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It goes by many names: "tossing your cookies", "the technicolor yawn", "retching", "barfing", "vomiting" (or "emesis" or "vomitus" for the Latin types) and "puking". For ultra cyclists, the problem seems to hit somewhere around the 200 mile point, although the "Manager of Digestive Services" (MDS) may start sending out pink slips earlier or later in an event (thanks to Jeanie Bandicoot Barnett for this delightful analogy). The syndrome seems to plague ultra cyclists, and is an all-too-common reason provided by those who DNF at events like Furnace Creek.
What causes it? Can you recover after it takes over your body? How can it be prevented? The short answer is that no one really knows. The longer answer follows.
To try to address these questions, I conducted a computerized search of the medical/scientific literature. I found 63,638 articles on "exercise", "physical exertion" or "endurance" and 12,714 articles that related to "vomiting". When I combined those two sets of articles, there were only 26 that referred to both "exercise" and "vomiting", and of those, 25 related to bulimia nervosa or anorexia nervosa (conditions in which people may use excessive exercise and/or vomiting to lose weight or prevent weight gain). The one article that was left wasn't particularly helpful - it simply indicated that endurance athletes sometimes suffer from intestinal problems, including vomiting. So that was a bit of a dead end (although the scientist in me perked up - would anyone out there like to fund a research study on cyclists who puke?). Next, I turned to articles that describe what happens to the gastrointestinal (GI) tract during exercise, and although they were provided some good background information, they didn't really answer the questions - most have looked at exercise of two hours or less. My final source of information came from athletes who have been there, and a blessedly small amount of personal experience.
The Gastrointestinal System and Exercise
It's well established that intense exercise (e.g., >85% VO2 max) shunts blood away from the GI tract and slows down digestion and absorption. However, at exercise intensities that ultra cyclists use, digestion is not impaired, provided hydration is maintained.
What Can Cause Vomiting?
Food Poisoning - Although probably not the primary cause of vomiting in endurance athletes, food poisoning should never be overlooked. Symptoms typically begin 8 - 12 hours after eating contaminated food, and the body rids itself of the offending bugs by using both ends of the GI tract. Make sure that your crew keeps "hot foods hot" (above 140oF) and "cold foods cold" (below 40oF). At temperatures between 60 and 120oF, a single bacterium can multiply to over 2 million in one hour. Be careful with pre-race meals, especially salad bars. Inadequately chilled dressings are sometimes a source of food poisoning. For an important race, e.g., RAAM, consuming your race diet, prepared and controlled by your crew, for the 48 hours before the event is a good precaution. If food poisoning hits you, consider it a day. You're not likely to recover in sufficient time to finish the event.
Gastric Distension - Although it holds less than 2 ounces when empty, the stomach expands to hold a quart or more. When filled beyond its limits, however, it can trigger vomiting. One of three reasons usually causes an overly full stomach.
- 1. Drinking too much fluid - Up to 1,000-1,400 ml of isotonic fluid can empty from the stomach per hour (approximately 2 small - 2 large water bottles). If greater amounts are consumed over a prolonged period of time, the stomach's capacity to act as a reservoir is exceeded, and vomiting results. Over-consumption of fluid is rarely a cause of vomiting in endurance athletes, but it can and does happen.
- 2. Drinking fluids that are too concentrated - The intestines regulate the amount of fluid that empties from the stomach, and they are sensitive to caloric concentration. Textbook figures are that the stomach empties about 6 Calories per minute (360 Calories/hour) on average. The more dilute the fluid, the faster it leaves the stomach - 1,000 ml of a solution with 360 Calories/1,000 ml would empty per hour, but only about 500 ml would empty if the solution was twice as concentrated and had 720 Calories/1,000 ml. Obviously, there's variability here, as some athletes consume well over 500 Calories/hour for many hours. But the point is that with concentrated fuel sources, athletes may reach the point where what they're taking in doesn't leave the stomach as quickly as it's entering. Over time, the stomach's capacity is exceeded, and "MDS" takes over.
- 3. Dehydration - Digestive problems are more common in the heat, and dehydration may contribute. Although moderate exercise per se does not slow digestion and absorption, if dehydration develops, the decrease in blood volume can lead to a diversion of blood flow away from the intestines. That's exacerbated if exercise intensity is higher than it should be. Over time, digestion and absorption are slowed, and this in turn contributes to a full stomach and vomiting. It seems ironic that one can be both dehydrated and have an overly full stomach, but it does happen.
Miscellaneous Assorted Causes
You may have experienced nausea and vomiting in an endurance event, and can't identify any of the above factors as a probable cause. Although documented evidence isn't available, 'overextending' may be a factor. Particularly if you haven't trained under the same conditions (and most of us aren't able to duplicate events like Furnace Creek in training), the combination of heat, nervous tension and excitement, exhaustion, and unusually large intakes of fluid and Calories may simply overwhelm your ability to adapt.
Can you Recover?
If you do vomit because of an overly full stomach, you'll probably feel noticeably better almost immediately. The extreme nausea may have passed, and your stomach is no longer too full. But it's still irritable, and needs some TLC to recover. The advice is to slow way down (get your heart rate well below 120 bpm) and start by sipping small amounts of water. If that's tolerated, progress to a liquid source of fuel - or whatever seems that it would "sit well". Continue to ride very easily and take in modest amounts of fluid and Calories for an hour or so. If you're feeling good at that point, you can increase the intensity somewhat, but continue to monitor yourself. If you start riding hard too soon, you'll be back where you started.