Upper-limb occupational exoskeletons to support the workers' upper arms are typically designed to provide antigravitational support. Although typical work activities require workers to perform static and dynamic actions, the majority of the studies in literature investigated the effects of upper-limb occupational exoskeletons in static and quasi-static activities, while only a few works focused on dynamic tasks. This article presents a systematic evaluation of the effects of different levels of antigravitational support (from about 60% to 100% of the arm gravitational load) provided by a passive upper-limb occupational exoskeleton on muscles’ activity during repetitive arm movements. The effect of the exoskeleton on muscle activity was evaluated by the comparison of muscle activations with and without the exoskeleton. The average muscle activation was computed considering shoulder full flexion-extension cycles, and sub-movements, namely the arm-lifting (i.e., flexion) and arm-lowering (i.e., extension) movements. Results showed a quasi-linear correlation between antigravitational support and muscle activity reductions, both when considering the full flexion-extension cycle and in the arm-lifting movement (reductions were up to 64 and 61% compared to not wearing the exoskeleton, respectively). When considering the arm-lowering movement, providing antigravitational support close to or higher than 100% of the arm gravitational load led to increased muscle activations of the extensors (up to 127%), suggesting that such an amount of antigravitational support may be not effective for a complete biomechanical load reduction on the shoulder district in dynamic tasks.

用于支撑工人上臂的上肢职业外骨骼通常设计用于提供抗重力支撑。虽然典型的工作活动需要工人执行静态和动态动作，但文献中的大多数研究调查了上肢职业外骨骼在静态和准静态活动中的影响，而只有少数作品关注动态任务。本文系统地评估了被动上肢职业外骨骼提供的不同级别的反重力支撑（约 60% 至 100% 的手臂重力负载）对重复手臂运动期间肌肉活动的影响。通过比较有外骨骼和没有外骨骼的肌肉激活来评估外骨骼对肌肉活动的影响。考虑肩部完全屈曲-伸展周期和子运动，即手臂举起（即屈曲）和手臂降低（即伸展）运动来计算平均肌肉激活。结果显示，在考虑完整的屈曲-伸展循环和举臂运动时，抗重力支撑和肌肉活动减少之间存在准线性相关性（与不佩戴外骨骼相比，减少分别高达 64% 和 61%）。当考虑手臂下降运动时，提供接近或高于手臂重力负荷 100% 的反重力支撑会导致伸肌的肌肉激活增加（高达 127%），这表明这样的反重力支撑可能并不有效在动态任务中完全减轻肩部区域的生物力学负荷。