Respiratory Muscle Fatigue and Lower Extremity Muscle Oxygenation

Inclusion Criteria: * Having a diagnosis of Stage 2-3 COPD according to the following clinical diagnostic criteria according to the American Thoracic and European Respiratory Societies (ATS-ERS). * Having been using the same medications for the last 4 weeks Exclusion Criteria: * Patients with severe comorbid diseases, unstable coronary artery disease, collagen vascular diseases and requiring high-flow oxygen therapy (˃ 3-4 L\\min). * Presence of any vascular problem that may affect lower extremity muscle oxygenation * Presence of another respiratory system disease other than COPD * Patients who have had an acute COPD exacerbation in the last 4 weeks * Patients experiencing COPD exacerbations during the study protocol * Presence of fatty tissue or scar tissue at the measurement points, which may impair the measurement quality. * Have already participated in another clinical trial within the last 30 days that may affect the results of the study. Inclusion Criteria for Healthy Cases * Being over 18 years of age * Not having any diagnosed chronic disease * Not being a smoker