Discomfort in the stomach and abdomen often troubles many runners. Many runners have experienced nausea and the urge to vomit during running, especially during high-intensity training or competitions. Diarrhea is more common in marathons, often occurring on the marathon track or at the finish line.

So why does running easily cause digestive reactions? Today, I will explain why the above situations occur during running.

————

Why do you feel nauseous and want to vomit while running a marathon?

First, it is important to know that the causes of nausea, vomiting, and diarrhea during running are different. Nausea and vomiting are one situation, while diarrhea is another. It is important to emphasize that headaches, nausea, and vomiting are not normal signs of fatigue and should stop exercising if they occur.

Improper diet

The most common cause of vomiting and nausea is eating too much or too late before running. When you start running, the stomach contents have not yet emptied, causing significant turbulence. Many inexperienced runners are familiar with this 'churning' feeling. Therefore, to maintain a 'relatively empty stomach without lacking energy' during the race, it is generally recommended to finish breakfast 2 hours before the marathon, with 60-70% fullness being ideal.

Eating the wrong types of food before the race, such as greasy or hard-to-digest foods, can also easily induce nausea and vomiting, even if eaten in small amounts or early. Therefore, the pre-race meal should follow the principle of 'zero fat, low protein, high carbohydrates.' Avoid drinking milk or eating eggs, as focusing too much on nutritional value at this time is meaningless.

Physiological inertia

Even running on an empty stomach, nausea and retching often occur. This is a manifestation of visceral physiological inertia.This is because the activities of the stomach, intestines, and other internal organs are mainly controlled by the parasympathetic nervous system, while skeletal muscle movements are mainly controlled by the sympathetic nervous system. During intense exercise, the parasympathetic nervous system is inhibited, and the sympathetic nervous system is excited.

During running, the demand for blood circulation and oxygen supply to the skeletal muscles increases, so the blood flow to the muscles increases while the blood flow to the internal organs decreases to meet the needs of muscle activity. This process is called blood redistribution during exercise. If the digestive system cannot adapt to the blood redistribution and changes in the nervous system, temporary physiological dysfunctions such as nausea and vomiting may occur.

————

What about diarrhea during a marathon?

Diarrhea generally does not occur during running because high-intensity exercise inhibits the activity of the large intestine. However, after the race ends and you rest for a while, or if the race pace is slow, the urge to go to the bathroom may arise.The causes of diarrhea differ from those of nausea and vomiting. Diarrhea may sometimes be due to the physiological inertia of the digestive system, but more often, it is due to other reasons.

Pre-race chill

Marathons are often held in the cool mornings of spring and autumn. If the temperature is low, especially on rainy days, diarrhea is more likely to occur. If the organizing committee provides ginger tea or other warming foods, runners can drink some to ward off the cold and prevent diarrhea.

Unfamiliar environment

For example, many runners from the east and north may experience discomfort when participating in races in the southwest due to the sudden encounter with the local humid and cold climate. The invasion of moisture and cold can cause diarrhea. In this case, drinking ginger tea or eating some spicy food can help alleviate the discomfort.

Improper diet

Similarly, improper diet can cause nausea and vomiting if you eat too much or hard-to-digest food 2 hours before the race. Diarrhea is more likely if you eat high-fiber foods the day before the race. While a high-fiber diet is generally healthy, it is advisable to reduce fiber intake 2-3 days before the race to decrease the volume of stool in the intestines. Additionally, runners who do not usually eat seafood should avoid it before the race, and it is best to avoid trying new foods when racing in different locations. Save the local delicacies for after the race.

Exercise stress

Exercise stress is the most important cause of exercise-induced diarrhea. Functional diarrhea caused by high exercise volume is very common among endurance athletes. Experts have found that the incidence rate is as high as 50% among triathletes. Functional diarrhea is also common in other sports such as road cycling.

The phenomenon of exercise-induced diarrhea is related to the body being in a high-intensity exercise state for a long time. The primary cause is changes in nerve activity and blood distribution, leading to weakened digestive tract activity and reduced adaptability. The digestive system tends to 'empty' its contents to reduce the burden, resulting in diarrhea. This is similar to the causes of nausea and vomiting.

————

Summary

Adequate warm-up activities can significantly reduce the physiological inertia of internal organs. Before the start of a road race, use the waiting time to do small movements, such as jogging in place or slowing down for the first 2 km as a warm-up.

Diet is also key to reducing the physiological inertia of internal organs. Eating too much or greasy food before the race increases the burden on the digestive system and physiological inertia. Since digestive system activity decreases during exercise, food stays in the stomach longer and takes longer to digest than at rest, causing more turbulence and discomfort.

Generally speaking, the higher the exercise intensity, the stronger the physiological inertia of the internal organs, and the more likely it is to cause nausea and vomiting. Therefore, in various middle and long-distance running events, distances longer than a half marathon are less likely to cause nausea and vomiting due to the longer duration and relatively lower intensity. In contrast, high-intensity races such as 800 meters, 1500 meters, and 5000 meters are more likely to cause nausea and vomiting.