Muscle Strength and Age Effects in Balance Recovery

摘要

The purpose of this project was to investigate a potential mechanism by which age-related reductions in muscle strength contribute to falls in older adults. Tripping and falling accidents are a major problem in both occupational and non-occupational settings. Older adults in particular have a higher incidence of falling and fall related injuries. Despite numerous studies that have implicated age-related strength reductions in the higher incidence of older adult falls, the mechanism by which strength reductions contribute to falls remains unclear. Determining this mechanism will help toward understanding why people fall, and contribute to the development of intervention strategies aimed at fall prevention. Age-related strength reductions may contribute to the higher incidence of older adult falls by limiting muscle forces during balance recovery. Insufficient muscle forces during balance recovery would not adequately decelerate trunk angular momentum and/or would not prevent the stepping leg from collapsing. As a result, the individual would fall. An existing experimental model of balance recovery was used to evaluate insufficient muscle forces during balance recovery as a mechanism contributing to tripping and falling accidents in older adults. The experiment involved repeatedly releasing subjects from progressively larger stationary forward leaning postures to simulate a tripping accident. Lower extremity muscle forces during balance recovery (quantified using joint torques) were estimated using an inverse dynamics analysis, and compared to experimentally-collected strength measurements. Muscle forces increased as the forward lean from which subjects were released increased. Ankle muscle force during balance recovery approached its maximum during recovery from the largest achieved lean angle, and the ankle muscle force that was predicted to be required for the next largest lean angle exceeded 100% of subject strength. These results imply that ankle strength limited the largest achieved lean angle (i.e. balance recovery ability), and suggest that increased ankle strength would increase the largest achieved lean angle. Further research is needed to determine if these results can be generalized to falls during walking (i.e. trips and slips) and falls outside of the laboratory.