The influence of age on the thresholds of compensatory stepping and dynamic stability maintenance.

The purpose of this study was to investigate the effects of age on compensatory-stepping thresholds and dynamic stability maintenance in response to postural disturbances. It was hypothesized that, with older age, anterior but not posterior stepping thresholds would be reduced. Thirteen young adults (31.1 ± 0.8 years), 11 middle-aged adults (57.6 ± 2.5 years), and 11 older adults (73.8 ± 5.3 years) participated in this study. Surface translations were delivered as subjects stood on a microprocessor-controlled treadmill. Subjects were instructed to "try not to step". Stepping thresholds were defined as the largest displacement at a given peak treadmill-belt velocity for which a subject could prevent stepping. The margin of stability was calculated to estimate the minimum dynamic stability at the stepping thresholds. Age-related declines in the ability to prevent forward steps were apparent. Anterior stepping thresholds were reduced with age. The minimum margin of stability associated with anterior stepping thresholds was not influenced by age. Therefore, smaller disturbance displacements caused middle-aged and older subjects to become dynamically unstable to the point of stepping. Posterior stepping thresholds were not influenced by age. It is concluded that an age-related decline in anterior, but not posterior, stepping thresholds was due to an impaired ability to maintain dynamic stability after a disturbance.