Ankle reflex stiffness during unperceived perturbation of standing in elderly subjects.

Postural reflex activity during unperceived perturbation of standing was investigated in 38 elderly subjects (70-96 years old) and 10 younger adults (19-48 years old), and it was related in the elderly group to a history of unexplained falling in the 12 months prior to testing. Ankle torque (T) and ankle angle (A) were recorded during unperceived forward pulls to obtain the ankle stiffness (DeltaT/DeltaA), providing a measure of postural reflex activity at the ankle. Elderly nonfallers and younger adults had similar ranges of normalized ankle reflex stiffness.