Many people who begin to engage in some type of more intense physical activity, tend to feel sick and want to vomit during exercise . But not only beginners, but also those who exercise longer, must have felt the sensation at least once.
WHY DOES IT HAPPEN?
When practicing high intensity physical exercise, the body uses anaerobic metabolism in the first 30 to 60 seconds. That is, the musculature moves from the energy accumulated in the muscle – breakdown of ATP from creatine phosphate.
However, this energy source runs out quickly and, soon, oxygen becomes responsible for transmitting energy to the body. We call this process aerobic metabolism . Both then start to act together and their waste is released by the breath.
When reaching the limit of effort that the body supports, usually through exhausting physical activity, the level of oxygen in the blood drops and the muscles start to produce lactic acid to supply the energy through the breakdown of carbohydrates.
However, with the body working at a higher level than its normal physical condition, the production of this lactic acid exceeds , and it begins to accumulate in the blood.
As a consequence, this substance in the bloodstream makes the blood more acid , causing the so-called metabolic acidosis . Nausea and vomiting are generated, precisely, by this feeling of acidity.
The urge to vomit during exercise is okay, as long as it is not frequent. Otherwise, you should see a doctor or a physiologist to find out what the real problem is.
HOW TO AVOID?
1 – DRINK WATER REGULARLY
Dehydration causes symptoms such as dry mouth, thirst, decreased urine volume, muscle tiredness, dizziness and headache and feeling sick. 
Drinking water regularly is therefore very important, as in addition to keeping you hydrated, thus preventing the urge to vomit during exercise , it is essential for you to replace all the liquid lost in the process.
The tip is to drink at least 3 glasses of water before exercising and 1 to 2 glasses every 15 minutes of exercise.
2 – FEED 1 OR 2 HOURS BEFORE EXERCISING
One of the biggest causes of dizziness and nausea during exercise is a low blood sugar level. When your stomach is empty and your body has already used up its entire calorie supply, you can start to sweat more than normal during exertion, feel dizzy, nauseous and even pass out.
The best way to prevent this is to consume a meal with at least 300 calories before any physical activity , containing mainly protein and carbohydrates. These nutrients will help to produce more energy for the exercise.
If you train early in the morning there is a greater chance of feeling sick and the urge to vomit during exercise. This is because the body has been without food for many hours, and an empty stomach in the face of a great physical effort induces these symptoms more easily. So try to make at least a light snack like a banana, for example. example. 
However, eating before exercise is not to start it immediately on a full stomach. It is important to give your digestive system a break so it can digest before doing any activity. The ideal is to wait between 1 and 2 hours after eating. Otherwise, the fluids necessary for the process will be removed from the muscles and go to the digestive system causing discomfort.
3 – FOCUS ON YOUR BREATHING
A sudden increase in blood pressure with physical exercise can make you feel sick and induce vomiting. Controlling your breathing will help to lower that blood pressure.
In addition, another tip when your heart rate is at its maximum is to reduce the intensity of the exercise. Exaggeration often leads to vomiting.
4- CONTROL ANXIETY
Stress and anxiety with day-to-day problems can be channeled to exercise causing nausea and the urge to vomit. If this happens, the suggestion is to slow down, relax and notice the likely return to normal.
5 – CONSUME ISOTONIC DRINKS IF YOU TEND TO HAVE LOW BLOOD SUGAR LEVEL.
Isotonic drinks like Gatorade, can help raise blood sugar levels to safe levels and further assist hydration.
If you still feel bad during exercise and have a tendency to have low blood sugar, the problem may be something like hypoglycemia.