Pain on the left side of the back is usually seen in the following cases: 1. The most common is strenuous exercise, or bending over for heavy work, which results in muscle strain in the chest and back, which in turn leads to pain, mainly manifested as widespread soreness, swelling, and sometimes radioactive pain. For this condition, the best treatment is to ensure adequate bed rest, and you can take oral non-steroidal anti-inflammatory and analgesic drugs, such as Xilabao capsules or Nimesulide dispersible tablets. The painful area can also be treated with topical creams or ointments, as well as hot compresses.2. Pain caused by misalignment of the small joints of the thoracic spine, also known as sprains, when the pain level is generally more intense, the best treatment is bed rest with medication.3. Intercostal neuralgia, intercostal neuritis or early manifestations of herpes zoster, for which medication is also usually used.