Stop Getting Sick - How Exercise Affects Your Immune System


I never get sick. Yet there I was in bed, coughing like a smoker being buried alive by booger filled tissues.

Paradoxically the reason I was sick, and the reason I never get sick were the same - Exercise.

Exercise comes with several health benefits including strengthening your immune system but at the same time it can be a stress that can leave you vulnerable to infection or cause symptoms to worsen.

In this article I will use my story to explain the relationship between exercise and your immune system.

  • You’ll learn how to best use exercise to boost your immune system,

  • Whether it’s best to sweat it out or rest when you feel under the weather

  • Why athletes get sick more often than normal people and what that means for you.

Why I Never Get Sick


I strongly believe that the reason I don’t get sick is because I live an active healthy lifestyle.

The research backs this up. For example a group scientist found that those who exercised and felt fit and active were 50% less likely to catch a cold.

On top of that, the severity of the symptoms were reduced by 41% in those who felt fittest and 31% in those who were most active.

The findings that exercise helps reduce illness has been replicated many times.

Why exercise helps reduce illness is still unknown. There are many theories but they are still unproven. However the relationship between being active and sickness is well established.

Which brings us to the next question - How much exercise do you need to reap these immune boosting effects?

Another group of scientists looked to answer this question. In their study of exercise habits and influenza they found that those who were inactive got sick more often than those who exercised moderately.

Those who were moderately active exercising between once a month and 3 times a week did the best.  

This shows that you don’t need to become a professional athlete to reap the immune boosting benefits of exercise.

In fact, the group of individuals who exercised more than 4 times a week were actually  most likely to get sick.

Yup, over exercising led to getting sick more often. Other studies have also shown that athletes tend to get sick more often than the general population.

Why? This leads us to the next part of our story - Stress.

Stress and the immune system

Most of us think of stress as that emotional feeling when you're overwhelmed. The reality is that stress refers to anything that disturbs the body’s ideal state - for example getting to hot.

Stress comes in many forms.

  • Psychological stress such as relationships, career, family and finances.

  • Environmental stress such as being to hot or cold, dark or light, pollution, altitude, etc.

  • Lifestyle stress such as drugs, diet, hygiene, smoking ect.

  • And Physical stress such as exercise, sports, physical labor and infections.

A little stress is good because it causes our body to adapt and get stronger.

This is also how exercise makes you stronger. You lift a weight applying a stress, the body adapts, and you become stronger.

However, too much stress can be bad. It can overwhelm the body preventing it from working as well as it should.

It’s important to understand that for life to exist every living organism needs to maintain a stable internal environment.

Humans are no different. Our body is constantly trying to maintain this balance.

For example consider temperature. Our body wants to be around 98.6 degrees. If we begin to get too hot our body works to cool us down. If we get too cold our body works to warm us up.

In terms of our immune system, our body is constantly working to keep our body rid of foreign bacteria and viruses.

However, when we are under too much stress from work, family,  exercise or other causes, our immune system cannot work as well as it should. The result is people under too much stress get sicker more often.

This also explains why too much exercise can also make us more likely to get sick. Exercise is a stress after all.

Studies have shown that people after a prolonged vigorous exercise session we’re more susceptible to infection. For example, the act of running a marathon may temporarily depress the immune system for up to 72 hours. Which  may explain why so many endurance athletes get sick right after races.

Adaptation of A diagram of the General Adaptation Syndrome model.- David McQullian

Adaptation of A diagram of the General Adaptation Syndrome model.- David McQullian

So how did the person who never gets sick get sick?

First was stress. I had just finished traveling to Bogota Colombia. While the city has improved a lot, it is still one of the most polluted cities in the world. For two days I inhaled  exhaust fumes.

Combine with a few poor night's sleep and a new environment my body was stressed and susceptible to foreign bacteria.

After my two days I had a mild cough and sniffles.

We all get sick, that’s life.

But what I did next was the difference between a mild respiratory infection and being bedridden for two days.

I left for the countryside. Besides the sniffles I felt good.

So on my first day out of the city I decided to go for a mountainous 30 kilometers hike.  

The next day things took a turn for the worst and the day after that was spent with a fever, coughing and sneezing.

My body was likely dealing with a mild infection and I went and over stressed it with a vigorous workout. The result is it was too much for my body to handle at once and the infection took a turn for the worse.

So what should you do when you start getting sick?

While vigorous exercise can worsen symptoms, mild exercise can improve them.

However, what you should do depends on you’re symptoms. Here are a few general guidelines you can use, however I am not a doctor and you should always use your best judgement.

If symptoms are above the neck and mild, for example sniffles or a headache you should be fine to do an easy workout.

If symptoms  are mild, or progress below the neck such as in a respiratory infection then you should avoid exercise. Instead of exercise think of activity.

Light physical activity may be beneficial for your recover. For example this may include, walking, tai, chi, low intensity bike riding, or home chores.

Listen to your body and be sure not to overextend yourself.

If symptoms progress to moderate and include fever, or fatigue you should take a rest day. Get rest and focus on giving your body what it needs to fight off the infection.

If symptoms continue progress or if at any point you have concerns then contact a medical professional for further actions.

If your sick, or thing you may be sick, you should avoid the gym to avoid spreading your sickness to others. Instead opt for something outside or in your home.


Exercise is great.

Moderate exercise is great for supporting and building good immune function. Having a strong immune system can mean that you will get sick less often, and that when you do get sick the symptoms will likely not be as severe or last as long.  

Aim to exercise a few times each week for best results.

If you are feeling under the weather, mild exercise or activity can be beneficial for improving symptoms and recovery. However exercise is a stress, and doing too much can make symptoms worse.

Take it easy and listen to your body.

If symptoms progress, take time off and focus on getting rest, hydration, and nutrient dense foods to help your recovery. Don't hesitate to contact your doctor if symptoms progress.