Soreness in the left arm can be caused by the following reasons: 1. Lactic acid buildup caused by frequent stretching of the arm in daily life, which induces soreness; 2. Soreness induced by muscle strain in the arm caused by maintaining a posture for a long time in daily life or lifting heavy objects for a long time; 3. Soreness induced by diseases, such as cervical spondylosis, frozen shoulder, joint Diseases such as cervical spondylosis, frozen shoulder, joint injury, etc. may cause arm pain. In the case of arm pain, patients can apply heat, physical therapy, infrared radiation and local massage to assist in the treatment. If the pain is severe, patients can also take oral Fenbid capsules for relief.