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Old 12-04-2006, 04:48 PM   #12
Neal Winkler
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Join Date: Oct 2006
Posts: 326
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From http://www.t-nation.com/readTopic.do?id=527120:

Quote:
"Runner's Diarrhea" Mike Pleacher, MD

Yes, they really devoted a full 45 minutes to this. It's hard to believe that people really give a shit (pun!), huh? Apparently, this is a bigger pain in the ass (pun!) than we could even imagine.

About 20-33% of endurance runners complain of lower abdominal cramping and/or a feeling of urgency and frequency during and after long duration races. Moreover, one study found that 20% of runners had occult blood in their stool after they completed a marathon. That kind of data collection must have been a crappy (pun!) job.

Butt (pun!) anyway, it's important to differentiate between upper and lower gastrointestinal symptoms. Upper GI problems relate to gastro-esophageal reflux disorder, nausea/vomiting and belching. They generally occur because of low esophageal sphincter pressure, increased gastric acid secretion, and reduced gastric emptying during exercise.

Conversely, lower GI problems "hit you much lower," and may be due to a number of factors:

1) Altered Intestinal Transit Time (also known as "Gum to Bum" time): This time period increases from 35 to 24 hours in sedentary people when they undertake endurance training. Strenuous activity, on the other hand, actually slows down transit time.

2) Changes in GI Tract Blood Flow: Around 80% less blood is delivered to the GI tract during intense exercise. This problem is further exacerbated by dehydration (80% of athletes experience lower GI symptoms when dehydrated by 4% or more).

3) Fluid and Electrolyte Shifts: Beyond just water shifts, there may be implications in terms of electrolyte effects on smooth muscle contraction in the GI tract.

4) Autonomic Nervous System Stimulation: Parasympathetic tone increases during low-intensity exercise; this increase corresponds to decreased transit time. In contrast, high-intensity work decreases parasympathetic tone and has the opposite effect.

5) GI Hormone Secretion: Gastrin, motilin and VIP secretion increase with exercise.

6) Mechanical Causes: I had to throw this one in there, as I was really surprised to hear it. An overly hypertrophied hip flexor, as is commonly seen in runners, can mechanically compress the colon and lead to lower GI distress.

7) Diet and Medications: Lactose intolerance is a differential diagnosis, and the high fiber diet followed by most aerobic training enthusiasts can potentially be excessive. Sorbitol and aspartame have been known to cause osmotic diarrhea, too. Antibiotics may lead to altered bacterial growth, and H2 blockers and magnesium-containing antacids (taken for upper GI relief) can lead to problems in the lower GI region.

All in all, the important point to take away from this presentation is that "aerobic training = diarrhea." Consider yourselves forewarned, cardio bunnies.
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