Exoskeleton Variability Optimization

NCT04338815 | Terminated Results DMC

• 2 other identifiers: 0376-19-FBP20GM109090
• Study Type: interventional
• Target: 9
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Peripheral Arterial Disease

Keywords

Exoskeleton

Outcome Measures

Primary Outcomes (4)

• 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

Study Arms (2)

Optimal Assistance Pattern

EXPERIMENTAL

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

Endurance Effectds

EXPERIMENTAL

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

Interventions

Exoskeleton Optimization OTHER

Participants will walk 10-minute trials while an optimization algorithm changes the assistance profile of the exoskeleton.

Optimal Assistance Pattern

Endurance Evaluation OTHER

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.

Endurance Effectds

Eligibility Criteria

• Age: 19 Years - 85 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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)

You may not qualify if:

• 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

Sponsors & Collaborators

• University of Nebraska: lead
• National Institute of General Medical Sciences (NIGMS): collaborator

Study Sites (1)

University of Nebraska Omaha

Omaha, Nebraska, 68182, United States

Location

MeSH Terms

Conditions

Peripheral Arterial Disease

Condition Hierarchy (Ancestors)

Atherosclerosis; Arteriosclerosis; Arterial Occlusive Diseases; Vascular Diseases; Cardiovascular Diseases; Peripheral Vascular Diseases

Limitations and Caveats

The effect on endurance arm was not analyzed since the preceding optimal assistance pattern aim was not successful based on the predefined convergence criteria.

Results Point of Contact

• Title: Philippe Malcolm
• Organization: University of Nebraska-Omaha

pmalcolm@unomaha.edu

617-487-1148

Study Officials

• Philippe Malcolm

  University of Nebraska

  PRINCIPAL INVESTIGATOR

Publication Agreements

• PI is Sponsor Employee: No
• Restrictive Agreement: No

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NON RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: April 3, 2020
• First Posted: April 8, 2020
• Study Start: January 31, 2022
• Primary Completion: March 28, 2025
• Study Completion: March 28, 2025
• Last Updated: June 19, 2025
• Results First Posted: June 19, 2025

Record last verified: 2025-06

Data Sharing

• IPD Sharing: Will not share

Locations

US (1)