The primary aim of this study is to study the feasibility of an aerobic training, in addition to conventional rehabilitation, in patients post sequela of interstitial pneumonia due to COVID-19. In particular, we wish to verify if patients could tolerate this kind of physical activity and if there are any adverse effects. The secondary aim is to evaluate if the aerobic exercise is effective in improving functional capacity and gait performance in these patients respect to the common physiotherapy.

The coronavirus disease 2019 (COVID-19) is an infectious disease caused by SARS-CoV-2 that mainly affects the respiratory system (Landi et al., 2020). While the majority (80%) of people infected with COVID-19 presents mild to moderate disease (Huang et al., 2020; Rodriguez-Morales et al. 2020), for a considerable number of subjects, generally >65 years and with comorbidities, the infection can have very serious sequelae (about 20%) (Yang et al., 2020). Of those requiring hospitalization, a high portion (20%) require management in the intensive care unit (ICU) often for an acute respiratory distress syndrome (ARDS) (Simpson and Robinson, 2020).

People with critical illness due to COVID-19 has not only a disease primarily affecting the lung, but present also a multi-organ involvement (Gemelli Against COVID-19 Post-Acute Care Study Group, 2020). During periods of critical illness and hospitalization, it is common to experience a loss of physical function (Rawal et al., 2017), characterized by the development of new or worsening of existing impairments. This decrease in physical functioning is thought to be attributed to prolonged periods of immobility, during which time people experience deconditioning, develop critical illness, polyneuropathy and myopathy (Rooney et al., 2020). This results in a motor disability and a reduction of independence in the activities of daily living (ADL) (Abate et al., 2020; Rodriguez-Morales et al. 2020; Herridge et al. 2011; Barnato et al., 2011).

Several authors reported that people with COVID-19 - even without motor limitation prior to hospitalization - in the post-acute phase show muscle weakness, reduced physical performance, exercise-induced oxygen desaturation and hampered performance of ADLs still when discharged home (Belli et al., 2020; Paneroni et al., 2020). In those with severe and critical COVID-19 course, the impairments in pulmonary function and physical performance may be identified four months after the infection (Guler et al., 2021). These findings suggest that there is a clear need to plan for post-acute and chronic rehabilitation for people recovering from COVID-19 (Barker-Davies et al., 2020).

People with COVID-19 are heterogeneous, with different manifestations and comorbidities, and show disabling sequelae when recovering from the infection. Consequently, rehabilitation, which is necessary for facilitating the recovery and the discharge to home, has to be patient-centered and tailored to individual patient needs and impairments (Barker-Davies et al., 2020).

Therefore, it may be useful to conduct a prospective longitudinal study on subjects with COVID-19 who have undergone a period of hospitalization for severe or critical COVID-19 and who were discharged from the post-acute ward to a rehabilitation post-COVID-19 ward. Moreover, since experts strongly recommended a low-/moderate-intensity physical exercise in the first weeks following hospitalization in the COVID wards (Spruit et al., 2020), there is the need to consider the addition of an aerobic exercise training to the usual rehabilitation.

The primary purpose of this randomized controlled clinical trial is to verify the experimental aerobic training may be feasible in subjects with a sequela of interstitial pneumonia due to COVID-19 (people with post-COVID-19) and performed without the manifestation of serious adverse events.

The secondary purpose is to verify whether the addition of aerobic activity can increase physical performance compared to a program in which no aerobic activity is foreseen.

Inclusion Criteria:

1. Defined diagnosis of interstitial pneumonia due to COVID-19;
2. Two negative nasopharyngeal swab test for SARS-CoV-2;
3. Functional independence before the COVID-19;
4. Mini-mental state examination (MMSE) score > 24.

Exclusion Criteria:

1. Positivity to COVID-19;
2. Patients living in a nursing home or not autonomous prior to the COVID-19;
3. Presence of moderate or severe heart disease (Grade III or IV, New York Heart Association);
4. Presence of neurological disease;
5. Low compliance;
6. Patients with low rehabilitation needs (FIM total score at admission >100)
7. Terminal illness (life expectation <6 months)