Work Physiological-Biomechanical Analysis of a Passive Exoskeleton to Support Occupational Lifting and Flexing Processes
Condition: Passive Upper-limb Exoskeleton
Study type: Interventional

Summary: 
      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: 
      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
    

Intervention name(s): Laevo ®; No Laevo ®
Intervention type(s): Device; Device
Intervention description(s): A passive exoskeleton supporting the lower back during bending and lifting tasks (for more information, visit the manufacturer's website: http://en.laevo.nl/).; The subjects will not wear any supporting device to perform the experiment, which serves as the control condition.
Other intervention name(s): Exoskeleton; No exoskeleton
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention 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)
Primary purpose: Prevention
Keywords: passive exoskeleton; forward trunk flexion; trunk rotation; muscle activity; inverse dynamics; modelling