What Causes Pain On The Left Side When Running? The Reason

Running is one of the most natural forms of exercise, but pain on the left side can stop you mid-stride. The most common cause is a side stitch, a sharp cramp under the ribs that usually comes from the diaphragm working harder than it is used to. However, left-sided pain can also signal issues with your spleen, digestive tract, or even your heart, so it is important to know the difference between a temporary cramp and something more serious.

What Causes Pain On The Left Side When Running

The most frequent culprit for left-side pain while running is a side stitch, medically known as exercise-related transient abdominal pain. This pain typically feels like a sharp, stabbing sensation just below the ribs, and it is more common on the right side but frequently occurs on the left as well.

The leading theory involves the diaphragm, the muscle that controls breathing. When you run, your breathing rate increases, and if your breathing is shallow or out of rhythm with your stride, the diaphragm can spasm or receive reduced blood flow. This lack of oxygen to the muscle produces a cramp-like pain.

Another contributing factor is the ligaments that connect your stomach and other organs to the diaphragm. The jarring motion of running can stretch these ligaments, especially if you run soon after eating or drinking. This stretching triggers nerve pain that feels like a sharp stitch.

When Is It Your Spleen?

The spleen sits on the left side of your body, just under the rib cage. During intense exercise, blood flow is redirected away from the digestive organs and toward the working muscles. The spleen acts as a reservoir, releasing stored red blood cells to increase oxygen delivery.

When the spleen expands and contracts rapidly, it can cause a dull, aching pain on the left side. This is different from a sharp stitch. Spleen-related pain often feels deeper and more diffuse, and it may radiate toward the left shoulder.

While a temporarily enlarged spleen from exercise is uncomfortable, it is generally harmless and resolves with rest. However, if the pain is severe, persistent, or accompanied by dizziness, you should stop running immediately and seek medical attention. An enlarged or ruptured spleen is a medical emergency, though this is rare in healthy runners.

Digestive Issues and Left-Sided Pain

Your digestive tract is another common source of left-side pain during a run. The descending colon runs down the left side of your abdomen, and the physical jostling of running can irritate it. This is especially true if you have eaten a large meal within two hours of your run.

Gas and bloating can also cause sharp pains that mimic a side stitch. When gas builds up in the colon, it stretches the intestinal walls, and the movement of running makes this stretching more noticeable. The pain may come and go as gas moves through the system.

For some runners, left-sided pain is related to constipation or the urge to have a bowel movement. The colon’s natural contractions, combined with the pressure of running, can create cramping that feels like a stitch but is actually intestinal in origin.

Muscle Strains and Skeletal Pain

Not all left-side pain comes from internal organs. The oblique muscles, which run along the sides of your torso, are heavily engaged during running to stabilize your core. If these muscles are weak or fatigued, they can strain, producing a pain that feels like a cramp.

Intercostal muscles, located between the ribs, can also spasm. These muscles assist with breathing, and when they are overworked, they can cause sharp pain that intensifies with each breath. This type of pain often worsens when you twist your torso or take a deep breath.

Unlike a side stitch, muscle strain pain may persist after you stop running. It may also be tender to the touch. Rest, gentle stretching, and avoiding high-impact activity for a few days usually resolve muscle-related pain.

Cardiac Concerns: When to Take It Seriously

Left-sided chest pain during exercise always warrants attention. While the vast majority of running-related pains are musculoskeletal or gastrointestinal, the left side is where the heart is located, and cardiac pain during exertion is a red flag.

Angina, which is reduced blood flow to the heart muscle, can cause pressure, tightness, or a squeezing sensation in the chest. This pain may radiate to the left arm, jaw, or back. Unlike a side stitch, cardiac pain does not improve with breathing adjustments or slowing your pace.

If you experience left-sided chest pain that is accompanied by shortness of breath, nausea, cold sweats, or lightheadedness, stop running and call emergency services. These symptoms can indicate a heart attack, and immediate medical care is essential. This is especially important for runners over 40 or those with risk factors like high blood pressure, high cholesterol, or a family history of heart disease.

How to Prevent and Relieve Side Pain

Prevention is the best approach for exercise-related left-side pain. Focus on your breathing pattern. Try to breathe in a rhythm that matches your stride, such as inhaling for two steps and exhaling for two steps. This keeps the diaphragm working smoothly rather than in sudden bursts.

Avoid eating a heavy meal within two hours of running. If you need fuel, choose something light and easily digestible, like a banana or a small piece of toast. Stay hydrated, but avoid drinking large volumes of water right before or during your run.

If a side stitch develops, slow your pace and focus on deep belly breaths. Press your fingers into the painful area and lean slightly forward. Some runners find that exhaling forcefully when the opposite foot lands helps relieve the cramp. If the pain does not subside within a few minutes of walking, stop and rest.

When to See a Doctor

Occasional side stitches that resolve with rest are normal and not a cause for concern. However, you should see a doctor if the pain is severe, happens every time you run, or lasts for hours after you finish.

Seek medical evaluation if the pain is accompanied by fever, vomiting, blood in your stool, or unexplained weight loss. These symptoms can indicate a more serious gastrointestinal condition, such as inflammatory bowel disease or a hernia.

For left-sided chest pain, never assume it is just a muscle cramp. If you have any doubt about the cause of your pain, especially if it is in the chest area, err on the side of caution and get checked by a healthcare professional.