Table 1 Inclusion and exclusion criteria of study

Inclusion criteria

1. Patient is in the post-acute phase and chronically critically ill, defined as more than 21 days ICU of treatment including mechanical ventilation, and at least 14 days more in an existing critical situation with the need for ICU treatment [27, 51, 52]

2. Acquired muscle weakness defined as a Medical Research Council (MRC) sum score of <48 points [1]

3. Defined diagnosis of critical illness myopathy (CIM) and/or polyneuropathy (CIP) confirmed by a neurologist according to published diagnostic criteria for CIP/CIM [24]

4. Older than 18 years of age

5. Richmond Agitation Sedation Scale (RASS) score from −1 to 1 [53]

6. Written informed consent of the patient or their legal guardian has been obtained

Exclusion criteria

1. Patients receiving palliative care

2. Comorbidities of the trunk or the lower limbs interfering with upright posture and walking function (e.g. amputation or fracture of lower limb)

3. Other neuromuscular or neurological disease and/or syndromes causing weakness in patients in the ICU (we will exclude patients with diseases and syndromes causing weakness in patients in the ICU [9], due to Guillain-Barré syndrome, myasthenia gravis, porphyria, Eaton-Lambert syndrome, amyotrophic lateral sclerosis, vasculitic neuropathy, cervical myelopathy and botulism)

4. Severe physical comorbidity before becoming critical ill (e.g. frailty due to neurological conditions)