The aim of the current study is the effect of SSOT during a 3-weeks inpatient pulmonary rehabilitation program. Further aim is to analyze exercise endurance, distinguishing between those exercising whilst breathing air at 760m "normoxia", breathing air at approx. 1600m "hypoxia", or breathing SSOT at 760m "hyperoxia" conditions during inpatient pulmonary rehabilitation.

The objective of the study is to provide long-awaited data concerning the use of SSOT during training. To date, it is not clear whether patients with chronic lung diseases who reveal a SpO2 > 88% at rest but desaturate during exercise and thus may not qualify for long-term oxygen therapy undergoing PR benefit from supplemental oxygen.

Inclusion Criteria:

• aged ≥ 18 years
• stable condition > 3 weeks (e.g. no exacerbations)
• resting SpO2 ≥ 88% and exercise induced hypoxemia defined by a fall in SpO2 by ≥ 4% and/or below 90% during a 6-minute walk test (6MWT)
• informed consent as documented by signature.

Exclusion Criteria:

• Severe daytime resting hypoxemia (SpO2 < 88%)
• long-term oxygen therapy
• unstable condition requiring adaptation of pharmacologic and other treatment modalities or requirement of intensive care or relevant severe concomitant disease
• inability to follow the procedures of the study, e.g. due to language problems psychological disorders, neurological or orthopedic problems with walking disability or inability to ride a bicycle
• women who are pregnant or breast feeding
• enrolment in another clinical trial with active treatment.

individual patient data will be shared upon personal request to the corresponding author