Walking(redirected from shanks' pony)
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a method of locomotion in animals and man resulting from the complex coordinated action of the skeletal muscles and the extremities. Bipedal, or two-legged, walking is characteristic of certain animals—for example, birds, some species of lizards, the kangaroo, and the anthropoid apes—and of man; multiped walking may be regarded as consisting of all the elements inherent in bipedal walking.
In bipedal walking the body is successively supported on each leg (the supporting leg), while the other one (the suspended leg) is simultaneously brought forward. In the cyclic sequence of walking one can single out the moment during which only one foot touches the ground (the single-support interval) and the moment during which the forward leg has already touched the ground while the back leg has not yet left it (the dual-support interval). The interval during which the leg is suspended is called the suspension interval. For each leg, the complete two-step cycle consists of the support interval and the suspension interval. With an increase in walking speed, the dual-support intervals are shortened, and they disappear altogether in running. During the support interval the active muscular effort of the extremities produces dynamic impulses, which communicate to the body’s center of gravity the acceleration required for progressive movement. At the moment when the foot is either pushing off or touching down, the amount of pressure exceeds the body’s weight; in the interval between these two moments, the pressure falls to a minimum. An increase in walking speed produces greater pressure at the support point.
In walking, man not only performs stereotypic movements adapted to his environment but also maintains his equilibrium. During this process the body’s center of gravity moves in all three planes. Along the vertical plane, the center of gravity is displaced by as much as 4 or 5 cm; it is at its lowest position in the dual-support period. In man, walking involves above all the muscles of the leg (the gastrocnemius, long peroneal, quadriceps, biceps, semimembranous, and semitendinous muscles) and of the pelvis (the gluteus medius and iliopsoas muscles). The movements of the shoulder girdle counterbalance the opposing rotations of the pelvis and lower part of the torso.
The succession and coordination of contractions in the various muscles are effected by a “walk generator,” which is located in the spinal cord and controlled by the higher sections of the central nervous system—primarily the subthalamic region of the diencephalon. The timing of the leg’s pushing-off and suspension phases is determined by signals proceeding primarily from the muscular receptors and from the distance (that is, hearing and vision) receptors; the signals’ corrective effects are mediated by the higher sections of the central nervous system—the cerebellum, the striopallidal system, and the cerebral cortex. Normal walking movements, however, may also occur in the absence of afferent signals; the interaction of the extremities is sufficient to produce coordinated walking. Depending on the intensity of the excitation transmitted to the spinal level, walking may shift into running, for example, or into a gallop. The mechanism involved is presumed to be identical in the case of animals and man.
The study of walking is of interest in connection with its applicability to athletics (competitive walking), military hygiene, orthopedics, and the use of prostheses, as well as the design of walking robots. Cyclography, ichnology (the study of footprints produced by walking), and electromyography are employed in the study of walking.
REFERENCESBernshtein, N. A. Opostroenii dvizhenii. Moscow, 1947.
Granit, R. Osnovy reguliatsii dvizhenii. Moscow, 1973. (Translated from English.)
Fiziologiia dvizhenii. Leningrad, 1976. (Handbook of physiology.)
Grillner, S. “Locomotion in Vertebrates: Central Mechanisms and Reflex Interaction.” Physiological Reviews, 1975, vol. 55, no. 2, pp. 247–304.
A. S. BATUEV and O. P. TAIROV