At one time or another, most runners have experienced abdominal pain during or after prolonged and strenuous running. One study In the May 1989 issue of the "International Journal of Sports Medicine" showed that 80 percent of marathon runners who lost at least 4 percent of their body weight experienced gastrointestinal (GI) problems.
Although stomach pain can occur during a run, a 2005 review of gastrointestinal problems in distance runners, published in "International SportMed Journal" purports most GI disturbances occur after prolonged running.
Dehydration
Running can cause dehydration--excessive water loss through perspiration. The stomach and intestine's smooth muscles need to be hydrated to function properly. Consequently, you may experience cramps when these muscles do not get enough water.
Sodium depletion has also been linked to cramps. Besides water, salts are the most abundant chemical constituents of our body fluids. Loss of sodium is a function of dehydration.
Overexertion
Intense exercise can cause fluid imbalances that contribute to GI distress. Overexertion creates rapid fluid shifts into the colon. These shifts have been linked to irritability and cramping. As sodium and potassium levels are depleted, the risk of GI symptoms increase.
Additionally, during intense exercise more blood is directed to your muscles, which results in less blood (and oxygen) for your stomach and intestines. Without proper oxygenation, GI symptoms also increase.
Novice runners are particularly prone to overexertion and the accompanying stomach problems. With improved fitness comes more efficient use of oxygen and fewer GI complaints.
The Up and Down of Running
The mechanical forces of running also contribute to stomach pain. In the February 1999 issue of the "American of Journal of Gastroenterology," Dr. Peters and colleagues showed that runners have more GI problems than cyclists. Running exerts approximately twice the acceleration/deceleration forces of a cycling workout of similar workload. This jostling is hard on the stomach and intestines and leads to GI problems. The impact of running may also explain why runners often have liquid stool after intense workouts: Rapidly repeated foot-strikes may cause semi-solid stool to be liquefied within the colon.
References
- Rice University: Abdominal Pain in Runners and Dehydration
- Marathon You Can Do It: Causes of Stomach Cramps
- International SportMed Journal: Gastrointestinal Problems in Distance Running
- "The American Journal of Gastroenterology"; Gastrointestinal Symptoms in Long-distance Runners, Cyclists, and Triathletes: Prevalence, Medication, and Etiology; Dr. Peters, Ph.D. et al; Feb. 1999
