There are often several causes of pain in the middle of the rib cage: 1. Intercostal muscle strain: this is often associated with long hours of ambulatory work, improper sitting posture, when twisting and working for a long time can cause an imbalance in the force on the bilateral intercostal muscle, causing strain on one side of the intercostal muscle, manifesting as soreness and pain in one side of the rib area. 2. Chondromalacia: the cause of chondromalacia is unknown, research has proven that it may be related to excessive mental stress or and viral infection. The manifestation of chondromalacia is pain and pressure limited to a single rib. 3. intercostal neuritis: this disease is caused by a viral infection and is characterized by a burning pain along one or both intercostal spaces, with a more intense pain sensation.