An experimental comparison of the relative benefits of work and torque assistance in ankle exoskeletons
- 1 September 2015
- journal article
- research article
- Published by American Physiological Society in Journal of Applied Physiology
- Vol. 119 (5), 541-557
- https://doi.org/10.1152/japplphysiol.01133.2014
Abstract
Techniques proposed for assisting locomotion with exoskeletons have often included a combination of active work input and passive torque support, but the physiological effects of different assistance techniques remain unclear. We performed an experiment to study the independent effects of net exoskeleton work and average exoskeleton torque on human locomotion. Subjects wore a unilateral ankle exoskeleton and walked on a treadmill at 1.25 m·s−1while net exoskeleton work rate was systematically varied from −0.054 to 0.25 J·kg−1·s−1, with constant (0.12 N·m·kg−1) average exoskeleton torque, and while average exoskeleton torque was systematically varied from approximately zero to 0.18 N·m·kg−1, with approximately zero net exoskeleton work. We measured metabolic rate, center-of-mass mechanics, joint mechanics, and muscle activity. Both techniques reduced effort-related measures at the assisted ankle, but this form of work input reduced metabolic cost (−17% with maximum net work input) while this form of torque support increased metabolic cost (+13% with maximum average torque). Disparate effects on metabolic rate seem to be due to cascading effects on whole body coordination, particularly related to assisted ankle muscle dynamics and the effects of trailing ankle behavior on leading leg mechanics during double support. It would be difficult to predict these results using simple walking models without muscles or musculoskeletal models that assume fixed kinematics or kinetics. Data from this experiment can be used to improve predictive models of human neuromuscular adaptation and guide the design of assistive devices.Keywords
Funding Information
- National Science Foundation (IIS-1355716)
- National Science Foundation (NSF) (DGE-1252552)
This publication has 46 references indexed in Scilit:
- A Simple Exoskeleton That Assists Plantarflexion Can Reduce the Metabolic Cost of Human WalkingPLOS ONE, 2013
- EMG-Driven Forward-Dynamic Estimation of Muscle Force and Joint Moment about Multiple Degrees of Freedom in the Human Lower ExtremityPLOS ONE, 2012
- Stance-phase force on the opposite limb dictates swing-phase afferent presynaptic inhibition during locomotionJournal of Neurophysiology, 2012
- Bionic ankle–foot prosthesis normalizes walking gait for persons with leg amputationProceedings. Biological sciences, 2011
- Muscle Synergies: Implications for Clinical Evaluation and Rehabilitation of MovementTopics in Spinal Cord Injury Rehabilitation, 2011
- Optimality principles for model-based prediction of human gaitJournal of Biomechanics, 2010
- Stance and swing phase costs in human walkingJournal of The Royal Society Interface, 2010
- Recycling Energy to Restore Impaired Ankle Function during Human WalkingPLOS ONE, 2010
- Invariant ankle moment patterns when walking with and without a robotic ankle exoskeletonJournal of Biomechanics, 2010
- A collisional model of the energetic cost of support work qualitatively explains leg sequencing in walking and galloping, pseudo-elastic leg behavior in running and the walk-to-run transitionJournal of Theoretical Biology, 2005