text: what is the exact cause of a stitch? (the sort you get when you're running, walking, doing lots of exercise, etc.) a side stitch is a piercing sensation just below the ribcage, usually felt when you're running. in the past, several different theories tried to explain the cause: trapped gas, swollen liver, stomach muscle cramps. however a recent and fairly conclusive theory holds that strain on the ligaments connecting the liver to the diaphragm is the cause.  the liver "hangs" from the diaphragm by fibrous bands called ligaments. running exerts a steady downward force on your liver, stretching these ligaments. in addition, when you exhale (usually as your left foot hits the ground), your diaphragm is pushed up. that means your liver falls with gravity as your diaphragm rises, placing considerable strain on those poor ligaments.   the result? a stitch. the cure? stop running immediately and press your hand just below the pain. this should raise your liver up, relieving the strain on the ligaments. inhale and exhale evenly as you press down.   as a preventive measure, take deep, full breaths while running. if you take shallow breaths, your diaphragm is consistently raised, which wreaks havoc on your ligaments. exercise is great, but remember to be kind to the rubber bands keeping your organs in place.