Protective facemask-induced facial thermal stress and breathing burden during exercise in gyms

During the COVID-19 pandemic, more than 90% of infections occurred in indoor environments such as restaurants and gyms. In particular, gym attendees are facing challenges of both infection risks and extra heat and breathing burdens with the use of protective facemasks (PFMs) during intensive exercise. To evaluate the PFMinduced thermal stress and breathing discomfort during high-intensity exercise, this study investigated the mechanisms of heat and air exchange between environment of inside and outside PFM via experiments and computational fluid dynamics simulations. In the experimental phase, the effects of the activity intensity and type of PFM on thermal and breathing comfort were tested. An uncomfortable microenvironment of the face covered by a PFM was found when the air temperature and absolute humidity increased by 4.1% and 23.1%, respectively, during high-intensity exercise, relative to the sitting scenario (30.8 degrees C, 0.026 kg/m3), together with a higher CO2 concentration (31.0% increase) and lower O2 concentration (8.3% decrease). Moreover, the masks newly designed provided better thermal and breathing conditions than traditional masks due to the larger surface area and lower thickness. In simulation phase, the model sensitivity analyses were conducted to assess the effects of eight factors on thermal and breathing comfort. The mask surface area is found to most highly affect not only the thermal comfort indices (temperature, absolute humidity) but also breathing comfort indices (the concentration of CO2 and O2). The study results provide an important reference for government policymaking, mask design, and public health.