CYCLING PERFORMANCE TIPS
The Athlete and the GI Tract
by R. Rafoth MD
Sun Mountain Lodge - 1/2004
Introduction - What are the issues?
Let's look at some real life stories.
I. A quote from Derek Clayton - after his world record marathon run (Runner's
"Two hours later, the elation had worn off. I was urinating quite large clots of
blood and I was vomiting black mucus and had a lot of black diarrhea. I don't
think too many people can understand what I went through for the next 48 hours."
II. JAMA 1980:
A 24 year old medical student and long distance runner presented with a history of
bloody diarrhea. He complained of three weeks of abdominal cramps after hard runs
and 1 week of blood mixed with loose stools. He sought medical advice and his evaluation
including a sigmoidoscopy, Ba Enema, and Upper GI/small bowel follow through were
all negative. He continued his strenuous running schedule and his symptoms gradually
disappeared. In the subsequent two years, he remained asymptomatic with the exception
of occasional recurrent episodes of diffuse abdominal cramping, watery diarrhea, and
rarely bloody diarrhea - almost always associated with particularly strenuous physical
exertion such as a marathon run.
III. JAMA 1981:
A 17 y/o man ran competitively in short sprint events, and often had bouts of abdominal
cramps during and after hard runs (both training and competition). After a
particularly vigorous training session, he developed a dull, aching epigastric pain
which then migrated to the RLQ and was associated with bloody diarrhea. When rebound and
an elevated WBC developed, a tentative diagnosis of appendicitis was made and the patient
went to laparotomy. A surgical diagnosis of Crohn's disease was made, but biopsies
demonstrated only non specific colitis. The patient resumed running and has had no
further abdominal symptoms.
These three stories raise several questions. And as I suspect many of you have had
digestive tract symptoms during running or another athletic event, these may be
questions that are personal as well.
- How common are GI complaints in the athlete?
- Do GI problems (and the extremes illustrated by these three stories) impact only
those competing at the limits of physical exertion?
- What is the physiology at work here?
- How would I counsel a patient who asked me about similar (although hopefully not as
It turns out that serious athletes often develop gastrointestinal (GI) symptoms and
disorders during training and competition. GI symptoms are common in athletes at all
performance levels, although they are more frequent and severe when the athlete is
performing near their physical maximum, either in terms of %VO2max or the duration of a
training or competition. The most common include lower GI symptoms of cramps and diarrhea,
and the non specific upper GI symptom of nausea.
As we review the effects of exercise on the GI system the focus will be on the athlete
who exercises, both in training and competition at >70% VO2 max, levels not
likely to be reached by those involved in purely recreational exercise. However, for
those weekend warriors who are not in the best of shape, it is not uncommon to reach 70%
of their VO2 max, and as a result, they are at risk as well.
- During Triathlons, GI complaints are more common than musculoskeletal injuries.
- GI symptoms may limit an athlete's performance. They are not only distracting, but
may lead to dropping out of the training session or competition.
- lower GI symptoms (diarrhea, need for a bowel movement, fecal incontinence) are
the most common reason athletes stop exercising, followed by abdominal cramps
- in a survey of 109 distance runners
- 43% had nervous diarrhea before competition
- 60% had to stop for a BM during training
- 12% had to stop during competition for a BM
- 47% had severe cramps during or after a hard run or competition
- 16% saw blood in their stool after a hard run
- GI symptoms may suggest the presence of underlying GI disease.
- epigastric and chest discomfort can suggest the possibility of ischemic heart
- diarrhea and rectal bleeding raise the specter of inflammatory bowel disease
and even malignancy.
- GI symptoms may limit oral intake, and as a consequence performance, during an event.
- This is a critical issue for participation in events lasting more than 2 hours
where endogenous glycogen reserves are depleted and, if not replaced or supplemented
beforehand, performance is impacted.
- Depending on the duration of the event or ambient temperature/humidity,
this may contribute to dehydration and decreased performance.
Next section - Normal Gastrointestinal Physiology
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