Passive Upper-limb Exoskeleton
Conditions
Keywords
passive exoskeleton, forward trunk flexion, trunk rotation, muscle activity, inverse dynamics, modelling
Brief 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
Interventions
DEVICELaevo ®
A passive exoskeleton supporting the lower back during bending and lifting tasks (for more information, visit the manufacturer's website: http://en.laevo.nl/).
DEVICENo Laevo ®
The subjects will not wear any supporting device to perform the experiment, which serves as the control condition.
Sponsors
Audi AG
BASF
BMW AG
Dachser Intelligent Logistics
Daimler AG
Deutsche Post AG
Iturri Gruppe
MTU Aero Engines AG
University Hospital Tuebingen
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
PREVENTION
Masking
NONE
Masking description
Subjects and experimenters will not be blinded, because it will be obvious which task will be performed by the subjects and measurements need to be tracked by the experimenter.
Intervention model description
1. 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. 2. 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. 3. 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). 4. 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.
Eligibility
Sex/Gender
MALE
Age
18 Years to 40 Years
Healthy volunteers
Yes
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.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Knee Compression Force | Average knee compression force (KCF) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Posture (Thoracic Kyphosis) | Average thoracic kyphosis over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Posture (Lumbar Lordosis) | Average lumbar lordosis over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Posture (Trunk Flexion) | Average trunk flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Posture (Hip Flexion) | Average hip flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Posture (Knee Flexion) | Average knee flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Muscular Activity of Erector Spinae Muscle. | Average RMS-value (%MVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Muscular Activity of Biceps Femoris Muscle. | Average RMS-value (%RVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Rating of Perceived Discomfort (RPD) | Change from baseline (0 min) to directly after (1.5 min) both experimental conditions | 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. |
| Heart Rate | Average heart activity over time period baseline (0 min) to directly after (1.5 min) the experimental condition | 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. |
| Evaluation of Workload | Directly after the experimental condition during which the exoskeleton was worn (~ 4.5-6.5 min) | 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). |
| Self-developed Participant Evaluation Questionnaire | Directly after the experiment (~2.5 hours) | 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. |
| Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Average RMS-value (%RVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition. | 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. |
Countries
Germany
Participant flow
Recruitment details
Volunteering participants were recruited via the collaborating investigators and by means of announcement e-mails to employees and students of the University and Hospital of Tübingen.
Pre-assignment details
39 volunteering participants were recruited, of which 2 were excluded from the study prior to the measurement due to a too high BMI (\> 30 kg/m2). A 3rd participant was excluded because he was the first that was measured and we had to adjust a few things to the measurement afterwards.
Participants by arm
| Arm | Count |
|---|---|
| With Exoskeleton, Then Without Exoskeleton Subject first performed the conditions (simulated, simplified, industrial standing work) with the exoskeleton, then without the exoskeleton. | 19 |
| Without Exoskeleton, Then With Exoskeleton Subject first performed the conditions (simulated, simplified, industrial standing work) without the exoskeleton, then with the exoskeleton. | 17 |
| Total | 36 |
Withdrawals & dropouts
| Period | Reason | FG000 | FG001 |
|---|---|---|---|
| First Intervention | Physician Decision | 1 | 1 |
| First Intervention | Withdrawal by Subject | 0 | 1 |
Baseline characteristics
| Characteristic | Without Exoskeleton, Then With Exoskeleton | With Exoskeleton, Then Without Exoskeleton | Total |
|---|---|---|---|
| Age, Continuous | 28.1 years STANDARD_DEVIATION 4.6 | 23.9 years STANDARD_DEVIATION 3.8 | 25.9 years STANDARD_DEVIATION 4.6 |
| Body mass index (BMI) | 23.3 kg/m^2 STANDARD_DEVIATION 2.1 | 22.6 kg/m^2 STANDARD_DEVIATION 2.1 | 22.9 kg/m^2 STANDARD_DEVIATION 2.1 |
| Height | 178.0 cm STANDARD_DEVIATION 6.7 | 179.7 cm STANDARD_DEVIATION 6.3 | 178.9 cm STANDARD_DEVIATION 6.4 |
| Race (NIH/OMB) American Indian or Alaska Native | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Asian | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Black or African American | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) More than one race | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Native Hawaiian or Other Pacific Islander | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Unknown or Not Reported | 17 Participants | 19 Participants | 36 Participants |
| Race (NIH/OMB) White | 0 Participants | 0 Participants | 0 Participants |
| Region of Enrollment Germany | 17 Participants | 19 Participants | 36 Participants |
| Sex: Female, Male Female | 0 Participants | 0 Participants | 0 Participants |
| Sex: Female, Male Male | 17 Participants | 19 Participants | 36 Participants |
| Weight | 73.8 kg STANDARD_DEVIATION 8.5 | 73.3 kg STANDARD_DEVIATION 9.4 | 73.5 kg STANDARD_DEVIATION 8.9 |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | 0 / 36 | 0 / 36 |
| other Total, other adverse events | 0 / 36 | 0 / 36 |
| serious Total, serious adverse events | 0 / 36 | 0 / 36 |
Outcome results
Primary
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.
Time frame: Average knee compression force (KCF) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition
Population: For some of the participants, we could not analyze the knee compression force (KCF) data, because some information was missing to apply the modelling procedure.
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Knee Compression Force | Average KCF during first intervention period | 845 N |
| With Exoskeleton, Then Without Exoskeleton | Knee Compression Force | Average KCF during second intervention period | 807 N |
| Without Exoskeleton, Then With Exoskeleton | Knee Compression Force | Average KCF during first intervention period | 742 N |
| Without Exoskeleton, Then With Exoskeleton | Knee Compression Force | Average KCF during second intervention period | 874 N |
Primary
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.
Time frame: Average RMS-value (%RVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition
Population: The results of the effect of wearing the exoskeleton during the static task are reported below, without taking into account the working direction (frontal or lateral, i.e. without or with trunk rotation, respectively).
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Biceps Femoris Muscle. | RMS during first intervention period | 26.6 %RVE |
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Biceps Femoris Muscle. | RMS during second intervention period | 35.8 %RVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Biceps Femoris Muscle. | RMS during first intervention period | 38.7 %RVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Biceps Femoris Muscle. | RMS during second intervention period | 31.3 %RVE |
Primary
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.
Time frame: Average RMS-value (%MVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition
Population: The results of the effect of wearing the exoskeleton during the static task are reported below, without taking into account the working direction (frontal or lateral, i.e. without or with trunk rotation, respectively). Note: the overall number of participants analyzed deviates in the first arm because data of one subject was excluded.
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Erector Spinae Muscle. | RMS-value during first intervention period | 11.2 %MVE |
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Erector Spinae Muscle. | RMS-value during second intervention period | 12.3 %MVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Erector Spinae Muscle. | RMS-value during first intervention period | 11.1 %MVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Erector Spinae Muscle. | RMS-value during second intervention period | 10.4 %MVE |
Primary
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.
Time frame: Average hip flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Posture (Hip Flexion) | Average angle during first intervention period | 39.9 degrees |
| With Exoskeleton, Then Without Exoskeleton | Posture (Hip Flexion) | Average angle during second intervention period | 29.8 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Hip Flexion) | Average angle during first intervention period | 33.1 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Hip Flexion) | Average angle during second intervention period | 40.4 degrees |
Primary
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.
Time frame: Average knee flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Posture (Knee Flexion) | Average angle during first intervention period | 16.4 degrees |
| With Exoskeleton, Then Without Exoskeleton | Posture (Knee Flexion) | Average angle during second intervention period | 9.0 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Knee Flexion) | Average angle during first intervention period | 11.7 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Knee Flexion) | Average angle during second intervention period | 17.9 degrees |
Primary
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.
Time frame: Average lumbar lordosis over time period baseline (0 min) to directly after (1.5 min) the experimental condition
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Posture (Lumbar Lordosis) | Average angle during first intervention period | 11.8 degrees |
| With Exoskeleton, Then Without Exoskeleton | Posture (Lumbar Lordosis) | Average angle during second intervention period | 12.2 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Lumbar Lordosis) | Average angle during second intervention period | 13.3 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Lumbar Lordosis) | Average angle during first intervention period | 13.2 degrees |
Primary
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.
Time frame: Average thoracic kyphosis over time period baseline (0 min) to directly after (1.5 min) the experimental condition
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Posture (Thoracic Kyphosis) | Average angle during first intervention period | 12.0 degrees |
| With Exoskeleton, Then Without Exoskeleton | Posture (Thoracic Kyphosis) | Average angle during second intervention period | 14.5 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Thoracic Kyphosis) | Average angle during first intervention period | 15.4 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Thoracic Kyphosis) | Average angle during second intervention period | 13.9 degrees |
Primary
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.
Time frame: Average trunk flexion over time period baseline (0 min) to directly after (1.5 min) the experimental condition
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Posture (Trunk Flexion) | Average angle during first intervention period | 38.5 degrees |
| With Exoskeleton, Then Without Exoskeleton | Posture (Trunk Flexion) | Average angle during second intervention period | 37.9 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Trunk Flexion) | Average angle during first intervention period | 39.6 degrees |
| Without Exoskeleton, Then With Exoskeleton | Posture (Trunk Flexion) | Average angle during second intervention period | 39.9 degrees |
Secondary
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).
Time frame: Directly after the experimental condition during which the exoskeleton was worn (~ 4.5-6.5 min)
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Evaluation of Workload | Physical Demand | 2.31 units on a scale | Standard Deviation 1.58 |
| With Exoskeleton, Then Without Exoskeleton | Evaluation of Workload | Temporal Demand | 1.10 units on a scale | Standard Deviation 1.35 |
| With Exoskeleton, Then Without Exoskeleton | Evaluation of Workload | Effort | 2.10 units on a scale | Standard Deviation 1.3 |
| Without Exoskeleton, Then With Exoskeleton | Evaluation of Workload | Physical Demand | 1.67 units on a scale | Standard Deviation 1.1 |
| Without Exoskeleton, Then With Exoskeleton | Evaluation of Workload | Temporal Demand | 0.88 units on a scale | Standard Deviation 1.01 |
| Without Exoskeleton, Then With Exoskeleton | Evaluation of Workload | Effort | 1.49 units on a scale | Standard Deviation 1 |
Secondary
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.
Time frame: Average heart activity over time period baseline (0 min) to directly after (1.5 min) the experimental condition
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Heart Rate | 85.29 beats per minute | Standard Deviation 10.19 |
| Without Exoskeleton, Then With Exoskeleton | Heart Rate | 83.16 beats per minute | Standard Deviation 10.49 |
Secondary
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.
Time frame: Average RMS-value (%RVE) over the time period running from baseline (0 min) to directly after (1.5 min) the experimental condition.
| Arm | Measure | Group | Value (MEDIAN) |
|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Rectus Abdominis | 1.85 %RVE |
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Vastus Lateralis | 3.85 %RVE |
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Gastrocnemius Medialis | 54.11 %RVE |
| With Exoskeleton, Then Without Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Trapezius Descendens | 3.77 %RVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Trapezius Descendens | 4.90 %RVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Rectus Abdominis | 1.57 %RVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Gastrocnemius Medialis | 54.11 %RVE |
| Without Exoskeleton, Then With Exoskeleton | Muscular Activity of Rectus Abdominis, Vastus Lateralis, Gastrocnemius Medialis and Trapezius Descendens Muscles. | Vastus Lateralis | 3.35 %RVE |
Secondary
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.
Time frame: Change from baseline (0 min) to directly after (1.5 min) both experimental conditions
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Rating of Perceived Discomfort (RPD) | RPD after first intervention period | 0.3 units on a scale | Standard Deviation 0.8 |
| With Exoskeleton, Then Without Exoskeleton | Rating of Perceived Discomfort (RPD) | RPD after second intervention period | 0.5 units on a scale | Standard Deviation 1 |
| Without Exoskeleton, Then With Exoskeleton | Rating of Perceived Discomfort (RPD) | RPD after first intervention period | 0.2 units on a scale | Standard Deviation 0.6 |
| Without Exoskeleton, Then With Exoskeleton | Rating of Perceived Discomfort (RPD) | RPD after second intervention period | 0.2 units on a scale | Standard Deviation 0.7 |
Secondary
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.
Time frame: Directly after the experiment (~2.5 hours)
Population: Reportedin units on a scale:~SUS: 0 (low usability) to 100 (high usability) TUI-userfriendliness: 3 (totaly not applicable) to 21 (totally applicable) TUI-scepticism: 4 (totaly not applicable) to 28 (totaly applicable)
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| With Exoskeleton, Then Without Exoskeleton | Self-developed Participant Evaluation Questionnaire | System Usability Scale (SUS) - total score | 75.44 units on a scale | Standard Deviation 12.87 |
| With Exoskeleton, Then Without Exoskeleton | Self-developed Participant Evaluation Questionnaire | Technology Usability Inventory (TUI) - user friendlines score | 17.92 units on a scale | Standard Deviation 2.61 |
| With Exoskeleton, Then Without Exoskeleton | Self-developed Participant Evaluation Questionnaire | Technology Usability Inventory (TUI) - scepticims | 11.53 units on a scale | Standard Deviation 4.08 |