In general, stretching the left side of the left subcostal pain may be due to muscle strain, myofasciitis, intercostal neuritis and other diseases. 1. Muscle strain: if the patient excessive exercise or exercise is not standardized, may cause muscle strain under the left side of the ribs, so that the local redness, swelling, congestion, pain, when stretching the waist, will pull a small degree of pulling to the injured area, so that the feeling of hidden pain. 2. Myofasciitis: when the left side of the ribcage cold and cold, chronic strain improper exercise, may cause local myofasciitis. Inflammation will stimulate the myofascia, coupled with stretching to the fascia, so there will be a hidden pain under the left side of the rib cage. 3. Intercostal neuritis: If the left side of the rib cage is infected by bacteria or mechanical damage, intercostal neuritis may be induced, and when stretching the waist, it will cause pain in the area where the intercostal nerve is distributed. It is recommended that the patient go to the hospital for examination to clarify the cause of the disease, and then take corresponding treatment measures under the guidance of the doctor.