From Big Medical Encyclopedia

BALANCE OF THE BODY — a condition of a steady position of a body in space.

In system of peripheral mechanisms of maintenance of R. of t. the reflex of a tension enters, with the help to-rogo freely connected bones and joints of a body form the rigid support capable to sustain body weight. Rise to reflex reduction of all anti-gravitational muscles of a body is given by contact of a sole of legs with the area of a support. During standing equally effective all forces directed to the general center of gravity (GCG) of a body located at the level of the second sacral vertebra it is projected to the central section of the square of a support. Such center of gravity position of a body causing a dorsiflexion in an ankle joint, bending in knee and coxofemoral joints is accepted for fiziol, a constant. The anti-gravitational muscular device demands the smallest efforts during the standing in a convenient pose when peripheral regulation of R. of t. the hl is carried out. obr. due to work of gastrocnemius muscles. I that pose am an example of static balance. At the same time it is not a static pose since is followed highly - and low-frequency oscillations (fluctuations) of a body in strict sense.

Any change of vertical position caused by the movement of the head, trunk or extremities leads to the shift of OTsT. Preservation of a dynamic equilibrium in the conditions of action of external and internal forces is reached by reflex reduction of postural muscles, i.e. the muscles providing preservation of a pose.

Specific postural reflexes (see) provide the movements during the walking, run and an equilibration of moving body weight in conditions when OTsT is transferred from one leg to another. Using the balancing movements, and also regulating basic efforts, the person is capable to keep balance at the moment when the center of gravity of his body exceeds the limit of the area of a support as, e.g., at the runner at the time of start. Other biomechanical feature of movements during the walking, run, driving the bicycle, circulation on a rope is that at their performance the bearing area is brought under a projection of the center of gravity.

The following group of postural reflexes is made by the protective movements which allow to keep balance when the body is affected by horizontal or rotary forces. Inclinations of the area of a support are followed by compensatory changes poses (see), covering all muscles of a body. This reaction disappears after a labyrinthectomy. Normal recovery of the lost balance is reached by means of the automated vypryamitelny reflexes entering a complex of difficult any movements (see).

Though muscle spindles are the main source of postural reflexes, reduction of anti-gravitational muscles can be caused from tangoreceptors of a sole of foot, a retina and vestibular mechanism. During the standing these afferent systems exert the stabilizing impact on fluctuations of OTsT thanks to activation of basic muscles on alpha and to gamma efferent pathways. Mechanisms of regulation of an excitation threshold proprioceptors (see) provide plastic adaptation of muscles to razlich to ny motive tasks (e.g., the steady isometric stress or bystry limit reduction). Visual and vestibular postural reflexes play especially important role in formation of the anticipating motor teams during the walking on a pulled surface (rise, descent). In patol, cases optomotor postural reflexes compensate loss of a proprioceptive afferentation, in normal conditions sight mediates interaction of systems of postural balance and orientation in near space.

Central regulation of R. of t., as assume, it is provided with hierarchically constructed functional system, edges integrates a raznomodalny afferentation, using the generalized parameters to which number position of a body in space belongs, apparently. Activity of this «watching» system registering a difference between a real and standard position provides the flowing and advancing regulation of postural components of arbitrary motive acts.

Consider that afferent ways of postural reflexes pass through medial and intra lamellar kernels of a thalamus, and the efferent centers are located in basal kernels at which defeat (e.g., at parkinsonism) there is a loss of postural reflexes. The below-located bulbar and spinal centers ex-tensor (including extensive) reflexes come normal under the braking centrifugal influence. Therefore at disturbance of anatomic integrity of pyramidal (cortical and spinal) ways the person has spastic paralyzes (see. Paralyses, paresis ). Frustration of postural reflexes does not exclude, obviously, a possibility of coordination of autokinesias at the expense of psychomotor system of regulation of motive acts.

The basic facts concerning function of balance of a body at the person were received in clinic and in a lab. conditions. Apply tsiklogrammetrichesky shooting of movements to assessment of various physiological and biomechanical characteristics (see. Tsiklografiya ), registration of electric activity of muscles of a body (see. Electromyography ), stabilografiya (see).

Bibliography: Gurfinkel V. S., Kots Ya. M. and M. L Chic. Regulation of a pose of the person, M., 1-965; Gurfinkel V. S., etc. Stabilization of the situation of the case — the main objective of postural regulation, Fiziol, the person, t. 7, No. 3, page 400, 1981; Zhukov E. K., Kotelnikova E. G. and Semenov D. A. Biomechanics of physical exercises, M., 1963; Brandt T. and. lake of Height vertigo and human posture, Advanc. Otorhinolaryng., v. 25, p. 88, 1979; Eklund G. Standing equilibrium and position sense affected by muscle vibration in man, Uppsala, 1973, bibliogr.; Martin J. P. The basal ganglia and posture, L., 1967, bibliogr.; Murray M. P., S e i r e g A. Scholz R. C. Center of gravity, center of pressure, and supportive forces during human activities, J. appl. Physiol., v. 23, p. 831, 1967; Roberts T. D. M. Neurophysiology of postural mechanisms, L. — Boston, 1978, bibliogr.

B. B. Bokhov.