At some point or another we have all been there: out for a run on a gorgeous day along our favorite route. Things are going great, our pace is where we want it to be, our legs have seemingly boundless energy, and we are just clicking along. Then, like some uninvited guest at a dinner party intent on talking politics or religion, that familiar stabbing sensation under the rib cage begins. Uninterested in the gloriousness of the day or the state of your legs, the side stitch intensifies to the point where you cannot stand it any longer, and you are forced to stop running.
After a time, the stitch abates and you start running again, but much like the uninvited dinner guest, it will not take a hint and it continues to be a major annoyance ruining what was set to be a spectacular workout. Instead of feeling powerful, you feel frustrated as you walk home.
Side stitches affect up to 70 percent of runners each year, and there’s even a fancy name for it: exercise-related transient abdominal pain (or ETAP). Yet despite possessing its own acronym and a wealth of research into its causes, the actual etiology remains very much a mystery.
The theories behind why side stitches happen
The most commonly accepted theory to explain the side stitch is known as the parietal peritoneum theory. The peritoneum is a highly innervated layer of tissue that encloses the abdominal cavity and has two layers, the visceral and parietal layers. The parietal or outer layer is adherent to the diaphragm and abdominal wall when irritated causes abdominal pain. The side stitch theory posits that the running motion specifically causes stretch on the parietal peritoneum that causes such irritation and leads to this pain.
Additional evidence to support this theory include the effects that the timing of eating can have on the development of a side stitch, related to how blood flow is diverted to or from the parietal peritoneum as well as to how stomach distension can impact tension on this membrane.
While the parietal peritoneum theory has gained acceptance among many researchers it is by no means viewed as the true answer. Various inconsistencies with this theory has led to a search for alternative explanations. Why for example do some runners never get side stitches while others get them all the time no matter when they eat or how they run? How is pace related to the development of side stitch? Why do more experienced runners seem less likely to experience this issue?
Various other etiologies have been postulated and investigated including diaphragmatic ischemia, stress on the ligaments that tether the abdominal organs like the liver or spleen and effects on the gastrointestinal tract. To date, none of these have proven to be completely satisfying as an explanation for the development of a side stitch.
A new explanation for the origin of side stitches – and how to stop them
More recently, another possible cause has been explored by researchers at Old Dominion University in Norfolk, Virginia. In a paper published in the Clinical Journal of Sports Medicine, scientists investigated whether psychological factors could be at issue with the development of this problem.
They surveyed 168 runners recruited from running groups posting on social media. Participants were asked a series of questions related to demographics, running behaviors and history, gastrointestinal issues (both related to running and in daily life), side stitch issues and a host of questions designed to assess psychological stress levels and sleep quality.
From the surveys the authors found that forty percent of participants experienced side stitches with no difference between men and women. Despite abundant research that demonstrates that non-athletes have an association between a lack of sleep and the development of abdominal pain, no such association was seen in this study. That is to say that runners who reported lower amounts or quality of sleep were not predisposed to side stitches when running.
Similarly surprising was the finding that pre-existing gastrointestinal issues were also not associated with side stitches. Those runners who reported having daily stomach issues or who were susceptible to developing stomach issues when running were no more likely to report side stitches than runners who did not have stomach problems when running or in life in general.
The one thing that did have an association with the development with side stitches was anxiety and stress. This was true regardless of runner age or level of experience. Across the board, higher levels of anxiety and stress was associated with higher likelihoods of developing a side stitch.
I mentioned earlier that there is less prevalence of side stitches in more experienced runners and this was seen to be true in this study. More experienced runners as well as older runners were much less likely to have side stitches than were inexperienced and/or younger runners. However, even amongst older or more experienced runners, higher levels of anxiety and stress was seen to be associated with higher levels of reported side stitches.
Side stitches: A reflection of your stress levels?
There are a couple of caveats to note when considering the results of this study. The first is that it is based entirely on survey responses and this is not the most robust data upon which to base scientific conclusions. Indeed, there is no way to use such data to establish causality only association. In other words we cannot say based on this study that anxiety and stress cause side stitches, only that they are associated. That is a big difference.
The second caveat is equally important, and that is that there is not yet a suitable explanation for exactly how anxiety and stress could cause side stitches. In order for this causality to be established such a biological premise would have to be identified. Still, in the absence of such a premise, given the findings of this study we should not discount the possibility outright. We have seen time and again how the mind can impact the body, and this may very well be just one more example.
So the next time you are out for a run and start to feel that old familiar pain in your side, consider the possibility that it has less to do with anything that you are doing physically and that it may be a sign of a state of mind.