The long-term objectives of this research are to: (1) identify preventable and treatable causes of falling that are unrelated to disease, and (2) to develop clinically practical interventions that will be effective in reducing the incidence of falling in elderly people. In contrast to other investigators who imply, or explicitly express a relationship between age-related increases in static postural sway and falling behavior, our work has resulted in the contention that the commonly observed (but not obligatory) age-related increase in static postural sway does not predispose a person to falling. Furthermore, it is hypothesized that in otherwise healthy, elderly people falls result following large postural perturbations from an inability to restore postural stability due, primarily to an age-related decrease in the ability to generate and coordinate multiple muscle/joint (lower extremity and trunk) powers. The proposed research is unique in that it will induce large postural perturbations that require stepping responses and to which recovery of postural stability is increasingly difficult and not always possible. The muscle power variables hypothesized to be crucial to recovery of stability will be computed from each postural perturbation condition, the clinically measurable correlates of these variables measured in the same subjects, and the relationships between these variables and the likelihood of falling characterized. The specific aims of this research are to (1) determine the relationships between measures of static postural stability and the likelihood of falling subsequent to large postural perturbations that require stepping responses; (2) characterize the critical kinematic and kinetic determinants of stepping responses that are associated with successful restoration of postural stability following (a) sudden release from statically unstable positions, (b) sudden accelerations and continued motion of the support surface, (c) trips induced during locomotion; (3) to establish the relationship between the lower extremity (ankle and knee) and trunk muscle powers that may be measured in the laboratory/clinic and the likelihood of falling during the experiments of Specific Aim 2. This research will identify specific age-related deficits in the neuromuscular system related to decreased ability to recover postural stability following large postural perturbations and provide direction toward specific clinical intervention. Ultimately, this research will contribute to improving and extending the independent lifestyles of elderly people thereby having a positive effect on the quality of life and the economics of aging.