lNature sometimes hides phenomena that surpass understanding. A team of scientists from the universities of Utrecht and Amsterdam (Netherlands) and Liverpool (United Kingdom) became interested in emu racing. Bipeds, like humans, accelerate while always keeping one leg on the ground, in a kind of accelerated race or march.
It is true that this summer there were walking tests at the Paris Olympic Games, but these athletic walkers and true athletes take longer than runners to cover the same distance without making less effort or expending less energy. So why do these great Australians, already deprived of the right to fly, complicate their lives without the pleasure of being acclaimed in a stadium?
The anthropocentrism of biomechanics has established that when a foot (or an animal’s paw) touches the ground while running, energy is stored in the musculature and tendons. It is then returned when the foot (or paw) takes off. This spring system optimizes the energy expended. Therefore, it was necessary to understand this paradox, summarized in the article published on September 25 in Scientific advances : “Animals generally minimize locomotor energy expenditure, but birds prefer to run over terrain, despite the higher energy costs. » Ratites, a family that includes birds that no longer fly (ostriches, emus, cassowaries, etc.), can far exceed 50 kilometers per hour.
Pasha van Bijlert, the first signatory of this work, used 3D modeling software developed for humans. They allow muscles and tendons to be placed on a reconstituted skeleton, using tomography to understand and calculate the forces necessary for movements. This makes it possible to dispense with in vivo studies.
spring effect
These feathered bipeds walk and run crouching. They cannot stand like humans. “No one can imagine where the knee is in a bird, because its thigh is on the side of the body, hidden by the feathers.explains Anick Abourachid, professor of functional anatomy at the National Museum of Natural History (MNHN) in Paris. When you see a flamingo walking you think its knee is backwards… but the joint you see is the ankle. The bone below, very long, corresponds to the sole of the foot for us. The birds walk on their fingers. »
Therefore, the question is how this crouching and tiptoe running can represent a compromise to save effort for the emu. And where is the spring effect, which helps limit fatigue? We will spare you the numerous equations whose parameters are the movement of the center of mass, the fraction of the stride period during which a foot is in contact with the ground, or the ground reaction force, to calculate the metabolic cost of transportation.
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