Biomechanical mechanisms underlying exosuit-induced improvements in walking economy after stroke
Jaehyun Bae, Louis N Awad, Andrew Long, Kathleen O'Donnell, Katy Hendron, Kenneth G Holt, Terry D Ellis, Conor J Walsh, Jaehyun Bae, Louis N Awad, Andrew Long, Kathleen O'Donnell, Katy Hendron, Kenneth G Holt, Terry D Ellis, Conor J Walsh
Abstract
Stroke-induced hemiparetic gait is characteristically asymmetric and metabolically expensive. Weakness and impaired control of the paretic ankle contribute to reduced forward propulsion and ground clearance - walking subtasks critical for safe and efficient locomotion. Targeted gait interventions that improve paretic ankle function after stroke are therefore warranted. We have developed textile-based, soft wearable robots that transmit mechanical power generated by off-board or body-worn actuators to the paretic ankle using Bowden cables (soft exosuits) and have demonstrated the exosuits can overcome deficits in paretic limb forward propulsion and ground clearance, ultimately reducing the metabolic cost of hemiparetic walking. This study elucidates the biomechanical mechanisms underlying exosuit-induced reductions in metabolic power. We evaluated the relationships between exosuit-induced changes in the body center of mass (COM) power generated by each limb, individual joint power and metabolic power. Compared with walking with an exosuit unpowered, exosuit assistance produced more symmetrical COM power generation during the critical period of the step-to-step transition (22.4±6.4% more symmetric). Changes in individual limb COM power were related to changes in paretic (R2=0.83, P=0.004) and non-paretic (R2=0.73, P=0.014) ankle power. Interestingly, despite the exosuit providing direct assistance to only the paretic limb, changes in metabolic power were related to changes in non-paretic limb COM power (R2=0.80, P=0.007), not paretic limb COM power (P>0.05). These findings contribute to a fundamental understanding of how individuals post-stroke interact with an exosuit to reduce the metabolic cost of hemiparetic walking.
Keywords: Exoskeleton; Gait biomechanics; Gait energetics; Post-stroke gait; Robotics; Stroke rehabilitation.
Conflict of interest statement
Competing interestsPatents have been filed with the U.S. Patent Office describing the exosuit components documented in this paper. J.B., K.G.H., K.O. and C.J.W. were authors of those patents and patent applications (PCT/US2013/60225 – Soft Exosuit For Assistance With Human Motion; PCT/US2014/68462 – Assistive Flexible Suits, Flexible Suit Systems, and Methods for Making and Control Thereof to Assist Human Mobility; PCT/US2014/40340 – Soft Exosuit for Assistance with Human Motion; PCT/US2015/51107 – Soft Exosuit for Assistance with Human Motion). Harvard University has entered into a licensing and collaboration agreement with ReWalk Robotics. C.J.W. and K.O. are paid consultants to ReWalk Robotics.
© 2018. Published by The Company of Biologists Ltd.
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Source: PubMed