Evaluation of Trunk Assistance Exoskeleton

Stadiometer measurements require an electronic comparator (Mitutoyo; model 543-730B) mounted on a height-adjustable structure that allows alignment with the longitudinal axis of the spine. To measure spinal compression, the participant should position themselves face down against the wall, feet shoulder-width apart (template on the floor), knees fully extended, arms at their sides, and the following points in "light" contact with the wall: forehead, nose, pelvis (or navel), and toes (without shoes, with socks). The assessor will be asked to take the measurements (10 measurements) at the end of expiration, where they will be asked to hold their breath for 2-3 seconds. The baseline for the lifting task sessions is measured before all lifting task blocks. This measurement, expressed in millimeters, reflects only the vertical position of the electronic comparator. Measure = Mean after Block X - Session's baseline mean(before block 1).

Participants score their muscular exertion perception in 5 muscle groups (quadriceps, hamstrings, hip extensors, lumbar extensors, thorax extensors) on the Borg CR-10 scale. The baseline for the lifting task sessions is measured before all lifting task blocks. There are 12 levels to this scale(Minimum=0(No exertion) maximum=10(maximal exertion), all integer values, 0.5 is also an option.

Maximal lifting strength is assessed by measuring pulling force on a bar at knee level with a strain gauge. The handle is held firmly by both hands. Participants were asked to bend at the hips and knees so as to keep an extended lower back during the trials, similar to a deadlifting position. During each trial, participants were asked to progressively pull harder on the bar without jerking for 5 seconds. The maximal value expressed in newtons during each trial was used. The baseline measurement is the mean of 3 trials with a 2 minute pause in between trials. Only 1 trial was performed after the last lifting block so as to better assess muscular fatigue by limiting time for recovery.

Participants scored the assistance they felt wearing an exoskeleton on a 5-level Likert scale(min: no assistance= 0, max: considerable assistance = 4).

Participants scored the estimated proportion of cycles where parasitic forces were experienced (min:0% of cycles=0 , max:100% of cycles=4) on a 5-level Likert scale.

Participants scored the magnitude of parasitic forces when these were experienced (min: no forces experienced=0 , max: very high forces experienced=5) on a 6-level Likert scale.

Participants scored the estimated proportion of cycles where the exoskeleton restrained their movement (min:0% of cycles=0 , max:100% of cycles=4) on a 5-level Likert scale.

Participants scored the magnitude of movement restrictions caused by the exoskeleton when these were experienced (min: no movement restriction experienced=0 , max: very high movement restrictions experienced=5) on a 6-level Likert scale.

Participants scored the estimated proportion of cycles where the exoskeleton caused postural instability (min:0% of cycles=0 , max:100% of cycles=4) on a 5-level Likert scale.

Participants scored the magnitude of postural instability caused by the exoskeleton when these were experienced (min: no postural instability experienced=0 , max: very high postural instability experienced=5) on a 6-level Likert scale.

Participants scored the pressure points caused by the exoskeleton when these were experienced on a 5 item 7-level Likert scale(min: no pressure points experienced=0 , max: extreme pressure points experienced=6). The 5 items were different anatomical regions (thighs, hips/lower back, back of thorax, front of thorax, above the shoulders). Combined score is the sum of all items (min: no pressure points experienced=0 , max: extreme pressure points experienced=30).

Participants scored the discomforts caused by the exoskeleton when these were experienced on a 5 item 5-level Likert scale (min: strongly disagree=-2 , max: strongly agree=+2). The 5 items were different types of discomforts (being hot, sweatiness, itching or iritation of the skin, pinch point, pain). Combined score is the sum of all items (min: no discomforts experienced=-10 , max: extreme discomforts experienced=10).

Participants responded to the statement "I think this exoskeleton is comfortable" on a 5-level Likert scale (min: strongly disagree=-2 , max: strongly agree=+2).