Face Masks: The Effect on Exercise Physiology

Woman running with face mask

How does wearing a facemask affect exercise physiology? Several studies find differences in physiological differences when wearing a facemask, but do they actually matter?

For most of us, the COVID-19 pandemic has drastically changed how we exercise. Group exercise activities have been cut. In many places, indoor gyms remain closed and for those that are open often face masks are required. Outdoor physical activity can limit COVID-19 transmission. Nonetheless, some people are more comfortable exercising outdoors with a face mask. What affect does wearing a face mask have on exercise physiology?

A recently published study published in the Scandavian Journal of Medicine and Science in Sports attempts to bring some clarity to this question (Return to training in the COVID-19 era: The physiological effects of face masks during exercise, 2020. Epstein, et al.). This study looked at the physiological effects of wearing a surgical mask or N95 respirator during short, aerobic exercise. 

Its important to remember that aerobic exercise involves cardiovascular-type workouts such as running, cycling or walking. In contrast, anaerobic exercise includes weight lifting and sprinting and may have different interaction with wearing a face mask. Aerobic exercise usually puts more stress on the pulmonary system, involving the lungs. Because facemasks principle affect on exercise is breathing (after all they are designed to filter air as we inhale and exhale) it makes to test them in the setting of aerobic exercise. 

For the aforementioned study, 16 male volunteers were tested while performing cycling with no mask, a surgical mask and a N-95 respirator. Different physiological parameters were measured such as heart rate, blood pressure, oxygen saturation, time to exhaustion and end-tidal carbon dioxide. The load varied as participants cycled. Participants rated the percieved exertion during the cycling exercise. Patients were randomly assigned to different orders of no mask, surgical mask and N-95 respirator with at least 24 hours of rest between tests. 

The participants were able to cycle 18 to 19 minutes until exhaustion with each of the three different tests (N-95, no mask, surgical mask). There was no difference in the time to exhaustion between groups. The authors also reported that there was no difference in the participants physiological parameters such as blood pressure, heart rate, respiratory rate, oxygen saturation and percieved exertion. However, there were differences in the end-tidal carbon dioxide.

End-tidal carbon dioxide is a measure of carbon dioxide in our breath at the end of the breathing cycle. Recall that breathing serves two primary purposes. Respiration brings oxygen into the blood stream, which serves as fuel for working muscle. In addition, carbon dioxide, a waste product of cellular metabolism, is revoved from the blood stream in the lungs and exhaled. During aerobic exercise the oxygen consumption and carbon dioxide excretion requirement increase. High levels of carbon dioxide are the primary driver of increased respiratory rate in exercising individuals. High carbon dioxide levels in the blood lead to respiratory acidosis, which leads to feeling short of breath,  and with elevation can cause headaches, confusion, anxiety and decreased exercise tolerance. 

End-tidal carbon dioxide was significanly higher during cycling with an N-95 mask compared to no mask. Just prior to exhaustion, end-tidal carbon dioxide was higher in the N-95 group compared to both the surgical mask group and no mask group. The surgical mask group had higher end-tidal carbon dioxide compared to the no mask group just prior to exhaustion, but all other time points no difference was elucidated.

End-tidal carbon dioxide in cycling subjects wearing N-95 mask, surgical mask and no mask

Other findings that have been associated with mask use include a small increase in body temperature, something not evaluated in this study. It should also be noted that this study used healthy male subjects with average age of 34. Other studies in participants with respiratory disorders, such as chronic obstructive pulmonary disease (COPD) or asthma, found more physiological differences with wearing an N-95 mask. For example, one study found that in participants with COPD, wearing an N-95 mask during a six minute walk was associated with increased heart rate, respiratory rate and end-tidal carbon dioxide (Risks of N95 Face Mask Use in Subjects with COPD, 2020. Kyung, et al.).

What does the results of these studies suggest? If safe to do so, wearing a surgical mask provides less inhibition to respiration compared an N-95. Since end-tidal carbon dioxide can lead to shortness of breath, it would be expected that physical performance would suffer during competition with either a N-95 or surgical mask. However, it is reassuring that the effects on performance would be minimal given that no statistically significant difference in time to exhaustion was found in the discussed study. 

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