Factors affecting reaction times to short anterior postural disturbances

One source of falls in the elderly may be an inability to sufficiently adjust to transient postural perturbations or slips. Identifying useful predictors of fall potential, as well as factors that affect the ability of an individual to detect a movement of the standing support surface may provide insight into postural stability and methods to increase stability in elders. The effects of acceleration, displacement, neurological status, and age on movement detection reaction times were studied in 25 individuals--1 young adults, seven neurologically intact elderly adults, and six elders with (diabetic) peripheral neuropathy. Acceleration detection thresholds for anterior perturbations of 1, 4, and 16 mm of the support surface was previously determined for each subject via a two-alternative forced choice (2AFC) protocol, with longer (16 mm) moves yielding lower 2AFC thresholds (12-39 mm/s(2)) that varied by group. Using the acceleration threshold value determined, and 125% of that threshold (suprathreshold), reaction times to the start of the platform movement were determined for all three displacements. Reaction times to an additional superthreshold movement (4 mm at 100 mm/s(2)) were also measured. Lower acceleration values over longer moves required longer reaction times for motion detection. Reaction times were also influenced by peak energy imparted to the subject through the move. The higher prevalence of falls in the elderly and elderly diabetic may be due to slowing reaction times compounded by larger amounts of imparted energy needed for detection of a slipping event.