locomotion

The movements of the arm depend on two muscles, the biceps and the triceps. To lift the arm, the biceps shortens and the triceps lengthens. To lower the arm, the opposite occurs: the biceps lengthens and the triceps shortens.

Ability to move independently from one place to another, occurring in most animals but not in plants. The development of locomotion as a feature of animal life is closely linked to another vital animal feature, that of nutrition. Animals cannot make their food, as can plants, but must find it first; often the food must be captured and killed, which may require great speed. Locomotion is also important in finding a mate, in avoiding predators, and in migrating to favourable areas.

The mechanism of locomotion in humans depends on the contraction of muscles stimulated by nerve impulses. Muscles are attached to the skeleton and create movement at joints. So, for example, the muscles of the legs contract to move the leg bones at joints such as the knee and hip. This movement is transmitted to the ground by the skeleton and results in locomotion.