# Optimizing impedance control of an ankle exoskeleton to improve post-stroke walking mechanics and energetics

> **NIH NIH F31** · NORTH CAROLINA STATE UNIVERSITY RALEIGH · 2020 · $41,422

## Abstract

Project Summary
 Approximately 80% of the 7 million stroke survivors in the United States are affected by hemiparesis, or
muscle weakness on one side of the body. When compared to unimpaired gait, hemiparetic walking is both
asymmetric and slow. High interlimb asymmetry has been documented in ankle joint power output, and preferred
walking speeds following a stroke range between <0.2 m/s and ~0.8 m/s compared to ~1.4 m/s in healthy adults.
Alterations in gait characteristics following a stroke are associated with limitations in walking performance
including altered loading on lower limb joints and increased metabolic cost. Changes in joint loading are
associated with secondary diseases including osteoarthritis, lower-back pain, and due to reduced activity,
cardiovascular disease. Additionally, increases in metabolic cost lead to rapid exhaustion, less activity and
limited mobility. Interventions designed to reduce mechanical asymmetries may reduce metabolic cost and
normalize joint loading for improved walking performance post stroke. Ankle exoskeletons have successfully
reduced metabolic cost of walking in healthy controls and preliminary studies have demonstrated the potential
of ankle exoskeletons to restore ankle function by applying ankle torque on the paretic limb. The long term goal
of this research is to develop a robotic ankle exoskeleton that can improve walking performance post stroke to
pave the way for a portable permanent walking aid. However, exoskeleton design for stroke is limited by a
knowledge gap regarding the influence of exoskeleton assistance timing and magnitude on mechanical gait
symmetry, metabolic cost, and joint contact loading. Understanding this relationship is critical because
exoskeleton assistance provided at the wrong time, or of insufficient magnitude could be useless, or even
detrimental to gait performance. We will use a combined experimental and computational approach to research
the following aims: (1) Determine how the timing and magnitude of exoskeleton assistance influence the
mechanical symmetry and metabolic energetics of post-stroke walking (2) Determine how timing and magnitude
of exoskeleton assistance influences joint contact forces. We will use an exoskeleton emulator system to
systematically vary exoskeleton assistance parameters (i.e. timing and magnitude) while directly evaluating user
metabolic, kinematic, and kinetic response. Because we cannot easily measure joint contact forces in vivo, we
will apply a computational simulation approach driven by the experimentally measured gait for each participant
walking with exoskeleton assistance. This work will elucidate the how timing and magnitude of exoskeleton
assistance impacts post-stroke walking asymmetry, metabolic cost and joint contact forces. Taken together,
these aims provide new and essential information to enable the development of exoskeletons capable of
minimizing comorbidities and restoring mobility to stroke survivors.

## Key facts

- **NIH application ID:** 9918154
- **Project number:** 5F31HD097872-02
- **Recipient organization:** NORTH CAROLINA STATE UNIVERSITY RALEIGH
- **Principal Investigator:** Emily McCain
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $41,422
- **Award type:** 5
- **Project period:** 2019-05-15 → 2022-05-14

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9918154

## Citation

> US National Institutes of Health, RePORTER application 9918154, Optimizing impedance control of an ankle exoskeleton to improve post-stroke walking mechanics and energetics (5F31HD097872-02). Retrieved via AI Analytics 2026-06-11 from https://api.ai-analytics.org/grant/nih/9918154. Licensed CC0.

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