There are many reasons for shoulder pain and arm soreness and weakness: 1. The most common reason is certain diseases of the shoulder and shoulder joint, such as frozen shoulder and inflammatory rotator cuff injury, etc. The pathology of these diseases is due to the inflammation that stimulates the shoulder joint and the muscles around the shoulder joint, and because the muscles of the shoulder and the muscles of the arm are connected to each other, they produce the soreness and weakness of the shoulder and arm at the same time. 2.Cervical spine diseases, such as cervical disc herniation, cervical spinal stenosis, etc., cause different degrees of disc protrusion due to long-term head bowing or other undesirable movements, resulting in cervical spine nerve tissue compression, resulting in discomfort radiating to the shoulder and arm, thus feeling sore, swollen and weak. 3.In addition to the above-mentioned causes, there may also be cold in the shoulder and arm, resulting in Different degrees of soft tissue injury, such as discomfort, it is recommended to go to the local regular hospital for medical consultation.