Why Does It Hurt on the Side of the Body While Running—and What Can You Do About It?

Most likely, everyone has encountered this for the first time during physical education classes — on another lap of jogging around the school stadium, you feel a pain in your side, and running becomes unbearable. This sharp pain can occur even during brisk walking, on the right or left side.

What causes it?

If you feel a sharp pain in the right side, it may be related to the liver; if in the left side, it may be related to the spleen. The reasons for such sensations stem from the suddenness of physical exertion.

At rest, the majority of circulating blood is located in the thoracic and abdominal cavities and does not circulate through the blood vessels, but is kept in reserve. During physical activity, there is a redistribution of blood flow in favor of the working muscles. However, if the muscles start to work suddenly, the autonomic functions that support their activity (breathing and circulation) require several minutes to adjust.

This means that if you start moving quickly without a proper warm-up, blood from the reserve enters the bloodstream but does not have enough time to quickly drain from the abdominal organs. The liver and spleen become engorged with blood, increase in size, and start to press against their capsules. There are pain receptors in these capsules, which send signals in the form of sharp pain.

This is a typical mistake made by beginners — starting to run fast right away. Firstly, this increases the risk of various unpleasant sensations, ranging from dizziness to pains not only in the side but also in the knees and unprepared ligaments. Secondly, starting with a fast run immediately raises your heart rate into the anaerobic zone, and you become very tired within the first few minutes — perhaps at this moment you will think, 'running is not for me.'

Proper breathing and a well-structured training plan can significantly reduce the risk of side pain. If you're looking to improve your running technique and train smarter, our Run Pass program offers expert-led sessions that help you build endurance and prevent common mistakes.

To run comfortably within your optimal heart rate zone, we at the Running School provide our students with heart rate monitors — as your heart gradually adapts to the workload, you’ll be able to progress much faster.

If you think that running slower than Usain Bolt is boring, read excerpts from the blog of runner Floris Girman about how to turn the irritation of slow running into enjoyment.

What to do when you feel a sharp pain in your side?

If the pain has already appeared, the first thing to do is to reduce the load — slow down your running pace or even switch to walking, and take a few deep breaths. Deep breathing helps accelerate blood flow away from the internal organs and normalizes circulation.

Another way to alleviate the pain is to pull in your stomach as much as possible. This effectively massages the liver, as pulling in the stomach causes the diaphragm to press the liver against the spine, squeezing blood out of it. When the overstretching of the liver or spleen capsule stops, the pain will subside.

There is another reason that can cause such discomfort — food. If you start running right after eating, the capsules of the liver can also become overstretched. This happens because the liver is involved in digesting food, and when food enters the digestive tract, its blood vessels expand. The bile ducts also expand, leading to bile flowing into the intestines — hence the unpleasant sensations.

Can this pain be prevented?

Yes, it can and should be. Before any workout, it is essential to warm up — even five minutes of simple exercises will relieve you of unpleasant sensations. Begin active physical activities no sooner than 2-3 hours after eating, and avoid drinking too much water during the workout.

Sudden pains in the side can ruin your running experience forever, but if you warm up, remember proper running technique, and don’t overeat before workouts, running will bring you joy, we promise!