Exploring the Relationship Between Exercise, the Immune System, & COVID-19

Sport and exercise science has always been the bedrock of everything we do at Wattbike. With the current COVID-19 pandemic shining a light on the current unhealthy state of the world, we decided it was time to take a deep dive into the scientific archives to explore the sometimes complicated relationship between exercise, the immune system, and medical conditions.

Did you know that physical inactivity is today the fourth leading risk factor for death globally? Inactivity also increases the risk of many health conditions, including: coronary heart disease, high blood pressure, stroke, metabolic syndrome, type 2 diabetes, breast and colon cancer, and depression. The World Health Organisation (WHO) adds that the failure to sustain adequate levels of physical activity shortens the lifespan of a person by 3-5 years. 

Lack of exercise is even argued to be as deadly as smoking, and it is estimated that low physical activity levels could be responsible for around 1 in 10 cases of heart disease (10.5%) and just under 1 in 5 cases (18.7%) of colon cancer in the UK alone. A study carried out by the University of Cambridge states that a lack of exercise is responsible for twice as many deaths as obesity,

In the current climate, being unfit and unhealthy has highlighted the increased risks that obese, overweight, and unfit people are facing in terms of virus protection. Obese or overweight individuals are almost twice as likely to die from COVID-19 and other types of influenza. Studies also show that patients who have type 2 diabetes or other metabolic syndromes are ten times more at risk of dying from COVID-19.

Have we got your attention yet?


The baseline general health in many Western populations has been in a shocking state for decades. Increased globalisation and improved technology has created a sedentary lifestyle, which paired with poor eating habits and consumerism, has led to more than 60% of adults in the UK and USA to be overweight or obese. Excess body fat disrupts the immune system and induces chronic inflammation, and has been linked to the cytokine storm that is responsible for Acute Respiratory Distress Syndrome often seen in influenza and other respiratory viruses.

This relationship manifested itself during the H1N1 influenza pandemic in 2009, where 61% of patients admitted to a hospital in California that died from the H1N1 Influenza were obese. It has also been found that obese adults tend to spread the Influenza A virus for 42% longer than non-obese individuals - which would suggest that obesity plays an additional role in virus transmission as well. This link becomes even more apparent when looking at the current pandemic where, out of the first 2204 patients to be admitted to NHS Intensive Care Units across the UK with COVID-19, 72.7% of them were overweight or obese.

So, it’s becoming quite clear that there seems to be a significant link between obesity and a weakened immune system. However, it is also important to note that metabolic diseases or dysfunctions associated with obesity, such as high blood pressure, high cholesterol levels, etc., can also affect people of a normal weight and BMI, so anyone can be metabolically unhealthy. Individuals who are of normal weight but have poor metabolic health have a three-fold risk of all-cause mortality and cardiovascular events compared to those of normal weight and metabolic health, and also a ten-fold risk of dying from COVID-19. So there is no such thing as a healthy weight, only a healthy person.



According to research collated by the NHS, exercise can reduce the risk of major illnesses by up to 50%, and lower your risk of early death by 30%. Physical activity also boosts your self-esteem, mood, sleep quality and energy, as well as reducing your risk of stress, depression, dementia and Alzheimer’s disease. Other research suggests that regular exercise can even reduce the risk of Acute Respiratory Distress Syndrome (ARDS), which affects up to 17% of all patients with COVID-19.

In other research undertaken by leading exercise researcher Dr. Zhen Yan, of the University of Virginia School of Medicine, it’s suggested that the antioxidant known as Extracellular Superoxide Dismutase (EcSOD) plays an important part in hunting down harmful free radicals in our bodies, protecting our tissues and helping prevent disease. What’s interesting here is that the production of EcSOD is enhanced even by a single session of cardiovascular exercise, and in contrast low levels of this antioxidant can be seen in patients with acute lung disease, heart disease and kidney failure. Dr Richard Simpson, an associate professor in the Department of Nutritional Sciences, Pediatrics and Immunobiology at the University of Arizona, agrees with Dr. Zhen Yan, and states that with each bout of exercise, and particularly whole-body cardiorespiratory exercise, millions of immune cells are immediately mobilised. Especially those types of cells that are capable of recognising and killing virus-infected cells.

The link between exercise and an improved immune system is further discussed by Professor Sanjay Sharma, who specializes in inherited cardiac disease, who states that there is lots of evidence showing that moderate exercise performed for 20-30 minutes 3-4 times per week strengthens the immune system and reduces the risk of viral infections. He also states that numerous scientific studies have shown that good levels of physical activity prior to developing a potentially serious infection such as the flu, prevents people dying from it. This can actually be seen during the 1998 Hong Kong flu, as people who continued to remain active were more likely to survive compared to people who did not exercise.

So how can we quantify, measure, track, and improve physical health, so we can better protect ourselves against disease, and ultimately live longer? It’s a big ask. But Wattbike has the answer: Cardiorespiratory fitness (CRF).



Scientific research on the benefits of exercise, and how our bodies react to it, have identified CRF as an accurate way to measure someone’s physical health. In simple terms, CRF tells you how effective your body is at transporting oxygen to the places where it’s needed the most. CRF quantifies the functional capacity of an individual and is dependent on the current state of a linked chain of processes in your body; your respiratory, cardiovascular and skeletal muscle systems. CRF is therefore health related - where low CRF is associated with high risks of premature death from all causes, and a high CRF is associated with a reduction in premature death from all causes.

CRF is a measure of VO2max, which is the amount of milliliters of oxygen per kilogram per minute that it takes for your body to function. Your VO2 max score is therefore related to the functional capacity of your heart. Research shows that by improving your CRF score by 8 points, you will improve your active life expectancy by 1 year. Talk about a lot of bang for your buck. 

Now, CRF has actually been around for a long time, but it has not really been understood or appreciated properly in the medical and health and fitness community. This slowly started changing in 1996 with a paper published by Blair et.al, where they investigated the influences of cardiorespiratory fitness and other precursors in cardiovascular disease in men and women, and showed that fitter individuals were less at risk of cardiovascular disease and early mortality compared to unfit individuals.

The past two decades have seen an exponential growth in the number of studies assessing the association between measures of CRF, mortality, and other health outcomes. In a growing number of studies, CRF has been demonstrated as a more powerful predictor of mortality risk than traditional factors such as hypertension, smoking, obesity, and type 2 diabetes. Mounting evidence has now firmly established that low levels of CRF are associated with a high risk of cardiovascular disease, all-cause mortality, and mortality rates attributable to various cancers. 

So although CRF is starting to become widely recognised as an important marker of health, it is currently the only major metric not routinely assessed in clinical practice. 


So, based on all the reasons listed above, testing is absolutely crucial for a health assessment, but also for the implementation of an exercise or training plan to help address an individual’s health and fitness level. Initial fitness testing provides a starting point and delivers basic information needed to devise an appropriate and successful training plan. Progress testing during a training plan allows for an on-going assessment of fitness, and enables changes to be made to the plan if necessary. Testing at the end of a training plan allows for full analysis of the progress made and also provides a contribution to future planning. 

The CRF test also functions like a risk assessment, and can be used as a preventative measure to determine if an individual is at particular risk of developing cardiorespiratory or metabolic disorders based on their fitness level.  

Enter; the Wattbike Health Assessment.


We created an easy-to-do, accessible, and accurate test that would give each individual their CRF score and predicted VO2max to show individuals their current health and fitness benchmarks; and assign each individual a personalised, effective training plan and individual training zones that will increase their CRF score at the end of the recommended training block. 

The Wattbike Health Assessment was launched in 2017 via the Wattbike Hub app. The Health Assessment is a free to access submax ramp test that quantifies each individual’s CRF and provides them with personalised data and training zones to enable them to improve their score; so anyone can improve their health and extend their active life. 

The accuracy and reliability of our Health Assessment was picked up by health giant Bupa, and in late 2019, our official partnership was announced. Today, anyone can sign up to undertake the Health Assessment at numerous Bupa clinics around the UK to examine and analyse every part of their health, or you could undertake the Health Assessment at home to gain insight into your cardiorespiratory fitness. 



All Wattbike products are independently verified to deliver unrivalled accuracy, so they provide you with great confidence to test, workout, and improve technique precisely. The Wattbike’s unique Pedalling Technique Analysis provides immediate gains in fitness by highlighting pedalling technique issues, and all Wattbike products provide the correct workout settings in relation to individual power and heart rate training zones, which are all established from the CRF test. .

The Wattbike is also unmatched in its ability to measure progress, re-test, and reset exercise and training zones as fitness improves, and each workout can be recorded, analysed and shared. Wattbike is also the very first company to launch a CRF Health Assessment in the UK, with personalised, structured, and scientific training plans to improve CRF over a 12-week period. These training plans offer individuals structure, consistency, and motivation, for optimum fitness improvement.

More than 100,000 Health Assessments have already been undertaken - so what are you waiting for?




Andersen, C. J., Murphy, K. E., & Fernandez, M. L. (2016). Impact of obesity and metabolic syndrome on immunity. Advances in Nutrition, 7(1), 66-75.

Ross, R., Blair, S. N., Arena, R., Church, T. S., Després, J. P., Franklin, B. A., ... & Myers, J. (2016). Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign: a scientific statement from the American Heart Association. Circulation, 134(24), e653-e699.

Araújo, J., Cai, J., & Stevens, J. (2019). Prevalence of Optimal Metabolic Health in American Adults: National Health and Nutrition Examination Survey 2009–2016. Metabolic Syndrome and Related Disorders, 17(1), 46–52. doi: 10.1089/met.2018.0105

Bornstein, S. R., Dalan, R., Hopkins, D., Mingrone, G., & Boehm, B. O. (2020). Endocrine and metabolic link to coronavirus infection. Nature Reviews Endocrinology, 16(6), 297–298. doi: 10.1038/s41574-020-0353-9

Clausen, J. S., Marott, J. L., Holtermann, A., Gyntelberg, F., & Jensen, M. T. (2018). Midlife Cardiorespiratory Fitness and the Long-Term Risk of Mortality. Journal of the American College of Cardiology, 72(9), 987–995. doi: 10.1016/j.jacc.2018.06.045

Huber, L., & Shilton, T. (2017, March 30). The 4th leading risk factor for death worldwide: physical inactivity is an urgent public health priority. Retrieved from https://ncdalliance.org/news-events/blog/the-4th-leading-cause-of-death-worldwide-physical-inactivity-is-an-urgent-public-health-priority

Lee, D.-C., Artero, E. G., Sui, X., & Blair, S. N. (2010). Review: Mortality trends in the general population: the importance of cardiorespiratory fitness. Journal of Psychopharmacology, 24(4_suppl), 27–35. doi: 10.1177/1359786810382057

Lee, I.-M., Shiroma, E. J., Lobelo, F., Puska, P., Blair, S. N., & Katzmarzyk, P. T. (2012). Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. The Lancet, 380(9838), 219–229. doi: 10.1016/s0140-6736(12)61031-9

Malhotra, A. (2020, April 16). Covid 19 and the elephant in the room. Retrieved from https://www.europeanscientist.com/en/article-of-the-week/covid-19-and-the-elephant-in-the-room/

NHS. (2012, July 18). Lack of exercise as 'deadly' as smoking. Retrieved from https://www.nhs.uk/news/lifestyle-and-exercise/lack-of-exercise-as-deadly-as-smoking/

NHS. (2018, June 11). Benefits of exercise. Retrieved from https://www.nhs.uk/live-well/exercise/exercise-health-benefits/

Runner's World. (2020, April 17). Why exercise should be part of your fight against coronavirus. Retrieved from https://www.runnersworld.com/uk/news/a32186719/coronavirus-protect-deadly-covid-19-complication/

Sharma, S. (2020, April 8). COVID-19: Specific advice regarding exercise by Professor Sanjay Sharma. Retrieved from https://www.c-r-y.org.uk/covid-19-specific-advice-regarding-exercise-by-professor-sanjay-sharma/

Simpson, R. j. (2020, March 30). Exercise, Immunity and the COVID-19 Pandemic. Retrieved from https://www.acsm.org/blog-detail/acsm-blog/2020/03/30/exercise-immunity-covid-19-pandemic

University of Cambridge. (2015, January 14). Lack of exercise responsible for twice as many early deaths as obesity. Retrieved from https://www.cam.ac.uk/research/news/lack-of-exercise-responsible-for-twice-as-many-deaths-as-obesity

World Health Organisation. (2020). Physical activity. Retrieved from https://www.who.int/health-topics/physical-activity