Work Physiological-Biomechanical Analysis of a Passive Exoskeleton to Support Occupational Lifting and Flexing Processes

Study Overview
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Brief Summary
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BACKGROUND Industrial tasks that are characterized by high loads, a high repetition rate, and/or awkward body postures, put employees at higher risk to develop work-related musculoskeletal disorders (WRMSD), especially low back pain. To counteract the prevalence of WRMSD, human-robot interaction could improve the power of a person and reduce the physical strain. For the lower back, a reduction of spinal loading could be helpful. The passive upper-extremity exoskeleton Laevo® is developed to support physically heavy work: it supports the back during bending and should, consequently, result in less low back pain (Laevo®, the Netherlands). OBJECTIVES The primary aim of this study is to assess to what extent wearing the exoskeleton changes: muscular activity of the erector spinae and biceps femoris muscles; knee compression force; posture of the upper and lower spine, trunk, hips and knees; ...in different tasks (static vs. dynamic), different trunk postures (trunk flexion vs. trunk flexion and rotation) and different knee postures (straight vs. stooped). Secondary aims of this study are to assess to what extent wearing the exoskeleton changes: muscular activity of the trapezius descendens, rectus abdominis, vastus medialis and gastrocnemius medialis; perceived discomfort; heart rate; internal loadings on the spine, using a lumbar spine model; the performance of subjects during functional activities (e.g., stair climbing) when wearing the exoskeleton (either turned on or off); ...in different tasks (static vs. dynamic), different trunk postures (trunk flexion vs. trunk flexion and rotation), different knee postures (stoop vs. squat), and different static holding positions(0° vs. 30° vs. 60°) with different weights (0kg vs. 8kg vs. 16kg).

Detailed Description
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METHODS Different experiments will be performed. The investigators will test six different experimental conditions in the laboratory, which are a combination of exoskeleton (with vs. without Laevo®), task (static vs. dynamic), and knee angle only for the dynamic task (flexed vs. extended). Within each combination, the investigators will test three different working directions (front vs. left vs. right), realized by changing the working posture (trunk flexion vs. left trunk rotation vs. right trunk rotation). Using the single Williams design for six conditions, the investigators estimated the sample size to include 36 subjects (i.e., a multiple of six). Using a force plate, acceleration and postural sensors, knee compression force can be estimated using 2D inverse modelling. With an electromyographic system, the muscle activity of selected target muscles at different body parts (i.e., legs, trunk, and shoulders) can be recorded. The heart rate will be recorded using electrocardiography. The investigators will test four different conditions, which are a combination of exoskeleton (with vs. without Laevo®) and knee angle (flexed vs. extended). Within each combination, the investigators will test three different loads carried (0kg, 8kg, 16kg) and five different trunk flexion angles (0°, 30°, 60°, 60°, 30°). Muscle activity, position, heart rate and ground reaction forces will be recorded. The investigators will test three different functional tests. The outcomes for this aim are time recorded for performing the functional or industrial task and perceived difficulty rated on an 11-point numeric rating scale. The investigators will use the lumbar spine model developed by the research group Biomechanics and Biorobotics of the research cluster Simulation Technology of the University of Stuttgart. The model includes a detailed lumber spine with non-linear discs, ligaments, and muscles. Using the measurements of the experiment, this model is able to predict how internal forces in the lumbar spine change as a result of external forces (i.e., wearing and using the Laevo® exoskeleton). ANALYSES Depending on the outcome parameter, different analyses will be performed including a various number of independent variables. The effects of exoskeleton (with vs. without), task (static vs. dynamic), knee angle (flexed vs. extended; only for the dynamic task), and working posture (trunk flexion vs. left trunk rotation vs. right trunk rotation) will be assessed using a four-factor repeated-measures analysis of variance (RM-ANOVA) or a generalized estimating equation (GEE) which is more robust. The effects of exoskeleton (with vs. without), knee angle (flexed vs. extended), load carried (0kg vs. 8kg vs. 16kg), and trunk flexion angle (0° vs. 30° vs. 60°) will be assessed using a RM-ANOVA or GEE. The effect of exoskeleton (with vs. without) on time and perceived difficulty of each functional or industrial test will be assessed using a paired T-Test. In addition, the muscular load of several muscles will also be evaluated. DATA PROTECTION All participating subjects will receive a refund of € 45 after study completion. Subjects will sign an informed consent and their data will be numerically pseudonymized to guarantee anonymity. SIMULATED TASKS Static sorting task, lasting 1.5 minutes, within which subjects are exposed to 6 experimental conditions: exoskeleton (2 levels: without vs. with) X working posture (3 levels: left trunk rotation vs. frontal orientation vs. right trunk rotation). Dynamic lifting task, two sets of five repetitions each, within which subjects are exposed to 12 experimental conditons: exoskeleton (2 levels: without vs. with) X working posture (3 levels: left trunk rotation vs. frontal orientation vs. right trunk rotation) X knee angle (2 levels: extended/stoop vs. bent/squat). Functional tasks: a course within which several occupationally relevant tasks (picking & placing, drilling) and standardized tests (sit-up-and-stand, stair walk) are evaluated on performance, subjectively perceived strain and muscle load. Static holding task, for which subjects were exposed to 18 different conditions: exoskeleton (2 levels: without vs. with) X holding weight (3 levels: 0kg vs. 8kg vs. 16kg) X trunk flexion angle (3 levels: 0° vs. 30° vs. 60°). IMPORTANT NOTE --- On this platform, results of the static sorting task ONLY will be reported. Results of other parts of the study will be reported in the respective publication. Links to these publications will be added as soon as they are published and available. --- IMPORTANT NOTE

Official Title
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Work Physiological-Biomechanical Analysis of a Passive Exoskeleton to Support Occupational Lifting and Flexing Processes

Conditions
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Passive Upper-limb Exoskeleton

Intervention / Treatment
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* Device: Laevo ®
* Device: No Laevo ®


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: The participant will give his voluntary informed consent after receiving oral and written information of the content and goal of the study. Exclusion Criteria: Aged <18 and >40 years; Female; BMI > 30 kg/m2; People under the influence of intoxicants, analgesics, or muscle relaxants; Alcohol abuse; People with cardiovascular diseases; People with a heart pacemaker; People with a disability who, due to their restriction at a workplace of this kind, will not be able to participate; People with Diabetes Mellitus; People with severe muscle contractions of the lower extremities, back or arms; People with acute ailments or pain; People who are unable to complete the examination program due to language or cognitive obstacles; Depending on the degree of severity, people with diseases of the veins and joints of the lower extremities, spine, muscle disorders, symptomatic neurological-psychiatric diseases, acute pain syndromes, maladies or other current diseases.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Static sorting Six conditions as combination of exoskeleton (without vs. with) and trunk posture (forward flexion vs. flexion + rotation left vs. flexion + rotation right) are investigated in a randomized order. Dynamic lifting Twelve conditions as combination of exoskeleton (without vs. with), work posture (forward flexion vs. flexion + rotation left vs. flexion + rotation right) and knee angle (extended/stoop vs. flexed/squat) are investigated in randomized order. Functional tasks Three tests with two conditions in randomized order (exoskeleton: without vs. with) will be investigated in fixed order (stair-climbing; timed-up-and-go; course with various simulated industrial workstations). Angle-force relation Twelve conditions as combination of exoskeleton (without vs. with), knee angle (extended/stoop vs. flexed/squat) and trunk flexion angle (0 vs. 30 vs. 60 degrees) are investigated in randmized order.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: With exoskeleton, then without exoskeleton<br>Subject will first perform the conditions (simulated, simplified, industrial standing work) with the exoskeleton, then without the exoskeleton. | Device: Laevo ®<br>* A passive exoskeleton supporting the lower back during bending and lifting tasks (for more information, visit the manufacturer's website: http://en.laevo.nl/).<br>* Other names: Exoskeleton;Device: No Laevo ®<br>* The subjects will not wear any supporting device to perform the experiment, which serves as the control condition.<br>* Other names: No exoskeleton;|
| Experimental: Without exoskeleton, then with exoskeleton<br>Subject will first perform the conditions (simulated, simplified, industrial standing work) without the exoskeleton, then with the exoskeleton. | Device: Laevo ®<br>* A passive exoskeleton supporting the lower back during bending and lifting tasks (for more information, visit the manufacturer's website: http://en.laevo.nl/).<br>* Other names: Exoskeleton;Device: No Laevo ®<br>* The subjects will not wear any supporting device to perform the experiment, which serves as the control condition.<br>* Other names: No exoskeleton;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Muscular Activity of Erector Spinae Muscle. | Root-mean-square (RMS) of the electrical activity of the erector spinae muscle using surface electromyography (sEMG). The sEMG signals will be continuously recorded, and the RMS will be normalized to a maximal voluntary contraction (%MVE) and averaged over the time period of each experimental condition. | Average RMS-value (%MVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Muscular Activity of Biceps Femoris Muscle. | Root-mean-square (RMS) of the electrical activity of the biceps femoris muscle using surface electromyography (sEMG). The sEMG signals will be continuously recorded, and the RMS will be normalized to a reference voluntary contraction (%RVE) and averaged over the time period of each experimental condition. | Average RMS-value (%RVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Posture (Thoracic Kyphosis) | The posture of the upper spine (thoracic kyphosis) determined using 2D gravimetric position sensors placed on the thoracic vertebrae T1 and lumbar vertebrae L1. The difference value between both sensors reflects the thoracic kyphosis, which was averaged over each experimental condition. | Average thoracic kyphosis over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Posture (Lumbar Lordosis) | The posture of the lower spine (lumbar lordosis) determined using 2D gravimetric position sensors placed on the lumbar vertebrae L1 and L5. The difference value between both sensors reflects the lumbar lordosis, which was averaged over each experimental condition. | Average lumbar lordosis over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Posture (Trunk Flexion) | The posture of the trunk determined using a 2D gravimetric position sensor placed on the thoracic vertebrae T10. The flexion angle of the sensor was averaged over each experimental condition. | Average trunk flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Posture (Hip Flexion) | The posture of the hip (hip flexion) determined using 2D gravimetric position sensors placed on the lumbar vertebrae L5 and the upper leg (femur). The difference value between both sensors reflects the hip flexion, which was averaged over each experimental condition. | Average hip flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Posture (Knee Flexion) | The posture of the knee (knee flexion) determined using 2D gravimetric position sensors placed on the upper leg (femur) and lower leg (tibia). The difference value between both sensors reflects the knee flexion, which was averaged over each experimental condition. | Average knee flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Knee Compression Force | The knee compression force (KCF) is calculated using 2D inverse modelling with continuous recordings from 2D gravimetric position sensors (for joint angles) and a force plate (for ground reaction forces). The average knee compression force will be calculated over each experimental condition and summarized for both the left and right knee, since the task is executed in the frontal plane. | Average knee compression force (KCF) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Root-mean-square (RMS) of the electrical activity of the rectus abdominis, vastus lateralis, gastrocnemius medialis and trapezius descendens muscles using surface electromyography (sEMG). The sEMG signals will be continuously recorded, and the RMS will be normalized to a refeernce voluntary contraction (%RVE) and averaged over the time period of each experimental condition. | Average RMS-value (%RVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition. | 
| Rating of Perceived Discomfort (RPD) | Discomfort (RPD) was assessed using an 11-point numeric rating scale (NRS), ranging from 0 (no discomfort at all) to 10 (maximally imaginable discomfort). It was assessed directly before (0 min) and directly after (1.5 min) each experimental condition. The experimental conditions consisted of either static or dynamic tasks, that lasted up to 1.5 minutes. | Change from baseline (0 min) to directly after (1.5 min) both experimental conditions | 
| Heart Rate | Continuous recording electrocardiography allows calculating the heart rate, a parameter reflecting the central stress state of the participant. The average heart rate will be calculated per time period. | Average heart activity over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 
| Evaluation of Workload | The NASA Task Load Index (TLX) of Hart and Staveland (1988) will be used to evaluate workload. This standardized tool contains six dimensions (mental demand, physical demand, temporal demand, own performance, effort, frustration), of which each scale ranges from from 0 (low) to 100 (high). We will include three dimensions of interest, i.e. physical demand, temporal demand, effort, and calculate the unweighted average of the score of these three dimensions (Hoonakker et al. 2011). | Directly after the experimental condition during which the exoskeleton was worn (  4.5-6.5 min) | 
| Self-developed Participant Evaluation Questionnaire | This questionnaire will consist of questions about usability and acceptance of the intervention (the Laevo device), stemming from standardized questions from existing questionnaires, including: the System Usability Scale (SUS): 10 statements about subjective perception of interaction with the Laevo system to be evaluated on a scale ranging from 1 (disagree) to 5 (agree); the Technology Usage Inventory (TUI): 30 statements on technology-specific and psychological factors with respect to the Laevo to be evaluated on a scale ranging from 1 (not true) to 7 (true); of these 30 questions, the investigators include only 7 statements belonging to the domains 'usability' and 'skepticism'. The questionnaire can only be filled out after the condition within which the technology (here: exoskeleton) was used. That means that results are only provided and, thus, reported from the arm with exoskeleton. | Directly after the experiment ( 2.5 hours) | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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passive exoskeleton, forward trunk flexion, trunk rotation, muscle activity, inverse dynamics, modelling