Cheetahs are the Fastest Land Mammals, but we don’t yet know exactly why. We have an idea of how to use “galloping” walking at its fastest, for example, and they have two different “flights”. The first involves their forelegs and hind legs under their body, and is called an “assembled flight,” while the second involves the forelegs and hind limbs outstretched, and is called an “extended flight.”
Extended flight is responsible for the fact that cheetahs can reach high speeds, but how quickly depends on ground forces and special conditions. Cheetahs also show significant spinal movement during flight as they alternate between bending and stretching in assembled and expanded spaces, allowing for rapid movement. Despite all this knowledge, we still do not understand much about the dynamics corresponding to these abilities.
Tomoya Kamimura at Nagoya Institute of Technology in Japan specializes in intelligent mechanics and motion.
“All animal running forms a flight phase and a tuning phase, and the dynamics of each phase are different,” Dr. Kamimura explains.
In the flight phase, all the legs are in the air and the whole body focuses on the ballistic movement. During the tuning phase, the body absorbs ground reaction forces through the legs.
“Thanks to such complex and hybrid dynamics, the observations can only make us, for the time being, elucidate the mechanisms behind animal running dynamics,” Dr. Kamimura continues.
Computer modeling brings insights
To gain a better understanding of the dynamic perspective of animal walking and spinal movement during running, researchers have relied on computer modeling with simple models, and it has been very successful.
Having said that, there are not yet many studies looking at the types of flight and spine movements that take place during a gallop, so the research team began a study that was published Scientific reports, relies on a simple model that mimics vertical and spinal movement.
The group’s study involved a two-dimensional model consisting of two rigid pieces and two massless rods representing a cheetah’s legs. The trunks were connected by a joint that repeated the bending movement of the spine and a torsion spring. The team also gave identical dynamic roles to the front and hind legs.
The team solved the simplified Motion Solutions that dominated the model, leading to six possible periodic solutions, two of which resembled two different flight types, such as a cheetah galloping, and four resembled only one flight type, unlike cheetahs. These were based on the criteria related to ground reaction forces provided by the solutions.
The criteria were then checked with measured cheetah data, and the team found that a cheetah galloping in real land met the criteria for two flight types through spine bending.
All of this led scientists to gain a new understanding of the speed of cheetahs. Periodic solutions also revealed that horse galloping involves an assembled flight as a result of limited movement of the spine, which means that the very high speeds achieved by cheetahs are the result of continued flight and spinal flexion.
“While the mechanism underlying this difference in flight types between animal species remains unclear, the findings broaden our understanding of the dynamic mechanisms underlying the rapid movement of cheetahs. In addition, they may be applied to the mechanical and control design of leg robots in the future,” says Dr. Kamimura.