Stress, anxiety, that co-worker that doesn't know how to shield his coughs; they all increase your chances of getting that seasonal cold. That being said, it’s virtually impossible to avoid everything in your life that may get you sick. So what can you do to overpower those illness-causing pitfalls and keep your immune system in tip-top shape? Research has shown that exercising may be the secret to keeping stress, anxiety, and even co-workers from knocking down your immune system's defenses.

We all have two basic sets of immunity. Our first line of defense is like the protective screen cover that comes with your phone, it does a nice job of keeping it shiny and scratch-free, but it’s not enough to truly keep your device protected. In other words, our innate immune system gives us the natural ability to fight off the disease and infection we were born with. The second is our acquired or adaptive immune system; this is the case you buy for your phone after you’ve dropped it and vow never to let that happen again. Our acquired immunity responds to foreign pathogens prevents illness from reoccurring. It’s also the immune system that you can boost through exercise.

According to McGraw Hills Exercise Physiology: Theory and Application to Fitness and Performance1, moderately intense aerobic exercise increases the levels of natural killer cells (which seeks out and kills pathogens) and antibodies (which counteract pathogens that cause illness) respectively. Meaning, exercise can actually help to keep you from getting sick, shorten the duration of illness if you do fall under the weather and help prevent any prior bugs you've had from attacking again.

In addition to working out, you also need to keep your stress levels in check to prevent sickness. According to Memmler's, The Human Body in Health and Disease,2 intense levels of stress may compromise our immune system. When stressed we secrete cortisol which is great if you are trying to outrun a lion, but in modern life it may do more harm than good. "People who work too much, are chronically stressed-out and live from crisis to crisis, basically use up all their cortisol. That is to say their adrenal glands [responsible for making cortisol] become so depleted that they can't make cortisol when they need it and thus ‘crash’,” says Jennifer Sudarsky, MD, Associate Clinical Faculty, UCLA/David Geffen School of Medicine. “This state of adrenal fatigue can manifest as malaise, depression or low exercise tolerance."

But before jumping on that StairMaster it may not always be beneficial to exercise while sick, however. "You don't want to use your vital energy for exercise when your body needs it for healing," says Allen Green, President of the American College for Advancement in Medicine. Green states that "exercise definitely improves immune function," but when his patients are ill, he advises them to cut back on exercise and not to push themselves. Ashley Wachsman, MD, agrees. “If you have a cold, you're good to exercise, but if you have severe flu symptoms such as a fever of 1010F, take it easy.” Having an unusually low tolerance to exercise or an abnormally low level of work capacity are signs that the workout or exercise you are attempting is too intense.

Considering the opposing information on exercising while sick, there are some helpful general guidelines recommended by The World Health Organization. Adults age 18-64 should complete 150 minutes of moderately intense aerobic activity or 75 minutes of intense aerobic activity throughout the week. For those of you who don’t always have the time to dedicate an hour or so to getting your workout in, don’t sweat it—the WHO also notes that the bouts of aerobic exercise only need to be ten minutes or more to be effective. If you aren’t sure how to gauge your intensity, I like to measure intensity in two ways, heart rate and rate of perceived exertion (RPE). When using heart rate as the measure, limit your heart rate to a maximum of 65% of your maximum heart rate. If using RPE use a simple one to ten rating system, one being virtually effortless, ten being completely exhausting for you to complete. Keep your RPE in the ballpark of five to six. Keep in mind this is in regards to aerobic exercise, much more research is needed to determine if resistance training will have the same effects.  

At the end of the day, exercise is widely accepted as a method to improve immune function. And you can always trust that your body will tell you if it’s overworked as our bodies’ are smartly programmed to protect themselves. I tell all of my clients to test the water before diving in; start with a mild five to ten minute warm up to alert your body that you intend to be active. If you feel better after the warm up than before, cautiously move into your workout. If you feel worse after the warm up, call it a day and give your body the rest it’s asking for.


1. Exercise Physiology: Theory and Application to Fitness and Performance

By: Powers, Scott K., and Edward T. Howley

McGraw-Hill Humanities/Social Sciences/Languages 2012

2. Memmler’s The Human Body in Health and Disease

By: Cohen, Barbara J., and Jason J, Taylor

Wolters Kluwer Health/Lippincott WIlliams and Wilkins 2013

3. Jennifer Sudarsky, MD, Associate Clinical Faculty, UCLA/David Geffen School of Medicine

4. Allen Green, MD, Board Certified in family medicine, President of the American College for Advancement in Medicine

5. Ashley Wachsman, MD, attending staff radiologist with the S. Mark Taper Foundation Imaging Center

6. The World Health Organization,