If the symptoms of hidden pain appear below the last rib on the left side, the following reasons may exist: 1. The most common disease that can cause pain symptoms in the location below the 12th rib on the left side is lumbar strain. This location has lumbar muscles, fascia and other soft tissues, lumbar fascia lesions appear relatively intense pain, most are lumbar muscle lesions will appear vague pain symptoms. The pain is usually aggravated by exertion, and prolonged sitting and excessive lumbar activity can also aggravate the pain symptoms, which can be relieved by rest. 2. The deeper level of this location is the lumbar transverse process, and patients with lumbar transverse process syndrome will also have hidden pain symptoms in this location. If the disease has just occurred, hidden pain may appear when the symptoms are not serious. As the disease increases, the symptoms will gradually worsen, and nerve irritation symptoms will appear, and the pain will radiate to the buttocks and even the thighs.