Side Stitch When Running: Why It Appears and How to Stop It

The sharp pain in the side can ruin a smooth outing or a long run in a matter of seconds. It appears without much apparent logic, forces you to slow down and, in some cases, to stop completely. Although it is a very common annoyance among runners, it is not a normal part of the effort and it is worth understanding it well in order to reduce how often it happens.

The good news is that it is usually related to habits that can be changed: how you breathe, how much you eat before training, what pace you set off at, and whether your trunk is prepared to withstand repeated impact. There is no universal remedy, but there is a combination of measures that, applied consistently, greatly reduces the chances of that side stitch showing up just when you were feeling most comfortable.

What lies behind that so uncomfortable stitch

Side stitch is an acute and temporary discomfort that is usually felt on one side of the abdomen, often under the ribs, although it can also radiate toward the upper part of the belly or even the shoulder. In medicine it is associated with transient abdominal pain, a term that already suggests its brief, changing and hard-to-predict nature. It is not an injury in itself, but it is a sign that something in the combination of breathing, effort and digestion is not working comfortably.

Over the years, different explanations have been proposed. One of the most accepted points to the diaphragm, the large muscle that separates the chest from the abdomen and takes part in breathing. When effort increases, breathing becomes faster and shallower, and that muscle can become fatigued or irritated. Another hypothesis speaks of the tension in the ligaments and structures that support the internal organs, subjected to the constant bounce of each stride. In practice, the runner perceives a simple and clear warning: something stabs, bothers, and asks you to ease off.

It is worth understanding it without drama, but not lightly either. Side stitch does not usually hide a serious problem, although it can be favored by poor running technique, insufficient preparation or a meal poorly timed. That mix explains why sometimes it appears on an easy run and other times it does not show up even during hard efforts. The body, in the end, responds like an orchestra: if one section comes in out of time, the whole thing suffers.

an orchestra: if one section comes in out of time, the whole thing suffers.

Why it appears more at some times than others

Fast, shallow breathing is one of the most common triggers. When the runner gets into oxygen debt too soon, the diaphragm works less efficiently and the abdomen moves with more tension. In people who are just starting to run, this pattern is especially common because the body has not yet learned how to distribute the effort properly. They set off too hard, the inhale shortens, and the side ends up demanding attention.

Food is another decisive factor. Running soon after eating increases the risk, especially if the meal was large, high in fat or very fibrous. The stomach is still busy, the digestive system needs blood, and the repeated impact of the jog makes coexistence between digestion and exercise more difficult. There is no need for a rigid rule for everyone, but there is a useful reference: letting 90 to 120 minutes pass after a light meal is usually a sensible baseline, while a heavy meal may require quite a bit more time.

The way you warm up also matters. A body that goes from rest to effort abruptly behaves like an engine started cold. Warming up prepares the breathing, the trunk muscles and the circulation, and that reduces the initial shock. Something similar happens with the starting pace: the first few minutes being too enthusiastic are fertile ground for side stitch, especially if combined with nerves, poor posture or irregular hydration.

Habits that greatly reduce the risk before heading out

Prevention starts several hours before training, not at the moment the first stitch appears. A runner who has slept badly, eaten irregularly or arrived at the session with built-up tension has more chances of noticing discomfort. That is why it helps so much to organize the session with a simple logic: eat in advance, hydrate during the day and do not turn the start of the run into a disguised sprint.

In practice, the most useful thing is to choose an easy-to-digest pre-run meal, low in fat and without excess fiber, especially if the outing will be intense or long. The stomach appreciates caution. There is no need to empty the plate, but it is best to avoid heavy, very seasoned or bulky combinations. If the workout is in the afternoon, the distribution of the day also matters: eating in an orderly way, without big binges or long periods of fasting, usually gives better results than improvising.

Hydration deserves a separate mention. Drinking too little during the day can worsen the perception of effort and make breathing fall out of rhythm too soon. Drinking too much right before running does not help either, because it adds weight and can cause a feeling of fullness or internal bounce. The middle ground usually works better: water spread throughout the day and a sensible margin before setting off.

There is another detail that is often underestimated: posture. A collapsed trunk, raised shoulders and a rigid abdomen encourage tension. Running upright, with the chest open and a slight activation of the core, does not eliminate the risk on its own, but it does improve overall mechanics. The body moves with less friction, like a well-oiled door that no longer squeaks when it opens.

Breathing as a real tool, not as a technical ornament

Breathing well does not mean breathing fast, but doing it with depth and continuity. Many runners confuse hyperventilation with efficiency and end up in a loop of short gasping that punishes the diaphragm. The key is to look for a broader pattern, with full inhalation and exhalation, without forcing or holding the air. When breathing becomes orderly, the body tolerates impact better.

At easy paces, a natural and relaxed pattern is usually enough. In more demanding efforts, it is worth avoiding breathing getting trapped up high, in the upper chest. The air should fill comfortably, not violently. Some runners find it useful to coordinate breathing with their stride to stabilize the movement, although there is no single model that works for everyone. What matters is that the chest does not stay blocked and that the exhale is not shallow.

Training breathing also means learning to recognize when the body is asking for an adjustment. There are days when the problem does not start in the abdomen but in excessive intensity. If the chosen pace forces you to gasp in the first kilometer, the margin for side stitch narrows. Breathing is a fairly faithful mirror of the real load; if it falls apart early, maybe the pace is above what is reasonable for that moment.

The role of the trunk and strength in prevention

A stronger core usually translates into a more stable stride. This is not about getting defined abs, but about building a midsection capable of supporting the trunk when running multiplies the bounce. That control reduces internal vibration and improves the transfer of forces between legs and torso. In other words, the body becomes less disorganized.

Strength work does not eliminate side stitch by magic, but it can reduce how often it appears. More functional abdominal and lower-back muscles help support posture, breathe with less tension and better handle changes of pace. It is also worth paying attention to trunk and hip mobility, because a rigid run ends up demanding too much from a single area.

Running technique matters more than it seems. A runner who bounces too much, overstrides or hits the ground hard increases the strain on the abdomen and diaphragm. You do not need a complex biomechanical review to notice improvements: sometimes it is enough to slightly shorten the stride, increase cadence and relax the shoulders. They are small changes, but the body notices them like turning down the volume on a radio that was far too loud.

What to do if it appears in the middle of training

The first thing is not to panic. Side stitch is annoying, yes, but in most cases it eases if you act calmly. Keeping the same intensity rarely helps; the sensible thing is to slow down, walk a few meters if needed and let your breathing regain order. Forcing the pace only makes the stitch stay or get worse.

It can also help to gently press the affected area while exhaling slowly. A prolonged exhale helps switch off the tension and, combined with a slight forward lean of the torso, usually offers some relief. There is no need to bend over abruptly or make exaggerated gestures; just look for a position in which the abdomen stops working in permanent defense mode.

When the discomfort eases, getting back to running should be done gradually. If you start up again recklessly, the problem can return within minutes. Walking for a few moments and resuming the jog progressively is usually more effective than trying to ignore the signal. The body does not always ask you to stop; many times it only asks to be listened to without a fuss.

Why some runners suffer from it more than others

Not everyone has the same predisposition to side pain. Experience, effort tolerance, running mechanics and the way you breathe all play a part. An experienced runner usually recognizes warning signs sooner and adjusts the pace more intelligently. Someone who is just starting out, on the other hand, may interpret effort as an invitation to push harder and end up entering a higher-risk zone.

There are also anatomical differences. Thoracic curvature, trunk mobility or the way tension is distributed through the abdominal muscles can change the likelihood of suffering it. Body structure does not condemn anyone, but it can make some people more sensitive than others. That is why two runners doing the same session do not always get the same result.

Context matters as much as anatomy. Sleeping little, running after a very sedentary day, heading out stressed or training in the heat can alter breathing and favor the appearance of discomfort. Side stitch is usually the sum of small disadvantages, not a single isolated cause. Understanding it this way avoids looking for a single culprit where what exists is a chain of factors.

When it is worth paying more attention

Not every side pain during a run is automatically side stitch. If the discomfort is intense, persistent, accompanied by fever, vomiting, breathing difficulty or also appears at rest, it is best not to attribute it to sport without further thought. In those cases we are no longer talking about the typical passing stab associated with effort, but about a condition that deserves medical evaluation.

Very frequent repetition without a clear pattern also deserves caution. If the pain appears every time under similar conditions, maybe the problem lies in pre-run nutrition, breathing or a systematic excess of intensity. Training should not always leave a bill in the side. When the body repeats the same complaint, it is usually pointing to a poorly adjusted routine.

Observation matters more than theory. Noting when it appears, what you had eaten, what pace you were running at and whether there was nerves, heat or fatigue can reveal quite useful patterns. There is no need for a clinical notebook, but there is a need for some runner’s memory. Small details usually explain the problem better than grand explanations.

A common discomfort that is better understood when you look at the whole picture

Side pain while running is not a mysterious enemy, but a frequent reaction of the body to a combination of effort, digestion, breathing and running mechanics. When that mix is reduced to a single factor, valuable nuances are lost. When the whole picture is observed, on the other hand, realistic solutions appear: setting off more calmly, eating better before training, breathing deeply and strengthening the core.

The advantage of this approach is that it does not promise miracles. It offers something more solid: habits that really change the experience of running. Sometimes the result will not be a total absence of discomfort, but a notable reduction in how often and how intensely it appears. And that, for someone who goes out to run several times a week, makes a huge difference between fighting every kilometer or letting the stride flow naturally.

In the end, running well is not only about going faster. It also means knowing when the body is tightening up, recognizing the moment when breathing breaks down and learning to respond with judgment. Listening to that stitch in time is part of a runner’s craft, just like putting on your shoes or choosing the route. The body speaks; understanding it is, many times, the best way to keep adding kilometers.

You may also like: Why do I have a side stitch without exercising: causes and signs.

Medical reference: Side stitch, Cleveland Clinic.