Several things surprised us about Chandrasekaran and Fernandes’ hypothesis that “exercise with facemask” may cause “hypercapnic hypoxia, potentially increasing acidic environment, cardiac overload, anaerobic metabolism and renal overload” [1].First, in the ‘Highlights’ section, the authors describe their paper as a “study [which] demonstrates potential complications associated with facemasks during exercise”. Yet the ideas presented in the paper are...