Text

Introduction: Musculoskeletal disorders (MSDs), particularly those affecting the upper extremities, remain a leading cause of work-related sick leave. Tasks performed above shoulder joint (SJ) height impose considerable biomechanical loads, significantly increasing the risk of MSD development. Although interest in upper-extremity exoskeletons as assistive devices is growing within the industrial sector, conclusive biomechanical evidence regarding their long-term efficacy remains limited. This study investigates the biomechanical and physiological effects of a passive upper-extremity exoskeleton during overhead tasks in the context of aircraft manufacturing.

Methods: A field study was conducted in an aircraft manufacturing plant involving 20 experienced workers performing typical overhead assembly tasks. Two representative tasks – structure assembly (S-Task) and equipment installation (E-Task) – were analysed. Inertial measurement units (IMUs) were used to capture movement patterns. Long-term recordings over > 12-month period was provided by Team A, while Team B conducted detailed shift-based analyses. Each approach included assessments of shoulder elevation angles and the resulting joint moments. Both tasks were performed with and without the support of a passive shoulder exoskeleton (EXO, PAEXO Shoulder). The biomechanical impact of the EXO was evaluated based on its known support characteristics. Additionally, participants completed questionnaires regarding usability, comfort, and acceptance. Workweeks with and without EXO support were compared using ergonomic assessment tools, including the Key Indicator Method for Musculoskeletal Load (LMM) and the CUELA Method, as outlined in the MEGAPHYS reports (BAuA 2019; DGUV 2020).

Results:CUELA and LMM evaluations indicated a high risk of musculoskeletal overload (S-Task: 37.7% NRPM/LMM score 140; E-Task: 32.3% NRPM/LMM score 133). Cumulative CUELA analysis of shoulder strain profiles (based on Potvin, 2012) revealed high muscular strain during S-Tasks (high-risk exposure >10% of working time) and increased strain during E-Tasks (increased-risk exposure >5% of working time). Use of the EXO reduced muscular strain by up to 11% MVC, corresponding to a reduction of shoulder joint moments of up to 9 Nm. Over the long term, EXO use led to a 14% increase in endurance (holding time improved from 5.0 s to 5.7 s) and a 12% reduction in handling events (from 387 to 340). Subjective evaluations indicated high perceived relief (4.1/5), increased well-being (4.4/5), and moderate comfort (3.9/5).

Discussion: The high muscular strain observed, particularly in S-Tasks, suggests a potential for non-reversible fatigue of the shoulder musculature. The reduction in muscular strain by up to 11% MVC through EXO use may enable sufficient recovery and could help prevent chronic fatigue under certain working conditions.

Conclusion: Using a passive shoulder exoskeleton showed beneficial effects in reducing biomechanical load and muscular effort. While these results alone do not justify the general conclusion that exoskeleton use significantly lowers the risk of developing MSDs, they are promising and warrant further investigation.