The genesis of postural sway with special reference to cardiovascular dynamics

In an attempt to determine the influence of cardiorespiratory events on sway behaviour. a series of four experiments were undertake.n on a total of 95 subjects, all young healthy adults. Sway tiehaviour, defined as the corrective force recorded between the soles of the feet and the surface of a biomechanical measuring platform (Kistler, 9261A), was first examined to determine the extent to which it is a function.of sex and physique. Height, weight and obesity measurements were taken from 58 subjects (29 male, 29 female) and their influence on sway behaviour analysed. The second experiment was an extended ideographic study designed to test the constancy of sway behaviour over a six-week period for ten subjects (six male, four female) in an attempt to identify the personal characteristics of postural sway. This led to the formulation of a dynamic model of postural sway behaviour based on cardiorespiratory events. In the third experiment the magnitude of the cardiac forces and stroke volume,by transcutaneous aortovelography, were measured on 18 subjects (eight male, ten female), and used to establish the direct effect of cardiac action on sway behaviour. In the final experiment the role of 18 antigravity muscles of the lower limbs and trunk in postural maintenance was examined in nine subjects (five male, four female) to test the widely held hypothesis that sway is a direct outcome of the dynamic equilibrium that exists between gravitatiqnal forces and the myotatic reflex responses. The validity of the model was tested by comparing the predicted sway based on cardiorespiratory events with actual sway behaviour.