Why are not the biggest animals the fastest?

We all know that cheetahs, which can run up to 120kph, are the fastest land animal on Earth, but why is this? Why could not elephants, for example, run faster?

Scientists now think it is 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 on 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 is not surprising that little animals aren’t that fast, why are not 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 study also estimated the running speeds of long-extinct animals such as dinosaurs. For example, the Tyrannosaurus Rex likely had a top speed of 27kph.

That’s 1.6kph faster than the top speed of an average human today, and 17.7kph slower than Usain Bolt, the world’s fastest man. So we may have had a fighting chance against the infamous terrible lizards.

“In the future, our model will enable us to estimate, in a very simple way, how fast other extinct animals were able to run,” Hirt said.