Why midsize animals are the fastest | Science News

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Why midsize animals are the fastest

New simulation suggests that speed has body mass limits

By
9:00am, August 11, 2017
cheetah and wildebeests

FULL SPEED AHEAD  The speed demons of the animal kingdom are hardly giants. A new study suggests larger animals run out of fuel for their muscles before reaching top speeds.

Speed has its limits — on the open road and the Serengeti. Midsize animals tend to be the speedsters, even though, in theory, the biggest animals should be the fastest. A new analysis that relates speed and body size in 474 species shows that the pattern holds for animals whether they run, fly or swim (see graphs below) and suggests how size becomes a liability.

This relationship between speed and size has long stumped scientists. Big animals have longer legs or flippers to get from point A to point B. And bigger bodies have higher metabolic rates and more fast-twitch muscle cells, needed to convert chemical energy into mechanical energy and rapidly accelerate. So, why aren’t wildebeests faster than cheetahs?

The make-or-break factor is the time it takes an animal to accelerate to its top theoretical speed, an upper limit based on mass and metabolic rate, researchers report July 17 in

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