Perturbation-evoked lateral steps in older adults: Why take two steps when one will do?

Abstract

Background: Hip fractures in older adults often result from a fall in the lateral direction. While younger adults tend to recover balance from a lateral perturbation with a single lateral sidestep, older adults are prone to multistep responses which are associated with an increased fall risk. This study compared the stepping characteristics and stability of single and multistep responses to lateral perturbation in healthy older adults.

Methods: Eighty-four older adults received lateral waist-pull perturbations to either side. Spatio-temporal stepping characteristics and balance stability were quantified.

Findings: Fewer steps were taken to recover balance when the first step was a lateral sidestep. The stability margin of single lateral sidesteps was greater than medial sidesteps and cross-over steps to the back but not significantly different from single cross-over steps to the front at step termination. Single step responses were more stable than multistep responses at step termination and at step initiation for lateral sidesteps and cross-over steps to the front. The decreased stability of multistep responses was attributed to an increased center of mass velocity and a smaller distance between the center of mass and base-of-support at step termination.

Interpretation: Although lateral sidesteps result in fewer steps than cross-over steps to the front, the stability margin was not significantly different at step termination. These results suggest difficulty terminating center of mass motion and/or inefficient center of mass control differentiates single and multistep responses. Future studies should investigate perturbation training and/or hip abductor muscle conditioning as a means of improving compensatory stepping reactions.

Keywords: Aging; Balance; Falls; Perturbation; Rehabilitation; Stepping.

Fig. 1.

Illustration of loaded (A) and unloaded sidestep strategies (B, C, and D). Pull direction is indicated by the arrow at waist-level. The increase in base of support (BoS) boundary is shown for each step type. Note that in CSF and CSB, the swing foot must step beyond the stance foot to increase the BoS boundary. The distance between the CoM and BoS (BoS-CoM) is also shown.

Fig. 2.

Estimated mean and standard error of the margin of stability of a lateral sidestep (LSS), cross-over step to the front (CSF), cross-over step to the back (CSB), and medial sidestep (MSS) at first step initiation (A) and step termination (B). Center of mass (CoM) velocity at step initiation (C) and step termination are also shown (D). Statistically significant differences are shown with brackets. A statistically significant step count main effect for CoM velocity at step termination is not shown in D (p < 0.001).

Fig. 3.

Estimated mean and standard error of the distance between the center of mass (CoM) and base of support (BoS) of a lateral sidestep (LSS), cross-over step to the front (CSF), cross-over step to the back (CSB), and medial sidestep (MSS) at first step initiation (A) and step termination (B). The lateral increase in the BoS resulting from compensatory stepping is shown in C. Statistically significant differences are shown with brackets.