All measurements are performed on two consecutive days at the beginning of a pulmonary rehabilitation program in a randomized cross-over study design. On the first day, each patient is randomly assigned to perform either the 2 minute walk test or the 6 Minute walk test. On the second day each patient performs the test that was not performed on the first day. All walk tests are performed by the same investigator on the same track and time of day, following the 2002 guidelines of the American Thoracic Society.

Patients wear a mobile pulse oximeter that continuously records heart rate and oxygen saturation during testing. Baseline values of oxygen saturation, heart rate and ratings of perceived exertion on the modified Borg scale (0 to 10) for dyspnea and leg fatigue are recorded at rest after 10 minutes of sitting.

Inclusion Criteria:

• confirmed diagnosis of chronic obstructive lung disease stage III or IV according to the Global Initiative for chronic Obstructive Lung Diseases definition
• ability to read and understand the German language and study procedures.
• written informed consent

Exclusion Criteria:

• severe acute exacerbation of chronic obstructive lung disease
• severe respiratory failure (partial Oxygen pressure at rest lower than 55 millimeter mercury)
• non compliance to the study protocol.