By Isobel Williams via SWNS
The reason the cheetah is the fastest land animal on Earth has been explained by scientists.
The big cat hits the ‘sweet spot’ where their muscles can contract the fastest relative to their size.
And the research principles uncovered could dictate getting the speediest robots.
Professor Christofer Clemente, from the University of the Sunshine Coast and The University of Queensland, said: “The key to our model is understanding that maximum running speed is constrained both by how fast muscles contract, as well as by how much they can shorten during a contraction.
“Animals about the size of a cheetah exist in a physical sweet spot at around 50kg, where these two limits coincide.
“These animals are consequently the fastest, reaching speeds of up to 65 miles per hour.”
While many key traits such as strength, limb length, lifespan and brain size tend to increase with animals’ size, maximum running speeds tend to be greatest in medium-sized animals.
To explore why this is, the international research team developed a physical model of how muscles set limits on land animals’ top running speeds.
Their findings suggest that there is not one limit to maximum running speed, as previously thought, but two: how fast versus by how far, muscles contract.
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.
The first limit termed the ‘kinetic energy capacity limit’, suggests that the muscles of smaller animals are restrained by how quickly they can contract.
The researchers explain that because small animals generate large forces relative to their weight, running for a small animal is a bit like trying to accelerate in a low gear when cycling downhill.
The second limit called the ‘work capacity limit’, suggests that the muscles of larger animals are restrained by how far their muscles can contract.
Because large animals are heavier, their muscles produce less force in relation to their weight, and running is more akin to trying to accelerate when cycling up a hill in a high gear.
Co-author Dr. Peter Bishop from Harvard University said: “For large animals like rhinos or elephants, running might feel like lifting an enormous weight, because their muscles are relatively weaker, and gravity demands a larger cost.
“As a result of both, animals eventually have to slow down as they get bigger.”
To test the accuracy of their model, the team compared its predictions to data on land animal speed and size collected from more than 400 species, from large mammals, birds and lizards to tiny spiders and insects.
The model accurately predicted how maximum running speeds vary with body size for animals that differ by more than 10 orders of magnitude in body mass – from tiny 0.1-milligram mites to six-tonne elephants.
Their findings, published in the journal Nature Communications, shed light on the physical principles behind how muscles evolved and could inform future designs for robots that match the athleticism of the best animal runners.
The most famous and fastest of these runners is the cheetah, which the researchers say is in a size sweet spot, giving it the perfect balance of these principles.
The model also suggests that land animals weighing over 40 tonnes would be unable to move, suggesting that extinct giants such as dinosaurs may have evolved unique muscular anatomies.
Lead author Dr. David Labonte, from Imperial College London’s Department of Bioengineering, added: “The fastest animals are neither large elephants nor tiny ants, but intermediately sized, like cheetahs.
“Our study raises lots of interesting questions about the muscle physiology of both extinct animals and those that are alive today, including human athletes.
“Physical constraints affect swimming and flying animals as much as running animals – and unlocking these limits is next on our agenda.”
