The classic side stitch during a run, clinically known as ETAP, is caused by a diaphragm spasm due to shallow breathing; learning to use your abdomen to breathe prevents the problem at its root.
- A side stitch doesn’t stem from a “tired liver” or your spleen, but from a spasm of the diaphragmatic muscle undergoing mechanical stress.
- Breathing “from the chest” (apical breathing) keeps the diaphragm contracted high in the chest, while the weight of your internal organs pulls it downward with every step.
- The preventive solution is diaphragmatic breathing: expanding your belly during inhalation to support your trunk and better oxygenate your tissues.
- To resolve the pain while running, use synchronization: exhale forcefully at the exact moment the foot opposite the aching side strikes the ground.
- Avoiding heavy meals or large amounts of fluids right before running helps keep your stomach light, reducing the downward pull on internal ligaments.
That Sharp Twinge That Forces You to Stop
You are running great. The pace is right, your legs are turning over without too much effort, and the temperature is perfect. Then, out of nowhere, a sharp, piercing twinge hits, usually located just under the ribs on your right side. Within a couple of hundred yards, you are forced to bend forward, press a hand against your side, and start walking.
It’s the classic “liver pain” (or spleen pain, if it hits on the left). The first reaction is to blame your breakfast or the glass of water you drank before heading out. Yet, digestion is only part of the story. This discomfort is so universal among beginners—and sometimes even experienced amateurs—that it has a specific medical acronym: ETAP (Exercise-related transient abdominal pain). It is not a disease, and you aren’t damaging your organs. You are simply managing your air poorly.
What Anatomy Says: The Diaphragm Spasm (The Famous Side Stitch)
To solve the problem, we need to shift our focus from the liver to the real culprit: the diaphragm. This is the dome-shaped muscle separating the chest cavity from the abdominal cavity, and it is the primary engine of our respiration.
The diaphragm is connected to internal organs (like the stomach and liver) by a series of ligaments. When you run, your body undergoes continuous impact forces. With every step, your internal organs are pushed downward due to gravity and inertia. If the diaphragm isn’t relaxed and moving in sync with this motion, those ligaments get violently yanked. It is like running with a heavy backpack that isn’t strapped tightly to your chest: with every stride, it bounces, yanking the straps on your shoulders. This continuous “yanking” causes an acute muscle spasm. That explains the sharp pain.
Why “Chest Breathing” Makes the Problem Worse
The main cause of this spasm is mechanical and lies in how we breathe. Most people, especially under physical exertion, tend to breathe apically. This means they only use the top part of their lungs, shrugging their shoulders and puffing out their chests.
When you breathe this way, your breaths are short and shallow. The diaphragm remains in a constantly contracted, elevated position at the exact moment the liver (your heaviest organ) is pulling it downward every time your right foot strikes the ground. The tension on the connective tissues becomes unbearable, and the muscle locks up to protect itself.
The Diaphragmatic Breathing Technique: Expand Your Belly, Not Your Shoulders
To prevent ETAP, you must retrain your breathing mechanics, shifting from chest breathing to diaphragmatic (or belly) breathing.
Learning it while standing still is simple: lie flat on the floor, place one hand on your belly and the other on your chest. Inhale through your nose, trying to make only the hand on your belly rise, keeping your chest completely still. Exhale by emptying your abdomen.
Transferring this technique to your running posture takes a bit of practice. When you run, focus on a deep exhale. Empty your lungs completely. When your lungs are empty, the subsequent inhalation will naturally draw air downward, expanding your abdomen. An expanded belly provides a solid base that supports your internal organs, reducing their bouncing and easing the tension on the diaphragm’s ligaments.
The Emergency Intervention: The Trick of Coordinating Your Exhale with Your Stride
But what should you do if the stitch strikes right in the middle of a workout or a race? There is an emergency intervention—a sort of “reset” that leverages the coordination between your breath and your footstrike.
Most runners exhale asymmetrically, naturally letting their exhale (when the diaphragm relaxes and rises) fall on the exact same foot every time (usually the right). If your right foot strikes the ground at that exact moment, the impact pulls the liver down, maximizing the tearing sensation.
The trick is to flip the sync. If you feel pain on your right side, focus and exhale forcefully at the exact moment your left foot touches the ground.
If the pain is on the left, exhale deeply when your right foot lands. Slightly slow your pace, force the exhale on the side opposite the pain for about ten steps, and try to relax your shoulders. This simple trick reverses the loading dynamic on your diaphragm, releasing the spasm and allowing you to resume your pace without having to stop.