Balance perturbations.

Impairments of balance and gait leading to loss of mobility, falls, and disability are common occurrences in many neurologic conditions and with older age. Much of our current understanding about posture and balance control and its impairments has come from investigations of how healthy individuals and those with neurologic disorders respond to situations that perturb standing balance during instructed voluntary tasks or in reaction to externally imposed challenges to stability. Knowledge obtained from these investigations has come from documenting the physical and physiologic characteristics of the perturbations together with the body's electrophysiologic, structural, kinetic, kinematic, and behavioral responses. From these findings, basic mechanisms, diagnostic and pathologic criteria, and targets for clinical care have been identified while continued gaps in understanding have been exposed. In this chapter, we synthesize and discuss current concepts and understanding concerning the sensorimotor control of posture and balance while standing. We draw insights gained from perturbation studies investigating these functions in healthy adults, and those with neurologic pathologies.