Evaluating adaptiveness of an active back exosuit for dynamic lifting and maximum range of motion

Abstract

Back exosuits deliver mechanical assistance to reduce the risk of back injury, however, minimising restriction is critical for adoption. We developed the adaptive impedance controller to minimise restriction while maintaining assistance by modulating impedance based on the user’s movement direction and nonlinear sine curves. The objective of this study was to compare active assistance, delivered by a back exosuit via our adaptive impedance controller, to three levels of assistance from passive elastics. Fifteen participants completed five experimental blocks (4 exosuits and 1 no-suit) consisting of a maximum flexion and a constrained lifting task. While a higher stiffness elastic reduced back extensor muscle activity by 13%, it restricted maximum range of motion (RoM) by 13°. The adaptive impedance approach did not restrict RoM while reducing back extensor muscle activity by 15%, when lifting. This study highlights an adaptive impedance approach might improve usability by circumventing the assistance-restriction trade-off inherent to passive approaches.

Practitioner summary: This study demonstrates a soft active exosuit that delivers assistance with an adaptive impedance approach can provide reductions in overall back muscle activity without the impacts of restricted range of motion or perception of restriction and discomfort.

Keywords:

• Low back pain
• electromyography
• biomechanics
• exosuit
• wearable robotics

Acknowledgements

We would like to thank the participants who volunteered for this study as well as Sarah Sullivan from the Wyss Institute Clinical Research team.

Author contributions

Conceptualisation: JC, MA, CJW; Development: JC; Protocol design: JC, DAQ, MA, DD, LA, CJW; Data collection: JC, DAQ, MA; Data analysis: DAQ; Funding acquisition: JC, MA, DD, LA, CJW; Writing – original draft: JC, DAQ, JMC; Writing – review & editing: JC, DAQ, MA, JMC, DD, LA, CJW

Disclosure statement

CJW and JC are inventors of at least one patent application describing the exosuit components described in the paper that have been filed with the U.S. Patent Office by Harvard University. Harvard University has entered into a licencing agreement with Verve Inc., in which CJW, JC and MA have an equity interest and CJW has a board position. The other authors report no conflict of interest.

Data availability statement

All data needed to support the conclusions of this manuscript are included in the main text or Supplementary Materials. Derived data supporting the findings of this study are available from the corresponding author C.J.W on request.

Additional information

Funding

This work was supported by the NIH BACPAC under grant 1UH2AR076731-01 (CJW, DD, LA); and the DOD under grant W81XWH2010609 (CJW).