The cause of right arm soreness may be shoulder tendon injury, cervical spondylosis and brachial plexus neuritis. 1. Shoulder tendon injury: The right arm tendon injury can be caused by trauma or sports injury, which can lead to the phenomenon of soreness in the right arm. 2. Cervical spondylosis: It can lead to the pressure of the nerves innervating the right side of the arm, causing abnormal muscle sensation in the right side of the arm, which can lead to the phenomenon of soreness in the right arm. 3. Brachial plexus neuritis: it can cause muscle numbness, pain and weakness in the right arm, and can also cause discomfort such as soreness. There may be other reasons for right arm soreness, you should go to the regular hospital in time, by the doctor according to the symptoms, signs and auxiliary examination to determine the cause of the disease, for the cause of the disease to give the correct treatment.