Simulating Ideal Assistive Devices to Reduce the Metabolic Cost of Running

Tools have been used for millions of years to augment the capabilities of the human body, allowing us to accomplish tasks that would otherwise be difficult or impossible. Powered exoskeletons and other assistive devices are sophisticated modern tools that have restored bipedal locomotion in individuals with paraplegia and have endowed unimpaired individuals with superhuman strength. Despite these successes, designing assistive devices that reduce energy consumption during running remains a substantial challenge, in part because these devices disrupt the dynamics of a complex, finely tuned biological system. Furthermore, designers have hitherto relied primarily on experiments, which cannot report muscle-level energy consumption and are fraught with practical challenges. In this study, we use OpenSim to generate muscle-driven simulations of 10 human subjects running at 2 and 5 m/s. We then add ideal, massless assistive devices to our simulations and examine the predicted changes in muscle recruitment patterns and metabolic power consumption. Our simulations suggest that an assistive device should not necessarily apply the net joint moment generated by muscles during unassisted running, and an assistive device can reduce the activity of muscles that do not cross the assisted joint. Our results corroborate and suggest biomechanical explanations for similar effects observed by experimentalists, and can be used to form hypotheses for future experimental studies. The models, simulations, and software used in this study are freely available at simtk.org and can provide insight into assistive device design that complements experimental approaches.

Citation: Uchida TK, Seth A, Pouya S, Dembia CL, Hicks JL, Delp SL (2016) Simulating Ideal Assistive Devices to Reduce the Metabolic Cost of Running. PLoS ONE 11(9):
e0163417.

https://doi.org/10.1371/journal.pone.0163417

Editor: Øyvindi Sandbakk,
Norwegian University of Science and Technology, NORWAY

Received: April 28, 2016; Accepted: September 8, 2016; Published: September 22, 2016

Copyright: © 2016 Uchida et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: OpenSim is an open-source software platform for modeling and simulation of movement, and is freely available at https://simtk.org/home/opensim and on GitHub at https://github.com/opensim-org/opensim-core. The muscle energetics model used in this study is available in OpenSim 3.3; a plug-in for use with OpenSim 3.2 is available at https://github.com/opensim-org/opensim-metabolicsprobes. The analyses performed in this study were based on simulations originally generated by Hamner and Delp (2013), which are freely available at https://simtk.org/home/nmbl_running. The data underlying the findings of this study are freely available at https://simtk.org/home/idealassist_run.

Funding: Funding was provided to all authors by Defense Advanced Research Projects Agency (DARPA) contract W911QX-12-C-0018 (Warrior Web) and by National Institutes of Health (NIH) grants R24 HD065690 and P2C HD065690 (NIH National Center for Simulation in Rehabilitation Research), U54 EB020405 (Mobilize Center NIH Big Data to Knowledge Center of Excellence), and U54 GM072970 (NIH National Center for Physics-Based Simulation of Biological Structures). CLD also received funding from National Science Foundation (NSF) Graduate Research Fellowship DGE-114747. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

The research investigates assistive devices' impact on running efficiency.