These are the reasons why you could feel like you are getting sick after or during exercise. Firstly, let me tell you that you are not alone. Many people experience this. The symptoms go away for most people after their bodies get used to it (for new comers who experience it). If you feel cold and chilli (instead of flu-like symptoms) from exercise, click here.
Why you could experience flu-like symptoms from exercise
It is very easy to become dehydrated during exercise. You don't only lose water through your sweat, but through your breathing (You exhale water vapor. Heavier breathing loses more water) and pee as well. On top of that, your body needs more water because it increases muscle volume in order to get more nutrients into the muscles and escort more waste products out of them. Getting dehydrated can cause dizziness, light-headedness and headaches which you might be associating with the feeling of being sick. Make sure that you get enough electrolytes as well. They are responsible for helping your body to hold onto the water you drink. When your electrolyte levels are low (they get depleted from exercise), your body struggles to hold onto water and it simply flows right through you.
Exercising outdoors - Dust
If you exercise outdoors, your body might be reacting to the dust levels in the air. I have recently moved from the suburbs to a more country-themed area. My running trails have turned from tarred surfaces into the dirt roads that you typically find in country regions. For a few hours after my run, I cough up some of the dirt that I've inhaled from the day's exercise. This is how my lungs get rid of the dust. Some people might sneeze or get snotty as their bodies try to remove the inhaled dust from their systems. Read more about exercising in environments with dust and what the safe levels are.
Similar to the above, your symptoms might be brought on by the pollen or other allergens in the air. Exercise opens up your airways and blood vessels, which makes it easier for these allergens to enter into your body.
Loosening of phlegm
Exercise opens up the airways and lungs. It also helps your body to get rid of sinus build up. If you were sick recently or have sinus in your cavities for some other reason, exercise might be assisting your body to expel it. This might make you think like you are getting sick, when phlegm removal is simply being sped up. Working out can aid in loosening phlegm that has been sticking around for long past its welcome date. Try to steam out the excess phlegm or sinus that you may have. Steams rooms are good for this.
You are getting sick (and exercise is bringing it out)
Exercise challenges your body. Your body gets stronger to adapt to the strain that exercise temporarily puts on it. The immune system takes a short-term hit from exercise. If your body is currently battling with an underlying, impending spell of illness; exercise might be warning you about what is soon to come. If this is the case, take a few days off to give your body all the energy that it needs to fight off the sickness. Also make sure that you get the right sleep and nutrients to help your body fight it off. Use these tips to get better quicker when you are sick.
Release of human growth hormone (HGH)
Exercise encourages the release of human growth hormone. It is a hormone that assists the body to recover and build muscle. Although it is very beneficial for recovery and muscle growth, too much of it in the system at once can make you feel nauseous.
You could be training too hard and failing to give your body a break to recover. This point is very important. You could be getting sick (and feeling those flu-like symptoms) for this reason. Over training can make you get sick more often because the exercise ends up challenging the body more than what it can cope with. See our article on breaking your plateau to determine whether over training is making you sick. Don't drag out your exercise sessions for too long. This is could be the reason why you feel horrible afterwards. You are pushing your body so hard that it is breaking down more than it is building itself up. You also need to have rest days. Here are great ways to have a fantastic rest day that really speeds up recovery.
Chronic Fatigue Syndrome or Fibromyalgia
www.avogel.co.uk says that Chronic Fatigue Syndrome or Fibromyalgia might be the reason why you feel sick after exercise. Symptoms that indicate that this is the case include dizziness, extreme exhaustion or nausea (although all of these symptoms could indicate over training as well). If this is the reason why exercise makes you feel sick, you need to see a doctor.
Nutrition that will help you
BCAA's (branched chain amino acids) will support performance during exercise, decrease the stress it places on your body and therefore minimize the temporary impact that exercise could be having on your body. As discussed in the article referring to over training (that I linked to in the point above), glutamine can help you recover quicker from both exercise and illness. You should always eat a balance diet that includes healthy, raw foods to maintain a healthy immune system.
Go through the list and see which best describes your current situation. Once you find the cause, you will be more equipped to deal with the issue. Always stay safe and put your long term health first when exercising. STAY STRONG!