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Athletes, Exercise & Immunity

by Stephanie Jamain 27 Feb 2020
Athletes, Exercise & Immunity

As athletes, we never like to miss training, or even worse a competition, due to illness. Putting all that time and effort into training to end up toeing the line on race day with low energy, muscle pain and congestion is far from ideal. Here are some tips to keep the common cold and infections away, adapting your training accordingly if you do get sick, and knowing when to take a break.

The relationship between exercise and immunity is U-shaped, meaning that moderate levels of regular exercise seem to reduce risk of infection, while the extremes – being sedentary or overtraining can make you more susceptible to infection. During training and competition season, there are different periods when your immune system can be down making you more prone to infection. Believe it or not, the first of these periods is when you start resting more, for example close to a competition, following a big race or entering post-season. This is partly due to increased levels of stress hormones like adrenaline and cortisol that suppress white blood cell functions. After strenuous exercise (>90mins of moderate to high intensity exercise at 55-75% of aerobic capacity performed without nutritional intake), athletes enter a brief period of “immune function depression” and are more susceptible to viral and bacterial infections.1 Your body, which is used to higher training volumes, intensities and adrenaline, is suddenly paused. Your immune system is likely already compromised by this high training regimen, is not able to fight viruses that you might come across on a daily basis. While this break is necessary to allow your body (and your immune system) to recover, be on the lookout for microbes. During periods of very intense training, during your weeks higher in volume, you are also prone to catch a virus more easily. Strenuous exercise causes physical damage to your body, leading to a cascade of host stress responses that may compromise the integrity of the immune system, thus making you more susceptible to infections. Basically, at moderate levels, exercise is beneficial for overall health and immunity, while too much or too little may suppress the immune system, increasing the risk of infection.

Illness prevention strategies include:

  • Minimize your exposure: This is mostly common sense but worth noting.
    • Wash your hands (often);
    • Avoid using other people's bottles, glasses, utensils etc.
    • Avoid busy areas (metro, bus, etc.), and stay away from sick people!
  • Promote a strong immune system:
    • Sleep: optimize your hours of sleep to 7-8 hours per night and during periods of fatigue, choose lighter workouts. See our blog on Sleep.
    • Hydration: maintaining a good level of hydration is essential to reduce stress on the body and also optimize immunity. One of the body's defense mechanisms is the array of enzymes found in saliva and nasal secretions. Adequate hydration therefore allows a better functioning of your defense system.
    • Nutrition: Eat a balanced diet and plan your food intake before and after your trainings to optimize both energy availability and recovery. Glucose is an important fuel substrate for immune cells such as lymphocytes, neutrophils and macrophages, which have a high metabolic rate. Adequate carbohydrate intake during exercise (30-60g of carbohydrates per hour of effort), and stable blood glucose concentrations helps attenuate the hormone responses that weaken immunity (cortisol, catecholamines), while providing glucose as energy substrate for immune cells which helps maintain immunity. Win win.


  • Plan your training schedule: Slowly increase training volume and intensity. Plan more intense efforts when a recovery period is possible thereafter. Make sure you allow for rest days. Use a coach to guide you, they are the best resource.

If unfortunately, you do get sick, here are some tips to manage:

If you have a fever, avoid training as this can have severe consequences on your heart. Take the time to rest, ultimately enabling you to come back quicker. If fever is prolonged (5 days or more), if you have trouble hydrating, if your consciousness is affected, you experience trouble breathing, or if you have chest or abdominal pain, consult a health care professional.

In a less severe context without fever, you should still take the time to rest, optimize hydration, taking ibuprofen and acetaminophen if necessary. Limit yourself to very low intensity exercises and listen to your body. High heart rate during low exertion or shortness of breath is a sign that you are overdoing it. Take this opportunity to optimize your flexibility, working on stretching and perhaps some core exercises. As you start feeling better, you can gradually resume your usual training over a few days.

Have a good season and remember to train wisely, your health is most important!

Dr Melissa Rattue, CMFC, MU, sports med specialist CASEM



  1. Gleeson M, Bishop NC and Walsh NP (2013) Exercise Immunology. London: Routledge (Taylor and Francis). ISBN 978-0-415-50725-7
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