CYCLING PERFORMANCE TIPS
The Athlete and the GI Tract
by R. Rafoth MD
Sun Mountain Lodge - 1/2004
Exercise Related Gastrointestinal Symptoms
Gastrointestinal symptoms are common in athletes - in triathletes they are more common
than musculoskeletal complaints and injuries. They are more common in high intensity
situations (performing at >70% VO2max), but can also be a problem with less intense
exercise in those who are out of shape as well as in endurance events.
What are the most common GI symptoms? The following symptoms are reported
by >50% of regular athletes during heavy exercise (both in training and competitive
- 150 participants (74 men and 76 women)
- walking 164 - 203 km over 4 days
- 24 % had nausea, headache and flatulence
- 2 stopped the walk due to GI symptoms
- Conclusion: GI symptoms during long distance walking can impair exercise performance
although these occur less frequently and are less severe in comparison with
prolonged intense exercise.
- Chest pain
- Abdominal cramps
- Side ache
With running, lower GI symptoms (cramps, diarrhea, and rectal urgency) are more common
than upper (nausea), with rectal urgency being the most common symptom in up to 63% of
regular runners followed by diarrhea in 54%.
Modifiers of GI Symptoms
These symptoms are modified in both severity and frequency by:
- The presence of symptoms in the non exercise period - if the athlete has
irritable bowel syndrome before they begin to exercise regularly, they will probably have
more symptoms afterwards.
- younger athletes have more symptoms than older ones (2 studies)
- GI symptoms are slightly more common in women (2 studies)
- most felt symptoms they were unrelated to their menstrual cycle
- Diet - this is important because of the many, varied approaches (eating and
supplements) used by athletes to give them "that extra edge".
- there is a reported increase in reflux and upper abd symptoms with the pre
exercise ingestion of:
- too big a meal too close to exercise
- hypertonic drinks - glucose syrups - honey/maple syrup
- foods high in dietary fiber (a problem for vegetarians)
- high protein diets
- supplements taken during exercise
- study of 3 drinks (water placebo, sports drink, semisolid feeding)
in 32 triathletes exercising 3 hours at 75% VO2max. Cross over
study with each subject trying each in 3 trials of alternating running
- 4/32 had to stop in each "arm" from GI symptoms (there was
no "best supplement").
- Training Status Less trained individuals have more symptoms. The gut does not
adapting with the stress of progressive training. But, training will help prevent GI
symptoms. An example of indirect adaptation. May be tied into the next one:
- Intensity of exercise(3 of 5 studies showed a correlation). Especially in
runners, symptoms seem most likely to occur after an episode of particularly severe
exertion OR during a period of rapid increase in training mileage.
- Mode of exercise
- symptoms are more common with running than cycling
- with running, lower GI symptoms are twice as common as upper (84 versus 44 %),
and in triathlons, most lower GI symptoms are during the run segment
- cyclists have (relatively) more upper GI symptoms that runners (bent over position?)
- events with a relatively stable body position
have fewer symptoms than running - mechanical effects on the viscera?
- speed skating
- cross country skiing
- Duration of exercise - symptoms are more common the longer the event
(marathon for example)
- Hydration status
80% of marathoners with a 4% weight loss have GI symptoms
Controlled dehydration in a sauna with a set exercise regimen - with dehydration
significant slowing of gastric emptying and increase in nausea for a set
amount of exercise.
- If one gets dehydrated, blood viscosity can change
- Symptoms increase when decrease in body weight is 3.5 to 4 %
- Certain non dietary supplements/meds
- herb extracts
- salt tablets
Next we'll talk about the most common exercise related GI system disorders.
- Gastroesophageal Reflux/Chest Pain
- GI bleeding