Every runner has experienced the dreaded side ache. Sometimes the pain is mild, you slow down, make adjustments, and work through it, sometimes it is debilitating and forces you to quit. There are many theories to explain the source of runner’s side stitch. Here, the two most conclusive ideas are discussed.
Peritoneum irritation is the cause of most side aches in runners. The parietal peritoneum is made up of layers of tissue lining the abdominal wall, visceral peritoneum is the tissue lining the organs. When these two rub together they create friction resulting in a sharp and localized pain. Once the rubbing stops, the side ache dissipates. Prevention is mostly anecdotal but some work has shown that avoiding large meals and large volumes of liquid, particularly hypertonic (salty, sugary) foods and beverages, at least two hours before a run has led to fewer side aches. A large meal will cause the stomach to expand, increasing the friction between the parietal and visceral peritoneum. Drinking plenty of water leading up to the two hour, pre run, buffer will ensure you are hydrated, also helping to prevent a side ache.
Visceral ligaments support abdominal organs and the diaphragm by attaching them to the abdominal wall and to other organs. In addition to the rubbing peritoneum, these are often jerked, tugged, and stretched due to the nature of running and the expansion and contraction of the lungs. When this happens they become irritated and can cramp. In addition staying hydrated and proper nutrient timing, running softly can provide relief. Perfecting run form and strengthening your core muscles to provide your organs with a smoother and more comfortable ride can offer much relief.
In both cases, the instance of side aches lessens as an athlete becomes more fit. Those who slowly ramp up their training schedule and include intermittent, high intensity training have been able to reduce or eliminate side aches during their runs. If you are stricken with a side ache, slow your pace, tighten your abdominal muscles, take deep breaths, placing your hands over your head or leaning forward to stretch the affected peritoneum or ligaments can also provide relief.