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Neural Prostheses for Locomotion

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Front. Neurosci. | doi: 10.3389/fnins.2018.00069

BI-ARTICULAR KNEE-ANKLE-FOOT EXOSKELETON PRODUCES HIGHER METABOLIC COST REDUCTION THAN WEIGHT-MATCHED MONO-ARTICULAR EXOSKELETON.

  • 1Center for Research in Human Movement Variability and Department of Biomechanics, University of Nebraska Omaha, United States
  • 2Department of Movement and Sports Sciences, Ghent University, Belgium

The bi-articular m. gastrocnemius and the mono-articular m. soleus have different and complementary functions during walking. Several groups are starting to use these biological functions as inspiration to design prostheses with bi-articular actuation components to replace the function of the m. gastrocnemius. Simulation studies indicate that a bi-articular configuration and spring that mimic the m. gastrocnemius could be beneficial for orthoses or exoskeletons. Our aim was to test the effect of a bi-articular and spring configuration that mimics the m. gastrocnemius and compare this to a no-spring and mono-articular configuration.
We tested 9 participants during walking with knee-ankle-foot exoskeletons with dorsally mounted pneumatic muscle actuators. In the bi-articular plus spring condition the pneumatic muscles were attached to the thigh segment with an elastic cord. In the bi-articular no-spring condition the pneumatic muscles were also attached to the thigh segment but with a non-elastic cord. In the mono-articular condition the pneumatic muscles were attached to the shank segment.
We found the highest reduction in metabolic cost of 13% compared to walking with the exoskeleton powered-off in the bi-articular plus spring condition. Possible explanations for this could be that the exoskeleton delivered the highest total positive work in this condition at the ankle and the knee and provided more assistance during the isometric phase of the biological plantarflexors. As expected we found that the bi-articular conditions reduced m. gastrocnemius EMG more than the mono-articular condition. We did not find that the mono-articular condition reduces the m. soleus EMG more than the bi-articular conditions.
Knowledge of specific effects of different exoskeleton configurations on metabolic cost and muscle activation could be useful for providing customized assistance for specific gait impairments.

Keywords: bi-articular, mono-articular, Biarticular muscle, exoskeleton, Walking, gastrocnemius muscle, soleus, metabolic cost, Pneumatic Artificial Muscles, pneumatic muscles, Ankle, Biomechanics, Biomechatronics, assistive devices, wearable robotics, Orthosis

Received: 07 Sep 2017; Accepted: 29 Jan 2018.

Edited by:

Mikhail Lebedev, Duke University, United States

Reviewed by:

Wiktor Sieklicki, Gdańsk University of Technology, Poland
Giuseppe Carbone, University of Cassino, Italy
Manish Sreenivasa, Universität Heidelberg, Germany
Jan Veneman, Tecnalia, Spain  

Copyright: © 2018 Malcolm, Galle, Derave and De Clercq. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Philippe Malcolm, University of Nebraska Omaha, Center for Research in Human Movement Variability and Department of Biomechanics, Omaha, United States, pmalcolm@unomaha.edu