  Postural body sway displacements for quiet standing subjects (measured with a
new ultrasonic device) are reported. Two of the well known strategies for
balancing, namely ankle and hip movements were probed. The data is modeled
using a Fokker-Plank-Langevin stochastic theory. Both analytic and computer
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 in determining the fall probability.
