https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7306735/

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“Exercise with facemask; Are we handling a devil's sword?” – A physiological hypothesis====

Exercising with facemasks might increase pathophysiological risks of underlying chronic disease, especially cardiovascular and metabolic risks. Social exercisers are recommended to do low to moderate-intensity exercise, rather than vigorous exercise when they are wearing facemasks. We also recommend people with chronic diseases to exercise alone at home, under supervision when required, without the use of facemasks. Given the identified and hypothesized risks, social distancing and selfisolation appear to be better than wearing facemasks while exercising during this global crisis.