity because land mammals, birds and fish can only accelerate for as long as they can draw from available energy stored in muscle tissue, they said.

For example, the researchers discovered that an intermediate body size like that of a cheetah, falcon or marlin – is optimal for hitting that sweet spot between brawn and energy burst.

Too small, and there's not enough musculature; too big, and there's too much mass.

The African elephant is the largest animal on land, but not the fastest. /VCG Photo

Knowing only an animal's weight and the medium it moves in – water, air or across land – is enough to calculate its maximum speed with 90 percent accuracy, they found.

The axiom even works retroactively for dinosaurs, they reported in the journal Nature Ecology & Evolution.

A parabola-like relationship between the body mass of animals and the maximum speed they are able to reach. For the first time, researchers are able to describe how this comes about, thanks to a simple mathematical model. /AFP Photo

"Scientists have long struggled with the fact that the largest animals are not the fastest," said lead author Myriam Hirt, a biologist at the German Center for Integrative Biodiversity Research in Leipzig.

If muscles were all that mattered "elephants would reach maximum speeds of about 600 kph (370 mph)," she told AFP.

Instead, tuskers peak at about 34 kph (21 mph).

Big beasts, in other words, run out of so-called anaerobic energy, supplied by the muscles, before being able to reach their theoretically maximum speed.

(Source: AFP)

The fastest animals /AFP Photo

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