GI Distress — The Not So Sexy Part of Long Distance Racing & Training (Part 1)


Endurance athletes that do long distance running (marathons and ultra marathons) or long course duathlon or triathlon (70.3 or 140.6 mile distance) have all likely had training runs or races that turned ugly due to GI distress. Warning, this is long for a typical blog post, but if you’ve ever had a race turn into a DNF (did not finish for any non-racing readers) or a very not-fun race, you’ll want to take the few minutes to read this so you can hopefully avoid future DNFs due to GI distress. You’ve spent a bazillion hours in training, what’s a few minutes to read what may help you cross the finish line successfully?!

What exactly is meant by GI distress? It’s a general medical term that encompasses lots of symptoms with nausea, puking or the runs (and not the athletic kind!) on the more severe end and stomach cramping, gas, burping, heartburn, and indigestion on the milder side. Many athletes have experienced this problem (one survey indicated as many as 83%!), so you may think this is just part of long distance events, but it doesn’t have to be so common! There are ways to limit this frequent distress. You can train your body to tolerate food and drink better with trial and error during training and some simple tips.

*Before proceeding, please be advised that this is general training advice and coaching and should not be used in place of medical evaluation and treatment. If you are having recurrent GI issues frequently or if symptoms take more than one day to resolve, please seek professional medical advice from your physician.

Runners with a history of GI issues during training are more likely to experience issues during a race. So if you know this is a common occurrence for you, be prepared and optimize things for race day.

Frequent Causes of GI Distress

The vast array of things that can trigger GI distress can be lumped into two categories: internal and external factors. Internal factors include decreased blood flow to the gut, mechanical stress (bouncing/jostling effect of running on stomach contents), stress or emotional issues and any stomach ailments (GI conditions, viruses or stomach bugs). External issues include anything related to nutrition, hydration and heat exposure.

  • Too much water ingested – drinking too much, especially if not balanced by adequate sodium intake can result in your system getting too diluted without enough sodium to keep things running smoothly.
  • Dehydration – too little water ingested – yes, both too much and too little can cause problems. You have to figure out how to be Goldilocks while running – not too much water, not too little water…get the amount “just right!” Studies have found that a loss of body weight greater than 2-3% can impair athletic performance. So staying hydrated is a key to help limit GI distress, but also to maximize your performance. Sweat pulls sodium from your bloodstream. Sodium is what helps hold water in your body. So prolonged sweating over a multiple hour race can lead to dehydration if not consuming adequate fluids AND sodium.
  • Too big of a sodium load at once – Your body is very finicky about how much of certain substances it needs to perform at peak. Electrolytes (sodium, potassium, calcium, and magnesium) are part of this finely tuned system. A big sodium load can be a “gut bomb,” especially late in a race! So keep this in mind as you hit the aid stations. At an ultramarathon, some of those tasty treats like bacon may sound so good after the sweet gels and chews you may have started with in the race. Just be aware that too much of a good thing may not be so good!
  • Blood flow is shunted away from the digestive system to provide oxygen to the major muscles being worked, so digestion suffers.
  • Jostling of stomach contents with running – ever see what happens when you shake up a bottle of Coke then open it? This can be your stomach when running! If you feel like you can’t get the food down, slow down your pace until you can eat. Stop if you need to. A minute or two break to refuel is not a make or break deal in finishing times when you’re talking about multi-hour races (unless you’re an elite level pro, and if so, you probably already know this stuff and can quit reading!)
  • Physical, mental and emotional stress on the body – all of these stressors which occur in a long race impair your body’s ability to function optimally and can result in an upset stomach.
  • Food & drink choices – some things just don’t sit well in people’s stomachs. This varies from person to person and the only way you know is by trying different things in your training.
  • Waiting to eliminate increases bowel irritation and stomach acid – got the urge to go? Try not to wait too long to go. Thinking you’ll save time in your race by skipping the port-a-john may result in a much slower race time or even a DNF if you irritate your system too much by waiting to go.
  • Pelvic floor muscle weakness – if the muscles that control urination and bowel movements are weak at the onset of a race, by the time you’ve been on course for hours, everything in your body is weaker and doesn’t function as well. Pelvic floor weakness can cause involuntary leaking with exertion. Waiting to eliminate can increase the likelihood of urine or fecal leakage if your pelvic floor is weak.
  • Heat exposure – heat accounts for blood flow being redistributed to the skin. Again, this means less blood flow to the gut to help digestion. Heat acclimation training can affect function 10-20%, so if you know you’re going to be racing in a warmer climate, make sure to do some training in warmer temps as much as possible.

Now that you know the causes, stay tuned for Part 2 tomorrow for pre-race strategies to minimize your risks!

Dr. Jeanne Williams, PT, DPT, OCS
We help endurance athletes (from beginners to pros) train and cross the finish line faster and injury-free!


Want To Get Relief Faster?

Choose which option works best for you
Scroll to Top