Strengths of the study
DISEASES
A special feature of our study is the complex study design which allowed to examine all 40 subjects in all four modules, partly even double-blinded, without and when wearing three different masks at different workloads and up to four hours continuously. Mask types were previously checked according to EN 149 and confirmed as representative mask models, especially according to the resistance of the filter material.The study participants covered a wide a range of age, fitness, and some common diseases. Subjects in other studies were younger and, in general, only well-trained subjects were examinedThe housing of a common bacterial filter was used as an adapter for the mask material to prevent influencing the ventilation measurement by the CPET silicone mask, which has been suspected as an influencing factor in studies where face masks were worn underneath the CPET maskTo prevent a systematic error due to one of the four different situations and to consider repeated measurements, an intraindividual comparison at the different examination times (i.e., each subject is compared to him/herself) was chosen. Due to the complex study design, we were able to compare the four different modules with each other and to link them by means of correlation analyses.We have placed special emphasis on a sufficient washout period between the modules or the wearing of the different masks which was previously critically discussed by several papers