The levels are related by a ratio called the fractal dimension.

A fractal pattern consists of a motif repeated at varying levels of magnification. A more recent interpretation is that sway has a fractal structure. In the past the variation was attributed to random effects. Furthermore, quiet standing involves activity in all joints, not just the ankles or hips. Analysis of postural sway shows much more variation than is seen in a physical pendulum or even a pair of coupled pendulums. Neither model is accepted as more than an approximation. Some investigators have replaced the ankle inverted pendulum analogy with a model of double linked pendulums involving both hip and ankle sway. Dysfunction in the core muscles has been implicated in back pain. The multifidi are intersegmental muscles. The transverse abdominals wrap around the spine and function as a compression corset. The core muscles are deep muscle layers that lie close to the spine and provide structural support. The core muscles play a role in maintaining stability. Electromyography has detected slight activity in the muscles of the calves, hips and lower back. The muscle exertion required to maintain an aligned standing posture is crucial but minimal. Īn analogy would be a ball that volleys back and forth between two players without touching the ground. Sway also occurs in the hip and there is a slight winding and unwinding of the lower back. Before each tilt reaches the tipover point the nervous system counters with a signal to reverse direction. The vertical body axis alternates between tilting forward and backward.

Also, human sway is too complicated to be adequately explained by spring action.Īccording to current theory, the nervous system continually and unconsciously monitors our direction and velocity. Recent studies, however, show that this spring action by itself is insufficient to prevent a forward fall. Traditionally, such correction was explained by the spring action of the muscles, a local mechanism taking place without the intervention of the central nervous system (C.N.S.).

Winter 1995 posture