Oxygen saturation

Question

Hello, how low can oxygen saturation drop during exercise?

Answer

Dear questioner,
Since this is a forum dedicated to cystic fibrosis, I assume your question pertains to exercise in the context of cystic fibrosis.
When a person with normal physical endurance and no pre-existing conditions engages in sports, its oxygen saturation remains normal—that is, greater than or equal to 95%—even under physical exertion. However, there are data regarding highly trained athletes who experience a temporary drop in oxygen saturation to below 90% during extreme sports; these are exceptional situations.
In cases of lung diseases such as CF (cystic fibrosis), a drop in oxygen saturation below 90% typically does not occur, provided that lung function ranges from normal to only slightly impaired. In fact, during an exercise stress test performed on a bicycle ergometer (following the Godfrey protocol), saturation levels usually remain between 96% and 100%. However, the situation may differ in cases of impaired lung function; therefore, an exercise stress test is a valuable tool for determining—on an individual basis—at precisely which level of exertion oxygen saturation drops below 90%. The heart rate recorded during the specific exertion level at which saturation has not yet dropped below 90% is noted; one can then proceed to train—without the need for supplemental oxygen—while monitoring one's heart rate (e.g., using a smartwatch) to ensure it remains within that established limit. If one wishes to train at a higher intensity, supplemental oxygen must be administered during the activity.
Consequently, individuals with lung disease and impaired lung function should undergo such a test prior to commencing a training regimen to ensure they can engage in sports safely.
Sincerely,
Daniela d'Alquen

17.05.2026