A study published in 2020 by the journal Clinical Research in Cardiology measured effects of surgical and N95 masks on healthy males as they exercised vigorously. The study found that "ventilation, cardiopulmonary exercise capacity and comfort are reduced by surgical masks and highly impaired by" N95 masks and that both masks "have a marked negative impact on cardiopulmonary capacity that significantly impairs strenuous physical and occupational activities." Moreover, a 2020 paper in the journal Medical Hypotheses found "there have been case reports of sudden cardiac death (SCD) occurring during exercise with facemasks" and details several mechanisms by which "facemasks may increase the risk of SCD." The CDC's "Science Brief" on cloth masks ignores these studies (and others) while cherry picking studies that use low exercise intensities, low exposure times, or imprecise measurements. Thus, the CDC creates a false and dangerous impression that exercising with masks is risk-free.