Inclusion Criteria:  Subject having suffered COVID19 in the 12 months before inclusion, attested by a positive PCR, positive serology test or positive chest CT scan. (COVID+ group). Subject having stayed clear of COVID19 (COVID-/control group). Subject having been well informed and having provided written informed consent before participation. Subject covered by social security of some sort. Subject with an oxygen saturation of SpO2 > 95% in ambient air on day of Richalet test performance. Subject presenting with no symptoms of COVID19 (anymore) on the day of the experiment. Subject having already performed the Richalet hypoxia exercise test as part of the altitude mountain consultation in the years 2015 to 2019 in any of the 13 hospital centers participating at the study.  Exclusion Criteria:  Subject with a history of respiratory, cardiovascular, neuromuscular, metabolic or renal pathologies. Subject with a history of psychiatric or behavioral disorder. Subject covered by L1121-5 to L1121-8 sections of the Public Health regulations (Code de la Santé Publique). Subject under guardian- or curatorship. Subject without social insurance. Subjet under the age of 18. Subject refusing to participate in the study. Subject diagnosed with an infection by a pathogen other than SARS-CoV-2.