The role of strategy selection, limb force capacity and limb positioning in successful trip recovery

Background: Fall occurrence, mainly due to tripping, increases with age. There are two main strategies of trip recovery: elevating and lowering. Strategy selection depends on trip stimulus timing within the swing phase of walking, but the choice and ultimate success of a strategy selection may also depend on individual physical characteristics. The aim of this study was to investigate: 1) recovery strategy choice by younger and older adults when perturbed in the 'strategy overlap' mid-swing phase, and 2) whether the interaction between recovery limb positioning and recovery limb force capacity determines recovery success in elevating strategy recoveries and accounts for strategy selection. Methods: A group of older (65-75 years) and a group of younger adults (20-35 years) completed a trip recovery protocol in a laboratory environment. An inverted pendulum model was developed to investigate how walking speed, recovery limb positioning and recovery limb force interacted and influenced successful trip recovery when perturbed in different swing phases. Findings: Older adults always adopted a lowering strategy when perturbed in late mid-swing (60-80%), while younger adults also adopted elevating strategies. Simulations showed that, when perturbed later in swing, a larger recovery step and higher recovery limb force were required for successful recovery. Interpretation: We suggested that a combination of insufficient recovery limb strength, response time and movement speed make it difficult for older adults to achieve a large enough recovery step for a successful elevating strategy recovery when perturbed later in mid-swing. (C) 2010 Elsevier Ltd. All rights reserved.