The fastest animals are neither large elephants nor small ants, but intermediate sizes such as: Cheetah(Acinonychus jubatus). Why does running speed deviate from the regular patterns that govern an animal's anatomy and most other aspects of performance? A new study shows that, as previously thought, maximum running speed This suggests that there is not one limit to speed, but two: the speed and distance at which the muscle contracts. The maximum speed an animal can reach is determined by which limit is reached first, and that limit is determined by the size of the animal.

University of the Sunshine Coast researcher Professor Christopher Clemente said: “The key to our model is understanding that maximum running speed is limited by how fast the muscles contract and how much they can shorten during contraction. ” he said. University of Queensland.

“Animals as big as cheetahs exist in a physical sweet spot of about 50 kg where these two limits meet. Therefore, these animals are the fastest, with speeds of up to 105 km/h (65 mph). will reach.”

The first limit is called the “kinetic energy capacity limit'' and suggests that muscles in small animals are limited by how fast they can contract.

Because small animals generate large forces relative to their body weight, running for them is similar to trying to accelerate in a low gear when riding a bicycle downhill.

The second limitation is called the “work capacity limitation” and suggests that muscles in large animals are limited by the range over which they can contract.

Large animals are heavy, so their muscles produce less force relative to their body weight, and running is similar to trying to accelerate up a hill in a high gear on a bicycle.

“For large animals like rhinos and elephants, running can feel like lifting huge weights because their muscles are relatively weak and gravity takes a big toll on them,” says Harvard University. says researcher Dr. Peter Bishop.

“As a result of both, animals eventually have to slow down as they grow.”

To test the model's accuracy, the authors compared its predictions to land animal speed and size data from more than 400 species, ranging from large mammals, birds, and lizards to small spiders and insects.

The model accurately predicted how maximum running speed varied with body size for animals whose weights varied by more than 10 orders of magnitude, from a tiny 0.1 milligram tick to a 6-ton elephant.

Their findings shed light on the physical principles behind how muscles evolved and could inform future designs of robots that can match the athletic performance of the best animal runners.

The new model may not only explain how fast animals can run, but also provide important clues for understanding differences between groups of animals.

Large reptiles, such as lizards and crocodiles, are generally smaller and slower than large mammals.

“One possible explanation for this may be that reptiles' limb muscles make up a small proportion of their body mass, meaning that reptiles reach their work limits quickly when they are light. It needs to stay small in order to move,” he said. Taylor Dick is a researcher at the University of Queensland.

The researchers' model, combined with data from living species, also predicted that land animals weighing more than 40 tonnes would be unable to move.

The heaviest land mammal living today is the African elephant, which weighs approximately 6.6 tons, but there are also land dinosaurs such as: Patagotitanit probably weighed well over 40 tons.

“This indicates that caution is needed in extrapolating the muscle anatomy of extinct animals from data from non-extinct animals,” the researchers said.

“Rather, the data indicate that extinct giants may have evolved unique muscle anatomy, which warrants further study.”

Dr David Labonte, a researcher at Imperial College London, said: “Our study raises many interesting questions about muscle physiology in both extinct animals and living animals, including human athletes.” said.

“Physical constraints affect animals that swim and fly just as they do animals that run, and lifting these constraints is our next challenge.”

a paper The survey results were published in a magazine nature communications.

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D. Labonte other. 2024. Dynamic similarity and unique allometry of maximum running speed. Nat Commune 15, 2181; doi: 10.1038/s41467-024-46269-w