Biomechanical Feasibility of passive shoulder exoskeleton in construction work

In construction environments, there are many complex tasks that require arm and shoulder elevation and heavy load lifting on unstable platforms, such as the tasks of brick or cinderblock laying, which can lead to shoulder and back musculoskeletal disorders (MSDs) and injuries. In order to alleviate such injuries, many construction industries have been attempting to adopt the use of exoskeletons. An exoskeleton is a mechanical system that can reduce muscular demand and the risk of developing MSDs and injuries. Despite these potential benefits of exoskeleton use, some collateral effects exist. For instance, the use of an exoskeleton can shift the body’s center of gravity (COG), restrict the functional range of motion of the joints, and cause subjective discomfort. Additionally, a change in the body COG can lead to adverse outcomes such as postural instability, which increases the risk of both fatal and non-fatal fall injuries. Furthermore, there remains a critical need to assess the feasibility of the exoskeleton in symmetric and asymmetric task conditions since the exoskeletons were originally designed to support pure symmetric lifting. Therefore, to assess the effectiveness of exoskeletons, particularly the use of passive shoulder exoskeletons in everyday construction works requiring both symmetric and asymmetric shoulder exertions and performed on unstable work platforms, I conducted a two-phase study. In phase 1, I recruited nine male participants (age: 32.33 ± 7.84 years old, height: 179.83 ± 5.38 cm, and BMI: 48.37 ± 7.33 kg/m2) to perform asymmetric lifting of cinderblocks from trochanterion height of the non-dominant side to two different destination levels: 1) the elbow height and 2) the shoulder height of their dominant side. Three commercially available exoskeletons—SuitX (Exo 1), Eksobionic (Exo 2), and Levitate (Exo 3)—were selected to perform the tasks. Both lifting tasks were performed on two different ground conditions—1) a baseline, stable solid platform and 2) an unstable, wobbling platform —under four exoskeleton (Exo) conditions: 1) No-Exo, 2) Exo 1, 3) Exo 2, and 4) Exo 3. The wobbling platform was custom designed to simulate a mast climb work platform that is commonly seen in brick and cinderblock laying tasks. In Phase 2, I recruited nine other male participants (age:28.89 ± 8.58 years old, height: 1.76 ± 0.08 cm, BMI: 49.78 ± 9.41 kg/ m2) to perform the same set of tasks (2 Ground conditions × 2 Height Levels × 4 Exo Conditions) under the symmetric condition where the origin and destination heights of the lifting were set in participants’ mid-sagittal plane. I acquired in-vivo full-body kinematics (using a ten-camera Kestrel 1300 motion capture system), biceps, triceps, upper trapezius, and anterior, posterior, and middle deltoids muscle activities (using Trigno-16 surface electromyography system), and 3D ground reaction forces and center of pressure (using Bertec force plates in solid, stable ground condition and K-invent portable force platforms in unstable, wobbling ground Condition 2). I leveraged these large datasets to achieve three study aims. Aim 1 focused on investigating the effectiveness of passive shoulder exoskeleton on reducing the muscular demand of shoulder and low back muscles, Aim 2 centered around studying their impacts on movement kinematics and kinetics of elbow, shoulder, and low back joints, and Aim 3 concentrated on exploring the effects of exoskeleton on the whole-body postural balance and the risk of falls for each of the aforementioned task conditions. I analyzed shoulder muscle activity, shoulder, low back, and elbow joint kinematics and kinetics, and the whole-body postural balance to address these three aims. I hypothesized that the use of exoskeletons would lead to a decrease in muscle activity, adversely impact normal body movement and joint reaction forces, and an increase in postural imbalance. I employed a partially nested four-way analysis of variance (ANOVA) with subjects nested within motion type factor (asymmetric x symmetric) and evaluated the main and interaction effects of each task condition (factors) on the independent variables normalized muscle activity, peak moment of shoulder, trunk, and elbow joints, range of motion of shoulder, trunk, and elbow joints, center of pressure (CoP), and sway parameters (sway ratio, sway velocity, and confidence ellipse area). Results showed that exoskeleton effectively reduced anterior deltoid and upper trapezius muscle activation, with SuitX (Exo 1) and Levitate (Exo 3) showing significant reductions in anterior deltoid activity by 16.14% and 23.41%, respectively (p < 0.01), compared to No-Exo. Additionally, Exo 3 decreased upper trapezius activity by 13.45% (p = 0.035). No significant results were observed for other muscle groups and for the Exo 2 (Exo 2). Concerning kinematics and kinetics, results showed that Exo 3 significantly reduced peak flexion-extension angles during symmetric tasks by 8.99% (75.26° vs. 82.69°, p = 0.024), while Exo 1 reduced asymmetric task angles by 11.72% (87.06° vs. 98.62°, p < 0.001), compared to No-Exo conditions. On the other hand, all exoskeletons increased peak abduction-adduction angles during symmetric tasks, with Exo 3 showing the largest increase of 8.94% (p = 0.009). Lastly, for the postural balance, results showed that Exo 1 and Exo 2 significantly reduced Sway AP by 8.68% and 7.06%, respectively (p < 0.05), compared to the No-Exo condition (~3.40). However, all exoskeletons significantly increased Sway Area during asymmetric tasks, with Exo 3 showing the highest increase of 51.69% (~3075.69 mm² vs. ~2027.62 mm², p < 0.01) compared to No-Exo conditions. This study is documented in eight chapters. Chapter 1 outlines motivation, specific aims, and hypotheses that guide this comprehensive investigation. Chapter 2 details the methodology for the literature review, including the databases searched and the selection criteria, followed by a synthesis of relevant studies aligned with the scope of this research. Chapter 3 examines the impact of exoskeleton use on muscle dynamics. Chapter 4 focuses on the analysis to joint-level biomechanics, evaluating changes in joint angles and moments. Chapter 5 explores postural adaptations associated with exoskeleton use, with particular attention to variations induced by ground conditions and task asymmetry. Chapter 6 concludes the exoskeleton investigation by outlining its current limitations and offering directions for future research. In Chapter 7 I have listed the study appendix, followed by my curriculum vitae in Chapter 8.