If you’ve ever been stopped in your tracks mid-run, ride, or workout by a sudden, sharp pain in your side, you’re not alone. Side stitches—technically known as Exercise-Related Transient Abdominal Pain (ETAP)—affect athletes across all disciplines, from runners to cyclists. But what really causes a side stitch, and how can you prevent it? In this comprehensive guide, we break down the latest research on ETAP, including risk factors, nutritional triggers, and the most effective prevention and treatment strategies to help you train and race pain-free.
Athletes from a wide range of sports report experiencing a side stitch in various situations, which has led both athletes and researchers to explore several theories about its causes and risk factors. In this article, we aim to demystify the dreaded side stitch and better understand its prevention and potential solutions.
While commonly known as a side stitch, the technical term is Exercise-Related Transient Abdominal Pain, or ETAP. Often misunderstood as a type of muscle cramp, ETAP is an unwelcome physical sensation that can involve sudden, sharp, or stabbing pain. It may also feel like cramping, aching, or general tightness in the abdominal area.
Risk Factors and Theories
Risk factors are thought to include ectomorphic (lean) body types, younger or less experienced athletes, and in equal prevalence among men and women—though these have not been consistently proven. Much of the early research relied on surveys and race reports spanning many sports and demographics, but these studies lacked control. Similar to the challenges of studying exercise-associated muscle cramps, ETAP is difficult to consistently induce and replicate in a research setting.
A few consistent risk factors have stood out, with many athletes reporting symptoms after consuming fluids or food and during activities involving repetitive torso movement, such as running or horseback riding. Early theories to explain these risk factors focused on three main causes, most of which involving the peritoneum—the smooth tissue lining the abdominal cavity and surrounding the organs (1):
- Reduced blood flow to the diaphragm (diaphragmatic ischemia)
- Stress on peritoneal ligaments (mechanical jostling or pressure from stomach contents)
- Irritation of the peritoneum (friction, pressure, or posture-related)
Nutrition’s Role in ETAP
Many athletes notice ETAP symptoms soon after eating or drinking. Early survey-based research found that 52% of athletes believed eating before exercise triggered ETAP, and 38% believed fluids did the same (1). Later studies found that exercise after eating caused ETAP in 30 out of 35 cases, while 19 cases still occurred even without pre-exercise nutrition (2). So why do so many athletes experience this, and what does the research suggest about nutrition’s role?
- Reduced blood flow to the diaphragm: On the surface, this makes sense—during intense exercise, blood flow to the gut can drop by up to 80% (3). However, ETAP has also been reported at low intensities, such as in horseback riders who aren’t under high respiratory strain. Additionally, symptoms often improve quickly when physical adjustments (like bending forward) are made to reduce strain on peritoneal ligaments. If blood flow alone were the cause, symptoms likely wouldn’t resolve so quickly.
- Irritation of the peritoneum: The parietal peritoneum is a thin lining that helps keep abdominal organs in place and secretes lubricating fluid to reduce friction between organs and surrounding tissue. This fluid depends on blood flow and breathing movements—both of which change during exercise. Drinking highly concentrated (hypertonic) beverages may worsen side stitches by slowing stomach emptying, increasing pressure and friction in the abdomen. Researchers also believe hypertonic fluids may disrupt the lubricant itself, contributing to irritation even when the stomach isn’t overly full.
- Stress on peritoneal ligaments: Like peritoneal irritation, mechanical stress on ligaments may explain why ETAP is more common in runners and horseback riders. A full stomach—whether from large meals or delayed emptying—adds weight and strain, leading to greater jostling and discomfort. This theory also overlaps with the one above.
While several theories exist, the two most promising explanations for ETAP are irritation and/or mechanical stress on the peritoneum. Many studies on this topic focus on runners or horseback riders, but ETAP is still common among cyclists—even though there’s less mechanical strain on the abdomen. When considering variations in bike fit, posture, nutrition planning and timing, and upper-body movement, some cyclists may be more prone to ETAP than others. Now, let’s take a look at how to avoid ETAP altogether.
Plan you meal times
Prevention
- Meal timing: Avoid large meals or drinks within two hours of exercise to allow the stomach time to empty, reducing abdominal pressure.
- Watch hypertonic fluids: Sugary sports drinks, soda, and juice can pull water into the gut and slow digestion, increasing risk. Both poor meal timing and hypertonic drinks increase stomach mass and prolong the time the stomach remains overly full on the bike.
- Improve posture (especially in the thoracic region): Haven’t had a proper bike fit? Skipped your winter core routine? Here’s your sign. Consider working with a physical therapist and/or a bike fitter.
- Support abdominal organs: Strengthening your core—or wearing supportive garments like a belt—may help. While belts can be hot or uncomfortable during rides, long-term core strength is likely a better solution.
Treatment If Experiencing ETAP
- Contracting the abs: Tighten your stomach muscles, lean forward, and press on the painful area. This may reduce pulling on ligaments attached to the diaphragm and relieve the pain.
- Using a tight belt: Some athletes use a weight belt with a towel between it and their stomach. Tightening the belt and tensing the abs can support the organs and reduce ligament strain.
- Changing breathing: Try keeping more air in your lungs at the end of each breath and exhaling slowly through pursed lips. This lowers the diaphragm and activates abdominal muscles, which may help ease the stitch (4).
- Other methods: Additional strategies include deep breathing, pressing on the painful area, stretching, and bending forward (1).
Final Note
Not all abdominal pain is ETAP. Athletes should monitor symptoms and consult a doctor if the pain is persistent or concerning, as other issues—such as problems with the spleen or kidneys—can also cause abdominal discomfort.
If you’ve been dealing with side stitches more often than you’d like, we hope this article has helped demystify the issue and offered useful strategies for prevention and relief. Since many of the relief techniques can be dangerous—or at least impractical—while riding, prevention is likely your best strategy. Still, knowing how to safely adjust and adapt mid-ride can go a long way toward staying comfortable on the bike.
In Eddy Merckx’s case it was a punch, but a side stitch can feel as bad
References
- Morton, D., & Callister, R. (2015). Exercise-Related Transient Abdominal Pain (ETAP). Sports Med, 45, 23–35. https://doi.org/10.1007/s40279-014-0245-z
- Sinclair, J.D. (1951). Stitch: the side pain of athletes. N Z Med J, 50(280), 607–612.
- de Oliveira, E. P., Burini, R. C., & Jeukendrup, A. (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine (Auckland, N.Z.), 44(Suppl 1), S79–S85. https://doi.org/10.1007/s40279-014-0153-2
- Plunkett, B. T., & Hopkins, W. G. (1999). Investigation of the side pain “stitch” induced by running after fluid ingestion. Medicine & Science in Sports & Exercise, 31(8), 1169–1175.
The post What Causes a Side Stitch? How to Prevent and Treat ETAP in Endurance Sports appeared first on PezCycling News.
