Exercising regularly has been proven to be beneficial and is one of the leading determinants of health for being associated with reduced risk for all-cause and disease- specific mortality while inadequate in exercise is responsible for 6-10% of the global burden of chronic diseases and 9% premature deaths. A few studies have reported that physical activity has protective effect against respiratory infection. With the stated benefits, it leads us to think of the possibilities that exercise may have some protective effect against COVID-19.
Before getting straight into the answer, we have to first understand the reaction and outcome of different bodyweight status against COVID-19 to have a better perspective on exercise and COVID-19. According to a study conducted in Third People’s Hospital of Shen Zhen, China, it was reported that obese patients tend to have symptoms of cough and fever as compared to patients who were not obese. Comparing to normal weight patients, the odds of overweight patients developing severe COVID-19 were 1.84 times while obese patients had odds of 3.40 times of developing severe COVID-19. Another meta-analysis evaluated 17 research reports on the risk of mortality on patients diagnosed with COVID-19 stated that Obesity was strongly associated with an increased risk of mortality – Class III obesity with relative risk of 1.92 followed by Class II obesity at 1.56, and Class I obesity at 1.27. It is obvious that these results show strong association with different bodyweight status. The higher the bodyweight status, the higher the risk of developing severe consequences from COVID-19.
According to WHO, bodyweight status is classified into six groups.
WHO BMI Classification (kg/m2)
Malaysia BMI Classification (kg/m2)
18.5 – 24.9
18.5 – 22.9
25 – 29.9
23.0 – 27.4
30 – 34.9
Obese Class I
27.5 – 32.4
35 – 39.9
Obese Class II
32.5 – 37.4
Obese Class III
The reason why obesity is highly related to the severity of COVID-19 was due to the immune dysfunction in human body. It is known that obesity is highly correlated to type 2 diabetes (T2DM) and metabolic syndrome. Obesity also puts the human body in a chronic (long term) inflammatory status. One of the adaptive mechanisms in T2DM is the increased expression of an enzyme called angiotensin-converting enzyme 2 (ACE2). These enzymes are highly exhibited in fat tissues.
Many will ask, why do we need to know about ACE2? The ACE2 is the putative receptor for the entry of COVID-19 with high affinity. The more obese the bodyweight status is, it means that there are more fat cells to express a greater level of ACE2 as compared to leaner bodyweight status. Hence, this explains why the results show that the severity of COVID-19 is strongly associated with the severity of obesity.
How Does Exercise Play A Role In Fighting COVID-19
Several research have shown that high intensity exercise has positive effect on inflammatory factors in obesity conditions. However, it was also reported that long intensive exercise can lead to higher level of inflammatory mediators and might elevate risk of injury and chronic inflammation, whereas moderate to vigorous exercise with appropriate rest time is most beneficial.
The ‘open window’ theory describes that a window period ranging about 12 to 48 hours after high intensity exercise is the period where fatigue, overtraining, and recovery happens. Being able to calibrate and train at appropriate level of overtrain and fatigue can be beneficial. However, it is important to understand the effect of overtraining and fatigue and why we experience that. One possible reason why we experience fatigue is because of the suppression of immune system after high intensity exercise due to the regulation of immune system to prevent overreacting towards increased level of oxidative stress from intense exercises. With the suppressed immune system, it prevents our body to react immediately to trigger recovery process which is why we feel fatigue right after a high intensity workout. This ‘open window’ may be a good opportunity for an increased susceptibility to upper respiratory illness.
In addition, there was evidence obtained indicated that intensive aerobic physical exercise can acutely increases concentration of ACE2 in muscles but resulted in lower circulating ACE2 levels in blood. It is unclear that whether the increased ACE2 expression also occurs in the lungs, heart, or other tissues that are more relevant to susceptibility towards COVID-19.
We have discussed about how COVID-19 gain access to the human body via ACE2 and the more fat tissues we have, the greater the amount of ACE2 is being expressed. The results obtained from researches have also proved that the severity of COVID-19 is strongly associated to the severity of obesity status of an individual. With appropriate exercise volume, we are able to obtain beneficial effects such as improved immune system and improved regulation of metabolic activities in our body which leads to improved weight management and reduction in fat tissues. However, it is not encouraged to conduct prolonged high intensity exercises due to its effect on suppression of immune system explained by the ‘open window’ theory as we do not want to increase our susceptibility towards COVID-19.
Therefore, it is recommended to conduct frequent moderate intensity exercises. The WHO recommends that healthy individuals should conduct AT LEAST a total of 150 minutes of moderate intensity exercises per week for adults and 300 minutes per week for children and adolescents. Among the recommended duration for exercising, it is also recommended to include a mixture of strength and resistance training and aerobic exercises, also known as exercises that are beneficial for cardiovascular health. Moderate intensity exercises should feel like a perceived effort of 7 to 8 out of 10, meaning we should feel like the exercise should be somewhat challenging but it is comfortable to sustain where there is some gap away from reaching failure. High intensity exercises generally have a perceived effort of 8 to 10 out of 10 where the limit is always challenged, the training is set to reach failure. If you are unsure of exercise intensity, it is recommended to consult an exercise professional or qualified personal trainer for guidance.