Due to the COVID-19 pandemic, face masks have become part of daily life and work . Only few studies have investigated potential negative effects of this measure . It was aim of this study to evaluate whether face masks may affect oygen saturation and heart reate under moderate physical effort . Ten healthy volunteers were asked to climb up four floors (96 steps) with and without a face mask . Oxygen saturation and heart rate were recorded before and after this procedure . Physical activity lead to a slight decrease of oxygen saturation of 3.0% (+/- 3.1) without and 3.7% (+/- 3.8) with face masks (p= 0.28). Heart rate increased by 31.0 (+/- 18.7) and 33.3 (+/- 15.9) beats per minute (p= 0.39). Desaturation was more pronounced in individuals> 40 years, however was uncritical in all cases . This study shows that in healthy adults the use of face masks does not significantly affect oxygen supply nor cause additional cardiac load.