The aim is to study the effect of SSOT during a 3-week in-patient pulmonary rehabilitation programme. Further aim is to analyse exercise endurance, distinguishing between those exercising whilst breathing air at 760m "normoxia", breathing air at 1600m "hypoxia", or breathing SSOT at 760m "hyperoxia" conditions, during in-patient pulmonary rehabilitation.

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

This sub-study will involve the subjects wearing the Respeck device and will focus on the effect of exercise on the respiratory signal measured by the Respeck.

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.

IPD will only be shared upon personal request to the corresponding author.