One Step, Two Steps, Three Steps More … Directional Vulnerability to Falls in Community-Dwelling Older People

Falls and their consequences are among the major health care problems affecting functional mobility and quality of life among older people. Even for people living independently in the community, falls are common occurrences (1,2). Although the causes of falls are varied and complex, a critical requirement needed for fall prevention is the ability to respond effectively to loss of balance. Protective stepping, an automatic reaction to instability, is a common strategy for maintaining balance in the everyday environment (3). Stepping is not a strategy of last resort but is often initiated well before the body approaches the limits of stability provided by the base of support (4) especially for older people (5,6). To effectively sustain standing balance, steps must be appropriately directed, timed, and executed to arrest the motion of the body center of mass by altering the base of support. Mounting evidence indicates that age-associated impairments in protective stepping contribute importantly to loss of balance and falls (3,6–8). An impaired ability to maintain lateral balance stability is especially relevant to falls among older people. For example, measures of mediolateral stability are associated with future falls (9) and past falls (10), and impaired control of lateral balance through stepping is particularly apparent for older adults (6,11,12). Furthermore, age-related falls often involve lateral body motion and associated hip fractures (13,14). Therefore, these observations underscore the specific challenges to maintaining balance and preventing falls that are linked with deficits in controlling lateral balance stability. Although there is accumulating support for the existence of a directional vulnerability to lateral instability and falls with aging, comprehensive and systematic investigations of this postulation are currently lacking. The aims of this study were (i) to determine the protective stepping response patterns evoked by different directions of externally applied waist-pull perturbations of standing balance and (ii) to identify the changes in stepping characteristics attributable to aging and in relation to the risk of falling. We hypothesized that the laterally oriented disturbances to balance would exacerbate the changes with age in protective stepping responses due to the increased demands for controlling lateral stability, and that these changes would be greater for those individuals who subsequently experienced falls.