Study design
The prospective, randomized, crossover study design was described in detail in a previous manuscript dealing with the influence of masks on cardiopulmonary performanceEach subject was tested with four mask situations: no mask (NM) as reference, surgical mask (SM; Type II, MedicalCare & Serve industryIndividually determined load levels resulting in a minute ventilation of 10 L/min (rest), 30 L/min (exercise (E1)), 50 L/min (E2), > 60 L/min (E3) and 10 L/min (post)—each lasting six minutes—were used for the physical exertion during ergometry and CPET. According to the German Social Accident Insurance this corresponds to light (rest and post), moderate (E1), heavy (E2), and very heavy (E3) workCardiopulmonary parameters and blood gases were measured and perceived exertion (Borg scale) was requested as described earlier