Gastro-intestinal complaints are very common amongst endurance athletes. An estimated 30 to 50% of distance runners experience intestinal problems related to exercise. Bill Rodgers, marathon legend, with 4 victories in both the Boston Marathon and New York City Marathon in the late 1970s said: "More marathons are won or lost in the porta-toilets than at the dinner table". This illustrates the magnitude of the problem for endurance athletes and in particular long distance runners and triathletes.
The most common complaints include ructation (belching), abdominal pain, nausea, gastroesophageal reflux (or heartburn), abdominal pains, abdominal cramping, increased flatulence, loose stool, diarrhea or even bloody diarrhea, and vomiting. Because diarrhea is so common amongst endurance runners this is also known as the “runner’s trots”. The complaints are normally divided into two categories: symptoms of the upper intestinal tract or symptoms of the lower intestinal tract (see figure). There is a third category of symptoms that cannot be classified as upper or lower gastro-intestinal problems but might be related to the gastro-intestinal tract (for example stitch). All of the symptoms may be experienced during any leg of a triathlon but they are more common during the run segment as this occurs later in the race and is physiologically the most demanding of the three activities.
Prevalence of gastrointestinal problems
The vast majority (83%) of 471 marathoners who completed a survey reported GI problems occasionally or frequently during or after running: 53% experienced the urge to defecate and 38% reported diarrhea. Women were more likely than men to experience these problems. Among 155 mountain marathoners, 24% had intestinal symptoms; 2 dropped out due to GI troubles.
In yet another study (1) 1,700 participants were surveyed after a marathon race. Lower gastrointestinal symptoms, such as diarrhea, abdominal cramps, urge to defecate, flatulence, and gastrointestinal bleeding were found to be more common than upper gastrointestinal symptoms such as nausea, vomiting, heartburn, bloating, and side ache (stitch). The most common symptom experienced was the urge to defecate (36% to 39% of the participants), both during and immediately after running. Bowel movements (35%) and diarrhea (19%) were reported quite frequently immediately after running. During the race, some runners (16% to 18%) had to stop to defecate, and some runners (8% to 10%) had to stop because of diarrhea. Bloody bowel movements were reported by 1% to 2% of the participants.
In a study we conducted at a long-distance triathlon (Embrunman) (2) we found that 93% of the participants of reported at least one symptom of gastrointestinal discomfort; 29% of these symptoms were rated as serious (complaints that would affect exercise performance).
Lower gastrointestinal symptoms are more often observed in women than in men, and some symptoms are more frequently reported by younger compared with older participants. Problems seem to occur more frequently during running than during activities such as cycling or swimming, possibly because of the vertical (i.e., up and down) movements of the gut during running. Individuals with pre-existing GI issues (such as reflux, lactose intolerance or irritable bowel syndrome) are more likely to get GI-symptoms during competition.
One can argue how reliable numbers when these numbers are obtained by different methods and each method will provide different values. However, whatever way one looks at the data or whatever method you trust most, one message is very clear: gastro-intestinal problems are very common and are a frequently quoted reason why a race has not gone according to plan. In the next blog we will look at some of the reasons why these problems occur. I will then post another blog that contains some potential solutions.
Jeukendrup AE, Vet-Joop K, Sturk A, Stegen JH, Senden J, Saris WH, Wagenmakers AJ. Relationship between gastro-intestinal complaints and endotoxaemia, cytokine release and the acute-phase reaction during and after a long-distance triathlon in highly trained men. Clin Sci (Lond). 98(1):47-55, 2000.