Should You Exercise While Sick?

It's hard to do much of anything when you're under the weather. Are there benefits to exercising while sick, or will working out just make you feel worse?

Brock Armstrong
10-minute read
Episode #371
The Quick And Dirty
  • Consistent exercise can help build and maintain a healthy immune system and reduce your chances of getting sick.
  • Very long or extra-hard workouts can weaken the immune system for a short period of time.
  • If an illness is above the neck, it is ok to exercise while sick (within reason) but if the illness moves below your neck, rest is best.

Note: This article was updated on January 27, 2020. Contents will not exactly match podcast audio.

I'm currently getting over a cold. In fact, as I write this I have a warm drink and a box of tissues right beside my laptop. It isn’t a bad cold (or even a man cold), it’s just enough to annoy me, interrupt my sleep, and cause me to miss a few workouts. It's my off-season (I'm not training for any events or races), so it isn't a big deal. But when it happens in the spring or mid-summer, I am not so cavalier about missing training sessions. In fact, I can get downright ornery.

It doesn’t seem to matter how many times I get sick during the race season or how many times the athletes I coach fall prey to the seasonal flu; I still do a lot of hand-wringing over whether or not I should exercise while sick. Should I be jumping on my bike or doing a heavy lifting session?

Well, don’t worry. This wouldn’t be Get-Fit Guy's Quick and Dirty Tips if I didn’t have a few guidelines for you to follow. But before I get to those, let’s talk about the immune system.

What is the immune system?

Your immune system is comprised of six components that do their best to protect you from foreign invaders.

  1. Lymph nodes and lymphatic system, which recognize and fight invading pathogens
  2. Respiratory system, which creates mucus, coughs and sneezes to trap and remove contaminants
  3. Skin, a relatively thin but very effective barrier against invading pathogens
  4. White blood cells, which attack pathogens in your blood and other tissues of your body
  5. Your spleen, a major organ that helps protect you from bacterial infections
  6. Your stomach, which contains acid that kills harmful bacteria and also contains good bacteria that help to fight pathogens and absorb nutrients. (Antibodies secreted by your intestinal cells also help to fight off foreign invaders.)

What does immune health mean?

Every day we come in contact with thousands of different viruses and bacteria. We touch things like a seat on a bus or a cart at the grocery store and then we touch our face. The bugs can then get access to our bodies through our mucosal surfaces (eyes, nose, mouth, or a break in our skin).

We actually swallow a surprisingly high number of bacteria and pathogens every single day.

The majority of the time the invading foe will be thwarted by our mighty white blood cells, which capture and kill the bugs before they can replicate and enter our bloodstream.

As gross as it sounds, we actually swallow a surprisingly high number of bacteria and pathogens every single day, but most of them die in our saliva or in the acid and healthy bacterial environment of the stomach. Unfortunately, some bugs are stronger than others or have mutated in ways to evade our immune response, and then we are susceptible until our immune system adapts and finds a way to kill the new version of the invader.

What does "immunocompromised" mean?

Being immunocompromised is simply a state in which a person's immune system is weakened or absent. But for us exercise enthusiasts, it gets more complicated than that.

When we engage in an acute bout of heavy exercise, that exhausting workout actually induces immune system responses, which are similar to those induced by infection. Normally, if you're well-rested, you will recover from this quite quickly. But in times—like when you're loading on the extra training sessions, loaded down with other life stresses, or exercising when you're sick—these immune responses persist and your chances of getting sick (or staying sick) are much higher.

In particular, endurance exercise and long bouts of training, if not properly managed by a dedicated coach, can weaken our immune system. The recruitment of white blood cells to fight off pathogens may be reduced and elevated levels of stress hormones (especially cortisol) can weaken the inflammatory component of the immune response. That can allow the pathogen to paint the town red.

Even if this doesn’t result in some achy and snotty illness, once in our system, pathogens and their accompanying toxins can cause inflammation. That inflammation requires energy to expunge from our bodies—the precious energy we normally would use to recover from a workout. This response will minimize our muscular recovery and hamper our ability to reap all the benefits of our hard training.

The main factors that can suppress the immune system are:

  • Increased intensity of exercise
  • Increased duration of exercise
  • Sleep deprivation
  • Psychological stress
  • A nutrient-poor diet
  • Calorie restriction
  • Low body fat
  • Frequent travel
  • Heavy drinking

Let’s get into the good news.

Can exercise strengthen your immune system?

According to the American College of Sports Medicine (ACSM), for the majority of fitness enthusiasts engaged in 30-60 minutes of exercise most days of the week, the number of sick days they take during flu season is reduced by at least 40 percent.

Yup! Regular physical activity actually strengthens your immune system.

Researchers in Britain tracked the health of 1,000 people (18 to 85 years old) for 12 weeks during fall and winter and asked them how often they exercised and how fit they felt. The researchers found the length of time cold symptoms lasted was shorter by 43 to 46 percent in people who worked out five (or more) times per week, compared to people who worked out only once per week or never.

For people engaged in 30-60 minutes of exercise, the number of sick days they take during flu season is reduced by at least 40 percent.

It also appears that recreational exercisers report fewer colds when they exercise regularly, and moderate exercise has been associated with a stronger immune system response and an increase in the production of macrophages (cells that attack bacteria).

The reason is thought to be that when you exercise, you improve blood flow and movement of your immune system’s lymphatic fluid, allowing your immune cells to circulate through the body more quickly to kill off bacteria and viruses more efficiently. The more consistently you exercise, the more immune system enhancement you can get.

Can exercise weaken your immune system?

Well, sure. Like all good things, you can certainly overdo it. Quite often when one of the athletes I coach finishes an Ironman triathlon or a marathon, they get sick a few days later (usually within a 72-hour window). Research has shown that as few as 90 minutes of high-intensity endurance exercise can make you more susceptible to illness for up to three days after the session.

The reason for this is a release of certain hormones that can cause a temporary decrease in the proper function of the immune system. When you perform a hard exercise session, you significantly increase the release of cortisol and adrenaline, your body’s “fight or flight” stress hormones, which can suppress the immune system.

So, if you are already sick with a cold or respiratory infection, high-intensity exercise such as heavy weightlifting or very long exercise such as marathon training can further weaken the immune system.

To help people decide whether to hit the gym or stay in bed, the ACSM offers the following recommendations:

  • Do exercise moderately if your cold symptoms are confined to your head. If you’re dealing with a runny nose or sore throat, moderate exercise is permissible.
  • Don’t “sweat out” your illness. This is a potentially dangerous myth, and there is no data to support that exercise during illness helps cure it.
  • Do stay in bed if your illness is “systemic”—that is, spread beyond your head. Respiratory infections, fever, swollen glands, and extreme aches and pains all indicate that you should rest up, not work out.

In a nutshell (and we’ll cover this again later) if your symptoms are from the neck up, go easy. But if you have a fever or general aches and pains, rest up and let your body get over the illness.

Can exercising while sick make you sicker?

Although high-intensity exercise can make you sicker if you are already under the weather, moderate levels of physical activity are okay.

One study at Ball State University on sport, exercise, and the common cold actually injected volunteer students with a cold virus, then tracked them for ten days, during which each participant logged all of their exercise sessions. In the exercise group that performed light aerobic activity for 40 minutes each day, there was no significant difference in cold symptom severity or duration. So while the exercising group didn’t get better any faster, they also didn’t get any worse.

Before you rush off to the gym to cough all over the treadmill, remember that exercising in public will expose the rest of humanity to the illness that you have.

But before you rush off to the gym to cough all over the treadmill, please remember that exercising in public while you are sick will expose the rest of humanity to the potentially contagious illness that you have. It is a much better idea to just go for a brisk walk outdoors or do some power yoga in your living room.

Speaking of a brisk walk outdoors, when in doubt (and weather permitting), exercising in an outdoor and natural environment may give us some of the best health benefits possible. According to a research paper on the great outdoors, moving your workout outside can help increase physical activity levels with lower levels of perceived exertion, which can reduce stress, relieve mental fatigue, and improve mood, self-esteem, and perceived health. The paper concludes that “exercise within green spaces and the great outdoors may be a useful natural medicine (vis medicatrix naturae) to address health challenges facing developed countries.”

When you should not exercise when you're sick

It is important to remember that exercising with a slight cold is very different from exercising with a fever or full-on flu, which can make you more miserable and potentially sicker. Fighting the flu requires the full strength of your immune system and the illness may be antagonized by dehydration or muscle fatigue that occurs when you exercise.

Because many competitive athletes (and Type A personalities) find the stress of missing a workout more upsetting than the stress of exercising when they feel sick, nearly every physician (and many of us coaches) will fall back on the "neck check."

Below the neck: Don't exercise when you have below-the-neck symptoms such as coughing that produces phlegm, body aches, fever, and fatigue. You should give your body a chance for some much-needed rest and recovery.

Above the neck: You may exercise if your symptoms are above the neck, such as a sore throat, nasal congestion, sneezing, or teary eyes, runny nose, and scratchy throat.

But even if your symptoms are above the neck, it is smart to take what some of us call a test-drive first. To do a test drive, simply start your workout easy and if your head seems to clear and you start or continue to feel peppy, it is OK to keep going. But if you feel like you start to feel worse or your symptoms increase, pull the plug and head back to the couch.

When can you return to exercise?

This is a tricky one and usually involves a few failed test-drives that we talked about earlier before a full return may be achieved, but the ASCM has some useful advice on this.

  • If your cold symptoms are confined to your head, intense exercise can be resumed a few days after symptoms subside (in cases of the common cold).
  • If you’re recovering from a more serious bout of cold or flu, gradually ease back into exercise after at least two weeks of rest.

My advice is not to rush! Like we learned from Shalane Flanagan, training time-outs can have their own benefits and here’s an interesting and perhaps motivating fact for you: you can't lose body fat while you are sick. This is because fat metabolism is impaired during infections. You instead rely heavily on muscle as an energy source especially during times of physical stress. So any weight loss you experience while sick is generally a loss of lean muscle mass.

How should you treat your cold?

For this I will defer to the House Call Doctor for some Quick and Dirty Tips on what to do if you catch a cold:

For a stuffy nose use decongestants. Some examples are phenylephrine or pseudoephedrine. Pseudoephedrine works better to open up the nasal passages, but does have greater side effects for people who can’t tolerate decongestants. There’s also long-acting 12-hour pseudoephedrine you can ask your pharmacist about. I tell my patients to try using a vaporizer or humidifier as well. It's similar to a hot shower effect and can help open up the nasal passages. This, combined with sipping on hot liquids all day long can make you feel a lot better.

For a runny nose use antihistamines, such as diphenhydramine for nights (it tends to make you sleepy), and loratadine, cetirizine, or fexofenadine for the daytime to avoid drowsiness.

For a fever or body aches use ibuprofen or other anti-inflammatories. Otherwise, acetaminophen is a good second option.

For a sore throat use sugar-free lozenges, throat sprays, or salt-water gargles (my current fave), which can soothe a scratchy throat.

For a cough use cough syrup. The cough associated with the common cold typically occurs secondary to a post-nasal drip from all that nasal drainage in the back of the throat. That’s why some patients actually become awakened in the middle of the night with a cough, because gravity simply pulls that drainage from the back of your nose down into your throat, irritates the throat, and causes a cough. A very pretty picture I’m painting, I know. This cough can linger for weeks past a cold. Once your nose dries up, this will go away, too. Until then, you can try over-the-counter cough syrups, guaifenesin to break up the mucus, and antihistamines to dry up the drainage.

Remember that the more active you are in general, the less likely you are to get sick in the first place.

Remember that the more active you are in general, the less likely you are to get sick in the first place. Keep in mind that a 2011 study of 1,002 adults found that those who exercised five or more days a week were 43 percent less likely to develop upper respiratory tract infections than those who exercised once a week or less. What’s the old saying attributed to Ben Franklin? “An ounce of prevention is worth a pound of cure.” But in this case, it’s an ounce of movement.

Ultimately, we know that getting some exercise when you have anything more serious than a sniffle or common cold is unlikely to result in significant physiological or fitness gains. We also know that at best training under these circumstances will be of lesser quality, and at worst could lead to serious consequences. So, let’s agree to stick to the neck check followed by the test drive. We are much more likely to perform well in our goal events, and also in our personal life, if we occasionally learn to take a time-out rather than trying to fit in one more sniffling, sneezing, aching, coughing, stuffy-head trip to the gym.

All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Brock Armstrong Get-Fit Guy

Brock Armstrong was the host of the Get-Fit Guy podcast between 2017 and 2021. He is a certified AFLCA Group Fitness Leader with a designation in Portable Equipment, NCCP and CAC Triathlon Coach, and a TnT certified run coach. He is also on the board of advisors for the Primal Health Coach Institute and a guest faculty member of the Human Potential Institute.