Exoskeleton Variability Optimization

Exoskeleton Variability Optimization for Reducing Gait Variability for Patients With Peripheral Artery Disease

Exoskeletons, wearable devices that assist with walking, can improve mobility in clinical populations. With exoskeletons, it is crucial to optimize the assistance profile. Recent studies describe algorithms (i.e., human-in-the-loop) to optimize the assistance profile with real-time metabolic measurements. The needed duration of current human-in-the-loop (HITL) algorithms range from 20 minutes to 1 hour which is longer than the average duration that most patients with peripheral artery disease (PAD) can walk. Because of this limited walking duration, it is often not possible for patients with PAD to reach steady-state metabolic cost, which makes these measurements are not useful for optimizing exoskeletons. In this study, investigators intend to develop and evaluate HITL optimization methods for exoskeletons and use the information to design and evaluate a portable hip exoskeleton. Shorter and more clinically feasible HITL optimization strategies based on experiments in healthy adults might allow utilizing these optimization strategies to become available for patient populations such as patients with PAD.

Study Overview

• Status: Terminated
• Conditions: Peripheral Arterial Disease
• Intervention / Treatment: Other: Exoskeleton Optimization; Other: Endurance Evaluation

Detailed Description

Exoskeletons, wearable devices that assist with walking, can improve mobility in clinical populations. With exoskeletons, it is crucial to optimize the assistance profile. Recent studies describe algorithms (i.e., human-in-the-loop) to optimize the assistance profile with real-time metabolic measurements. The needed duration of current human-in-the-loop (HITL) algorithms range from 20 minutes to 1 hour which is longer than the average duration that most patients with peripheral artery disease (PAD) can walk. Because of this limited walking duration, it is often not possible for patients with PAD to reach steady-state metabolic cost, which makes these measurements are not useful for optimizing exoskeletons. Shorter and more clinically feasible HITL optimization strategies based on experiments in healthy adults might allow utilizing these optimization strategies to become available for patient populations such as patients with PAD.

This study will test different methods for optimizing exoskeletons. It will consist of an habituation session to the hip exoskeleton, an optimization session to find the optimal actuation settings using an algorithm that converges toward the optimum based on real-time measurements (human-in-the-loop algorithm) and a post-test at the end of optimization session to compare different conditions. The outcomes will be evaluated by surface electromyography, exoskeleton sensors, ground reaction force, walking speed, indirect calorimetry, and motion capture (Vicon).

• Study Type: Interventional
• Enrollment (Actual): 9
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Nebraska
    • Omaha, Nebraska, United States, 68182
      • University of Nebraska Omaha

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 19 years to 85 years (Adult, Older Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Ability to provide written consent
• Chronic claudication history
• Ankle-brachial index < 0.90 at rest
• Stable blood pressure, lipids, and diabetes for > 6 weeks
• Ability to walk on a treadmill for multiple five-minute spans

• Ability to fit in exoskeleton

  • Waist circumference 78 to 92 centimeters (31 to 36 inches)
  • Thigh circumference 48 to 60 centimeters (19 to 24 inches)
  • Minimal thigh length 28 centimeters (11 inches)

Exclusion Criteria:

• Resting pain or tissue loss due to peripheral artery disease (PAD, Fontaine stage III and IV)
• Foot ulceration
• Acute lower extremity event secondary to thromboembolic disease or acute trauma

• Walking capacity limited by diseases unrelated to PAD, such as:

  • Neurological disorders
  • Musculoskeletal disorders (arthritis, scoliosis, stroke, spinal injury, etc.)
  • History of ankle instability
  • Knee injury
  • Diagnosed joint laxity
  • Lower limb injury
  • Surgery within the past 12 months
  • Joint replacement
  • Pulmonary disease or breathing disorders
  • Cardiovascular disease
  • Vestibular disorder
• Acute injury or pain in lower extremity
• Current illness
• Inability to follow visual cues due to blindness
• Inability to follow auditory cues due to deafness
• Pregnant

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Non-Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Optimal Assistance Pattern; An optimization algorithm will change the assistance pattern on the hip exoskeleton during walking sessions and the optimal assistance pattern will be determined when gait variability is minimized.	Other: Exoskeleton Optimization; Participants will walk 10-minute trials while an optimization algorithm changes the assistance profile of the exoskeleton.
Experimental: Endurance Effectds; Endurance of participants using ground reaction force (Bertec treadmill), walking speed (Bertec treadmill), indirect calorimetry (Cosmed), and motion capture (Vicon) will be determined.	Other: Endurance Evaluation; Participants will walk 2 trials at a speed of 1 meter per second until the participant indicates claudication or a maximum duration of 6 minutes, which ever comes first.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Time to Convergence	Convergence is determined when the estimated optimal exoskeleton settings vary less than 10%. The time to convergence is measured.	10 minutes
Peak Extension Timing	The time to peak extension moment of exoskeleton is measured by plotting the exoskeleton moment versus stride cycle percentage and finding the timing when the peak in the extension moment occurs expressed in percent of the stride cycle.	20 seconds
Peak Flexion Timing	The time to peak flexion moment of exoskeleton is measured by plotting the flexion moment versus stride cycle percentage and finding the timing when the peak in the flexion moment occurs expressed in percent of the stride cycle.	20 seconds
Largest Lyapunov Exponent	Largest Lyapunov exponent (the rate of separation of infinitesimally close trajectories) of lower limb kinematics is determined. Largest Lyapunov exponent is calculated using Wolf's algorithm. The theoretical range is from zero to plus infinity. Zero indicates an entirely stable periodic movement pattern. Higher values indicate more unstable and chaotic movement patterns. Lower values are considered better, and higher values are considered worse for gait stability.	20 seconds

Collaborators and Investigators

• Sponsor: University of Nebraska
• Collaborators: National Institute of General Medical Sciences (NIGMS)
• Investigators: Principal Investigator: Philippe Malcolm, University of Nebraska

Study record dates

Study Major Dates

• Study Start (Actual): January 31, 2022
• Primary Completion (Actual): March 28, 2025
• Study Completion (Actual): March 28, 2025

Study Registration Dates

• First Submitted: April 3, 2020
• First Submitted That Met QC Criteria: April 7, 2020
• First Posted (Actual): April 8, 2020

Study Record Updates

• Last Update Posted (Actual): June 19, 2025
• Last Update Submitted That Met QC Criteria: June 17, 2025
• Last Verified: June 1, 2025

More Information

Terms related to this study

• Keywords: Exoskeleton
• Additional Relevant MeSH Terms: Vascular Diseases; Cardiovascular Diseases; Atherosclerosis; Arteriosclerosis; Arterial Occlusive Diseases; Peripheral Arterial Disease; Peripheral Vascular Diseases
• Other Study ID Numbers: 0376-19-FB; P20GM109090 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No