Purpose: Text books attribute the side pain "stitch" during exercise to changes in blood flow to the viscera, but the little available research favors stretching of visceral ligaments. We therefore induced and modified stitch experimentally to investigate its cause and possible treatments.
Methods: Ten active healthy young men reported the intensity of stitch during sessions of intermittent exercise after drinking either no fluid (control) or a body-mass-adjusted volume (14 mL x kg(-1)) of each of four fluids: water, Exceed, decarbonated Coca-Cola, and a hypertonic solution of the nonabsorbable sugar lactulose. Each exercise session consisted of five 5-min bouts of hard running on a treadmill, with 10-min rests between each bout. In another experiment, seven subjects reported the effect of several physical maneuvers on stitch during exercise after drinking decarbonated Coca-Cola.
Results: Stitch developed to a similar intensity with all fluids during the first two bouts of running; thereafter, stitch declined only with Exceed, reaching the intensity with no fluid by the last two bouts. Bending forward while tightening abdominal muscles, tightening a belt around the waist, or breathing through pursed lips with increased lung volume alleviated stitch within seconds, but attempting to relax abdominal muscles or increasing the impact of foot strike had little effect.
Conclusions: Our observations cannot be explained readily by mechanisms involving digestion-induced changes in blood flow but are consistent with the notion that stitch arises when the fluid-engorged gut tugs on visceral ligaments.