Postural Control in a Fall Risk Situation in the Elderly: Stepping Over an Obstacle Under Dual-Task Conditions

Avoiding and negotiating obstacles is a common cause of falling in the elderly. There is also evidence that walking under dual-task conditions, which requires a high level of attention, is associated with an elevated risk of falls in older adults. To better understand the role of dual-tasking in the disturbance of postural control when subjects are faced with obstacles, we used a simple quantification method to assess postural control after obstacle clearance. Sixty healthy elderly volunteers (aged 66-85 years) were tested for their postural stabilization on a force platform under the five following conditions: i) simple walking, ii) walking and stepping over an obstacle, and iii to v) walking and stepping over the obstacle under dual or triple-task conditions, the secondary task being either motor or cognitive for the dual-task and a combination of both for the triple-task. Postural control was assessed by determining both the distance covered by the center of pressure (COP) and the root-mean-square of the medio-lateral COP displacement. Only the latter differed significantly between walking conditions. In the “walking plus stepping” conditions, the motor and cognitive secondary tasks led to opposite effects, the motor task perturbed whereas the cognitive task improved postural control. These findings highlight the adverse effects of performing a secondary motor task while walking under challenging conditions, and confirm the appropriate prioritization of postural control over a cognitive task in cognitively unimpaired older subjects. These results also indicate that this near ecological approach may be useful for fall risk investigations in the elderly.