Stability of Systems to Control Upright Postures in Stabilometry

In upright postures, the body continuously moves in a unique and complex rhythm; the amplitude and frequency of this rhythm depend on various sensory and motor system functions [2]. The base supporting the body is an area surrounded by bilateral soles. To maintain a stable posture, it is necessary to control the spatial perpendicular line from the body’s center of gravity within the narrow base [3-5]. The bilateral legs provide the ground reaction force required to support the body; however, the center of gravity continuously sways. This is because of the location of the head-upper limbs-trunk, which accounts for twothird of the body weight, is located at a distance that is two-third of the height from the floor. The human mechanism for maintaining upright postures is termed the righting reflex. Physiologically, the righting reflex is a body equilibrium function controlled by the involuntary regulatory system [6]. Elucidating the body’s equilibrium function is essential for diagnosing symptoms related to impairment of the balance function, such as those of progressive cerebellar degeneration, basal ganglia disorder, and Parkinson’s disease [7].