Effect of Inhalation of Low Dose CO2 on Exercise Performance at High Altitude

Objective: To determine whether the supplement of low-dose CO2 by the novel device could improve exercise performance at high altitude. Methods: The lowlanders (\<500m) who have no history of travelling to high altitude (\>1000m) a year before the study will be recruited. And the subjects who are high-altitude residents and have not left high altitude over the last twelve months will also be recruited for the study. Subjects will be randomly and blindly given either CO2 mixed with air or air alone during endurance shuttle walking test (ESWT). Blood gases will be measured before and after inhalation of CO2. ESWT time, ventilation per minute (VE), blood oxygen saturation (SPO2), and end-tidal CO2 concentration (ETCO2) will be measured during exercise and will be compared during inhalation of CO2 and during inhalation of ambient air.