A study published in 2021 by the journal Applied Sciences measured the effects of a surgical mask on 72 recreational athletes as they ran at their maximum speeds. The study found that the mask increased the average time to complete a 50-meter race by 12.51% and a 400-meter race by 19.09%. It also found that the mask "increased blood lactate concentration, sympathetic autonomic modulation, perceived exertion, perceived stress, and decreased blood oxygen saturation." Likewise, a study published in 2021 by the British Journal of Sports Medicine measured the effects of a cloth mask on 31 healthy young adults as they ran at max speed on a treadmill. The study found that the mask "led to a 14% reduction in exercise time" and reduced their "maximal oxygen consumption" by 29%. While ignoring those studies and others, the CDC's "Science Brief" on cloth masks portrays masks as undisruptive to exercise by cherry picking studies that use low exercise intensities and low exposure times.