Effects of aging-related losses in strength on the ability to recover from a backward balance loss

Although muscle weakness is a risk factor for falls, its direct influence on the ability to prevent a fall is largely unknown. This study therefore investigated the effect of aging-related losses in strength on the ability to restore static balance following a recovery step from a backward balance loss. A six-link, sagittal-plane musculoskeletal model with 10 Hill-type musculotendon actuators was developed to simulate the strength characteristics and balance recovery motions of young and older adults. Using this model, feasible regions for balance recovery were mapped for each age group for “slow” and “fast” initial conditions of backward and downward velocity. For both conditions, there was considerable overlap between the feasible regions of young and older adults, with both age groups able to restore static balance from similar initial hip heights. However, the ranges of initial center of mass positions, relative to the rear heel, for which balance could be restored did not extend as far anteriorly or posteriorly for older adults. The feasible region did not extend as far upward, downward, or posteriorly for the “fast” condition, with these differences between conditions being similar in each age group. The results suggest that aging-related losses in strength impair the ability to recover from a backward balance loss only if older adults take a very short or very long recovery step behind the center of mass, even for high velocities at step touchdown. Training of the stepping response might therefore be more effective than strength training in preventing backward falls.