Movement is a characteristic of the living world. It corresponds to a displacement in space, of the whole body (…) or of one of its parts.
Movement is made possible by the contraction and extension of muscles.
These are under the direction of the central nervous system.
Among the vertebrates, skeletal muscles are connected to bones by tendons, which enables the use of the joints.
This work requires a continual input of energy, principally in the form of glucose.
Legs, wings and fins are referred to as limbs. These are perfectly adapted to the milieu in which the animal evolves.
In pushing on the ground, the air or on water, a limb produces pressure that is at the origin of the propulsive force.
Thus, the horse’s hoof pushes the ground toward the rear, which propels the body forward.
In the same way, the wings of a bird drive air downward, which produces an upward force that keeps the bird in the air.
We should understand that the displacement is possible because the medium offers resistance.
Movements are often rapid and involve numerous muscles. It is very interesting to decompose a movement into simple images.
This is what Etienne Jules Marey in France, and Edward Muybridge in the United States, did near the end of the 19th century, thanks to chronophotography. This technique, an ancestor of the motion picture, enables one to obtain several images per second.