Inclusion Criteria:  • Adult individuals (age ≥18 years) recovered from COVID-19 (diagnosed using a polymerase chain reaction test from a nasopharyngeal sample), with or without lasting fatigue symptoms, which appeared following COVID-19, while at least two months have elapsed since COVID-19 diagnosis.  Exclusion Criteria:  Individuals hospitalized in intensive care unit and/or required mechanical ventilation during their acute illness. Individuals diagnosed with pulmonary veno-thromboembolism/pulmonary infarction, on current oxygen supplementation, with sleep apnea/hypopnea syndrome or with post-COVID-19 chest imaging suggesting pulmonary fibrosis. Individuals with heart failure, acute coronary syndrome or percutaneous cardiac intervention during the year prior to the diagnosis. Individuals who underwent surgical procedure under general anesthesia during the year prior to the diagnosis. Individuals with cerebrovascular disease and a history of cerebrovascular accident or transient ischemic attack. Individuals with paralysis of the lower limbs, amputees, bedridden, those assisted with walking aids or wheelchair. Individuals with myopathies or myositis, degenerative neurological or muscular diseases, and myasthenia gravis. Individuals with pre-COVID-19 diagnosis of chronic fatigue syndrome, fibromyalgia, major depressive disorder, obstructive sleep hypopnea/apnea syndrome, or sleep disturbance necessitating pharmacotherapy. Individuals with chronic illnesses (autoimmune diseases and malignancies) necessitating immunosuppression (including corticosteroid therapy) or immunomodulation (including anti-cancer agents). Individuals with thyroid dysfunction prior to their diagnosis with COVID-19: uncontrolled hypothyroidism or hyperthyroidism and those with imbalanced thyroid stimulating hormone (TSH) level. Pregnant women. Individuals with chronic use of opioids.