Training when you’re sick: Are you doing more harm than good or can you ‘sweat out the toxins’?

Igray and black stethoscopet happened again. Never fails. I got the man-flu.

It happens a few times every year. One day I’m feeling great, crushing the trials, and then I wake up the next morning with a sore throat, an unstoppable cough, and a sinus headache from hell. Like any other guy my first instinct is denial. “I am not sick!” So what do you think I do? Well, like any other guy I self-medicate with cough drops and over the counter cold medicine, and I go about my day as usual of course, including whatever workout I have planned. Sometimes I would feel better after a good sweat session, but other times I would wake up the following day worse for the ware. If I was still sick I would blame it on not working out hard enough, not sweating enough, not eating right, or just downright being so damn healthy my body was like “whoa we are too healthy man we need to get rid of some of this health!” Whatever excuse I told myself, the man-flu would stick around for weeks.

So I got to thinking…. how does exercise affect our immune system? Was I prolonging my illness or could I actually sweat it out by pushing harder?It is generally accepted that exercise makes us stronger and healthier. So doesn’t that mean that more exercise and harder exercise should make me invincible???

I decided to find out what the science says.

It turns out that elite athletes have a potentially increased susceptibility to infections immediately following intense periods of training or competing in a marathon endurance event. Most of the research into the how and why of this phenomenon focuses on upper respiratory tract infections (URTI).

In 1993, Nieman et al. compiled data from 2,311 Los Angeles marathon runners. The runners self-reported URTI symptoms (sore throat, runny nose, cough, etc.) following the 1987 Los Angeles Marathon. They found that 12.9% of runners experienced an infectious episode in the two weeks following the race, compared to only 2.2% of sedentary individuals of the same time period. Another epidemiological study from Peters and Bateman looked at 150 random runners competing in a 56 km race in Cape Town, South Africa. They found that 33.3% runners compared to 15.3% of the control group had sore throats or nasal symptoms. The same researchers repeated this study with two other ultramarathon races in South Africa with similar results, suggesting that runners are twice as likely to develop a URTI (1).

So what gives?

In 2012, Eda et al. found that secretory IgA (SIgA) levels are significantly d ecreased following intense exercise. SIgA is the most abundant antibody secretion in our skin, salvia, GI tract, and respiratory tract and is responsible for protecting us against microbes. The decrease in SIgA  lasts for at least two hours post-workout (2).

Additionally, Nieman published another article in 2007 with evidence suggesting that following marathon-type exertion, runner experiences immunodepression for a period of up to 16 hours post-workout. This ‘open window’ of decreased immunity allows infectious microbes to gain a foothold in our bodies and cause us to get sick when normally they would not. The reason for this is that following a marathon event or longer, our cortisol levels are extremely high from the physical stress of the exercise. Increased cortisol causes a decrease in our innate immune cells, specifically natural killer cells and cytotoxic T-cells, which are responsible for protecting us against microbes (3).

What does this all mean?
Essentially, intense prolonged exercise (75% of VO2 max) confers a weakened ability to fight infections. Coupling that with a variety of other factors such as poor diet and psychological stress from work and life also weakens the immune system.

What can we do to prevent ourselves from getting sick?

  • Washing our hands frequently will help of course
  • Proper nutrition, possibly adding a vitamin C supplement. Vitamin C is a well-known antioxidant which neutralized harmful free radicals which are created during periods of inflammation and infection
  • Adequate sleep. It is well documented that lack of sleep causes deterioration of the body’s immune system.
  • Resisting overtraining. This is a big one in our sport. Overtraining compromises our immune system as well.

Interestingly, the same research articles I cited for this post found that moderate exercise (60% of VO2 max) actually boosts our immune system, suggesting that backing off from intense training can help us overcome an infection.  Also, light to moderate exercise had no negative effects on individuals who actively reported having URTI symptoms.

The Bottom Line: Light to moderate exercise is OK when you have the man-flu or common cold, but intense exercise will compromise your ability to recover from the infection and can prolong your symptoms.

Thanks for reading! If you liked this post let me know in the comments. I have a master’s degree in health science; I love combining my passion for running and my interest in anatomy and pathology and could write more posts like this nerdy one 😉

Nieman DC. Exercise, infection and immunity. Int. J. Sports Med. (1994). S131-S141.
Eda N, Shimizu K, et al. Effects of high-intensity endurance exercise on epidermal barriers against microbial invasion. Journal of  Sports Science and Medicine. (2013). 12; 44-51.
Nieman, DC. Exercise effects on systemic immunity. Immunology and Cell Biology. (2000). 78; 496-501.

3 thoughts on “Training when you’re sick: Are you doing more harm than good or can you ‘sweat out the toxins’?

  1. Thanks for taking the time to research the topic, and for the clarifying post!

    Will definitely apply the lesson to my own training. Keep the posts coming!

    Liked by 1 person

  2. I can feel my body is bit “broken” after intense training. I try to listen and go slower on my runs. If I do get sick, I also go slower. I rarely rest all together though. I am not sure if that is the right thing to do or not, but it is what I do.

    Liked by 1 person

    1. The research I read said as long as the illness is “above the chest” you can exercise. Think headache, sinus infection, ear infection, sore throat. Once the infection moves to your lungs they say it’s best to rest entirely until you recover because you risk making yourself worse. Several people died from the seasonal flu this year so it’s definitely not something to mess around with!

      That said, I’m like you and I train through the sick. It’s hard for me to not go 100 percent because that’s just how I am. I think it does keep me sickee for longer sometimes but it’s just how I do it.

      Liked by 1 person

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