Those flu-like symptoms after exercise aren’t all in your head. Here’s what science has to say.
You know the moment you wake in the morning after a tough workout and realize it hurts to move an inch? That bittersweet hurts-like-hell experience is called delayed onset muscle soreness, or DOMS for short.
But perhaps you came down with cold or flu symptoms shortly after one of these painful recovery periods and the uncomfortable I’m-dying-from-the-inside-out feeling that seems to spread directly from your muscles to your nose, lungs, sinuses, and throat. It’s like your body is poisoning itself to punish you for putting it through such a tough workout. But is that a real thing? Can you really be so sore that you have flu-like symptoms after exercise?
Turns out, there’s a well-accepted theory that prolonged, intense exercise results in short-term weakened immune function, according to an article published in the Journal of Applied Physiology. It started in the early 1990s with a study by David Nieman, Ph.D., who introduced the “J-shaped curve” suggesting that regular moderate exercise may decrease the risk of upper respiratory infections (aka the common cold) while regular intense exercise may increase the risk of these infections. Because many parts of your immune system change immediately after heavy physical exertion, this “open window” of altered immunity (which may last between three hours and three days) may give bacteria and viruses a chance to strike, according to a study in Sports Medicine.
More recent studies support the idea that working out too hard can make you sick by bogging down your stay-healthy system. A study of 10 elite male cyclists found that a long session of intense exercise (in this case, two hours of hard cycling) temporarily boosts aspects of the immune system response (such as certain white blood cell counts), but also temporarily decreases some other variables (such as phagocytic activity, the process your body uses to protect itself from infectious and noninfectious environmental particles and to remove unwanted cells), according to a study published in Exercise Immunology Review.
A review of relevant studies also found moderate exercise may lead to an enhanced immune system and anti-inflammatory response, which improves recovery from respiratory viral infections while intense exercise may shift the immune response in a way that gives pathogens a better foothold. And if you exercise hard two days in a row, you might see the same effect; CrossFitters who did two consecutive days of high-intensity CrossFit workouts suppressed their normal immune function, according to a study published in Frontiers in Physiology.
“Exercise in the long term is very good for you: It reduces inflammation throughout your body and makes you in much better shape from a cardiovascular standpoint, a lung standpoint, and an inflammation standpoint,” says Purvi Parikh, M.D., an allergy and immunology specialist at NYU Langone Health. “But in the short term, right after intense exercise, it will put strain on your body, and you’ll have a lot of inflammation in your muscles, your chest, and all over because it’s really strenuous work, she explains.
While the theory is well-accepted and makes a lot of sense, there needs to be more research to prove exactly what’s going on. After all, you can’t exactly put people through a grueling workout and then force them to swap spit with someone crawling with germs in the name of science. “It would be difficult (and unethical) to conduct a study in which people are exposed to infectious agents after exercise,” says Jonathan Peake, co-author of the article published in the Journal of Applied Physiology.
So while your super tough HIIT workout might be to blame for your random cold, take it with a grain of salt. You’re still getting tons of benefits from HIIT-style exercise, so you shouldn’t ditch it entirely in the name of staying germ-free.
Your best bet if you’re feeling flu-like symptoms after exercise is to amp up your focus on recovery to even out your risk: “Even without exercise, lack of sleep and stress weaken your immune system and pre-dispose you to getting sick, and if you add a heavy workout on top of that, you’re even more vulnerable,” says Dr. Parikh. (Here are just a few benefits of recovery, plus how to make the most of it.)
In fact, getting adequate sleep, minimizing psychological stress, consuming a well-balanced diet, avoiding deficiencies of micronutrients (particularly iron, zinc, and vitamins A, D, E, B6, and B12), and eating carbs during prolonged training sessions should help decrease the negative effects of intense exercise on your immune system, according to a study published in Limits of Human Endurance. So make sure you’re taking care of your body (in addition to crushing your tough workouts) and you’ll be just fine.
