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Should You Train When You’re Sick?

It Depends! According To This MD

Dr. Jeffrey Krebs, MD FACP is a board certified Internal Medicine specialist who has been practicing for over 35 years. He is a former competitive figure skater, a 7-time Ironman and multiple 70.3 finisher, an elite Age Group runner who has raced Boston Marathon 8x with #9 coming up this year and will be competing in his third Age Group World Marathon Championship later this year in Sydney, Australia. He is a certified swim instructor and a run coach.

An article from Men’s Health Magazine was recently referenced in The Tempo titled “Should I Workout If I’m Starting To Feel Sick.”  This brief article suggests that exercise boosts the immune system and infers that it is ok to train when ill.  I take issue with some of what the article states and would like to clarify a few things. 

First of all, I would like to distinguish between viral and bacterial illnesses. Bacterial infections almost always require a doctor’s visit and antibiotic therapy. Far and away, however, the most common infections that we deal with are viral. When we talk about the common cold, upper respiratory tract infections (URI), “the flu,” etc., we are talking about viruses.

  • You are likely familiar with Influenza Virus, Coronavirus (causing COVID-19), and RSV but there are also Adenoviruses, Rhinoviruses, and a lot more.

  • When we get infected, the viruses enter our cells, often without being deactivated or destroyed. Their goal is to replicate, exit the cells, and infect more cells.

Once we are infected, our immune systems go to work. We develop fevers to raise our core temperature to destroy the virus. In this case, the fever is good. As the viral infection continues, we may develop chills, sore throat, headache, muscle aches, nasal congestion, cough, sneezing, watery eyes, and with some viral infections, nausea, vomiting, and diarrhea. A lot of what we experience is a result of our immune system at work and not necessarily a direct result of the virus. 

Viral infections may be minor or they may be serious. Knowing when to seek medical attention is important. You should see a physician for prolonged fever, shortness of breath, a decrease in your oxygen saturation (SaO2, aka O2 Sat.), elevated resting pulse, deep cough, cough with the production of dark brown, dark green or bloody sputum, persistent nausea, vomiting or diarrhea, blood in your stool or vomiting blood. In addition, if you test positive for COVID, seek medical attention as soon as possible since you may be a candidate for anti-viral therapy.

Many of us as endurance athletes have monitoring devices (Garmin for example) that can monitor our pulse and O2 sat, making it easy to know when something is amiss.  Any O2 Sat below 90% is an indication to see a physician but I argue that if your O2 sat is normally in the high 90’s% and it drops to the low 90’s% and stays there, that would be an indication to seek medical evaluation ASAP. If your resting pulse is normally in the 50’s and now it is in the 70-80’s, that is significant.

As endurance athletes, we are trained to monitor our bodies. We need to use the info given to act accordingly. This is often difficult because we love to train, love to complete every workout, and love to check those “boxes.”

  • You need to know that there are times when we benefit more from rest than we do by performing a suboptimal workout that does not enhance our training.

When is it ok to train during an illness? A lot has to do with what your symptoms are and I might add, what you are taking for your symptoms.  For example, a simple “head cold” with nasal congestion may not preclude you from training but if you are taking sedating antihistamines that might affect your reflexes and cognition, I would not recommend jumping on a bike or going for a run that requires you to navigate traffic, road debris and other obstacles.

In general, if you have fever…do not exercise. Exercise in this situation may further raise your core temperature which can lead to unwanted tissue damage. If you have diarrhea, stay out of the pool…PERIOD! Many people have the false belief that exercising while sick will help your body fight off a viral infection. This is not true and can actually be detrimental to your healing and recovery. In general, it is ok to train if your symptoms are from the neck up (nasal congestion, watery eyes, mild headache, mild sore throat) but not ok if you have symptoms below the neck (cough, shortness of breath, nausea, diarrhea). But again, it is never ok to exercise if you have a fever. 

When we are sick, our bodies are utilizing very important resources to help us fight the infection. At the same time, we often have poor oral intake due to poor appetite so we go into a calorie deficit. Fever and sweats can lead to dehydration.  That coupled with poor fluid intake when we are sick is also detrimental to our bodies. We should not exercise in a calorie and fluid depleted state. By doing our best to rest, properly hydrate and take in needed calories, we can help positively influence the supply and demand of resources. Any exercise, even easy Z2 work, will further deplete our systems during this critical time.

How long should you take off from exercise with a viral illness? The answer is not straight-forward and is dependent on what type of infection you have. For true Influenza, for example, the virus takes about 7-10 days to run its course. In the case of Covid-19, you will want to stop exercising for about 7 days or until all symptoms have resolved. With COVID-19, it is important to monitor heart rate since the coronavirus can adversely affect it. If you had diarrhea, you will need to stay out of the pool for a full 10-14 days AFTER the diarrhea resolves, even if you feel great.

Many will ask: “What about my training?  Will I lose fitness?”  If you have been training regularly, taking a week off to recover from an illness will not be detrimental to your training overall. Yes, you will probably loose a little endurance while you are recovering, especially the older you are, but you should regain that which is lost within 7-14 days of returning to training.

One more thing…if your symptoms are only from the neck up and do not include fever, you can safely train through your symptoms without the fear that your training will adversely affect or prolong your recovery.

It is always better to avoid getting sick if possible. I recommend staying away from people with known illness, wiping down gym equipment BEFORE using it (and after, of course), avoiding large indoor groups when possible, especially during cold and flu season, and if not possible, wear a mask. There are few things worse than putting in all of the training and then showing up at a race sick due to an exposure at the airport, on an airplane or at the race expo. Take care of yourself.


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