More than 60% of patients infected with COVID-19 have long-term symptoms. These symptoms are associated with common ground-glass opacities on computed tomography scans and chest radiographs. The pathophysiology of long-term persistent symptoms is largely unknown, but hypoxia and hypoxic tissue damage, decreased pulmonary diffusion capacity, ventilation-perfusion mismatch, and lung fibrosis caused by COVID-19-associated pneumonia are thought to cause long-term symptoms. Desaturation may occur during exercise due to hypoxia, pneumonia and lung involvement in patients with post-COVID syndrome. Oxygenation of peripheral muscles may decrease due to hypoxemia, but there is not enough study on this subject yet.

Post-COVID syndrome is defined as unexplained signs or symptoms that develop during or after infection with COVID-19 and persist for 12 weeks. Long-term symptoms include fatigue, dyspnea, impaired exercise and lung function.It is important to understand physiological mechanisms underlying persistent dyspnea, fatigue, and impaired exercise capacity after COVID-19 infection to develop appropriate rehabilitation interventions while improving these symptoms. The pathophysiology of long-term persistent symptoms is largely unknown, however hypoxia and hypoxic tissue damage caused by COVID-19-associated pneumonia, decreased pulmonary diffusion capacity, ventilation-perfusion mismatch and lung fibrosis have been hypothesized. The effect of hypoxemia associated with COVID-19 on oxygenation of peripheral muscles and muscle oxygenation at submaximal and maximal exercise intensity has not been investigated, yet.

The aim of our study is to evaluate and compare quadriceps femoris muscle oxygenation in submaximal and maximal exercise tests in patients with post-COVID syndrome.

Patients referred from Gazi University, Faculty of Medicine, Department of Chest Diseases for pulmonary rehabilitation to Cardiopulmonary Rehabilitation Unit located in the Faculty of Health Sciences were recruited, Department of Physiotherapy and Rehabilitation, between March 2022 and May 2023. Muscle oxygenation during six-minute walk test and cardiopulmonary exercise test on two different days was measured and compared.

Inclusion Criteria:

• Between the ages of 18-75
• Diagnosed with pulmonary involvement COVID-19
• Volunteer to participate in the study

Exclusion Criteria:

• Body mass index >35 kg/m2
• Acute pulmonary exacerbation, acute upper or lower respiratory tract infection
• Aortic stenosis, complex arrhythmia, aortic aneurysm
• Serious neurological, neuromuscular, orthopedic, other systemic diseases or other diseases affecting physical functions
• Cognitive impairment that causes difficulty in understanding and following exercise test instructions
• Participated in a planned exercise program in the last three months
• Uncontrolled hypertension and/or diabetes mellitus, heart failure and cardiovascular disease
• Contraindication for exercise testing and/or exercise training according to the American College of Sports Medicine

Thirty eight patients with pulmonary involvement post-COVID syndrome were recruited for the study. Pulmonary involvement of the patients was determined by a pulmonologist according to the results of computed tomography.Patients referred from Gazi University, Faculty of Medicine, Department of Chest Diseases for pulmonary rehabilitation to Cardiopulmonary Rehabilitation Unit located in the Faculty of Health Sciences were recruited, Department of Physiotherapy and Rehabilitation.