Clinical trial NCT05347810: Comfort Thresholds for Repetitive Forces
Official title: Comfort During Prolonged Exposure to Repetitive Forces Mimicking Exoskeleton Use
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Healthy
Keywords: Exoskeleton
Safety
Comfort
physical Human-Robot Interaction
Lead sponsor: Roessingh Research and Development
Sponsor class: OTHER
First posted: 2022-04-26
Enrollment: 15
Sex: ALL
Minimum age (years): 18
Maximum age (years): 85
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: yes
Allocation: NA
Intervention model: SINGLE_GROUP
Intervention model description: The study is a cross-sectional intervention study with one measurement session, where participants will provide a continuous comfort rating during exposure to repetitive normal and shear forces.
Primary purpose: OTHER

Brief summary: Exoskeletons can be used for rehabilitation, as assistive device for patients, or to support workers during strenuous tasks. To fulfil their purpose, they need to apply forces to the user's musculoskeletal system. The forces are transmitted at skin level through an interface, often in the form of cuffs. Adverse events causing discomfort and injuries to the skin and underlying tissue can be attributed to those interaction forces. While there is some information about safe limit values for impact forces or pressure and shear applied for short durations, little is known regarding comfort and safety thresholds for repetitive forces applied over long durations as is the case in exoskeleton use. This study therefore aims at gaining new knowledge on safe and limit values, based on discomfort (staying below pain threshold), for continuous repetitive shear and normal forces applied through a cuff.

Therefore, the primary objective is to determine comfort thresholds for prolonged exposure to repetitive normal and shear stress exerted to the human thigh via a cuff with straps, using different force patterns comparable to those exerted during exoskeleton use. The secondary objectives are to determine the feasibility of the experiment, the influence of subject characteristics on comfort thresholds, the occurrence of skin injuries or other negative signs, and whether characteristics of muscle activity can be related to discomfort.

Detailed description: Rationale: Exoskeletons can be used for rehabilitation, as assistive device for patients, or to support workers during strenuous tasks. To fulfil their purpose, they need to apply forces to the user's musculoskeletal system. The forces are transmitted at skin level through an interface, often in the form of cuffs. Adverse events causing discomfort and injuries to the skin and underlying tissue can be attributed to those interaction forces. While there is some information about safe limit values for impact forces or pressure and shear applied for short durations, little is known regarding comfort and safety thresholds for repetitive forces applied over long durations as is the case in exoskeleton use. This study therefore aims at gaining new knowledge on safe and limit values, based on discomfort (staying below pain threshold), for continuous repetitive shear and normal forces applied through a cuff.

Objective: The primary objective is to determine comfort thresholds for prolonged exposure to repetitive normal and shear stress exerted to the human thigh via a cuff with straps, using different force patterns comparable to those exerted during exoskeleton use. The secondary objectives are to determine the feasibility of the experiment, the influence of subject characteristics on comfort thresholds, the occurrence of skin injuries or other negative signs, and whether characteristics of muscle activity can be related to discomfort.

Study design: The study is a cross-sectional intervention study with one measurement session, where participants will provide a continuous comfort rating during exposure to repetitive normal and shear forces.

Study population: The aim is to include 20 healthy participants in total, matching the age groups 18-35 and 55-85.

Intervention: A pre-defined set of prolonged repetitive force patterns will be applied to each participant's thigh though a contact force which is similar to cuffs commonly used in gait exoskeletons. The forces will be applied by a custom made actuated test device and are based on normal use of exoskeletons.

Main study parameters/endpoints: The main study parameter is the level of discomfort as indicated continuously by the participants through a slider with a visual analogue scale. The scale reaches from no discomfort at all to maximum imaginable discomfort. A separate switch which releases all forces if activated by the participant is used to detect onset of pain.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The study is non-therapeutic, so no direct benefits for the participants are involved. The procedures are non-invasive and safety measures are taken to avoid excessive force exertion to the participants or other unsafe situations. Therefore, subjects suffer no negative effects or disadvantages, except for the invested time and the discomfort experienced during the force execution. Pain will be avoided as participants can trigger a release of the forces at any time. Any changes to the participants' skin or other negative signs will be monitored and followed up on until they have resolved.

Eligibility criteria: Inclusion Criteria:

* Between 18 and 35 or between 55 and 85 years of age
* Able to provide informed consent

Exclusion Criteria:

* Unable to follow simple instructions
* Insufficient knowledge of the Dutch or English language to understand the purpose and methods of the study
* skin lesions at the thigh
* sensory impairments
* severe blood pressure fluctuations
* inability to sit in required posture in experiment chair for 60 minutes
* taking blood thinners or showing signs for increased bleeding tendency

Primary outcomes:
measure: Perceived discomfort as indicated on a 10 mm visual analog scale (VAS) by the participants, ranking from 'no discomfort' to 'worst imaginable comfort' (10)
timeFrame: 80 minutes
Secondary outcomes:
measure: Number of completed test sessions/dropouts
timeFrame: 160 minutes
measure: Occurrence of injuries or other negative signs
timeFrame: 30 minutes
measure: Surface Electromyography (EMG) recordings of Rectus femoris
timeFrame: 120 minutes
Other outcomes:
measure: Height in meters
timeFrame: 2 minutes
measure: Body weight in kg
timeFrame: 2 minutes
measure: Age in years
timeFrame: 1 minute
measure: Gender
timeFrame: 1 minute
Locations:
city: Enschede
country: Netherlands
facility: Roessingh Research and Development
Study officials:
affiliation: Roessingh Research and Development
name: Gerdienke Prange, PhD
role: PRINCIPAL_INVESTIGATOR
References: