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COVID19 Special – A Critical Overview of the Effects of Exercise on the Immune System

By April 7, 2020 April 9th, 2020 No Comments

Given the current COVID-19 global pandemic it is helpful to remind ourselves the importance of exercise to help keep our immune system strong in the fight against infection. Now, the importance of exercise and health is by no means new, as illustrated by this excerpt by the classic English poet, John Dryden (1631-1700):

“Better to hunt in fields, for health unbought,
Than fee the doctor for a nauseous draught.
The wise, for cure, on exercise depend;
God never made his work for man to mend.”

Nevertheless, step forward almost 400 years and the science brings clarity and a sharpened understanding to the long known benefits of exercise.

In the 1994, David Nieman proposed the J-Curve (see figure below), which suggests that a moderate level of physical activity decreases the risk of upper-respiratory tract infection when compared to a sedentary lifestyle. It is well supported that a sedentary lifestyle depresses the strength of your immune system. For example, Matthews and colleagues (2002) observed over 500 adults between 20 and 70 years old and found moderate activity levels decreased the risk of upper respiratory tract infection by 20%.


The ‘J curve’. A proposed relationship between exercise workload and infection risk (from Nieman, 2000, p 407).

Overall, it has been seen that exercise enhances the body’s response to viral and bacterial infection. How does exercise enhance the immune response though?
In asking this question we’re opening up the complex area of immunology, so for the sake of this article let’s keep it brief. Essentially, the body has two levels of defence against infection: a) the innate and b) the adaptive. The adaptive is the line of defence that is able to build immunity to future infection by a similar bacteria or virus. The innate system could be likened to the first line of defence, put simply these defence cells circulate round the body and mop up foreign matter (hence the pac-man reference in the article feature image!). One type of innate defence cell is the neutrophil.

Let’s take a closer look at neutrophils.

So here’s one specific example of exercise enhancing the immune system: after physical activity the response and numbers of neutrophils circulating in the blood stream increase, helping to improve the body’s first line of defence against infection. I point you towards some further reading at the end of this article if you want to dive into the deep end on the mechanisms.

Now, back to Nieman’s J-curve. So we’ve said that a moderate amount and intensity of exercise can enhance the immune system. However, on the other side of the J-Curve, it was proposed that high amounts and intensity of exercise may lead to an increase in risk of infections. However, evidence to back this part of the model has not been so forthcoming. For, example, reports suggest the rate of upper respiratory infection rate in athletes and general population are similar.
It’s important to note here that there are other factors that can affect the immune system other than exercise, these include: nutrition, stress, anxiety and sleep. Another area to consider is aging. Typically, the immune system’s effectiveness will decrease with age (fancy name alert: immunosenescence) but exercise has been shown to limit or delay the deterioration.

So you’re probably thinking… “Ok exercise helps my immune system, I kinda knew that but it’s interesting to hear about one of the potential mechanisms. But the question is how much exercise should I do to help keep my immune system strong?”

As a rule of thumb participating in exercise 5 times a week for 30 minutes at a moderate intensity. A moderate intensity would be one where your breathing rate increases significantly but you can still maintain a conversation uninterrupted.

If you would like more specific guidance on your correct exercise intensity to be training at please get in touch or why not sign up to one of our online memberships. I also point you to a previous article on starting up with cardio training. And finally, remember, exercise can help boost your immune system, but our greatest fight against infection like COVID19 is practicing good hygiene and social distancing.

by Laurence Houghton PhD, High Performance Coach, Warwick Workout.

Further reading
“Current Knowledge and New Challenges in Exercise Immunology”, German Journal of Sports Medicine, Alack et al, 2019.“Exercise, Infection, and Immunity”, International Journal of Sports Medicine, Nieman, 2000.

“Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan”, Frontiers Immunology, Campbell and Turner, 2018.

“The effect of caffeine ingestion on human neutrophil oxidative burst responses following time-trial cycling”, Journal of Sports Sciences, Walker, G., Dziubak, A., Houghton, L. et al., (2008).

“Moderate to Vigorous Physical Activity and Risk of Upper-Respiratory Tract Infection”, Medicine & Science in Sports and Exercise, Matthews et al. (2002).