Running pain under the left rib cage may be caused by excessive respiratory muscle activity, chronic gastroenteritis, intestinal cramps and so on. 1. Excessive respiratory muscle activity: pain under the left rib cage when running is mainly due to excessive respiratory muscle activity caused by strenuous exercise, resulting in the pleura being pulled, triggering pain. 2. Chronic gastroenteritis: if affected by infection, intestinal flora imbalance, autoimmune factors, drugs and toxins and other factors, resulting in pain under the left ribcage when running, patients mainly manifested as abdominal pain, diarrhea, constipation and other symptoms, serious patients will also appear mucus stool or watery stool. 3. Intestinal spasm: the pain under the left rib cage when running may be caused by intestinal spasm, mainly due to the strong contraction of the smooth muscle of the intestinal wall, resulting in paroxysmal abdominal pain, usually associated with local cold, indigestion, intestinal parasitic infections and other factors, and in severe cases, there will be vomiting, cold sweat and so on. If the patient feels uncomfortable, need to go to the regular hospital in time, with the help of the doctor, the relevant examination, according to the results of the examination, targeted treatment.