[Last Review: Mar. 22, 2020]
General Consensus | Home exercise is an important factor in preserving function during a period of acute pulmonary illness. At the same time, home exercise can be unsafe for some people depending on the severity of Novel Coronavirus (COVID-19) symptoms or cardiovascular risk. Family or friends should initially observe all physical activity from a safe distance (e.g. greater than 2 meters distance or via videoconferencing) and it should be possible to contact emergency services from the exercise setting. Low-intensity physical activity is recommended as an initial starting point for home exercise among persons managing symptoms of COVID-19. People should stop exercising immediately and call for medical attention if they experience the following symptoms:
- Rapid loss of breath/extreme breathlessness
- Cannot speak after a short rest period
- Feeling dizzy or faint
- Chest pain or symptoms of a heart attack
- Severe pain
- Feeling ‘off’
Does strenuous exercise lower viral immunity, increasing the risk that COVID-19 will progress?
In the early 1990’s, it was commonly believed that vigorous or endurance exercise created a brief period, or “open window” period, for contracting an upper respiratory tract infection (URTI). This continues to be discussed within the literature, primarily because it is known that cortisol (a stress hormone with immuno-suppressive functions) temporarily spikes in response to vigorous or endurance exercise. Key studies informing this hypothesis include epidemiological studies of distance runners. Compared to matched controls, it was found that runners who participated in a distance running event reported twice the amount of URTI symptoms in the two week period following the race. This finding was also confirmed across multiple large-scale observational studies of marathon runners in the late 1980’s. These findings suggested the existence of a “J-shaped” curve, where people who over-train experienced more frequent and severe symptoms of a URTI. The mechanism behind these changes are that the body is known to temporarily modulate non-specific immune responses in order to reduce the inflammatory response immediately following exercise.
However, it has been suggested more recently that other factors associated with strenuous exercise may actually have a greater influence on the development of URTI symptoms. For example, specific nutrient deficits — such as protein deficiency — can temporarily impair immune function. Other influencing factors include: fatigue, psychological stress (anxiety), exposures to pathogens and exposures to large crowds. Therefore, for the common cold, vigorous exercise does not independently increase the intensity of URTI symptoms when related factors are controlled. It remains unknown whether vigorous or endurance exercise would cause a worsening of viral symptoms for persons living with COVID-19.
Does exercise enhance the body’s ability to identify and kill cells infected with the SARS-CoV-2 virus?
Although there is limited information available on how SARS-CoV-2 — the infectious agent that causes COVID-19 — interacts with the host immune system, emerging data suggests that the virus activates a cascade of non-specific (innate) immune responses which contributes extensively to the development of inflammation and flu-like symptoms. This inflammatory response eventually leads to atypical pneumonia, and appears to also produce an acute decline in respiratory function. In some people, this progresses further to acute respiratory distress syndrome, or ARDS.
Emerging evidence suggests that SARS-CoV-2 will progress to a symptomatic COVID-19 infection when a person exhausts their supply of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, which are necessary for the effective control of new viral infections in the body. While individuals continue to have an inflammatory response, the virus itself appears to exhaust the antiviral component of both non-specific and specific immune responses.
Interestingly, a single bout of vigorous exercise is widely known to produce a profound rise in circulating lymphocytes. The rise in lymphocytes in peripheral blood is also one of most commonly reproduced findings in human exercise physiology. There is also known to be a dramatic but transient rise in the functional capacity of lymphocytes after vigorous exercise. Similarly, strong evidence supports the idea that exercise induces a state of “immune surveillance” for viral pathogens. So, while exercise does dampen the non-specific component of immunity, it does not appear to cause immune suppression within the acquired (specific) branch of immunity which is important to viral protection.
Therefore, vigorous exercise is likely to enhance a person’s immune system capacity in the short term by augmenting specific immune responses. This temporarily enhances the ability of the body to detect and destroy SARS-CoV-2 infected cells. Exercise also appears to reduce non-specific immune responses which, in turn, reduce the negative impacts from inflammation in the body. These positive impacts are likely counterbalanced by several functional limitations that the disease creates, making it difficult to exercise safely.
What are the risks of exercising with COVID-19 symptoms?
The main risk of exercise among people with respiratory illness is related to the added stress it can place on the body. Many people with flu-like symptoms report significant muscle aches, fatigue and exertion in response to simple movements like walking on level. In the case of COVID-19, there is the additional pressure of breathlessness among many people affected by the disease. These limitations are important, as a person can easily overload their cardiac or respiratory capacity during exercise. The main risk, therefore, is a serious cardiac or respiratory concern during exercise.
Extensive research supports the idea that early mobilization and therapeutic exercise — even while ventilated — can positively impact the course of Acute Respiratory Distress Syndrome (ARDS) in ICU. The positive effect of exercise on ARDS outcomes in ICU settings appears to be mediated by:
- Reversal of the process of Acute Lung Injury (ALI) induced muscle wasting
- Reduced systemic inflammation, by modulation of non-specific host defenses (lower neutrophilic influx into alveolar space, reduced GCSF and reduced cytokine expression)
- Increase in diaphragmatic strength, reducing the physical work of breathing at rest
- Improved blood flow (perfusion) to key structures within the lungs, improving gas exchange
Therefore, it is wise for a person exercising at home to initially have supervision (at a distance) by a family or friend. It is also important to have telephone access to emergency medical responders, should exercise induce a major event. To prevent these risks, exercise should initially be well-tolerated and not induce any significant distress. A review of evidence for ICU patients with ARDS found that low to moderate exercise intensity (5-25 min twice daily) seemed to be protective and induce significantly positive outcomes in a controlled setting.
Do home exercise programs exist for people with mild COVID-19 symptoms?
Yes. Low-intensity home exercise programs exist, and are especially safe when supervised (at a safe distance) by a care provider, family member or friend. The Canadian Centre for Activity and Aging has endorsed the Home Support Exercise Program, which is commonly used as a safe exercise program among older-adults with respiratory conditions in home care settings. Some exercises may need to be adapted to ensure safety among people living with COVID-19 symptoms.
Bermon S, Castell LM, Calder PC, Bishop NC, Blomstrand E, Mooren FC, et al. Consensus statement immunonutrition and exercise. Exerc Immunol Rev (2017) 23:8–50.
Bredin SD, Gledhill N, Jamnik VK, Warburton DE. PAR-Q+ and ePARmed-X+. Can Fam Phys (2013) 59 (3) 273-277.
Campbell JP, Turner JE. Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan. Front Immunol. 2018;9:648. Published 2018 Apr 16. doi:10.3389/fimmu.2018.00648
Nieman DC, Johanssen LM, Lee JW, Arabatzis K. Infectious episodes in runners before and after the Los Angeles Marathon. J Sports Med Phys Fitness (1990) 30(3):316–28
Nieman DC. Exercise, infection, and immunity. Int J Sports Med (1994) 15(Suppl 3):S131–41. doi:10.1055/s-2007-1021128
Peters EM, Bateman ED. Ultramarathon running and upper respiratory tract infections. An epidemiological survey. S Afr Med J (1983) 64(15):582–4
Prompetchara E, Ketloy C, Palaga T. Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic. Asian Pac J Allergy Immunol (2020) [in print] doi:10.12932/AP-200220-0772
Rovina N, Koutsoukou A, Koulouris N. Therapeutic exercise in improving acute lung injury: a long distance to be covered. Ann Transl Med. 2015;3(18):273. doi:10.3978/j.issn.2305-5839.2015.09.13
Spence L, Brown WJ, Pyne DB, Nissen MD, Sloots TP, McCormack JG, et al. Incidence, etiology, and symptomatology of upper respiratory illness in elite athletes. Med Sci Sports Exerc (2007) 39(4):577–86. doi:10.1249/mss.0b013e31802e851a
Zheng, M., Gao, Y., Wang, G. et al. Functional exhaustion of antiviral lymphocytes in COVID-19 patients. Cell Mol Immunol (2020). [in print] doi:10.1038/s41423-020-0402-2