## 1 Introduction
Moreover, they amplify work fatigue and exhaustion while diminishing overall well-being. They also precipitate substantial organisational and societal costs (estimated at approximately 17.2 billion EUR, 45-55 billion USD), through prolonged sick leaves, reducedproductivity, and increased staff turnover rates [19; 20]. Consequently, countless organisations and institutions strive to alleviate WMSDs by implementing ergonomic solutions or occupational hazard prevention across diverse industries and professions. In the realm of workplace ergonomics, the elucidation and mitigation of movement asymmetry are paramount. Movement asymmetry entails the unequal utilisation or positioning of disparate body parts during work activities [21]. Evidence substantiates that asymmetrical positioning and awkward movements during work precipitate numerous injuries and MSDs [22; 23; 24], alongside general fatigue [25], bodily pain, and a sensation of overexertion [26]. Furthermore, there is indicative evidence that appropriate posture, the absence of awkward positions, and ergonomic movements may enhance well-being, mental health [27], and positive work attitudes, such as motivation [28] and satisfaction [29; 30]. Observational methodologies frequently serve as the preferred approach to evaluate the physical workload, identify occupational hazards, monitor the impacts of ergonomic adjustments, and investigate these phenomena. Although numerous methods exist, such as the Occupational Repetitive Actions (OCRA) [10], Job Strain Index (JSI) [31], and Assessment of Repetitive Tasks of the Upper limbs (the ART tool) [32], no singular method suffices for all purposes or objectives [33]. The interplay between workplace ergonomics and employee well-being has recently attracted heightened attention [27; 34], especially within the context of assembly line work environments. Movement asymmetry--unequal or imbalanced physical activity during work--is emerging as a pivotal factor in deciphering this relationship. While ergonomic principles traditionally advocate for symmetry in the movement to minimise energy expenditure and optimise efficiency, real-world scenarios, notably in manufacturing settings, frequently deviate from this ideal due to task nature and workplace design. Despite their prevalence and influence, the specific mechanisms through which asymmetrical movements contribute to WMSDs and the overall well-being of workers remain insufficiently explored. To address this knowledge gap, this study aims to answer the following research questions:  
1. What is the extent and nature of movement asymmetry among assembly line and machining workers, and does it pose an occupational risk for developing work-related musculoskeletal disorders (WMSDs)? 2. How do these asymmetrical, repetitive movements impact various aspects of workers' overall well-being, including both physical and mental health? To address these questions, this research rigorously examines the risk factors linked to movement asymmetry in the workplace and develops a comprehensive observational technique for evaluating movement ergonomics. Additionally, this study explores the connection between asymmetrical movements in assembly line and machining workers and their overall well-being. This inquiry is especially relevant in settings where repetitive and unbalanced physical activities are the norm, such as in manufacturing or assembly line work, underscoring its pertinence to health promotion and preventive strategies in occupational health.