Side stitch, side cramp, side ache, and subcostal pain are terms used to describe an acute, sharp, localized abdominal pain related to exercise. This vexing but relatively benign condition is also called exercise-related transient abdominal pain (ETAP) [1,2].
In a series of studies, Morton  shed light on side stitch, an affliction that dates back to Shakespeare and Pliny the Elder, yet has received little attention or study in the medical literature. In a comprehensive epidemiologic study, questionnaires were given to 965 participants in six different sports. ETAP was shown to be remarkably similar in its features as described by these sportsmen. It was concluded that ETAP seems to be a single condition, not a variety of pains. It is defined by these researchers as a localized pain that may occur in any region of the abdomen, but is most common in lateral aspects of the mid abdomen. The pain is mostly described as sharp or stabbing when severe, and as cramping, aching, or pulling when less intense. It seems to be exacerbated in the postprandial state and is perhaps most common in activities involving repetitive torso movement, especially when the torso is extended .
According to Morton , ETAP is most common in the young and declines with age. It is most common in running, swimming (where it occurs usually in the right lumbar area), and horseback riding athletes, but also occurs in team sport athletes, and is less common in cyclists. Nearly one in five runners reported having ETAP within the prior year, often recurrent'on maybe 10% to 20% of their runs'and in the same location each time. It commonly causes the victim to reduce exercise intensity or stop, but often is relieved soon after stopping. When especially severe, it can take longer to abate and leave residual soreness. In the studies by Morton and Callister [1,2], sex and body type did not seem to influence ETAP. In those training more frequently, ETAP is less common, but these athletes are not entirely free from pain and at its worst their pain can be just as severe as in less involved sportsmen [1,2]. In a questionnaire study of 848 participants in a 14-km community run, 30% of runners and 16% of walkers developed ETAP, twice as often on the right side as on the left. Of those who got ETAP, 42% said it hurt their performance [4•].
Another group of researchers studied 32 male triathletes who underwent three long (3-hour) exercise bouts, alternating cycling and running. This study had a complex design; it was a double-blind cross-over study of two different supplements and a fluid placebo. In general, most gastrointestinal (GI) symptoms were more common and lasted longer during running than cycling. Specifically, side ache was far more common in running than in cycling. Also, side ache correlated with belching and with some measures of exercise intensity .
In my experience as a college team internist, side stitch is more common in female athletes, especially in cross-country runners, soccer players, and swimmers. However, I have seen it in male runners and even in a backup quarterback doing 100-m sprints in preseason training. Side stitch has been seen in aerobic dancing, basketball, and even tennis. The literature is mixed on any sex-related trend. Yet, in a questionnaire study of 606 well-trained endurance athletes, female runners and cyclists were more likely than their male counterparts to have upper or lower GI symptoms in general, and female triathletes were more likely than male triathletes to report side stitch .
The classical side stitch, when severe, is unique and often a provisional diagnosis can be made from a careful history and physical examination. If the pain is mild or the setting atypical, or the athlete is vague on details, other conditions could be confused with a side stitch (Table 1).
If the sticking side pain or discomfort is high on the left, one would not want to miss a tender, enlarged spleen from infectious mononucleosis . If the pain is more acute and intense, high on the left, and especially if the athlete is at altitude, one has to consider splenic infarction from sickle cell trait, which occurs in blacks and whites alike .
If the pain is acute and in the flank, and especially if it radiates to the groin, renal colic is a strong possibility . Famed triathlete Tim DeBoom, two-time Ironman World Champion, was defending his title in the 2003 Ironman race in Kona, Hawaii, when he developed abdominal pain that moved to his back. A medical van followed DeBoom for 2 miles, as the stabbing pain increased and finally brought him to a halt halfway through the run. As reported in triathlon magazines, DeBoom later passed at least one kidney stone and had ultrasound treatment to break up more stones.
If the flank pain is acute and bilateral in a sprinter or middle-distance runner, one should consider the little-known syndrome of exercise-induced loin pain and acute renal failure. This acute illness occurs soon after a hard anaerobic workout, with abdominal and flank pain, nausea and vomiting, and acute renal failure. Unlike the more common syndrome of acute rhabdomyolysis, the acute loin pain syndrome can be associated with baseline hypouricemia and the acute renal failure is not from myoglobinuria, but perhaps from uric acid crystallization in renal tubules . We presented one such case, in a 19-year-old female sprinter, at a recent sports medicine meeting .
If the stabbing pain is high in the side, at or above the costal margin, especially in a rower, one should consider intercostal muscle strain or a stress fracture of one of the lower ribs [12,13]. If the pain is more anterior, toward the right or left upper quadrant, one should consider a strain of an abdominal wall muscle, in which a localized tender area can be found, the pain is provoked by specific postures, and the pain is unchanged or increases when the abdominal muscles are tensed . If the pain is lower in the abdomen, toward a lower quadrant, exercise-associated intestinal ischemia should be considered .
Finally, the recent literature has a few case reports of exceptions that prove the rule. A 14-year-old girl had recurrent running-associated abdominal pain that was usually periumbilical and progressed from dull to sharp, from chronic constipation . A 28-year-old triathlete had recurrent acute, sharp stabbing right-sided abdominal pain, usually during the running part of the race, that responded to lysing adhesions between the ascending colon and the anterior abdominal wall . An elite runner had recurrent exercise-associated abdominal pain (and diarrhea) related to compression of the celiac axis by the medial arcuate ligament . And a 29-year-old elite distance runner had repeated episodes of running-related severe stitching pain in the right upper quadrant that responded to lysing congenital supernumerary ligaments binding the gallbladder to the abdominal wall . These zebras remind us that when we hear hoof beats, odds favor a horse: most athletes with a side stitch will have the classical type on which we focus here.
Cause of Classical Side Stitch
Debated are three main explanations for classical side stitch. The most popular explanation perhaps is diaphrag-matic ischemia and spasm. Support comes from the pain being localized, lateral, and mostly sharp; that is, more consistent with somatic than visceral pain. Also, some observations'and my experience'suggest the pain correlates with intense exercise and seems to improve as the athlete becomes fitter. Evidence against a diaphragmatic origin includes the high prevalence among horseback riders, an activity not usually of high respir-atory demand; the pain being sometimes low in the abdomen, and the lack of change in spirometry measures during a bout of ETAP .
A second possible explanation is that ETAP is from stress placed on peritoneal ligaments (such as the gastro-phrenic, lienophrenic, and coronary ligaments) that extend from the diaphragm to the abdominal viscera. Support comes from the observation of ETAP in horseback riding, a relatively passive jolting activity, the postprandial exacerbation of ETAP, and the alleged beneficial effect of wearing a supportive belt. Evidence against a ligamental source is the localized and sharp nature of the pain and that ETAP occurs in swimmers, with no vertical jolting [1,3].
A third theory for ETAP is irritation of the parietal peritoneum, which has been called an exertional peritonitis. The main function of the peritoneum is to lubricate mobile viscera. The parietal peritoneum is innervated in the abdominal region by the lower six intercostal nerves and in the subdiaphragmatic portion by the phrenic nerve. Irritation of the parietal peritoneum can cause localized, sharp pain. Such irritation could stem from friction between the visceral and parietal folds of the peritoneum. If irritated, the parietal peritoneum is sensitive to movement, which could be perceived as a sharp, stabbing pain. Morton and Call-ister [1,2] favor this third theory for ETAP, although Morton  recently offers a fourth theory-'that in some cases, spine problems and mechanical compression of thoracic intercostal nerves may play a role in ETAP.
A novel study was designed to distinguish between diaphragmatic spasm'from shunting blood flow away from the diaphragm to the gut and limb muscles during exercise'and the ligamentous stress theory of ETAP. The premise was that fluids of different digestibility or absorbability should distinguish between these two competing theories. Ten active young men who claimed to suffer from stitch reported the intensity of stitch during intermittent treadmill running after drinking either no fluid or four different fluids. In general, stitch was less of a problem with no fluid and differences among fluids were minor. Also, the intensity of stitch was so minor it raised the question whether the subjects were reporting just abdominal discomfort from intestinal distention .
This study also examined different physical maneuvers to increase or decrease the stress on ligaments connecting viscera to diaphragm. Supporting the ligamentous theory of ETAP, stitch pain decreased with contraction of abdominal muscles, breathing out through pursed lips, and tightening a belt around the abdomen. Contrary to this theory, however, stitch did not increase with man-euvers meant to increase ligamentous stress: increasing the impact of footstrikes or relaxing the abdominal muscles. The authors concluded that this study supports the case for a ligamentous origin of ETAP over that for a decrease in blood flow to the diaphragm. They also offered practical advice for avoiding stitch . Suggested solutions for stitch tend to be anecdotal and similar whether the advisor thinks stitch stems from diaphragmatic spasm or ligamentous stress.
Workup for Side Stitch
One group of authors suggests that the basic workup for ETAP should include physical examination, blood count, measurement of hepatic and pancreatic enzymes, and abdominal ultrasonography . In my opinion, however, no laboratory workup is necessary for classical side stitch: a careful history and physical examination suffice. The setting is often suggestive; for example, a female cross-country runner racing on a downhill stretch early in the season suddenly suffers a sharp cramp in the right upper side of the abdomen. The location, timing, and type of pain, along with a reassuring physical examination and response to physical maneuvers, help make the working diagnosis of side stitch. Then the sport medicine physician's efforts seem better directed at practical solutions, not laboratory testing.
Solutions for Side Stitch
These solutions are all anecdotal; none has been systematically studied. They are divided into measures to stop a stitch and those to prevent a stitch. They are expressed in lay terms, as practical tips.
To stop a stitch
At the first twinge of a side stitch, slow your pace, bend forward, and push your hand inward and upward on the area of pain. Tighten your abdominal muscles, as if to resist a punch in the stomach. Breathe out through pursed lips. Change your footstrike-to-breathing cadence: if the stitch is on the right and you normally exhale when your right foot hits the ground, exhale instead when your left foot hits the ground. Vice-versa for a stitch on the left. If the stitch becomes unbearable, stop exercising and walk slowly with your arms raised over your head, to stretch out tightness, or lie on your back with hips elevated; this can relieve stitch in a few minutes.
To prevent a stitch
Avoid large meals or drinks shortly before a workout. On the run, sip small amounts of fluid regularly; do not quaff large amounts at once. Try wearing a light, wide belt around your waist that you can tighten when necessary. Some observers think those who get stitches tend to be “chest breathers,” not “belly breathers.” Work on becoming a belly breather, to put your diaphragm through its entire range of motion. Lie on your back and place a heavy book on your belly. Make the book rise as you inhale and fall as you exhale. This also helps strengthen abdominal muscles, which may also help prevent a stitch. Finally, improve your fitness for the exercise in question. As you become fitter, side stitch tends to abate.
Side stitch is common, painful, annoying, and performance-limiting, but it is fleeting and benign. Although the exact cause of side stitch is still debated, practical solutions offer lasting help. Maybe most important: Relax! No one ever died from a side stitch.