Abdominal pain in runners is a very frequent problem. The two most common areas involved are,
In the former, cramps occur as a result of very vigorous breathing and are thought to be related to decreased oxygen supply to these muscles. Usually, slowing down and grabbing or massaging the affected muscle will alleviate the pain. Triathletes have the added burden of having to exercise in 3 different body positions. The change from one sport to another can put sudden demands on a muscle group that may not have been as extensively used in the preceding sport.
Gastrointestinal (GI) complaints take a variety of forms -- eructation (belching), flatulence, nausea, vomiting, diarrhea, bloating, intestinal cramps, and stomachache. Running causes more GI complaints than swimming and cycling. In some studies on marathon runners and triathletes, up to 40 - 50% experienced some form of GI complaint.. While not everything is understood about why this happens several concepts have emerged from the literature. Dehydration contributes significantly to GI disturbances, especially when >4% of body weight has been lost (see fluid balance test), and the pre-race diet is very important.
A few points about dehydration. The maximum rate of gastric emptying, and thus absorption, during exercise is approximately 800 ml per hour. The maximum sweat rate can average close to 2 liters per hour. Thus even if you hydrate as much as possible during a race you still can't match losses. Hyperhydration (drinking 400 - 600 ml of cold water 10 - 20 minutes before exercise) can help delay dehydration. Cold liquids are emptied from the stomach at a faster rate than fluids at body temperature. The greater the volume in the stomach the faster the rate of emptying -- up to a point. This is reason behind the recommendation to drink every 10 - 15 minutes. But one should avoid having too much volume in the stomach since this gives the uncomfortable sensation of a "full stomach". Another important point is that gastric emptying is delayed by simple sugars -- a 10% glucose solution can decrease the rate by 50%. The delay appears to be due to osmolality. Since most sports drinks contain less than 10%, osmalility is not a big concern. Linking the glucose molecules into larger chains decreases the osmolality may improve gastric emptying. This is the reason so many sports drinks have maltodextrins and other long chain polymerized carbohydrates. Studies have demonstrated that many of these commercial products have nearly equal hydrating properties to water. Also, drinks containing less than 10% glucose (or other simple sugars) are very well absorbed -- being nearly equal to water.
Iso- and hypotonic liquids are good for hydration. Athletes should definitely avoid hypertonic beverages.
With respect to pre-race diet, a 1992 analysis during a 1/2 Ironman revealed some interesting features related to GI complaints. All of the triathletes who had eaten within 30 minutes of the start vomited while swimming. If the pre-race meal (eaten anytime) had a higher fat or protein content, vomiting was more common. Hypertonic beverages caused more severe GI symptoms during the race. All of the triathletes who experienced intestinal cramps had eaten fiber-rich foods in the pre-race meal.
Another study looked at carbo loading in the days prior to exercise. One group ate the traditional pasta and rice diet, while another group ate less, but substituted the difference with a maltodextrin drink (supplement). Both groups had similar muscle glycogen concentrations (as determined by muscle biopsy) and treadmill times until exhaustion, but the supplement group had less GI complaints.
Minimize residue in the upper digestive tract - this may benefit some who suffer during a race. Athletes may accomplish this by supplementing with a high carbo beverage, and decreasing their intake of fiber and "heavy" foods the day before, and the morning of, a race. It is important that caloric needs not be compromised.
A final point to consider is that most athletes adapt and have less GI complaints as their training progresses. There certainly is no one right answer for everyone, but hopefully as you learn more and experiment with your diet and hydration, the symptoms will lessen.
Severe, progressive GI symptoms may be signs of a more serious problem and athletes are advised to consult their doctor.
last update 12/97