Nothing will ruin a run or completely destroy your race time more than a sudden stomach cramp prodding you to find a toilet ASAP. Oh, the joys of when running makes you poop! Is it best to keep running to the nearest bathroom, or slow down and regain control as you walk? And most importantly, how can you make sure this won’t happen next time you hit the pavement? (Seriously. It’s so inconvenient.)

“It happens to different people for different reasons, but most common sense is that it’s because you’re moving, and that up and down motion seems to stimulate the colon a bit,” Lisa Ganjhu, D.O., gastroenterologist and clinical associate professor of medicine at NYU Langone Medical Center, tells SELF. When you get moving, your colon does too, which can sometimes make you feel the need to go RIGHT NOW. This is one of the biggest reasons why running makes you poop.

On top of the basic mechanics, lots of people eat sugary energy-boosting gels and candy, or sip on sports drinks when they’re running. “That can cause some diarrhea because of the level of sugar,” Ganjhu says. More sugar prompts your body to release more water into the GI tract, which can make the stool more loose. If you’re active and drinking lots of fluids regularly, that in itself can also make you more prone to diarrhea. “People who are simply drinking more water are more likely to have softer stools,” says Ganjhu. On the other hand, dehydration during a run can cause GI problems, too.

Running also prompts your body to divert blood away from your GI tract and to the body parts that are working hardest. Experts suggest that this may also contribute to GI distress—they know that when blood flow to the intestines is compromised long term due to a chronic condition, it causes abdominal pain, diarrhea, and the urgent need to go to the bathroom. Though a long run is a different situation, the thought is that the change in blood flow may cause a less intense, yet similar, effect.

Those who are new to running especially may not know yet what sits best with them before a run. “Everyone is a little bit different as far as how their body reacts to different things, so usually my advice if if you’re running a race, don’t do anything new the day of. During practice runs, try out different foods,” Ganjhu suggests. It’s also best not to eat immediately before running—most experts suggest to wait an hour or two before you lace up to avoid any digestive issues. Also, dial back a bit on the fiber and fat right before a run to avoid both diarrhea and bloating. No reason to make running even more challenging for yourself.