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Departments: Fitness Focus


How Exercise Affects your Immune System

DeSimone, Grace T. B.A., ACSM-CPT, ACSM-GEI

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ACSM's Health & Fitness Journal: 3/4 2021 - Volume 25 - Issue 2 - p 3
doi: 10.1249/FIT.0000000000000656
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I’m sure you have heard the expression “the best defense is a good offense.” Maintaining your health is a great example of improving your offense when you need it for defense. When society is attacked with a health risk such as a pandemic or influenza, people turn their attention to lifestyle changes that boost their defense. Exercise is a simple habit that can improve your health and mood but also affect your immune system.

Your system of defense: Your immune system is a network of cells, tissues, and organs that team up to attack foreign invaders and neutralize infection and disease. Think of any movie, book, game, or sport where the mission is to protect the community from anything that can weaken it. Your body works in the very same way. It identifies the threat and strategizes to neutralize or destroy it.

Exercise mission: ACSM and the Centers for Disease Control and Prevention remind us that adults should participate in moderate intensity aerobic physical activity for a minimum of 30 minutes 5 days per week, or vigorous intensity aerobic activity for a minimum of 20 minutes 3 days per week. Every adult should perform activities that maintain or increase muscular strength and endurance for a minimum of 2 days per week (1).

Seek and defend: Every exercise session that meets the above requirements activates the army of immune cells to seek and defend against invaders. Cardiorespiratory exercise is particularly effective at deploying this defense, which increases the rate at which the army of cells can search for invaders. In addition, regular exercise has been shown to improve immune responses to vaccination, lower chronic inflammation and improve various cancers, HIV, cardiovascular disease, diabetes, and cognitive impairment (2). This does not mean exercise will guarantee invaders are diminished, it simply means that you are increasing your odds of your immune system putting up a good fight.

More is better? All exercise recommendations include the four-letter word REST. Too much of any “good thing” can be counterproductive. Research shows that overdoing strenuous exercise can weaken the immune response especially in athletes training for an event (3). Like all healthy habits, you need to be consistent and avoid the all-or-none approach. If you are exercising regularly, it all adds up. The temptation to do too much too soon always exists and can take its toll on some individuals physically and mentally.

Under the weather? When your body is fighting the common cold or another “invader,” adding exercise may not be a good idea. Every situation is unique, and each of us needs to take all circumstances under advisement with our medical professional. An easy rule of thumb for exercise is that you should not exercise with a fever or when in major distress. If you have a mild cold, for example, test-drive moderate exercise for 10 minutes. In that time, if you feel better, monitor yourself and continue, but if you feel worse, cease activity and enjoy a day off.

Map a plan: Consider working with an ACSM Certified Personal Trainer® to create a plan that suits your individual needs and consult with your medical professional for advice unique to you and your body.

Physical activity recommendations from the World Health Organization (4)

• Replace the amount of sedentary time with more physical activity of any intensity (including light intensity).

• Doing some physical activity is better than doing none. If adults are not meeting these recommendations, doing some physical activity will benefit their health.

• Adults should start by doing small amounts of physical activity and gradually increase the frequency, intensity, and duration over time.

For more information:


1. American College of Sports Medicine. Physical Activity Guidelines. [cited 2020 December 11]. Available from:
2. Duggal NA, Niemiro G, Harridge SDR, Simpson RJ, Lord JM. Can physical activity ameliorate immunosenescence and thereby reduce age-related multi-morbidity?Nat Rev Immunol. 2019;19:563–72.
3. Simpson RJ, Campbell JP, Gleeson M, et al. Can exercise affect immune function to increase susceptibility to infection?Exerc Immunol Rev. 2020;26:8–22.
4. WHO Guidelines on Physical Activity and Sedentary Behaviour. Geneva: World Health Organization; 2020. License: CC BY-NC-SA 3.0 IGO.
Copyright © 2021 by American College of Sports Medicine.