That sharp, stabbing pain in your side during a run is a side stitch, and it’s one of the most common complaints among runners. Doctors call it exercise-related transient abdominal pain, or ETAP. It typically strikes just below the ribs on one side (more often the right), and while it’s harmless, it can be intense enough to stop you mid-stride.
The good news: side stitches are preventable, and once you understand what triggers them, you can make a few simple changes that dramatically reduce how often they happen.
What Actually Causes the Pain
Despite decades of research, scientists still don’t have one definitive explanation. The leading theory centers on the peritoneum, a two-layered membrane that lines your abdominal cavity and wraps around your internal organs. A thin layer of fluid sits between those two layers, allowing them to glide smoothly against each other. When something disrupts that fluid, whether through increased friction, changes in fluid volume, or irritation of the membrane itself, the result is that familiar sharp or cramping pain.
An older and more popular explanation blames the diaphragm, the large muscle beneath your lungs that controls breathing. The idea is that during intense exercise, blood flow gets diverted away from the diaphragm to your working leg muscles, causing a cramp. While this theory is intuitive, it doesn’t fully hold up. Side stitches occur in swimmers and horseback riders too, activities that don’t load the diaphragm the same way running does. The peritoneal irritation theory better accounts for the range of activities that trigger the pain.
Another theory involves the ligaments that suspend your organs, particularly the liver and stomach, from the diaphragm. The repeated jarring of running could tug on these ligaments, creating pain. This would explain why running, with its constant vertical impact, is one of the worst sports for side stitches.
Why What You Drink Matters More Than You Think
One of the clearest findings in side stitch research is that sugary, high-concentration drinks are a major trigger. In one study, 83% of participants developed side pain after drinking a high-sugar beverage before running on a treadmill, compared with 70% after isotonic or low-sugar drinks. That difference might sound modest, but the pain was also more severe with the sugary option.
The reason ties back to the peritoneum. The fluid lining your abdominal cavity is highly sensitive to shifts in concentration between itself and the bloodstream. When you drink something very sugary (think fruit juice, regular soda, or concentrated energy drinks), it slows stomach emptying, keeping your stomach heavier for longer. But it also appears to change the fluid balance around the peritoneum itself, increasing irritation independent of stomach fullness. A separate study found that even plain water caused more side stitches than a sports drink matched to your body’s natural fluid concentration, suggesting that the composition of what you drink genuinely matters.
The practical takeaway: if you need to hydrate before a run, a standard sports drink or small sips of water are safer choices than juice, soda, or concentrated carbohydrate gels dissolved in too little water.
Eating and Timing
Eating too close to a run is one of the most reliable ways to trigger a side stitch. A full stomach adds mass to your abdominal cavity, increasing the mechanical stress on the peritoneum with every stride. The general recommendation is to avoid large meals or significant fluid intake for at least two hours before running. Smaller, low-fiber, low-fat snacks are less problematic if you need fuel closer to your run, but the less you have sitting in your stomach when you start, the better your odds.
How to Stop a Side Stitch Mid-Run
When a side stitch hits, your instinct to slow down is exactly right. Reducing your pace immediately lowers the mechanical stress on your abdomen and gives your breathing muscles a chance to relax. If that alone doesn’t work, try these steps:
- Press into the pain. Use two or three fingers to apply firm, steady pressure directly on the sore spot. Hold it for 10 to 15 seconds while continuing to walk or jog slowly. Many runners find this provides quick, partial relief.
- Switch to deep belly breathing. Breathe in slowly through your nose for a few seconds, letting your belly expand rather than your chest. Then exhale fully. This helps relax the diaphragm and the surrounding muscles.
- Bend slightly toward the painful side. A gentle side bend while exhaling can ease tension in the area.
Most side stitches resolve within a few minutes once you slow down. If you stop completely, the pain usually fades even faster.
Preventing Side Stitches Before They Start
Beyond watching your food and drink timing, one of the most effective long-term strategies involves your breathing pattern. Most runners naturally fall into a rhythm where they always exhale on the same foot strike. Over time, this creates an asymmetric load on one side of the torso. The American Lung Association recommends a 3:2 breathing pattern: inhale over three steps (left, right, left), then exhale over two steps (right, left). On the next cycle, the pattern naturally shifts so you’re exhaling on the opposite foot. This spreads impact evenly across both sides and has been linked to fewer side stitches.
It takes practice to nail this rhythm, and it feels unnatural at first. Try it during warm-ups or easy runs until it becomes automatic. Many runners who adopt rhythmic breathing report that their side stitches drop off significantly or disappear entirely.
Gradual warm-ups also help. Jumping straight into a fast pace is a reliable trigger, especially in cold weather. Starting with five to ten minutes of easy jogging gives your body time to adjust blood flow and breathing patterns before you pick up intensity.
Who Gets Side Stitches Most Often
Younger runners report side stitches far more frequently than older runners, which might seem counterintuitive. The reason isn’t entirely clear, but it may relate to changes in abdominal tissue elasticity with age or simply to the fact that younger athletes tend to eat and drink less carefully around exercise. Beginners also experience stitches more than experienced runners. As your body adapts to regular running, the frequency and severity of side stitches typically decrease on their own, even without any deliberate prevention strategy.
Fitness level doesn’t make you immune, though. Competitive athletes still get side stitches during races, particularly when they push into unfamiliar intensity levels or change their pre-race nutrition. The condition is extremely common across all levels of running.
When Side Pain Signals Something Else
A true side stitch is temporary. It comes on during exercise, responds to slowing down, and resolves completely within minutes of stopping. If your side pain lingers after you’ve cooled down, recurs at rest, or comes with symptoms like fever, nausea, pain radiating to your shoulder or back, or changes in bowel habits, it’s worth getting checked out. Persistent right-side pain could point to gallbladder issues, while left-side pain might relate to the spleen or other organs. Pain that worsens over days rather than resolving after each run is not a side stitch, regardless of where you feel it.