Posture sway and the transition rate for a fall

Postural body sway displacements for quiet standing subjects (measured with a new ultrasonic device) are reported. Two of the well-known strategies fo r balancing, namely ankle and hip movements, were probed. The data are mode led using a Fokker-Planck-Langevin stochastic theory. Both analytic and com puter simulation techniques are employed. The Kramers transition rate for a fall is expressed as a function of experimental parameters. The root mean square velocity is especially important for determining the fall probabilit y. (C) 2001 Elsevier Science B.V. All rights reserved.