Postural Control

 



Postural control is the ability to maintain body position during standing and while moving through space.  The visual, vestibular, and proprioceptive sensory systems provide information to the central nervous system in order to maintain postural control.  The body is not perfect at maintaining postural control and the inherent noise in this system is defined as postural sway.  Postural sway is the phenomenon of constant displacement and correction of the position of the center of gravity within the base of support.

The vertical stance of the human body is an inherently unstable system in a gravitation field.  Typically in biomechanics the body is modeled as an inverted pendulum as seen in Figure 1 at right.

Postural sway is a popular measure for many biomechanical studies done today.  Force platforms are regularly used to measure postural sway.  Force platforms measure vertical ground reaction forces and the center of pressure.  The resulting data can be used to evaluate steadiness, symmetry is postural control, and dynamic stability[1].  For example, Figure 2 depicts a force platform measurement of the center of pressure in the medial-lateral (ML) and anterior-posterior (AP) directions of a subject with eyes open and eyes closed.

An inverted pendulum is especially unstable when perturbed.  However, the human body is even more complicated because of the many joints that make up the skeletal system.  Also, the human body has a relatively small area of support within which the center of mass must fall (see Figure 3 below). 

Physiological Background on Postural Control


Figure 2: Center of Pressure (COP) of eyes open and eyes closed standing [2]
 

Figure 1: Body as inverted Pendulum [2]

Figure 3: Human body modeled with multiple joints of inverted pendulums. [2]