In brief:
- Regular moderate training strengthens the immune system and reduces the frequency of upper respiratory tract infections.
- A single extremely long, exhausting effort can temporarily raise susceptibility to infection, but that doesn’t mean immunity is suppressed.
- The WHO recommends 150–300 minutes of moderate physical activity per week for adults, which also supports resistance in older adults.
- Lasting benefits come from consistency, not from a single hard workout.
Training and immunity is a topic surrounded by plenty of myths — does sport really strengthen your resistance, or does it wear the body down and leave it open to illness? The short answer: regular moderate physical activity supports the work of the immune system and lowers the risk of infection, whereas overdoing it in one go has only a temporary, passing effect. Below we look at what the science actually says.
How do training and immunity interact?
Every workout sets immune cells in motion. During exertion, large numbers of natural killer cells and T cells are released into the bloodstream and then head to the tissues where they’re needed most — this is called immune surveillance (Campbell & Turner, 2018). The drop in blood cell counts after exercise used to be wrongly interpreted as immune suppression, but today we know it is a redistribution of cells, not their destruction (Campbell & Turner, 2018). That explains why active people don’t have a weaker immune system, but rather a more alert one. Practical experience in clubs confirms the same: for example, Striding Day at the Reva-Sport sports club. Training on a treadmill shows how a moderate aerobic training load is manageable and easy to repeat regularly.
Does regular sport reduce illness?
Yes. A large population-based review found that regular physical activity reduces the incidence of upper respiratory tract infections by roughly a third and also improves vaccine response (Chastin et al., 2021). In observational studies, people who were active on at least five days a week came down with upper respiratory tract infections significantly less often than people with a sedentary lifestyle (Nieman & Wentz, 2019). Movement improves circulation, promotes the circulation of immune cells and reduces chronic low-grade inflammation — all of which support the body’s defenses (Nieman & Wentz, 2019). In autumn, when viruses spread, consistency is especially important; it’s also worth reading Immunity and training in autumn.
Can too much training weaken immunity?
A single very long, exhausting effort — a marathon, for example — can raise the risk of respiratory symptoms for a few hours, but a recent analysis stresses that this doesn’t mean true immune suppression, rather a temporary physiological adaptation (Simpson et al., 2020). Other factors are often behind the symptoms too: cold, dry air, large crowds at competitions, travel stress and lack of sleep (Simpson et al., 2020). For a recreational athlete who trains moderately and recovers adequately, there is practically no such risk. Keeping a balance — varying training loads and proper recovery — is precisely the key, as shown by events such as SPA&SPORT CUP 2019 as well as by well-thought-out nutrition, for example when it comes to the products Science in Sport (SiS) talks about.
How much physical activity do you need to support resistance?
The World Health Organization recommends 150–300 minutes of moderate or 75–150 minutes of vigorous aerobic activity per week for adults, plus two muscle-strengthening workouts (WHO, 2020). For older adults, the recommendation adds balance and strength exercises, which help maintain muscle mass and the immune function linked to it. It is consistent, manageable training load — not a single hard workout — that gives lasting benefits for resistance. You’ll find more practical recommendations in the WHO physical activity guidelines.
References
- Campbell JP, Turner JE (2018). Debunking the Myth of Exercise-Induced Immune Suppression. Frontiers in Immunology. PMID: 29632525
- Chastin SFM et al. (2021). Effects of Regular Physical Activity on the Immune System, Vaccination and Risk of Community-Acquired Infectious Disease in the General Population. Sports Medicine. PMID: 33359872
- Nieman DC, Wentz LM (2019). The compelling link between physical activity and the body’s defense system. Journal of Sport and Health Science. PMID: 31193280
- Simpson RJ et al. (2020). Can exercise affect immune function to increase susceptibility to infection? Exercise Immunology Review. PMID: 32139352
- World Health Organization (2020). WHO Guidelines on Physical Activity and Sedentary Behaviour. WHO. https://www.who.int/publications/i/item/9789240015128
Frequently asked questions
Does training really strengthen immunity?
Yes, regular moderate physical activity improves the circulation of immune cells and reduces the frequency of respiratory infections (Chastin et al., 2021).
Is it safe to work out when you’re sick?
With a mild cold, moderate activity is usually fine, but if you have a fever, muscle aches or chest symptoms, you should rest until you’ve recovered.
Can hard training weaken immunity?
A single extremely long effort can raise the risk of symptoms for a few hours, but it is not true immune suppression (Simpson et al., 2020).
How much physical activity do you need to support immunity?
The WHO recommends 150–300 minutes of moderate aerobic activity per week plus two strength training sessions (WHO, 2020).
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