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Gastrointestinal (GI) problems are probably the second most encountered complaint after dehydration.  However, gastrointestinal distress can potentially be terribly debilitating, and, despite months of training, can completely destroy your race day performance.

Common GI issues include cramping, nausea, bloating, vomiting, and diarrhea.  Gastroparesis is a medical term which means decreased gut motility or delayed emptying of the stomach and small intestines.  As one could imagine, delayed emptying in the stomach is the main culprit resulting in bloating, cramping, nausea, and vomiting.  There are a number of factors that cause GI distress and gastroparesis, and typically it is a combination of these factors that causes the problem.

1 - Diversion or shunting of blood to the muscles.  During exercise the muscles require a greater supply of oxygen to create energy.  Blood carries oxygen, so this increased demand of the exercising muscles for oxygen and energy results in increased blood flow to the muscles.  Increased blood flow to the muscles can result in a shunt of blood away from other body parts, most commonly the gut (in other words, as the body attempts to increase the blood supply to the muscles, less blood is supplied to the intestines).  This relative decrease in blood flow to the gut can slow gut motility down and cause gastroparesis.

2 - Excess carbohydrate intake - during moderate intensity exercise (by this I mean the intensity level you would maintain for a marathon, 1/2 ironman, or full ironman distance) most athletes can generally only digest around 250 to 300 calories per hour (which is around 65 to 75 gms of carbohydrate - 4 cals per gm of carbohydrate).  Increased intensity levels and hotter temperatures will cause this number to be a little lower.  Certainly some athletes are able to digest more (and I have heard of individuals who claim to be able to digest 1,000 calories per hour!), but I think that is certainly the exception rather than the norm.

3 - excess osmolality in the gut - by this I mean the ratio of gms of carbs to 100 ml of fluids.  Example - I am trying to calculate the gms of carbs per scoop of accelerade - I think it is about 22.5gms/scoop - at any rate this is just an example - 5 scoops x 22.5 gms = 112.5 gms of carbs per 1000 ml.  This turns out to be a concentration of 11.25 gms per 100 ml which is equivalent to 11.25% osmolality.  Generally, most athlete's guts can only tolerate 6 to 8% osmolality.  I googled Accelerade (sorry, I am not super familiar with the contents), and found that the main ingredient was sucrose, and that fructose was in the top 5 ingredients.  (I have to admit, they have an impressive array of flavors).  I also noted that their serving recommendation is one scoop per 12 oz (360 ml) which comes out to be a little over 6% osmolality - however that would be a lot of water bottles to get the energy that you need - not very realistic.  When the osmolality of your energy source (fluid or solid) is too high, it will draw water into the gut...  causing that bloated feeling and leading to gastroparesis.  Additionally, simple sugars such as sucrose and fructose seem to draw more water into the gut then more complex carbs like maltodextrin.

4 - Excessive water intake can also cause bloating and decreased motility.  Also, excessive fluid intake can also dilute your salt (sodium) stores and cause hyponatremia.  And, I am sure you will find this surprising, but symptoms of hyponatremia include upset stomach and nausea.  Most athletes under stress can tolerate 0.5 to 1 liter of water per hour. 

5 - Excessive caffeine intake has well known adverse effects on gut motility.
 

CRAMPS

Cramps are the mildest symptoms that occur when the blood flow to the gut s compromised.  Virtually everyone has experienced intestinal cramping during training or racing at one time or another.  However, if you seem to experience cramps on a regular basis, you may want to take a closer look at your hydration status and your food intake. 

Your hydration status will have a significant impact on the degree of shunting of blood flow from the gut.  If your overall volume status is low, more blood will be redirected from the gut to the muscles during exercise.  So if you experience cramps on a regular basis, the first step to improving this is to make better efforts to maintain good hydration.  When you are training hard for a marathon, triathlon, or other endurance event, hydration needs to be an all day experience with the same importance (or greater) than eating.  If your urine is routinely dark yellow, you are clearly not hydrating well enough.

The next most effective means to decrease cramping is to look closely at what you eat and when you are eating it.  There is no right or wrong answer here;, everyone is different in what their stomach can tolerate before and during exercise.  Intestinal function during exercise is something that I find quite interesting - it amazes me how some people can eat ham sandwiches on the bike portion of an ironman triathlon while others need to stick to a liquid and gel diet (I, unfortunately, am closer to the latter...).  The important thing is to discover what works best for you, practice it, and stick with it during your race.  Here are some recommendations if you find you are not the kind of person who can eat ham sandwiches during exercise:

- no solid food 2 to 3 hours before your work-out session or your race.  Base the amount of time on the intensity of your event; allow more time after eating for greater intensity or longer workouts.

- in addition to maintaining good overall hydration, drink 400 to 600 ml (12 to 20 ounces) of fluids 1 to 2 hours before exercise.  This will help top off your fluid stores.  Then add an additional 125 to 180 ml (4 to 6 ounces) about 15 minutes before your session.  I refer to this as "priming your gut," or preparing your stomach to empty further 4 to 6 ounce boluses that you will consume later during your exercise.  Your stomach responds better to modest fluid boluses than it does to small sips.  In other words, you will maintain better gut function and stomach emptying by consuming 4 to 6 ounces every 15 to 20 minutes than by consuming frequent small sips.  Be very careful not to over-do it though; consuming more than 6 ounces at a time could slow down the emptying and result in cramps or bloating.

- maintain a healthy sodium (salt) intake.  Unless you have problems with your kidneys or blood pressure, it is important to consume an adequate amount of salt in your diet.  If you are training or racing vigorously, you are going to lose a lot of salt in your sweat.  Make sure your diet includes a good deal of salty foods (most athletes will note periods where they CRAVE salty foods during times of increased intensity and duration of their training).  Additionally, consider using electrolyte drinks in addition to water if you do not consume a lot of salt in your diet.   If you are someone who sweats a lot or has white streaks on their body after long workouts, you need to make sure you are consuming a lot of salt to make up for what you are losing during exercise. 

- consider using salt/electrolyte supplementation (Endurolytes from e-caps or other electrolyte capsules) during long workouts and races.

- do not neglect good hydration the morning of your race.  You may be well hydrated the day before your event, but do not forget you will lose water overnight while you sleep so make sure you replace that in the morning. 

NAUSEA

The causes of nausea are generally similar to cramps in respect to inadequate hydration or consuming the wrong foods (or just the wrong time) before exercise.  The recommendations also are the same as above.

However, another important cause of nausea is hyponatremia, a potentially serious electrolyte disorder, that occurs from either excessive salt losses, excessive water intake, or a combination of both.  This is a fairly common condition affecting endurance athletes, especially in events that last four hours or more.  I will discuss more about hyponatremia in another section, however a very common symptom of hyponatremia is nausea.

The key to this is sodium (salt) supplementation and appropriate fluid intake during exercise.  I discuss sodium supplementation in depth here; but here are some basic recommendations:

- salt supplementation is very important for training or races that last longer than 4 hours

- 200 to 600 mg of salt should be consumed per hour depending on the temperature and the intensity of the exercise.  Most salt capsules or tabs contain approximately 100 mg of salt each.  This means that you need to take 2 to 6 capsules/tabs every hour during exercise.  If you think about a 12 hour triathlon, you potentially could consume 30 capsules or more.  During a triathlon, I generally begin with 2 Endurolytes per hour on the bike.  As the temperature increases I take 2 Endurolytes every 30 minutes.  I average about 30 to 35 Endurolytes per ironman.  It may seem like a lot, but I have never had to go to a medical tent for an IV after any race.

VOMITING

BLOATING

Bloating is that feeling that your stomach is full of fluid and/or food that just will not digest.

DIARRHEA

Diarrhea is an unfortunately common complication of endurance athletics that can have rather devastating consequences.  I am not sure why they call them the "runs," because it is hard as hell to run when you have a case of bad diarrhea.  There are very few people who will suffer from diarrhea during a race and not have their finish times affected.  I developed a gastrointestinal illness the day before an ironman race in 2005 and had quite an "interesting" race day.  I only had to stop twice on the bike, but I lost track of the number of stops I made on the run (I would have made more, but there were not enough available port-a-potties that day).

There are a number of different causes and unfortunately once the diarrhea starts, it is hard to stop it.  Prevention is the key here.

PASSING GAS

I just want to touch on this very briefly.  Although some may have concerns about increased flatulence during exercise, this is actually a good sign (although your neighbor or training partner may not agree with that statement).  Passing gas during exercise is a sign of good intestinal function - so feel free to let it out!