Study Flowchart
The study was conducted in a metabolic chamber to strictly control daily calorie intake and physical activity levels. With the use of stratified randomization, participants were randomly assigned to receive interventions with and without the N95 mask (9132; 3M) for 14 hours (8:00 to 22:00), during which they exercised for 30 minutes in the morning and afternoon using an ergometer at 40% (light intensity) and 20% (very light intensity) of their maximum oxygen consumption levels, respectively. Venous blood samples were taken before and 14 hours after the intervention for blood gas and metabolite analysis (eMethods, eTable, and eFigure in A sample size of 30 participants was required, based on our preliminary data of the mean (SD) heart rate between masked (87.5 [3.4] beats/min) and unmasked (85.7 [2.9] beats/min) conditions and to achieve 85% power and a significance level of .05. Analysis was performed on a per-protocol basis. Differences were estimated using a linear mixed-effects model. Where significant, Bonferroni-corrected post hoc tests were performed. Statistical tests were 2-sided. Statistical analyses were conducted using R, version 4.02 (R Group for Statistical Computing).