Exercise and the Immune System

This read is structured along three topics of exercise immunology. While giving you some basic, evidence-based information about the effects of exercise on the immune system, we will also provide insight into how our CrossFit training is supporting your immune health and what you should consider during the Covid-19 outbreak.

Summary and application:

  • Acute exercise supports the immune system and improves defense activity and metabolic health: Stay active even during these challenging times, your immune system will benefit. Follow our daily Home-Wods to boost your immune system (and add some burpees while you’re at it) and join our Zoom Classes to keep up your routine.
  • There is a dose-response relationship between training workload and illness risk: If you do long, hard and intense training sessions your immune system is temporarily compromised. Make sure you plan enough time for recovery and fuel your body appropriately. Don’t drastically increase your weekly exercise load.
  • Regular exercise training improves immune regulation, strengthens anti-inflammatory agents and the body’s immune system pathways on multiple levels: Join our Zoom Classes to support your daily schedule and habits. Encourage and support less active people close to you to move more. Keep showing up! You can count on our support and advice.

Acute and chronic effects of exercise on the immune system

The immune systems responds immediately to exercise in a dose-response relationship. This means that the degree of physiological stress is in direct correlation with training intensity, duration and volume.

Acute bouts of exercise (high-intensity, less than 60min) increases blood flow in body tissue as well as the circulation of leukocytes and natural killer cells[1] by 50-100% and 150-300%, respectively. After exercise, your body’s ability to destroy infected cells is improved a whole lot. These immune-protective agents circulate in the blood and end up in various cell tissues. Done on a regular basis, acute exercise enriches the blood with anti-inflammatory agents and strengthens your body’s defense mechanisms.


[1] Leukocytes and natural killer cells play a critical role in immune defense and metabolic health.

What about longer, more strenuous exercise sessions?

As mentioned above, the immune response is linked to the workload. Research has been able to associate strenuous exercise workloads[2] to immune dysfunction, inflammation and tissue damage. After strenuous exercise, the body is in high need of oxygen to repair damaged tissues and cells. This high oxygen demand decreases the capacity of immune cells to consume oxygen. Without the necessary oxygen, the cells don’t have enough energy to repair and grow. This effect is oftentimes referred to as the „open window“. The body is more susceptible to infections and illness because the immune system is compromised. Recovery strategies including proper nutrition (carbohydrate and fluid replacement) are crucial to minimize this effect.


[2] i.e. marathon competitions, ultra-distance running or similar extreme exercise loads. These kind of sessions trigger extremely high physiological, metabolic and psychological stress.

How do we apply this information to our training?

Short, high-intensity workouts have a direct effect on strengthening your immune defense and chronic exercise improves the body’s defense system by increasing anti-inflammatory agents. Long, grueling sessions evoke a high stress-response and can compromise the body’s defense system. Proper recovery strategies are crucial to minimize the damage. Our current programming (Home Wod) won’t expose your body to such highly stressful situations on a regular basis. With the spread of the virus, don’t drastically increase your exercise sessions, but try to exercise as you did before the pandemic (in frequency and duration).

Clinical benefits of the exercise-immune relationship

Does exercise and its resulting physiological adaptations of the immune system have added beneficial effects?

Physically fit individuals have lower resting levels of inflammation-related biomarkers compared to inactive or unfit populations. Chronic or systemic elevated levels of inflammation biomarkers are directly linked to atherosclerosis, cardiovascular disease, metabolic syndrome, insulin resistance, sarcopenia, depression and many other diseases. Research is still trying to investigate this interplay, but evidence supports that regular exercise and the anti-inflammatory effects over time are able to counter the disease process on a molecular level. Exercise promotes the recirculation of key immune cells and supports anti-inflammatory and antioxidant agents, which counter the development of chronic metabolic diseases.

What does this imply for your training?

Our training sessions not only improve your body’s immune response, but also enhances its anti-inflammatory functions and reduces the risk of chronic metabolic diseases. Showing up regularly is crucial! Make sure your close friends and family members exercise regularly. Let them join your Zoom Classes and grind through our Home Wods together.

Nutritional influences on the immune response to exercise

Recovery is crucial to support the immune system after exercise. Nutrition is a large part of it, and can directly influence your ability to recover. Refueling your body with healthy carbohydrates reduces the level of inflammation and increases biomarkers of the immune system. This is valid for long, endurance based sessions lasting longer than 90 minutes.

Polyphenols also play an important role in counter-acting the physiological stress from exercise. They support the body’s anti-inflammatory, antiviral, antioxidative and immune cell signaling functions. Where do we find these micronutrients? Fruits such as berries, apples, plums, bananas as well as vegetables like red onions, spinach, chicory or beans and nuts are rich in polyphenols.

How do I incorporate this into my daily life?

In order to keep your immune system as functional as possible, make sure you refuel after your training sessions so that you metabolic recovery is supported in the best way possible. Eat nutrient rich food such as healthy carbs and antioxidants (found in plant-based foods) and stay hydrated. Make sure your body is equipped in the best way possible to fight any infections or virus.  

Literature on this topic for further reading:

Nieman, D. & Wentz, L. (2019). The compelling link between physical activity and the body’s defense system. Journal of Sport and Health Science.

Nieman, D. (1994). Exercise, upper respiratory tract infection, and the immune system. Official Journal of the American College of Sports Medicine.

Pedersen, B. & Hoffman-Goetz, L. (2000). Exercise and the Immune System: Regulation, Integration, and Adaptation. Physiological Reviews.

Kakanis, MW. et al. (2010). The open window of susceptibility to infection after acute exercise in male athletes. Exercise Immunology Review.

Chevalier, Blanchard & Dusfour (2020). Covid-19: List of training advices & precautions by the co-president of the club of sport cardiologists (France) & associated sports medicine doctors.