Muscle soreness in the left arm is usually associated with muscle injury due to over-exercise, frozen shoulder, myalgic neuritis, etc. Patients can be treated with medications such as ibuprofen and surgery depending on the cause of the condition. 1. Muscle injury: Muscle injury can be caused by over-exercise or severe pulling of muscles, which in turn can lead to muscle soreness. Patients can take Chlorzoxazone tablets to relieve the soreness; left arm soreness caused by frozen shoulder can be treated with drugs such as ibuprofen and acetaminophen. 2. Frozen shoulder: For patients with mild frozen shoulder, it is recommended to strengthen the rehabilitation training such as wall climbing exercise. Heat treatment such as infrared rays and ultra-short wave can also be used. For patients with severe frozen shoulder, closed and surgical treatment can be used to relieve the symptoms. 3. Myoneuritis: Bacteria, viruses and other invasive intermuscular nerve tissue can lead to myoneuritis, which may cause arm muscle pain. It can be treated by taking vitamin B12, amoxicillin, ceftriaxone sodium and other drugs. When patients have symptoms of left arm muscle soreness, they need to consult a doctor to clarify the cause of the disease and follow the doctor’s instructions to take the appropriate method of treatment.