Why Are Cheetahs the Fastest? A Study Explains

Lifespan, strength, and brain size tend to increase with an animal's size, yet speed does not. The largest land animal, the elephant, wouldn't come close to catching the fastest land animal, the cheetah. It's no anomaly. The fastest animals on land, in water, and in air are all of intermediate size, per Cosmos. It's a curiosity researchers say they can now explain. In a new study, scientists uncovered two factors that determine an animal's maximum running speed: the speed and extent of muscle contraction. According to a release from Imperial College London, "the maximum speed an animal can reach is determined by whichever limit is reached first—and that limit is dictated by an animal's size."

"Animals about the size of a cheetah exist in a physical sweet spot at around [110 pounds], where these two limits coincide," says Australian biomechanics researcher Christofer Clemente, a co-author of the study published Monday in Nature Communications. Large, heavy animals like elephants do not exist in this sweet spot but instead hit what researchers call the "work capacity limit." "Their muscles produce less force in relation to their weight" and are limited by the extent to which they can contract, per the release. For them, running is a bit like "trying to accelerate when cycling up a hill in a high gear."

Smaller, lighter animals, on the other hand, hit the "kinetic energy capacity limit." Their muscles "generate large forces relative to their weight" but are limited by the speed at which they can contract, so running for them is like "trying to accelerate in a low gear when cycling downhill," per the release. The international team of researchers tested their findings against data from more than 400 species of land animals and returned accurate predictions of maximum running speeds in ones as large as elephants and as small as mites. In a rather unsettling addition, Earth.com notes the team's insight "could potentially guide the development of robots that emulate the athleticism of nature's finest runners." (More cheetahs stories.)