Step by adaptive step: How younger and older adults navigate obstacles

Background

Younger adults, while approaching and crossing an obstacle, destabilize step length over several steps to ensure accurate foot placement around the obstacle and thereby avoid a trip. Destabilized step length has two potential effects: it facilitates corrections in foot placements to achieve the required accuracy, but it may also impair balance by perturbing the relation between the base of support and the motion or state of the whole-body center of mass. Therefore, destabilized step length in younger adults reflects a greater concern for tripping versus small variations in step length.

Research question

Do healthy older adults demonstrate greater step length destabilization than younger adults while approaching and crossing stationary obstacles?

Methods

Healthy younger and older adults approached and crossed a stationary visible obstacle multiple times. The across-trial foot placement data were analyzed using the uncontrolled manifold method to obtain the inter-step covariance (ISCz) index for several approach steps and the obstacle crossing step. Higher index value indicates higher step length stability and vice-versa.

Results and significiance

Younger and older adults destabilized step length (ISCz index reduced) while approaching and crossing the obstacle (p < .0001). The ISCz index was 14.5 % lower for older adults indicating that they destabilized step length more than younger adults (p = .02). Given the higher costs of a trip-induced fall, the pattern likely represents a rational adaptation by the older adults to avoid tripping. This pattern in the ISCz index could be used to assess the health of the neuromuscular control system in clinical populations.