One step, two steps, three steps more ... Directional vulnerability to falls in community-dwelling older people

Abstract

Background: Falls leading to disability are common occurrences with advancing age. Stepping is a natural protective option for maintaining balance and preventing falls. There are directionally dependent challenges for protective stepping associated with falls among older individuals. The aim of this study was to determine the stepping response patterns evoked by different directions of externally applied postural disturbances in younger and older adults and in relation to falls.

Methods: Seventy-five community-dwelling adults were tested: 26 younger adults and 49 older adults. Fall history of older participants was tracked prospectively for 1 year after testing. Steps were randomly evoked in 12 directions by a motorized waist-pull system. The number of recovery steps, type of stepping strategy, and first step kinematic characteristics were determined.

Results: Younger participants mainly used single recovery steps regardless of the perturbation direction. For the older groups, multiple steps occurred predominantly and were least for the forward-backward directions and greatest for the lateral directions. Trials with three or more recovery steps were increased laterally only for the fallers. Overall, fallers initiated stepping earliest, but other stepping characteristics were similar between the groups for forward-backward perturbations. Aging differences in stepping strategies for diagonal and lateral perturbations included numerous interlimb collisions. Adaptive changes in stepping characteristics between forward and lateral perturbations were also observed in relation to age and risk of falls.

Conclusions: These results indicated an age-associated reduction in balance recovery effectiveness through stepping particularly for the lateral direction among older individuals at greater risk for falls.

Keywords: Balance; Falls; Motor control..

Figure 1.

Schematic diagram of the motorized waist-pull perturbation system used to evoke protective stepping for balance recovery. The system combines a height adjustable pulley cable system mounted on vertical posts and a directional switching system that selectively perturbs balance in one of six possible directions via the pulling cables attached to the participant’s waist belt. Participants were perturbed in 12 directions, 6 sagittal and 6 frontal perturbations, presented in a counterbalanced order.

Figure 2.

Number of steps for each perturbation direction. Average (±1 SEM) percentage of the total trials with (A) one step, (B) two steps, or (C) three steps or more, observed in response to the 12 directions of perturbation for the younger participants (grey circles), older nonfallers (filled grey squares), and older fallers (dashed empty squares). B = directly backward perturbations; F = directly forward perturbations; L = directly leftward perturbations; R = directly rightward perturbations.

Figure 3.

Number of interlimb collisions for each perturbation direction. The total number of interlimb collisions during first step balance recovery in response to the 12 directions of perturbation for each group. B = directly backward perturbations; F = directly forward perturbations; L = directly leftward perturbations; R = directly rightward perturbations.

Figure 4.

First step characteristics by type of steps. Average values (±1 SEM) for (A) step duration, (B) step clearance, and (C) step global length are presented for the younger participants (grey circles), older nonfallers (filled grey squares), and older fallers (dashed empty squares) during forward, lateral loaded steps (LS), and lateral unloaded steps (US). Step clearance and global length were normalized to body height (BH).