The EMG startle response to free fall was studied in young and old normal subjects, patients with absent vestibular function, and patients with akinetic-rigid syndromes. The aim was to detect any derangement in this early phase of the "landing response" in patient groups with a tendency to fall. In normal subjects the characteristics of a voluntary muscle contraction (tibilais anterior) was also compared when evoked by a non-startling sound and by the free fall startle.Methods
Subjects lay supine on a couch which was unexpectedly released into free fall. Latencies of multiple surface EMG recordings to the onset of free fall, detected by a head mounted linear accelerometer, were measured.