Altering Compliance of a Load Carriage Device in the Medial-Lateral Direction Reduces Peak Forces While Walking

Jean-Paul Martin,Qingguo Li

doi:10.1038/s41598-018-32175-x

Abstract

Altering mechanical compliance in load carriage structures has shown to reduce metabolic cost and accelerative forces of carrying weight. Currently, modifications to load carriage structures have been primarily targeted at vertical motion of the carried mass. No study to date has investigated altering load carriage compliance in the medial-lateral direction. We developed a backpack specifically for allowing a carried mass to oscillate in the horizontal direction, giving us the unique opportunity to understand the effects of lateral mass motion on human gait. Previous modelling work has shown that walking economy can be improved through the interaction of a bipedal model with a laterally oscillating walking surface. To test whether a laterally oscillating mass can experimentally improve walking economy, we systematically varied step width above and below the preferred level and compared the effects of carrying an oscillating and fixed mass. Walking with an oscillating mass was found to reduce the accelerative forces of load carriage in both horizontal and vertical directions. However, load eccentricity caused the vertical force component to create a significant bending moment in the frontal plane. Walking with an oscillating mass led to an increase in the metabolic energy expenditure during walking and an increase in positive hip work during stance. The device’s ability to reduce forces experienced by the user, due to load carriage, holds promise. However, the requirement of additional metabolic energy to walk with the device requires future study to improve.

Highlights

During gait, the trunk oscillates in the vertical direction, and moves medio-laterally with each step
We propose altering the mechanical compliance of a load carriage device in the medial-lateral direction to study the mechanics and energetics of walking in the presence of an oscillating carried mass
The horizontal displacement of the carried mass significantly increased during oscillating conditions (Fig. 1c) (F(38) = 49.5, p = 2 · 10−8)

Summary

Introduction

The trunk oscillates in the vertical direction, and moves medio-laterally with each step. Lateral stability assistance, given by tethering subjects laterally to the lab environment using elastic elements, has shown to augment gait by decreasing the metabolic cost of walking[22,23,24]. This demonstrates that walking economy can be improved through a restorative force proportional to pelvis displacement from a global centreline. We propose altering the mechanical compliance of a load carriage device in the medial-lateral direction to study the mechanics and energetics of walking in the presence of an oscillating carried mass. We further hypothesize that reduced joint work will lead to a decrease of the metabolic power of walking compared to the fixed condition

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