We all know that cheetahs, which can run up to 75 mph, are the fastest land animal on Earth, but why is this? Why couldn’t elephants, for example, run faster?

Scientists now think it’s because the muscle cells in big animals run out of fuel before they can reach their theoretical maximum speed, Science magazine said.  

A new study released Monday charts the speed limits of hundreds of animals, ranging from tiny fruit flies to gigantic blue whales. They found that medium-size animals (whether on land, in air or sea) are generally the fastest.

While it’s not surprising that little animals aren’t that fast, why aren’t big ones? “By the time large animals get up to higher speeds while sprinting, their rapidly available energy reserves also soon run out,” study leader Myriam Hirt of the German Centre for Integrative Biodiversity Research told Live Science.

Just as cheetahs are fastest on land, medium-sized marlins are fastest in the sea and medium-size falcons are fastest in the air, researchers found.

“A beetle is slower than a mouse, which is slower than a rabbit, which is slower than a cheetah — which is faster than an elephant,” said the study, which was published in the peer-reviewed journal Nature Ecology and Evolution.

“The exciting part of this proposal is that it applies equally well to animals on land, in the air and in water,” according to a “News and Views” article that accompanied the study.

Many explanations have been proposed for why the largest animals are slower than smaller species, ranging from morphological constraints to the ability of bones and muscles to withstand the forces experienced during locomotion, the accompanying article said. “Yet none of these explanations, however neat and tidy they may be, apply equally to all animals.”

The new study attempts to rectify that. 

The…