The most common causes of big arm pain in right arm plank are muscle strain, frozen shoulder, rotator cuff injury and so on. 1. Muscle strain: If the patient has strained the muscles of the big arm, the damaged muscles may be pulled in the process of lifting the right arm flat, and then the pain occurs. 2. Frozen shoulder: If the patient has inflammation around the shoulder joint, it may pull the inflamed area in the process of lifting the right arm, which will cause inflammation reaction and pain in the right arm. 3. Rotator cuff injury: If the patient’s rotator cuff is damaged due to chronic strain and trauma, it may be pulled to the damaged area in the process of lifting, which may cause pain. There are many causes of right arm pain, if the symptoms continue to be unrelieved, it is recommended to go to the hospital in time to find out the cause of the disease, the doctor targeted treatment.