Many structures and organs are adversely affected after COVID-19. The most obvious and common problem is lung involvement. In the pathology report of the patients, it has been shown that there are changes such as diffuse alveolar damage, bronchiolitis and interstitial fibrosis. The most prominent effect of COVID-19 in patients with reduced lung functions is reduced diffusion capacity. While the disease severity worsens, pulmonary fibrosis becomes more pronounced in cases. The complaints of dyspnea and fatigue of patients after discharged continue. Inspiratory and expiratory respiratory muscle weakness are observed in more than 50% of patients with COVID-19, measured in the first month after the discharged. This respiratory muscle weakness is associated with myopathy due to hypoxemia, oxygen support, prolonged bed rest and corticosteroid use, regardless of disease severity. It is seen that these patients with COVID-19 need exercise training because of lung involvement, decreased exercise capacity and persistence of some symptom complaints after the discharged.