Posture

POSTURE, a term used to denote the variable external form of the positioning of the human body and its parts. P. depends on many conditions—biomechanical, neurological, and psychological. Biomechanical factors are related to the action of gravity and the structural features of the skeleton, joints, and muscles. From the neurological side, P. is determined by the activity of static nerve mechanisms belonging to the extrapyramidal nervous system (subcortical ganglia, cerebellum, red nucleus system) and affecting muscle tone; the influence of higher cortical (frontal) mechanisms on posture is also undoubtedly present. At the same time, posture is regulated by means of reflexes to extero- and proprioceptive stimuli; according to experiments on animals (Magnus and others), vestibular and cervical reflexes have special importance for body position. The influence of psychological factors on P. is expressed 1) in that P. serves as a manifestation of pantomime, reflecting the emotional state, with which changes in biotone are also associated (P. in fear, sorrow, etc.), or 2) in that P. is established with a certain purpose, for example, during specific work. The features of human posture, its difference from the posture of animals, and its genesis basically depend on labor activity. In the process of 'the humanization of the ape' (Engels), the hands gradually freed themselves from static and locomotor functions and adapted to work, and with this inevitably connected the change in the posture of man, who stood on his feet. Habitual postures characteristic of humans change with age. Children have postures of an atavistic character (for example, in the quadrupedal syndrome of Schaltenbrand—P. on all fours when getting up). Changes in posture associated with the moment when the child begins to stand depend not only on the development of the corresponding nerve mechanisms but also on biomechanical causes (in children under one year, poorly developed lower extremities cannot support the weight of the body). Childhood is further characterized by a lordotic position when standing, while old age by a kyphotic one. Individual features of habitual postures, in addition to professional skills and age, depend on body build, the development of adipose tissue, etc. Professional, cultural, and living conditions are of great importance in this regard (for example, the posture when sitting among Eastern peoples who do not use European furniture). Of particular importance are professional skills. The posture of a schoolchild when writing, a worker at a machine or tractor, etc., is determined by the features of the working position. The correctness of posture in the sense of its correspondence to the characteristics of the organism and the requirements of the workplace is of great importance in production and hygienic respects. Changes in working conditions (especially during the period of socialist reconstruction) also change habitual postures. The posture of a burlak has long passed into the realm of legend, and before our eyes the stooped posture of a plowman, trudging behind his plow, is also disappearing. New working conditions, with a different emotional attitude toward work (cheerfulness, enthusiasm), create new postures—P. Pathological changes in posture depend on various causes. Changes in the skeleton, joints, and muscles (for example, in muscle atrophy), soreness of certain parts of the body, etc., more or less sharply affect P. Of even greater importance are changes in posture associated with damage to the central nervous system (especially extrapyramidal mechanisms), for example, in diseases of Parkinson, Wilson, in double athetosis, torsion spasm, etc., as well as in paralyses of cortical origin. Very characteristic are the features of posture in chronic epidemic encephalitis, in epileptic seizures. Special postures are observed in some oligophrenics (for example, the ape-like posture of microcephalics). The features of posture in schizophrenia are more complex, being associated both with possible damage to extrapyramidal systems and with psychological influences. An even more definite dependence on the psyche is noted in the formation of postures in manic-depressive patients, hysterics (for example, expressive postures during seizures), etc. From what has been said, it is clear that the study of the posture of patients has important diagnostic significance in many cases.