Reactive Control and its Operation Limits in Responding to a Novel Slip in Gait

Feng Yang,Yi-Chung Pai

doi:10.1007/s10439-010-0082-7

Abstract

The purposes of this study were: (1) to examine the reactive control of the resultant joint moments at the lower limbs in response to a novel and unannounced slip; (2) to establish individualized forward-dynamics models; and (3) to explore personal potential by determining the operation limits of these moments at each lower limb joint, beyond which the resulting motion at this or other joints will exceed its/their normal range(s). Ten young subjects' kinematics and kinetics, collected during regular walking and during their first exposure to a novel and unannounced slip, were randomly selected from an existing database. An inverse-dynamics approach was applied to derive their (original) resultant joint moments, which were then used as input to establish forward-dynamics models, each including an individualized 16-element foot model to simulate ground reaction force. A simulated annealing (SA) algorithm was applied to modify the original moments, so that the subsequent output (baseline) moments can closely reproduce these subjects' recorded motion. A systematic alteration of the baseline moments was employed to determine the operation limits. The results revealed that the subjects reactively increased the hip extensor and knee flexor moments and reduced their ankle plantar flexor moments of their single-stance limb following slip onset. The "baseline" correction of the original moments can reach as much as 21% of the original moments. The analysis of the operation limits revealed that these individuals may be able to further increase their knee flexors more so than increase the hip extensors or reduce ankle plantar flexors before causing abnormal joint movement. Such systematic approach opens the possibility to properly assess an individual's rehabilitation potential, and to identify whether this person's strength is the limiting factor for stability training.

Highlights

Falls are a major cause of injury and even death in adults aged 65 and over[31]
The reactive control of the central nervous system (CNS) for slip recovery was characterized by an increase in the stance hip extensor and knee flexor moments, and a reduction in the plantar-flexor moments from those of regular walking (Fig. 3)
The experimental error was successfully reduced by the optimization routine in each individualized forward-dynamics model, such that the baseline moments could closely reproduce the originally recorded joint motion (Fig. 4)

Summary

Introduction

Falls are a major cause of injury and even death in adults aged 65 and over[31]. Falls initiated by a slip account for about one quarter of all falls among elders[21,23]. To resist slip-related falls during walking, the central nervous system (CNS) must reactively modify the resultant moments of the lower limbs that can provide stability recovery while support upright posture against gravity[12,18,28,37]. A better understanding of one’s reactive control of the joint moments at the lower limbs during recovery from a slip is imperative in order to properly assess this individual’s risk of future falls and to effectively prevent them from occurring. Such individualized, reaction-based approach is more resemblance and more relevant to the real life situations than volitional-performance-based evaluation common in clinical practice.

Methods

Results

Conclusion