Assessing the Efficacy of Passive Exoskeletons for Construction Work: Lab-Based Study

The experimental protocol will require approximately 3 hours of the participant's time. It will be comprised of six stages:

Stage I: Body Discomfort and Handedness Questionnaires First, the research team will administer an interview questionnaire to the participant to obtain information on participants' body pain/discomfort level and to determine the participant's hand dominance using the Edinburgh Handedness Inventory.

Stage II: Anthropometric body measurements and strength testing Several anthropometric body dimensions will be measured in the standing upright position using a standard tape measure and anthropometer. Body measurements will include standing height, shoulder height, waist to floor height, leg length, knee height, upper and lower arm length, foot length, and inter shoulder distance. Study participants' body weight will be measured using a standard weighing scale. Maximum power grip strength on both hands will be measured for 3 trials using a standard hand-held grip dynamometer.

Stage III: Fitting BSEs Four types of commercial BSEs (backX, Laevo 2, FLx ErgoSkeleton, V22 ErgoSkeleton) will be introduced to participants. Following manufacturers' instructions, participants will be allowed to test each device, fit the device to their body for comfort by using adjustable features (e.g., straps).

Stage IV: Optical motion capture marker, wearable inertial sensors, and surface electromyography (sEMG) sensor placement A commercial motion-capture system (Qualisys AB, Kvarnbergsgatan, Göteborg, Sweden) will be used to monitor and analyze body segment motion trajectories in a three-dimensional space. Several optical markers will be placed on anatomical landmarks of study participants including the head, shoulders, arms, hands, back, pelvis, legs, and feet. Hypo-allergenic double-sided tape will be used to attach the optical markers to the anatomical landmarks. Wearable inertial sensors will be attached using hypoallergenic double-sided tape at the low-back near the waist (S1), upper back (T6), sternum, upper arm (R, L), lower arm (R, L), thigh (R, L), and shank (R, L). Eight sEMG sensors will be placed on Descending Trapezius (TRP), Anterior Deltoid (AD), Iliocostalis Lumborum (ILL), Rectus Abdominis (RA), External Oblique (EO), Cervical Erector Spinae (CES), Latissimus Dorsi (LD), and Vastus Lateralis (VL) to measure muscle activation level while performing simulated work tasks, which are described in Stage VI.

Stage V: Maximum Voluntary Contraction (MVC) measurement for muscle activation While performing work tasks, muscle activation level varies between muscles and between subjects. A common way is to normalize myoelectric activities of each muscle for every participant by measuring isometric Maximal Voluntary Contraction (MVC). In this study, the investigators will measure 11 MVCs before the start of actual work tasks. Our MVC tests will be based on a study of trunk muscles. Before the MVC measurement, participants will be asked to warm up by 5 stretch exercises: (a) Stand upright with his feet shoulder-width apart. Place his hands on his buttocks for support. Look upwards and slowly lean backward. Keep his legs sturdy. (b) Stand upright with his feet shoulder-width apart. Place one hand on his buttocks for support. Look up and slowly lean backward. Reach over with his opposite hand. Rotate the upper body at the waist. (c) Kneel on one foot. Place his hands on his hips. Push hips forward. If necessary, hold on to something to keep balance. (d) Stand upright with his feet shoulder-width apart. Cross his arms and place his hands on shoulders. Slowly rotate his shoulders to one side. To increase the intensity of this stretch, use his hands to help rotate sideways. (e) Kneel on all fours. Support himself with one hand and reach towards his ankle with the other. Keep his back parallel to the ground. Keep the back straight, parallel to the ground, and his thigh in a vertical position. Distribute his weight evenly on both hands and knees. After the warm-up, the MVC testing will be performed, which includes (1) upper trunk flexion: subject will be in a sit-up posture positioned on a bench with the legs bent and feet strapped down with a belt. He then will attempt to flex the upper trunk in the sagittal plane while her thorax will be manually braced by the experimenter; (2) upper trunk twisting (R and L): In the same sitting supported position, the subject will attempt to twist the upper trunk in the horizontal plane while his thorax will be manually braced by the experimenter;(3) lower trunk flexion: subject will attempt to flex the lower trunk in the sagittal plane while he will be in a supine laying position, but with knees and hips both bent to approximately 90 degrees. His thorax will be strapped down with a belt and his legs will be manually braced by the experimenter; (4) lower trunk twisting (R and L): In the same lying and supported position, the subject will attempt to twist the lower trunk in the horizontal plane while his legs will be manually braced by the experimenter;(5) upper trunk bending (R and L): subject will attempt to side bend the upper trunk in the frontal plane while he will be in a side-lying position, with the knees bent and strapped with a belt, and thorax and arms will be manually braced by the experimenter; (6) lower trunk bending: subject will maintain a right and left side bridge position while maximally resisted downward pressure on the pelvis will be applied by the experimenter;(7) upper trunk extension: subject will be strapped in a prone position, with the torso horizontally cantilevered over the end of the bench (Biering-Sorensen position). He will then attempt to extend the upper trunk in the sagittal plane and retract the shoulders (squeezing the scapulae together) while manual resistance will be applied on the shoulders by the experimenter; (8) lower trunk extension: subject will attempt to extend the lower trunk and the hips against manual resistance when in a prone position, with the torso on the bench and the legs horizontally cantilevered over the end of the bench; (9) shoulder rotation and adduction (R and L): subject will attempt to adduct and internally rotate the shoulder against manual resistance with the shoulder abducted and elbow flexed, both to 90 degrees. In addition, two unresisted maximal abdominal contractions will be performed in standing; (10) maximal effort abdominal hollowing: subject will attempt to maximally activate the deep abdominal muscles while drawing in the lower abdomen; (11) maximal effort abdominal bracing: subject will attempt to maximally activate all the abdominal wall without any change in the position of the muscles. In all MVC testing, participants will be asked to exert their maximum force at a static posture (instructions will be given by our researcher) for every five seconds. For the first two seconds, they will be asked to ramp up to their maximum and maintain the force for the next three seconds. MVCs will be tested at least two times for each muscle group.

Stage VI: Data collection in simulated construction work tasks Postural data will be recorded from participants while performing six simulated concrete work tasks (i.e., shoveling, framing, carrying and lifting of construction materials, hammering, and tying rebars) at different intensities. The material they will be lifting, carrying, shoveling, and holding will not go over the safety limit of 30 lbs, as stated by NIOSH. Participants will perform the tasks with vs. without wearing different BSEs. Task trials will be video recorded for visual correspondence when analyzing motion capture and inertial sensor data. Participants will be given two minutes rest break between tasks and thirty seconds rest break between trials. The order of task conditions within each work task will be randomized.

• Task 1: Shoveling and moving construction material from location A to B. Distance between A and B will be set to 0.5m, both located at the ground level. Participants will be asked to shovel construction materials with three different weights (i.e., dirt, cement, and gravel). Participants will be asked to shovel at a high-frequency rate (15 scoops per minute).
• Task 2: Framing 30" wall using a power screwdriver. The frame will be placed on the floor, versus an elevated surface (28" height). Participants will be asked to use a power screwdriver to drive a screw into and out of the frame.
• Task 3: Carrying construction materials of different weights (i.e., wood frames and pipes) for up to 10 meters in each trial. The maximum weight of the carried materials will not exceed 30 lbs.
• Task 4: Lifting construction materials of different weights. The same materials will be used as the carrying task.
• Task 5: Pounding a punching bag located in the ground vs. 18 inches high vs. 36 inches high using a sledgehammer of different weights (i.e., 0, 6, 12, 16, and 20 lbs.).
• Task 6: Tying rebar in a framed grid located on different height levels (i.e., 0", 50").

The tasks and intensity levels were selected to be diverse yet reproducible (in terms of body postures) and resemble common tasks encountered in concrete work tasks.

Participants will be asked to answer questionnaires asking their experience, usability, and acceptability on each exoskeleton after they complete each work task.

The data collection process will end with removing optical markers and wearable sensors. Participants will be offered a rest break and refreshment if needed and followed by compensation and completing the payment form.