Airway resistance will be measured using the forced oscillation technique (FOT). The parameters Rrs, Xrs, and ∆Xrs will be compared before and after a pulmonary rehabilitation cycle at moderate altitude. Additionally, the differences between low and moderate altitude will also be examined.

Inclusion Criteria:

• Aged ≥18 years
• Stable clinical condition for >3 weeks (e.g., no exacerbations)
• Resting SpO₂ ≥88% and exercise-induced hypoxemia defined as a drop in SpO₂ of ≥4% and/or a level below 90% during the 6MWT
• Informed consent documented by signature

Exclusion Criteria:

• Severe daytime resting hypoxemia (SpO₂ <88%)
• Long-term oxygen therapy
• Unstable clinical condition requiring adjustment of pharmacological or other treatment modalities, need for intensive care, or presence of relevant severe comorbidities
• Inability to comply with study procedures (e.g., due to language barriers, psychological disorders, neurological or orthopedic impairments, walking disability, or inability to ride a bicycle)
• Women who are pregnant or breastfeeding
• Enrolment in another clinical trial involving active treatment

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