Hidden pain on the left side of the back may be caused by factors such as trauma or exertion, or it may be caused by pathological factors such as intercostal neuritis, coronary heart disease and fasciitis. 1. Trauma or fatigue: due to trauma, the back muscles are damaged, or the soft tissues are overworked due to excessive exercise, and lactic acid builds up in the soft tissues, which can lead to localized muscle pain, and the symptoms can be gradually relieved with proper rest. 2. Intercostal neuritis: Intercostal neuritis caused by viral infection and other factors, the pain may be distributed along the intercostal space, and the pain symptoms may be aggravated when taking a deep breath or coughing. 3. Fasciitis: Aseptic inflammation of the muscle fascia of the back caused by trauma or strain injury, resulting in back pain, stiffness and tightness. 4. Coronary heart disease: When myocardial ischemia leads to angina pectoris, severe pain in the left side of the chest radiates to the back, causing tugging pain, and an electrocardiogram may show myocardial ischemia. The left side of the back hidden pain may also have other causes, need to go to the hospital in time to check, clear diagnosis after targeted treatment.