Effects of Additional Support on the Maintenance of Human Vertical Posture

Effects of contact of a hand or fingertip with an additional support on human balance on stationary and movable surfaces were studied. Contact with a fixed or free vertical bar was established either by a handgrip or a touch with the tip of the index finger. Amplitudes and lengths of posturograms under conditions of free standing and standing with additional proprioceptive information were compared. It was shown that contact with an additional support during standing on a stationary surface with closed eyes decreases the amplitude of sagittal sway of the center of gravity by 1.3- to 2-fold as compared to standing without such a contact, independently of the contact type and the degree of bar mobility. During standing on a movable platform (which resulted in a three- to fourfold increase in the amplitude of sway as compared to standing on the floor), the grasp of the fixed bar decreased the amplitude of sagittal sway by five- to ninefold and the touch led to a three- to fourfold decrease. The sway of the common center of gravity upon contact with the movable bar during standing on the unstable platform was reduced by half on both planes independently of the contact type. The results suggest that sensory information from receptors of the hand contacting with a stationary or movable support substantially supplements the current neural representation of the spatial position of the body, correcting and changing the direction of postural reactions and the perception of the location of external objects, which ensures the ability of the CNS to maintain the balance under complicated conditions and to provide highly stable standing.