## 1 Introduction
In terms of external power sources, electric motors are mostly used for active exoskeletons, while passive exoskeletons utilize the human power of the roerer, along with compliant materials and mechanisms [7; 13]. Attributed to their additional weight and strength requirements, active exoskeletons may be less flexible, along with having a lower dexterity when compared to lightweight passive exoskeletons [14]. The lighter structure of passive exoskeletons also creates a better safety perception for workers [9]. Exoskeletons are also categorized regarding which part of the human body to which they provide support. Exoskeletons that provide arm support are utilized for overhead and shoulder-level tasks. Lots of prototypes and commercialized products have been developed and tested recently, however, no standards have been developed yet to evaluate and approve the efficiency of industrial exoskeletons [15]. Therefore, researchers or companies evaluate them according to their own background and/or experience. There is a general propensity to perform EMG tests under some criteria and defined static tasks. [PERSON] et al. [12] investigated an occupational exoskeleton and confirmed the reduced activity in the shoulder musculature with the use of the exoskeleton. [PERSON] et al. [15] indicated a better task performance and prolonged working time, and, consequently, less perceived fatigue, owing to the use of an occupational exoskeleton. [PERSON] and [PERSON] [16] reported the increased productivity of welders and painters with the exoskeleton usage. Recently, [PERSON] et al. [17] examined and compared three different industrial exoskeletons and evaluated the influence of them on the shoulder and torso muscles. They carried out the tests for different arm levels of riveting tasks in aircraft manufacturing and compared the results with wearing no exoskeleton. [PERSON] et al. [18] and [PERSON] et al. [19] also inspected an upper-extremity exoskeleton and measured its effects on related muscles for various altitudes of work tasks. However, some welding, grinding, and similar work require workers to stretch both the upper arms and forearms for operations. In the present work, an innovative, passive upper-extremity exoskeleton for supporting both over-the-head tasks and forearm-stretched tasks is introduced. A prototype is produced with a collaboration between the Bursa Uludag University, Mechanical Engineering Department and OCALIS Engineering Inc. company. The moment around the shoulder joint is calculated first, then, these moment values are used as inputs for the exoskeleton design. Additionally, the deltoid muscle force is calculated, which is the main muscle responsible for performing defined tasks. The design verification is performed by evaluating the effects of the presented exoskeleton on the related muscles under two different tasks. One is a widely preferred overhead condition, which is named Task 1 (T1), and the other is at the shoulder level, in which both the upper arm and forearm are kept parallel to the ground and pointing forward, which is named Task 2 (T2). The interventions for the aforementioned tasks were carried out at Eskisehir Technical University, Sports Science Faculty, Motion and Motor Control Laboratory. Comparisons between the muscle activities with and without the exoskeleton are provided and the effect of the exoskeleton is discussed in detail.