Passive and active contributors to postural stabilization

The neuro-physiological mechanisms involved in postural stabilization are not well understood. Human body mechanically resembles an inverted pendulum that is inherently unstable. Active and passive mechanisms at muscle level, as well as other visual and vestibular processes, are attributed to stability. The available evidence suggests that muscle stiffness alone is insufficient to stabilize body sway, and must rely on active mechanisms of stabilization that are unlikely to have a reflex nature due to the intrinsic delays in the reflex pathways and the low-pass characteristics of the muscle response. The role played by the central nervous system in active control of stance thus remains an open and intriguing question. In this study we present simulation results to support an active-passive model of postural stabilization. Besides expanding our understanding of the postural stabilization process, the insight gained would be useful to promote intervention techniques for therapists and clinicians working with fall-prone individuals.