Everyone is required to wear a mask when doing activities outside to prevent SARS-CoV-2 transmission. Meanwhile, exercise is also a component that is often recommended to increase the immune system in preventing COVID-19. 

Impacts of Wearing a Mask During Exercise
Wearing a Mask During Exercise

Gupta et al. reported that wearing a mask can create a "therapeutic" environment as well as a barrier against viral entry into the nasal and oropharyngeal. However, wearing a mask during exercise is not completely safe; it can even result in unexpected events in vulnerable individuals, such as sudden cardiac arrest. This raises questions about the safety aspect of wearing masks during exercise in the era of the COVID-19 pandemic. Then what are the impacts of wearing a mask during exercise?

Physiological Impacts of  Wearing a Mask During Exercise

Basically, masks are permeable so that they can filter out droplets containing bacteria and viruses. Wearing a mask while exercising has been researched to cause hypoxia and hypercapnia due to breathing air that has been previously exhaled.

Physiological changes (hypoxia and hypercapnia) have been reported in wearing surgical masks, N95 masks, and full-face respirator masks during exercise. Studies reported these physiological changes while wearing surgical masks and strict N95 masks. In contrast, studies examining the wearing cloth masks that are often used daily are not yet available.

Hypoxia and hypercapnia can affect the physiology of the human body on various sides, from cell metabolism, immune response, cardiorespiratory stress to the potential for cardiac arrhythmias.

a. Changes in Cell Metabolism

The metabolism of all cells, including muscle cells, is highly dependent on the supply of oxygen (O2) and the exchange of carbon dioxide (CO2) gas between the respiratory tract and the atmosphere. [10] In contrast to resting conditions or light physical activity, anaerobic metabolism dominates during moderate to heavy intensity activities. Finally, lactic acid is formed, which requires a large supply of oxygen to break it down.

The closed-circuit between inspired and expired air due to wearing a mask during exercise will cause the expiratory air to be re-inhaled, thereby increasing the concentration of CO2, worsening anaerobic metabolism, and ultimately increasing the intensity of acidity in the cellular environment (excess lactic acid).

This condition resembles a physiological effect in patients with chronic obstructive pulmonary disease (COPD), characterized by discomfort, fatigue, dizziness, headache, shortness of breath, muscle weakness, and decreased consciousness.

b. Immune Response Changes

Exercise using a mask will induce an acidic environment through anaerobic metabolism. This can affect the mobility of the hypoxic natural killer cells to the target cells. When exercising wearing a mask, the humidity and air temperature in the upper airway are changing, which causes immotile cilia syndrome, thus increasing the individual's susceptibility to infection.

c. Increased Cardiorespiratory Stress

Wearing a mask while exercising can affect O2 and CO2. It can also increase heart rate (via sympathetic stimuli) and blood pressure exponentially, even at low-intensity physical activity. These physiological changes will increase the pressure on the aorta and left ventricle, which triggers cardiac overload and coronary demand. In general, adjusting the respiratory load can still compensate for the increased cardiorespiratory stress.

However, wearing a mask during exercise will further worsen respiratory load, increasing the load on the respiratory muscles and pulmonary artery pressure, exacerbating cardiac overload and an imbalance between oxygen supply and demand. The changes above can be compensated for in healthy individuals, but not in individuals with chronic disease.

d. Potential Cardiac Arrhythmias

In addition to the dangers of increased cardiac overload and myocardial oxygen demand, hypoxia, and hypercapnia due to rebreathing water when wearing a mask during exercise can trigger heart rhythm disturbances or arrhythmias.

Hypoxia arising from adrenergic stimulation will increase the phosphorylation of L-type calcium channels, resulting in the addition of Ca2 + influx to cardiac myocytes during the plateau phase. This can lead to an extended duration of action potential and the induction of early afterdepolarization (EAD).

Cyclic adenosine monophosphate (AMP) accumulation occurs during hypoxia or ischemia, which triggers delayed afterdepolarization (DAD). Hypoxic conditions alone were sufficient to induce ectopic foci via micro-reentry in a human left ventricular model. Hypoxic episodes can easily lead to lethal ventricular tachyarrhythmias in individuals with myocardial fibrosis or long QT syndrome.

When hypoxia is acute, the action potential duration can be shortened, leading to reduced ventricular effective refractory (ERP). If hypoxia duration is longer, the uncoupling of endothelial nitric oxide synthase occurs and can increase reactive oxygen species (ROS). This will cause oxidative stress associated with the initiation or worsening of ventricular arrhythmias through abnormal expression/activity of the cardiac ion channels of sodium and calcium.

Hypoxia can also reduce the function of the voltage-gated sodium channel Nav1.5 leading to reduced INa and a change in gap junction function that mediates electrical coupling between adjacent cardiac myocytes. Besides, hypercapnia-induced acidosis can lead to persistent membrane depolarization and a reduction in the cardiac action potential phase 0 slope. The combination of these will trigger arrhythmogenesis.

e. Changes in Kidney Functions

Voulgaris A et al. reported that hypoxic hypercapnia (in the case of obstructive sleep apnea) could reduce renal blood flow and glomerular filtration rate, thereby increasing the risk of decreased kidney function. This result can be extrapolated to a similar condition due to wearing a mask during sports. Another change in kidney function is aciduria, which can damage the renal tubules, especially in individuals with chronic kidney disease.

f. Changes in Brain Metabolism

Acute hypercapnia can have many effects on brain tissue. Hypercapnia can increase intracranial pressure and reduce cerebral perfusion that triggers cerebral ischemia. Also, hypercapnia can reduce amino acid excitability and minimize cerebral metabolism.

Stevens D et al. conducted a study on obstructive sleep dyspnea. This study provided clear evidence that Hypoxemic hypercapnia affects postural stability, proprioceptive, changes in gait velocity, and falls. Evidence of this can be extrapolated to older people with respiratory tract disorders who exercise/wear masks.

Clinical Evidence regarding Wearing a Mask while Exercising

In a prospective cross-over study, Fikenzer et al. Quantified the impact of mask-wearing on lung function. Researchers observed lung function changes in 12 healthy men divided into a group without a mask, a group with a surgical mask, and a group with a respirator (N95 mask).

They found that the two groups who wore masks had worse results at maximum power output (Pmax) and maximum oxygen uptake (VO2max / kg). These two parameters are generally associated with exercises. Respirator groups showed the worst impact. Ventilation was also significantly reduced in both groups of mask users, especially the N95 masks. Wearing a mask could reduce VO2max by 13% and ventilation by 23%. 

This study concluded that surgical masks and N95 masks harm healthy adult individuals' cardiopulmonary capacity, significantly impaired during exercise. However, more extensive studies are needed in more varied age groups.

Roberge et al. performed a controlled clinical trial on ten health workers who performed 1-hour walking sessions on a treadmill at a speed of 2.7 km/h and 4 km/h using N95 masks with or without an exhalation valve.

In this study results, there were no significant differences between the N95 mask group and the control group on physiological variables, exertion scores, and comfort scores. There were also no significant differences in moisture retention between the N95 mask groups with or without the exhalation valve. However, two subjects showed a peak P (CO2) of ≥50 mmHg.

There was an increase in carbon dioxide dead-space and decreased oxygen levels that do not meet the Occupational Safety and Health Administration's appropriate ambient workplace standards.

WHO's Recommendations regarding Wearing a Mask during Exercises

Currently, the World Health Organization (WHO) does not recommend wearing masks during exercise. Wearing a mask is considered to reduce the ability to breathe comfortably. In addition, sweat due to exercise can cause the mask to get wet faster, causing difficulty breathing and helping microorganisms' grow on the mask. The recommended effort to prevent COVID-19 during exercise is to maintain a minimum distance of 1 meter from other people.

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