Effect of age on lower extremity joint moment contributions to gait speed

Abstract

We investigated the relationship of hip, knee and ankle function to gait speed in healthy elderly subjects. We hypothesized that the hip extension moment would make a significantly smaller contribution to propulsion power in the elderly than in healthy young subjects even when the elders were ambulating at speeds comparable to those of the young subjects. We analyzed the free speed gait of 16 young and 14 elderly subjects, and the fast gait of the elder subjects. In elderly subjects free speed gait linear power transfer from the leg to the upper body due to the hip and knee moments was decreased compared with young subjects walking at their normal gait speed. However, when asked to walk fast, elders significantly increase knee and hip moment contributions to hip linear power to levels comparable to those of young subjects at a similar speed. These results refute our hypothesis and support our earlier findings indicating that kinematic alterations at the hip are a cause of reduced gait speed in the elderly.

Introduction

Gait analysis has been used in an attempt to detect subtle differences between the gait of elders and that of younger persons. It is widely documented that elderly people tend to walk more slowly and that this speed reduction is due to a reduction in step length rather than cadence [1], [2], [3], [4], [5]. Reduced ankle joint power in late-stance is associated with slower overall walking [2], [5], [6]. Judge et al. [6] asked elders to walk fast and found that their ankle plantar flexor moment did not increase, suggesting that ankle plantar flexor weakness may be causative of slow gait. However, in a recent study of healthy elders, Kerrigan et al. found that ankle plantar flexion power did increase when elders were asked to walk fast [5]. Kerrigan did, however, find a consistent limitation of hip extension that persisted when speed increased. Limited hip extension could contribute to reduced stride length and, therefore, reduced speed in the elderly.

Kerrigan found that healthy elders could voluntarily increase hip, knee and ankle moments and powers when asked to walk fast, suggesting that kinetic factors did not limit their performance. However, joint moment and power parameters do not directly quantify propulsion and support [7], [8]. Model based gait analysis techniques have been used to integrate kinematic and kinetic information, and to characterize propulsion and support in healthy young subjects [7], [8], [9], [10]. Using an induced acceleration analysis [9], [11], Kepple et al. [8] showed that ankle plantar flexion moment contributed to body support and progression in late-stance. More recently, Meinders et al. [7] used a combination of joint power, linear power flow and segmental energy analyses to determine how energy generated, as joint or muscle power, was stored in the leg or transferred to the upper body for propulsion and support. If the induced acceleration analysis approach for determining the instantaneous action of each individual joint moment is applied to linear power flow analysis, one can determine how each joint moment contributes to power transfer from the leg to the upper body without an additional segmental energy flow analysis [10]. Eliminating the segmental energy flow analysis is desirable as this analysis is complex and subject to significant errors when calculated from gait laboratory data [12].

The purpose of this work is to investigate the contributions of the lower limb joint moments to propulsion and support in elders’ gait. We analyzed the linear power at the hip joint and determined the contribution of each joint moment to the total hip joint linear power. We expected to find that impaired hip kinetic function would be identified as a contributor to gait impairment in the elderly. Specifically we hypothesized that the hip extension moment would make a significantly smaller contribution to propulsion power in the elderly than in healthy young subjects even when the elders were ambulating at speeds comparable to those of the young subjects.