Do you feel sick after exercise? A scientist explains why and how to prevent it

Many of us exercise to feel better. While some of us experience “runners’ high” after a workout, unfortunately some of us leave the gym feeling nauseous. Although this is usually only temporary, it can still be uncomfortable.

Fortunately, there are some good explanations for why this might be happening, so if this happens to you, there’s probably no reason to be alarmed.

When we exercise, there is an increase in blood flow to the working muscles, brain, lungs, and heart.

This increase in blood flow is driven by the sympathetic part of the autonomic nervous system (which helps regulate all of our body’s involuntary responses, such as heart rate, blood pressure, and digestion). It does this by widening the arteries so they can carry more blood to these tissues.

But the sympathetic nervous system, which normally drives our “fight or flight” mechanism, simultaneously narrows the blood vessels that go to our gastrointestinal system (such as our stomach) during strenuous exercise by up to 80 percent.

It does this because there is a limited amount of blood in the body, and the increased demand for oxygen by some tissues can only be met by altering the amount of blood going to other tissues.

This means that the blood supply can be reduced in areas that currently do not need as much oxygen at the time. This may be the case whether or not you have eaten recently.

But let’s say you’ve recently eaten before going to the gym or going for a run. When we eat, the food stretches our stomach, which results in the release of acid and enzymes needed to digest the food.

The stomach muscles also become more active during digestion, causing increased oxygen demand and blood flow to the stomach and other gastrointestinal tissues. A different part of the autonomic nervous system causes increased blood flow to the gastrointestinal structures when they need to be active.

The significant conflict in the body of different tissues that demand oxygen can be one of the reasons why nausea occurs during or after a workout. The body has to adapt blood flow to the tissues as demand changes.

So when we exercise, blood must go to the muscles, heart, lungs, and brain, which means blood flow is reduced in less active tissues, like the GI tract, even if it’s currently digesting our dinner. . When blood flow is reduced in this area, the intestinal nerves are activated, which subsequently leads to nausea.

In addition to this, the stomach and other abdominal organs can also be compressed during exercise, which can further contribute to feelings of nausea. This is particularly a problem when squatting, as the heart rate and oxygen demand in the tissues increase, so the body draws larger volumes of air into the lungs.

This causes the diaphragm (under the ribs) to press harder on the abdominal organs. Other muscles, such as those of the abdominal wall, also help, further compressing the abdominal organs with each breath. This can lead to significant nausea and even vomiting, even on an empty stomach.

Some evidence even suggests that exercise, particularly long-distance running and other endurance events, can damage the stomach lining, likely due to decreased blood flow and available oxygen to the organ. This would also cause nausea.

In extreme circumstances, this can result in bleeding from the lining of the stomach, particularly in long-distance and endurance athletes.

when to eat

If you exercise immediately or up to an hour after eating, you are more likely to experience nausea, regardless of the level or intensity of exercise.

It takes about two hours for the stomach to break down solid food and enter the small intestine, so if you feel nauseated after exercising, it’s best to wait at least two hours after a meal.

What you eat before a workout can also determine if you experience nausea. Foods that are high in fiber, fat, and even protein are linked to a higher chance of nausea after a workout.

Supplemental proteins, particularly whey or shakes, are also digested more slowly. This is likely to contribute to nausea during training as the stomach tries to digest it.

Certain fats, particularly saturated fats, can induce nausea differently: Animal models show that they irritate and damage the lining of the gastrointestinal tract, which activates nerves in the lining of the stomach that connect to the vomiting center (located in the medulla oblongata) in the brain.

Drinking sports drinks or other high-carbohydrate beverages (such as juices, energy drinks, and sodas) is also linked to nausea during and after exercise. This may be because these drinks are digested very slowly and stay in the stomach longer than other drinks.

If you’re someone who often experiences nausea after exercising, there are a couple of things you can do. First, change or reduce your usual training and increase the intensity slowly. This is because the longer the workout, the more blood is constantly being drawn from the stomach.

Make sure you drink enough water before and after exercising, as too little or too much can cause nausea for a variety of reasons.

As for eating, avoid two hours beforehand and choose the right foods, such as high-quality carbohydrates (such as bananas or sweet potatoes) and protein, as well as unsaturated fats (such as nuts). Not only will these fuel the body, but they won’t be as difficult to digest as other foods if you plan on exercising.

Adam Taylor, Professor and Director of the Clinical Anatomy Learning Centre, Lancaster University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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