Mechanisms and models of postural stability and control.

Though simple in appearance, postural stabilization is a complex neuromuscular task requiring coordination among multiple joints. Mechanisms of postural stability and control in the body include supraspinal processes responsible for anticipatory postural adjustments (APA) and internal model control, lower level motor servo, and passive viscoelasticity of the musculo-tendon complex (MTC). Nevertheless, active control mechanisms may have limited effectiveness due to intrinsic delays in the reflex pathways and muscle low-pass characteristics. The use of control-oriented mathematical models, aided by analytical methods, help provide insight into neuro-physiology. Control of balance in human upright standing is particularly well suited for modeling, and is also a popular experimental paradigm. This paper examines neuro-physiological basis of postural stability and control in the background of popular biomechanic and neuroscientific models.