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

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).

METHODS Different experiments will be performed.

1. 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.
2. 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.
3. 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.
4. 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.

1. 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.
2. 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.
3. 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

1. 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).
2. 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).
3. 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.
4. 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

Eligibility Criteria:
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.