Some people steer clear of exercise because they have trouble mustering the motivation, while others avoid it because working out just doesn’t make them feel good; it literally makes them a bit nauseous. Often with nausea during physical activity, there’s something about the routine that just isn’t quite right.
Here are some of the most widespread reasons people feel ill during or after a workout, and what can be done to avoid the nausea.
1. Eating too close to your workout. For most people, eating any closer than 2-3 hours before a workout can cause indigestion issues because of the undigested food that you still have in your stomach. Laying on your back with a full stomach can often cause discomfort by itself; when you add in heavy breathing and contracting your core muscles during an exercise, the added pressure can push food and acid back up into your esophagus, causing heartburn and even nausea.
2. Eating too much, or eating food with high fat content. If it has been over three hours since you last ate and you are still experiencing nausea during exercise, it is probably because you overate or the meal that you ate was too high in fat content, both of which cause your digestion to slow.
When you eat too much food at one time, you overload your body's capacity to digest food by diluting the amount of acid in your stomach. This slows the rate at which your stomach processes food and empties. Even a small meal that is high in fat content will slow the rate that the stomach will empty, causing your food to sit longer in the belly, which can create discomfort similar to the instances where you have overeaten. Either situation can easily cause nausea during physical activity.
3. High intensity workouts. Working out too hard can also make you feel sick. This kind of nausea can happen whether you have just eaten or not eaten all day. What happens is that during very high intensity exercise your body struggles to get enough oxygen to keep functioning aerobically, and getting that oxygen to where it needs to go takes all of your available blood volume. When that blood volume is being pulled in two different directions (by the muscles for exercise and the stomach for digestion), your muscles will always win, causing the blood to drain from your stomach.
If you have anything in your stomach at all, even residual acid, your body will try to get rid of it during an intense workout. This can easily cause exercise induced nausea and/or, in extreme cases, vomiting into the closest trash can.
4. Too much fluid intake. Drinking too much while you are actually working out strains the body. If you have too much fluid in your stomach, putting excessive pressure on your abdomen (from breathing heavily and/or contracting your core muscles) can cause the water to push back up into your esophagus.
This is made worse by the fact that acid floats on top of the water in your stomach; the acid can be pushed back up into your esophagus (not just the water). Working out intensely with lots of water in your belly can cause nausea very quickly.
Talk to your doctor to be safe. These are the likely culprits of exercise making you sick to your stomach but it's best to be safe. Especially if you can’t get rid of the nausea by changing one or all of the above factors, then you should see a doctor. If you are having problems with heartburn on a regular basis, even when not exercising, this could be a sign of a more serious problem.
Whatever you do, don’t stop exercising. It will always be better for your health than any negative factor brought on by it, you just may need to do a few modifications in order to make it less taxing on your body.