Gastrointestinal Problems in Runners
Stephen M. Simons, MD* and Robert G. Kennedy, MD
*South Bend Primary Care Sports Medicine Fellowship Program,
53880 Carmichael Drive, South Bend, IN 46635, USA.
Current Sports Medicine Reports 2004, 3:112–116
Current Science Inc. ISSN 1537-890x
Copyright © 2004 by Current Science Inc.
The most publicly notable and often quoted gastrointesti-
nal (GI) event in sports came from Derek Clayton follow-
ing his world record-setting marathon in 1979, “Two hours
later, the elation had worn off. I was urinating quite large
clots of blood, and I was vomiting black mucus and had
black diarrhea” . This is clearly a reference to the poten-
tial GI stresses following intense physical activity. My own
personal anecdote came as a finish line observer to a com-
munity marathon. While I was standing near the finish, the
winner was nearing the end. The crowd’s joyous greeting
was followed by a curious silence. The cause of this
reaction was soon apparent as the winner crossed the line
with feces-coated legs and quickly disappeared to the near-
est shower, missing his well-deserved victors reception.
Gastrointestinal symptoms are experienced by 30% to
65% of long distance runners and although less studied,
no doubt many other athletes . Pathophysiologic pro-
cesses hypothesized include mechanical factors, visceral
vasoconstriction-reducing splanchnic blood flow, medica-
tion influences, and the biochemical changes of exercise.
Blood flow to the splanchnic system declines from 1.56 L/
min at rest to 0.3 L/min at maximal exercise . The clini-
cal consequences range from a minor nuisance to perfor-
mance impairments and even potentially life-threatening
bleeding. Some GI symptoms are the direct consequence of
intense exercise. Athletes seeking advice or assistance with
these problems are usually concerned with the interrup-
tion to training or performance impairment caused by the
symptoms. The clinician must remain vigilant to the possi-
bility of underlying GI pathology unmasked by exercise or
masquerading as common exercise sequelae. Advising
these athletes, particularly with dietary manipulations,
may allow them to achieve their maximum training and
Upper Gastrointestinal Effects of Running
Among the upper GI afflictions of runners are gastroesoph-
ageal reflux disease (GERD), ulcers, nausea, and vomiting.
Of course, nonrunners experience all of these maladies. A
study of 93 runners found that nausea and heartburn
symptoms occur more commonly in nonrunners than
runners, and that runners have more nausea and heartburn
when not running . Similarly, runners may suffer from
problems such as hiatal hernias, decreased lower esoph-
ageal sphincter tone, and Helicobacter pylori infection.
Gastroesophageal reflux disease is a common problem
among runners. Even people without prior history of GERD
demonstrate reflux on manometry testing when put through
vigorous exercise . Reflux is closely associated with belch-
ing during running . Eating prior to exercise causes more
esophageal reflux. Although weight lifting may cause more
reflux than running, running causes more than cycling .
This is in spite of runners benefiting more from gravity and a
presumed lower intra-abdominal pressure.
A comparison of runners, cyclists, and triathletes found
that 36% of the runners complained of upper GI symp-
toms, which was fewer than cyclists . The prevalence of
symptoms is directly related to intensity of the run. In
extreme endurance runs, more runners reported moderate
to severe symptoms. In a 67-km race, 17% reported upper
GI complaints of this severity, whereas runners in a 160-
km race reported this at a rate of 47% [9,10]. In fact, the
majority of the upper GI symptoms (nausea and vomiting)
occurred in the last half of the 160-km race. Even with pro-
longed walking, nausea is a common complaint, but prob-
lems are less frequent and less severe .
This article reviews the literature regarding gastrointestinal
disturbances specifically in runners. Upper gastrointestinal
problems such as reflux, nausea, vomiting, and gastritis are
reviewed. Exercise has been found to alter esophageal
motility. These symptoms worsen with increased exertion
as well. H2 blockers have been found helpful for reflux and
nausea. The lower intestinal problems of motility and blood
loss are discussed. These problems are generally more
common and more directly related to running. Also
reviewed are endotoxin involvement and transient
abdominal pain. Much of the literature deals with marathon
and ultramarathon running, showing the extreme effects
of running and exertional stress on the body; however,
recreational runners may not be so afflicted as these
Gastrointestinal Problems in Runners • Simons and Kennedy 113
Esophageal motility is affected during exercise. Esoph-
ageal contractions become less frequent, shorter, and weaker
with increasing exercise in cyclists . At 90% VO2max,
reflux episodes and esophageal acid exposure occurred sig-
nificantly more frequently. The same study, however, found
no significant change to various GI hormones. Cyclists had
no changes in reflux, gastric pH, or GI transit time at 70%
VO2max; however, lower esophageal pressure decreased and
esophageal peristalsis increased . It is reasonable to
extrapolate that increasing running intensity would have a
similar increase in esophageal dysmotility. Choi et al. 
found that fed runners had significantly more gastroesoph-
ageal reflux with increasing running intensity, due to disor-
ganized esophageal motility.
Although there is an association of reflux with chronic
cough and asthma exacerbation, a small study showed no
significant correlation between reflux and exercise-induced
bronchospasm in asthmatics . However, GERD with
exercise may be confused with cardiac pain. DeMeester et
al.  found 46% of patients with anginal symptoms and
normal coronary arteries had reflux on 24-hour pH moni-
toring. In a similar population, Schofield et al.  found
44% had exertional reflux on stress testing with a strong
correlation with chest pain during the exercise. Exertional
pH monitoring provided improved diagnostic certainty for
noncardiac chest pain, with 68% of patients showing
pathologic reflux and 27% having chest pain with exercise
stress test apparently related to reflux .
The simplest treatment options involve modification of
food intake and exercise. Runners should avoid eating within
3 hours of running. Additionally, foods high in fat and pro-
tein should be avoided due to the consequent decrease in
gastric motility. If possible, the runner should decrease the
peak intensity of the workout. If these methods are unsuc-
cessful or impossible, medical management may help.
Antacids, H2 blockers, and proton pump inhibitors can
be helpful. Antacids have a short duration of action and
their effects may wane on longer runs. Some antacids con-
tain magnesium hydroxide, causing loose stools, a problem
already faced by many runners. Conversely, aluminum-
based antacids may lead to constipation. Histamine block-
ers can be used prophylactically. One study found that 300
mg ranitidine prior to running significantly reduced reflux
with no adverse effects . Although no studies have been
made, proton pump inhibitors would likely provide a simi-
lar benefit. There are no long-term data that reflux related to
running is harmful, or that treatment will positively or nega-
tively effect performance. Use of these medicines should be
for comfort only.
Vomiting and nausea
Runners also commonly experience nausea, retching, vom-
iting, and loss of appetite. Some athletes (and coaches)
will not consider a workout vigorous unless it induces
some retching. Although runners report more retching
while running, Sullivan et al.  found no increased rate of
vomiting while running. In the lower intensity, longer
duration ultramarathon, there was a strong correlation
between nonsteroidal anti-inflammatory drug (NSAID)
use and nausea/vomiting . Similar to reflux, eating
prior to exercise worsens the incidence of nausea .
Cimetidine 800 mg alleviated nausea and vomiting symp-
toms in ultramarathon runners when taken 1 hour prior to
the race and a repeat dose at the 50-mile mark .
Gastritis and ulcers
At the Chicago marathon, a majority of participants
reported use of aspirin or ibuprofen before or during the
race. Ibuprofen (but not aspirin) was found to increase GI
permeability, which represents a breakdown in the GI tract
barrier . Interestingly, half of the NSAID users and half
of the nonusers reported GI symptoms. Other studies have
found increased permeability with aspirin [22,23].
In a group of young, competitive runners, the vast major-
ity of those suffering anemia had gastritis and/or esophagitis
on endoscopy [24•]. In an ultramarathon setting, runners
who used 800 mg cimetidine 1 hour prior to the race and at
the 50-mile mark had an 11% rate of Hemoccult (SmithKlein
Diagnostics, Norristown, PA)-positive stool compared with
87.5% of the controls . However, a similar study in mara-
thon runners produced no significant difference between the
drug and placebo, indicating the source was more likely in
the lower tract .
Cheng et al.  noted a decreased prevalence of
duodenal ulcers in a group of physically active men. In this
study, men walking or running more than 10 miles per
week had a relative hazard of 0.38, and those going less
than 10 miles 0.54. There was no significant association in
women or with gastric ulcers and other differences in base-
line characteristics (smoking, NSAID use, and alcohol use)
were not reported. This protective effect is hypothesized to
be due to improved immune function, decreased gastric
acidity, or stress control, although there are no direct data
to support this.
Exercise-related Transient Abdominal Pain
The side stitch is a pain typically felt in the right or left
upper quadrant. The pain may also be referred to the
shoulder, possibly implicating hepatic, splenic, or phrenic
nerve involvement. A majority of athletes report some his-
tory of exercise-related abdominal pain, specifically 69%
of runners . These sufferers describe the more severe
pain as sharp and the less severe as a cramping, aching, or
pulling. This syndrome seems to decrease with increasing
age and training status, but sex and body mass index do
not affect the frequency [28•]. Thus, runners should be
encouraged to continue their regimen with the expectation
that the symptoms will improve.
One anecdotal method that seems to help less experi-
enced runners deal with this affliction is rhythmic breathing
technique. The runner should inhale during three steps and
114 Abdominal Conditions
exhale on the fourth, leading to a sequence of exhaling every
other right foot strike. This provides an alternative focus of
concentration in addition to standardizing the diaphrag-
matic interaction with foot strike.
Running Effects on Previous
There is minimal evidence regarding running and inflam-
matory bowel disease or irritable bowel syndrome. Seden-
tary patients with Crohn’s disease have been found to
tolerate a low-intensity walking program without exacer-
bating the condition . However, due to the problems
of dehydration, electrolyte disturbances, and blood loss
during a flare up of inflammatory bowel disease, strenuous
running should be avoided . Among women with irri-
table bowel syndrome, those who are more active reported
less fatigue . Further, women with irritable bowel were
less likely to be active.
Lower Gastrointestinal Tract
Lower GI tract symptoms include lower abdominal cramp-
ing, urge to defecate, increased bowel frequency, and diar-
rhea. The prevalence of these symptoms is variously
reported to occur in 37% to 71% of runners either during or
following a run [8,32,33]. Considering such a high preva-
lence of these symptoms, it is reasonable to expect training
interruptions, socially awkward circumstances, and perfor-
mance disappointments. Such an interruption proved costly
to one elite marathoner. She was forced to stop at a service
station at 22 miles, returned to the race, and still won. How-
ever, she inadvertently trimmed 30 meters off the 42-km
course, was disqualified, and lost the $41,000 prize money
. Peters et al.  recently followed GI symptoms in 606
runners, cyclists, and triathletes for 12 months. Running,
either as the lone activity or as the running portion of the
triathlete’s training, caused a preponderance of lower GI
symptoms when compared to nearly equal upper and lower
GI problems in cyclists. Ultra-endurance activity may show
different patterns of GI disturbance. In the previously
mentioned study, Glace et al.  followed 19 runners
participating in a 160-km event. Half of the participants
experienced GI disturbance. In contrast to previous studies
of shorter event duration, upper GI symptoms predomi-
nated and occurred mainly after 88 km. The authors specu-
late the slower pace contributed to the differing GI
disturbances in this ultra-distance event.
Several hypotheses are postulated to explain these
lower GI symptoms, but none conclusively satisfy all
observations. The hypotheses include fluid shifts,
decreased splanchnic blood flow, dehydration, increased
parasympathetic tone, increased sympathetic tone with
intense exercise, and hormone changes. The mechanical
effect of intra-abdominal jostling most certainly plays
some role. Empiric evidence for this mechanical contribu-
tor is supported by studies that note the increased preva-
lence of GI symptoms among runners compared with
cyclists . Although not specifically stated in these stud-
ies, it would seem intuitive that a semisolid stool liquefies
from the churning effect caused by decelerating the colon
contents when the foot strikes the ground. Rehrer and
Meijer  confirmed that running imposes approxi-
mately twice the acceleration/deceleration forces rendered
by bicycling at a similar workload. Rapid fluid shifts into
the colon may cause irritability and cramping . Intense
exercise can decrease splanchnic blood flow quite substan-
tially, and dehydration further reduces the blood supply;
80% of marathon runners losing at least 4% of body
weight experienced GI problems . But the cohort of
ultra-endurance runners studied by Glace et al. 
showed that GI disturbances could also occur in the
absence of dehydration, although most were after pro-
longed running. Improved fitness through training reduces
the dramatic blood shift away from the GI tract and there-
fore at any given workload the more highly fit experience
fewer GI disturbances .
Several chemical and hormonal changes that occur
with running are implicated as the source of GI distur-
bances. Sorting through the quagmire of chemical changes
is staggering. A cohort studied by Rehrer et al. , complet-
ing a 67-km alpine marathon, showed postrace elevations
of cortisol, adrenaline, and noradrenaline. GI symptoms
were more closely correlated with lower postrace cortisol
and noradrenaline levels and elevated postrace potassium.
Causal relationships were impossible to confirm. Pro-
found elevations of several GI hormones are thought to
provide metabolic support of increasing fuel demands and
not simply represent generalized stress reactants .
These include vasoactive intestinal polypeptide (VIP),
gastrin, secretin, pancreatic polypeptide, neurokinin A,
pancreastatin, and motilin. VIP acting as a vasodilator is
thought to combat the splanchnic vasoconstriction.
Mucosal compromise associated with running seemingly
allows entry of endotoxins into the portal circulation. Nor-
mal gram-negative bowel flora contain lipopolysaccharide
(LPS) in the cell wall. This LPS is largely confined to the
lumenal side of the bowel wall. LPS breeches the mucosal
barrier and enters the portal circulation with intense exercise
causing a measurable anti-LPS response. Increasing LPS lev-
els and decreasing anti-LPS is evident in the first 16 hours
after a long-distance triathlon . The latter decrease is due
to the LPS/anti-LPS complexes removal from circulation.
Brocke-Utne et al.  suggested that nausea, vomiting, and
diarrhea are related to this rise in LPS. Jeukendrup et al. 
suggested that endotoxemia was not a direct cause of GI
symptoms, but rather an intermediate step contributing to
release of cytokines tumor necrosis factor-α and interleukin-
6. The latter are then directly correlated with GI complaints
Gastrointestinal Problems in Runners • Simons and Kennedy 115
. Brouns and Beckers  assert that the well-trained
runner generally experiences fewer GI symptoms. Although
there are many possible explanations, increased levels of
induced anti-LPS may be a positive training response,
thereby lessening the effects of LPS release. Endotoxic entry
to the portal circulation may also contribute to portal vein
thrombosis via a hypercoagulable state .
Lower gastrointestinal bleeding
The incidence of GI bleeding in runners is estimated by
reports of frank hematochezia and occult blood testing
among marathon race competitors. A flurry of studies was
conducted in the 1980s during peak marathon participa-
tion, but more recent incidence data are lacking. Also, race
participation allows for incidence estimates among more
serious runners, but incidence figures are not available for
the recreational runner. Utilizing occult blood testing and
more recently Monohaem (a monoclonal antibody test
specific for human hemoglobin) can only document the
presence of stool hemoglobin without differentiating the
source between upper or lower GI tract. Endoscopy is often
unremarkable but has shown significant bleeding sites at
the cecum and splenic flexure [24•,42]. Incidence figures
for GI bleeding ranges from 7.4% up to 85% in ultramara-
thon distances [43•].
The etiology of lower GI bleeding focuses on ischemic
colitis. Blood flow to the GI tract can decrease to 20% of
normal. If this is sustained then mucosal injury and necro-
sis occurs. Exercise intensity and duration are associated
with higher rates of blood loss. Watershed areas between
mesenteric arteries are probably most vulnerable. Mechan-
ical irritation to the mucosa is also suggested as a potential
contributor to injury.
The clinician must remain vigilant to non–exercise-
related reasons for GI blood loss. Inflammatory bowel
disease predominates in the young population, whereas
carcinoma is more prevalent in the older runner. Hemor-
rhoids, anal fissures, arteriovenous malformations, colonic
polyps, infectious diseases, and other sources of bleeding
may be precipitated by intense exercise. Frequent or severe
GI bleeding deserves a work-up for blood loss anemia. This
is particularly important in the runner who notices a
Management of lower GI disturbances focuses on
dietary manipulations, dietary timing, and pharmacologic
means. During important training or competition phases
the runner can reduce the incidence of problems by trying
a low-fiber diet, minimizing lactose products, and increase
nutrition with an elemental diet. Pre-race vitamin E sup-
plementation might reduce the incidence of GI distur-
bance, but does not affect symptom severity .
Buchman et al.  also studied the effects of arginine and
glycine on marathon runners; they found no evidence to
suggest reduced ischemic bowel injury.
Antidiarrheal medications such as loperamide are used
cautiously for frequent diarrhea episodes, but Putukian
and Potera  worry about depressing the central nervous
system. Concerns about interfering with sweating mitigate
the use of anticholinergic medications.
Runners experience a myriad of GI symptoms that could be
avoided with a more sedentary lifestyle. However, these
complications rarely threaten the health of the runner and
are more of an annoyance to be persevered or averted.
There are measures that can be taken to alleviate these
problems (Table 1). Further study of the endotoxin role
provides a potentially enlightening insight into some of
these problems. However, until this research provides a
direction for treatment, we must work with the exercise
regimen and dietary changes, as well as occasional medica-
tion, to provide aid to runners with GI disturbances.
References and Recommended Reading
Papers of particular interest, published recently,
have been highlighted as:
• Of importance
•• Of major importance
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Table 1. Methods for reducing the risk of
Eliminate suspect foods and slowly reintroduce
them one at a time
Increase the time between eating and training
Limit intake of gas-forming foods
(eg, broccoli, onions, beans)
Limit intake of fiber-rich foods
Avoid coffee and other caffeine
Experiment with liquid meals before races
Never try a new supplement or drink for the
first time in a race
Increase training volume and intensity steadily
Don’t take large doses of vitamin C, sodium bicarbonate,
or carbohydrate drinks before races
Keep well hydrated
Try to evacuate before exercise
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116 Abdominal Conditions
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