Since the first cases of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were reported in Wuhan, China, at the end of 2019, this infection has spread around the globe, becoming a pandemic. The use of face masks and respirators is an important public health measure to reduce or prevent transmission of SARS-CoV-2 [1, 2]. Because of people’s arduous efforts in coordinating control of the epidemic, the situation in China and other regions is improving. Medium-risk regions are promoting resumption of production, work, and schools in an orderly manner. When students returned to school, unfortunately, some tragic events have been reported in China. Over the past few months, several students without documented cardiac issues experienced sudden death when they were running in physical training classes with surgical masks or N95 respirators. Although there is no conclusive evidence such as an autopsy result that demonstrates face masks and respirators are the cause of such adverse outcomes, it is potentially dangerous to run or exercise outdoors with a face mask or a respirator.
There are several potentially harmful side effects of wearing face masks or respirators when running and exercising outdoors. Face masks and respirators lead to less air being inhaled and subsequent breathlessness. Some studies show increases of 120% in inspiratory and expiratory flow resistances when N95 respirators are used, and the air exchange volume was reduced by an average of more than 30% . The mean carbon dioxide levels rise and the mean oxygen levels drop in the breathing space inside face masks and respirators . Furthermore, the exhaled carbon dioxide can accumulate, and can subsequently be inhaled during each respiratory cycle. This increases the frequency and depth of breathing, leading to oxygen deficiency, hypoventilation, and hypoxemia. This process contributes to glucose breakdown and a dangerous rise in lactic acid levels, predisposing individuals, especially runners breathing at a higher rate and needing much more air, to a high risk of sudden death. In addition, it is difficult for individuals to breathe because of high breathing flow resistances and insufficient oxygen. The sympathetic nervous system is stimulated by the shortage of oxygen and the heart rate increases. The interaction between respiration and heart rate variability induces respiratory sinus arrhythmia, which has been used to evaluate the function of the vagus nerve and can affect the prognosis of the cardiovascular system . Although experts argue that such extreme symptoms are unlikely for most people, however, in subsets of individuals with underlying cardiovascular and respiratory disease, or with particularly tightly fitted masks and respirators, the side effects may be exacerbated during exercise such as running . In a study of more than 200 paramedics, approximately 30% reported experiencing headaches when they wore face masks or respirators . N95 and surgical masks can produce unsuitable temperature and humidity in a small space and have an additional effect on the respiratory and circulatory systems; this is also one of the causes of discomfort. Besides, the greater effort of breathing through face masks or respirators during exercise such as running will lead to an elevation of blood pressure, which is associated with an increase in cardiovascular mortality .
In addition, as individuals run, hands are often used to adjust face masks and respirators, which may lead to inadvertent touching and contamination by respiratory droplets. This may increase the transmission of SARS-CoV-2, especially when social distancing measures are being relaxed and the individuals may be asymptomatic carriers of COVID-19.
Although sudden death associated with wearing of a facemask during running is a rare event, the risk is higher especially in those with existing cardiac comorbidities. In such cases, a mask designed specifically for runners with no or less side effects of oxygen deficiency should be considered instead .