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Powered hip exoskeleton improves walking economy in individuals with above-knee amputation


Above-knee amputation severely reduces the mobility and quality of life of millions of individuals. Walking with available leg prostheses is highly inefficient, and poor walking economy is a major problem limiting mobility. Here we show that an autonomous powered hip exoskeleton assisting the residual limb significantly improves metabolic walking economy by 15.6 ± 2.9% (mean ± s.e.m.; two-tailed paired t-test, P = 0.002) in six individuals with above-knee amputation walking on a treadmill. The observed metabolic cost improvement is equivalent to removing a 12-kg backpack from a nonamputee individual. All participants were able to walk overground with the exoskeleton, including starting and stopping, without notable changes in gait balance or stability. This study shows that assistance of the user’s residual limb with a powered hip exoskeleton is a viable solution for improving amputee walking economy. By significantly reducing the metabolic cost of walking, the proposed hip exoskeleton may have a considerable positive impact on mobility, improving the quality of life of individuals with above-knee amputations.

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Fig. 1: Powered hip exoskeleton and experimental setup.
Fig. 2: Metabolic cost of walking with and without the exoskeleton.
Fig. 3: Lower-limb kinematics averaged across all participants.
Fig. 4: Average kinematics, kinetics and energy injection during walking with the exoskeleton on a treadmill at 1 m s−1.

Data availability

All data are freely available in an open repository19.

Code availability

Code is freely available upon written request to the corresponding author.


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We wish to acknowledge the contribution of all study participants. We would like to thank M. Tran, S. Sarkisian and C. Buchanan for their help with the development of the powered hip exoskeleton and related interfaces. We would like to thank J. Mendez for assistance in collection and processing of all data from participants and G. Hunt for help proofreading the manuscript. We would also like to thank C. Hansen and C. Duncan for their help with participant recruitment. Funding for this study was provided by the Congressionally Directed Medical Research Program of the Department of Defense under grant number W81XWH-16-1-0701 awarded to T.L. and by the National Science Foundation under grant number 2046287 awarded to T.L.

Author information

Authors and Affiliations



T.L. directed the project. T.L. and M.K.I. invented the controller and implemented it on the powered hip exoskeleton. M.K.I., D.A. and T.L. conducted the experiments with human participants. M.K.I. and D.A. analyzed the data. All authors contributed to manuscript preparation.

Corresponding author

Correspondence to Tommaso Lenzi.

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The authors declare no competing interests.

Additional information

Peer review information Nature Medicine thanks Gregory Sawicki and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Michael Basson was the primary editor on this article and managed its editorial process and peer review in collaboration with the rest of the editorial team.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Tables 1–4.

Reporting Summary

Supplementary Video 1

Side-by-side comparison of all participants walking on a treadmill with and without the exoskeleton.

Supplementary Video 2

Side-by-side comparison of all participants walking overground with and without the exoskeleton.

Supplementary Video 3

One participant dons and doffs the exoskeleton.

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Ishmael, M.K., Archangeli, D. & Lenzi, T. Powered hip exoskeleton improves walking economy in individuals with above-knee amputation. Nat Med 27, 1783–1788 (2021).

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