Adaptive Ankle Resistance from a Wearable Robotic Device to Improve Muscle Recruitment in Cerebral Palsy

  • Benjamin C. Conner
  • Jason Luque
  • Zachary F. LernerEmail author
Original Article


Individuals with cerebral palsy can have weak and poorly coordinated ankle plantar flexor muscles that contribute to inefficient walking patterns. Previous studies attempting to improve plantar flexor function have had inconsistent effects on mobility, likely due to a lack of task-specificity. The goal of this study was to develop, validate, and test the feasibility and neuromuscular response of a novel wearable adaptive resistance platform to increase activity of the plantar flexors during the propulsive phase of gait. We recruited eight individuals with spastic cerebral palsy to walk with adaptive plantar flexor resistance provided from an untethered exoskeleton. The resistance system and protocol was safe and feasible for all of our participants. Controller validation demonstrated our ability to provide resistance that proportionally- and instantaneously-adapted to the biological ankle moment (R = 0.92 ± 0.04). Following acclimation to resistance (0.16 ± 0.02 Nm/kg), more-affected limbs exhibited a 45 ± 35% increase in plantar flexor activity (p = 0.02), a 26 ± 24% decrease in dorsiflexor activity (p < 0.05), and a 46 ± 25% decrease in co-contraction (tibialis anterior and soleus) (p = 0.02) during the stance phase. This adaptive resistance system warrants further investigation for use in a longitudinal intervention study.


Gait Task-specificity Co-contraction Training Soleus Untethered 



Cerebral palsy


Physical therapy


Graphical user interface


Gross Motor Function Classification System


Maximum voluntary contraction






Tibialis anterior


Correlation coefficient


Cohen’s d



The authors would like to thank Nushka Remec, P.T., Emily Frank, R.N., Elizabeth Orum, and Jennifer Lawson for their assistance with data collection and processing. Research reported in this publication was supported in part by the Eunice Kennedy Shriver National Institute Of Child Health & Human Development of the National Institutes of Health under Award Number R03HD094583. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was also supported in part by The University of Arizona College of Medicine – Phoenix MD/PhD Program.

Conflicts of interest

ZFL is a named inventor on a pending utility patent application that describes the exoskeleton utilized in the study. ZFL is a co-founder of a company seeking to commercialize the device.

Supplementary material

10439_2020_2454_MOESM1_ESM.pdf (229 kb)
Electronic supplementary material 1 (PDF 229 kb)


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Copyright information

© Biomedical Engineering Society 2020

Authors and Affiliations

  1. 1.College of Medicine – PhoenixUniversity of ArizonaPhoenixUSA
  2. 2.Department of Mechanical EngineeringNorthern Arizona UniversityFlagstaffUSA

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