If you feel pain in your abdomen (not necessarily in the lower abdomen) when walking or running, it is usually a spasm of the diaphragm (commonly known as a bout of gas), which can be recovered with some rest. Some patients have diverticulosis of the small intestine and during running, intestinal torsion or intussusception may occur, producing persistent abdominal pain, which then requires immediate examination and treatment in hospital and, in severe cases, surgery. It is important to note that people who have lacked exercise for a long time and suddenly engage in strenuous exercise are prone to myocyte necrosis also known as rhabdomyolysis syndrome, and severe cases may present with systemic manifestations, which include abdominal pain.