The COVID-19 pandemic has confined the population with orders requiring social distancing, restrictions on public gatherings, the closure of recreational facilities and a cessation of sporting activities. It is, therefore, not surprising that the quantity of physical activity in which one can engage would have decreased. It is, however, especially important to stay active at this time, by whatever means necessary.

Dr Sharmella Roopchand-Martin, in an article published in this column in the Sunday Guardian, provided suggestions for keeping fit in a constrained environment.

This critical activity may help in the fight against COVID-19. There is currently no cure for the disease and recovery is highly dependent on the response of the immune system. To slow down the replication of the virus and reduce recovery time, a healthy immune system is required. This is where exercise helps. Exercise can aid in boosting the immune system and as a result decrease the risk of complications from the COVID-19 virus.

What is the immune system?

When we refer to the human immune system, we refer to the biological complex that identifies and destroys foreign materials such as viruses and bacteria. The immune system tags foreign materials, using antibody molecules, making them a target for removal by lymphocytes, phagocytes and the complement system. The typical healthy human has millions of antibodies capable of identifying specific viruses and bacteria. It is because of this vast library of antibodies that our bodies can quickly identify and destroy harmful pathogens, thereby preventing or limiting the severity of life-threatening illnesses. The immune system also has a ‘memory’, created during an immune response. As a result, the immune system can quickly remember and destroy pathogens that had entered the body before. This is the basic principle of a vaccination – we introduce a weakened or inactive form of the virus so the body can prepare a response to the virus to be filed away, ready for use in the event of a future infection.

How does exercise help?

Decades of studies have confirmed that exercise induces considerable physiological changes in the immune system. During exercise, neutrophil, monocyte and lymphocyte (cells of the immune system) concentrations are increased.

After exercise, the neutrophil and monocyte concentrations remain elevated while lymphocyte concentrations are lowered.

The total lymphocytic function in the blood can be considered suppressed after exercise. Research has confirmed that an impairment or reduction of cell-mediated immunity after intense exercise of a long duration. Exercise may lower the expression of adhesion molecules which then increase during recovery (Kurokawa et al., 1995; Pendersen & Hoffman-Goetz, 2000)

How much exercise do I need?

Exercise done in moderation generally boosts the immune system but extreme exercise will reduce immune function. If the duration of the exercise is too long and too intense, then the concentration of lymphocytes may decrease. The enhancement or reduction of immune responses depends also on the duration of rest between each exercise session.

For example, researchers found that when volunteers exercised daily at 65% maximum oxygen capacity for one hour, there was an increase in natural killer cells. In another study, volunteers were subjected to intense cycling for two 13-minute sessions which were separated by one hour of rest and that resulted in a significant increase in leukocytes, neutrophils and lymphocytes. This contrasts with the decrease in lymphocytes noted after cycling was done at 75% maximal oxygen capacity for one hour, then 45 minutes and finally 30 minutes, separated by two hours of rest, a clear demonstration that moderation is necessary.

Repetitive exercise conveys the most significant benefits to the immune system. The parameters for the immune system are increased above the initial point (before the beginning of an exercise programme) even during recovery periods. Athletes who have been training for years tend to have higher natural killer cells when compared to untrained individuals.

If untrained, walking activity for a few months has proven effective in increasing natural killer cell activity even in obese individuals.

Final thoughts Generally, moderate exercise training in a population before a viral infection will reduce the rate of disease in the population and lower the risk of death. Exercise during the incubation period of an infection, however, provides no benefit to an infected person and may even decrease the immune response.

That means if exposed to someone infected with COVID-19, initiating an exercise programme at that point does not provide an advantage in fighting the disease and may worsen symptoms. If experiencing symptoms, consult a physician before starting an exercise programme.

While we await a vaccine for the disease, or for community immunity, it is important to remain active to decrease the likelihood of any major complications because of the infection.

Dr Aldeam Facey can be reached at Aldeam.Facey02@uwimona. edu.jm