The presence of an obstacle influences the stepping response during induced trips and surrogate tasks.

Falling is a frequent cause of serious injury in older adults and trips are a dominant cause of falls in this rapidly growing population. Although there are few laboratory protocols that induce actual trips, there are many protocols that utilize surrogate tasks. These surrogate tasks, which are time-critical but do not involve an obstacle, appear to share a number of biomechanical characteristics with stepping responses following a trip. However, although rapid and safe negotiation of the obstacle and restoration of dynamic equilibrium are common requisites for success, we expected that stepping response kinematics during a successful recovery from a trip over a previously unseen obstacle would be substantially different than those of surrogate tasks without an obstacle. Unexpected trips were induced in 13 older men and women by an obstacle, the presence of which the subjects were previously unaware. Selected kinematics of the leading and trailing limb stepping responses during recovery from the induced trip were compared to those of two surrogate tasks that did not involve an obstacle. Multivariate analysis of variance (MANOVA) revealed that step height, step length, peak horizontal velocity, and peak vertical velocity of the leading and trailing limbs were significantly different during recovery from the induced trip compared to the surrogate tasks. These between-task performance differences may limit the extent to which performance of the surrogate tasks accurately and precisely reflect the potential to recover dynamic equilibrium following a trip. Therefore, these findings may be applicable in the design of new or modification of existing interventions to reduce falls in older adults.