# Development and Biomechanical Evaluation of a Back Exoskeleton to Support Lifting Tasks
## 1 Introduction  
Musculoskeletal disorders, such as low back pain and disc herniations, are prevalent among workers whose jobs involve frequent, repetitive, and physically demanding tasks, particularly those that require the handling of heavy loads over extended periods [1]. One high-risk profession is caregiving, where daily tasks include lifting and transferring patients from beds to wheelchairs and assisting them in walking [2]. To mitigate these risks, various ergonomic aids, such as lifting devices, sliding boards, and techniques for back-friendly lifting, are available [3]. However, despite these measures, physical strain remains high, and many of these aids are either time-consuming to use, restricted to specific locations, or impractical for flexible application in dynamic work environments. As a result, an approach to reduce physical strain is the use of task-specific exoskeletons. These wearable support devices are designed to provide personalized and adaptable support in physically demanding work environments while addressing the limitations of traditional lifting aids [4, 5]. However, exoskeletons do not reduce the external loads acting on the body; instead, they influence the distribution and management of these loads by the musculoskeletal system. Their assistive function primarily affects the internal strain on biological structures rather than eliminating the mechanical load itself. By redistributing forces from more vulnerable body regions, such as the lower back, to stronger areas, exoskeletons can reduce stress on specific muscle groups and joints. In the fields of healthcare and nursing, exoskeletons have received positive qualitative feedback, particularly regarding their ability to reducepain and fatigue while improving posture [6]. By reducing back muscle activity [7] and spinal compression forces [8], these devices can lower the risk of developing lower back pain (LBP). Moreover, exoskeletons can help reduce common work-related risk factors for musculoskeletal disorders in the healthcare sector, such as high physical exertion, repetitive tasks, and prolonged awkward postures [9]. Exoskeletons vary in form, structure, and function, each with inherent advantages and limitations depending on the materials used, structural design, and intended applications [10; 11; 12; 13]. A key structural distinction exists between soft and rigid exoskeletons. Soft materials, such as textiles and elastomers, offer flexibility and enhance user comfort, whereas rigid materials like metals and composites provide durability and superior load-bearing capacity. Due to their ability to withstand both tensile and compressive forces, rigid components are preferred for applications requiring higher force transmission. The choice of material is influenced by factors such as the level of support needed, duration of use, and user-specific requirements. To leverage the advantages of both material types, hybrid exoskeletons integrate soft fabrics at human-system interfaces while employing rigid components to redistribute supportive forces and counteract unwanted compression. This design approach strikes a balance between comfort and structural integrity, thereby optimizing performance for specific tasks [14]. Exoskeletons can provide support in five distinct ways: enabling, enhancing, facilitating, stabilizing, and complementing movement [5]. The specific type of support influences the design and functionality of the exoskeleton. To achieve these different forms of assistance, exoskeletons rely on various actuation methods and structural principles. Regarding their supportive function, exoskeletons can utilize either passive mechanisms, such as elastic bands or hydraulic cylinders, or active actuators, including electric motors and pneumatic systems. The choice of actuation method depends on factors such as the required force output, response dynamics, and capacity of the available power source.