You're halfway through a jog, feeling good, breathing steady—and then it hits. That sharp, stabbing pain just below your ribs that makes you want to stop and double over. Why does your body do this to you when you're trying to do something healthy?

Side stitches have plagued runners, swimmers, and anyone who's ever sprinted for a bus since humans started moving fast. Despite being incredibly common, this mysterious pain has puzzled scientists for decades. The good news? We now understand enough about what's happening inside to both explain the pain and help you avoid it.

Your internal organs don't just float freely inside you. They're held in place by ligaments—tough bands of tissue that connect your stomach, liver, and spleen to your diaphragm, the dome-shaped muscle beneath your lungs that powers your breathing.

When you run or jump, these organs bounce. Each footfall sends a small jolt through your body, and your organs respond by tugging downward on the ligaments connecting them to your diaphragm. Meanwhile, your diaphragm is moving upward as you exhale. This opposing movement creates tension, like two people pulling a rope in different directions. The result is that sharp, localized pain usually felt on the right side—where your liver, your heaviest organ, does most of the pulling.

This explains why stitches tend to strike early in a run before your body finds its rhythm. It also explains why eating before exercise makes things worse—a full stomach adds extra weight bouncing around, increasing the strain on those supporting ligaments.

Takeaway

Your organs are anchored, not floating. When exercise makes them bounce against a moving diaphragm, the tension in connecting ligaments creates that familiar stabbing pain.

Your diaphragm works harder than you might realize. This thin sheet of muscle contracts about 20,000 times per day just during normal breathing. When you exercise, it has to work much faster and harder to keep up with your body's demand for oxygen.

Like any muscle working overtime, your diaphragm can cramp. When you're breathing rapidly and shallowly during intense exercise, you might not be giving your diaphragm enough time to fully relax between contractions. The muscle gets stuck in a partially contracted state—a spasm. This feels like a tight, aching pain that spreads across the upper abdomen rather than the sharp, localized stitch from ligament stress.

Breathing patterns matter enormously here. Most people naturally exhale when their dominant foot strikes the ground. If you consistently exhale when your right foot lands, your diaphragm is in its most vulnerable contracted-and-rising position exactly when your liver is bouncing hardest downward. This rhythmic mismatch compounds both the ligament stress and the muscle fatigue.

Takeaway

Your diaphragm is a muscle that can cramp just like your calf or hamstring. Shallow, rapid breathing during exercise prevents it from fully relaxing, setting the stage for painful spasms.

The most effective prevention starts with how you breathe. Instead of shallow chest breathing, focus on deep belly breaths that fully engage your diaphragm. Practice this during warm-up: place your hand on your stomach and feel it push outward as you inhale. This trains your diaphragm to move through its full range of motion, making it more resilient during harder efforts.

Timing matters too. Wait at least two hours after a large meal before intense exercise. If you need fuel closer to activity, choose small amounts of easily digestible food. Avoid high-fat and high-fiber options that sit heavy in your stomach and add to the bouncing-organ problem.

When a stitch does strike, don't just push through. Slow your pace, take several deep breaths, and try pressing gently on the painful area while exhaling slowly. Some runners find relief by changing their breathing rhythm—if you normally exhale when your right foot lands, switch to exhaling on the left foot strike. This simple change redistributes the stress on your diaphragm and can release a stitch within seconds.

Takeaway

Prevention comes from giving your diaphragm room to work—deep belly breathing, proper meal timing, and gradual warm-ups teach your body to handle the demands of movement without cramping up.

Side stitches aren't a sign that you're out of shape or doing something wrong. They're simply your body's mechanical response to the competing forces of bouncing organs and a working diaphragm. Understanding this takes some of the frustration out of the experience.

With attention to breathing patterns, meal timing, and proper warm-ups, most people can dramatically reduce how often stitches interrupt their workouts. Your body isn't working against you—it just needs you to work with its design.