A portable exotendon assisting hip and knee joints reduces muscular burden during walking.

Longfei Cheng,Jiejunyi Liang,Wenbin Chen,Xiaowei Xu,Bo Huang,Caihua Xiong

doi:10.1098/rsos.211266

Longfei Cheng, Jiejunyi Liang + Show 4 more

Open Access

https://doi.org/10.1098/rsos.211266

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Abstract

Assistive devices are used to reduce human effort during locomotion with increasing success. More assistance strategies are worth exploring, so we aimed to design a lightweight biarticular device with well-chosen parameters to reduce muscle effort. Based on the experience of previous success, we designed an exotendon to assist in swing leg deceleration. Then we conducted experiments to test the performance of the exotendon with different spring stiffness during walking. With the assistance of the exotendon, peak activation of semitendinosus decreased, with the largest reduction of 12.3% achieved with the highest spring stiffness (p = 0.004). The peak activations of other measured muscles were not significantly different (p = 0.15–0.92). The biological hip extension and knee flexion moments likewise significantly decreased with the spring stiffness (p < 0.01). The joint angle was altered during the assisted phases with decreased hip flexion and knee extension. Meanwhile, the step frequency and the step length were also altered, while the step width remained unaffected. Gait variability changed only in the frontal plane, exhibiting lower step width variability. We conclude that passive devices assisting hip extension and knee flexion can significantly reduce the burden on the hamstring muscles, while the kinematics is easily altered.

Highlights

Humans have evolved with muscular and skeletal systems suitable for locomotion, such as long Achilles tendons [1], short royalsocietypublishing.org/journal/rsos R
To minimize movement of the device resulting from assistive forces and increase the moment arms relative to the hip and knee joints, the waist belt is located above the ilium, and the ankle strap is located above the lateral malleolus
The exotendon provided the highest assistance magnitude in the EXO41 condition, with peak values of 0.090 N m kg−1 at the hip joint and 0.066 N m kg−1 at the knee joint, which accounted for about 14.6% and 12.8% of the hip and knee peak joint moments during the assistance phases, respectively

Summary

Introduction

Humans have evolved with muscular and skeletal systems suitable for locomotion, such as long Achilles tendons [1], short royalsocietypublishing.org/journal/rsos R. Toes [2] and elastic foot arches [3], which makes it challenging to develop assistive devices. The 2 earliest assistive device dates back to the 1890s [4], success in reducing the metabolic cost of locomotion has not been achieved until recently. The success in the recent development of assistive devices is not an accident, and it is based on the knowledge of human anatomy, biomechanics and physiology of locomotion. Effective assistance requires coordinated interaction between the human and the device. The device provides appropriate assistive torque at joints, while the human body makes adjustments, such as muscle recruitment, making use of the assistance. Improving the device design from these two perspectives is the key to augmenting human locomotion ability

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