The goal of this project is to find out whether illusory movements are suitable for patients in the early phase of burn disease, and how they influence patients' metabolism.

We are going to test these hypotheses:

• The use of illusory movements is suitable for patients with burns of 20 % TBSA and more in the early acute phase of the burn disease.
• The use of illusory movements reduces the extent of muscle catabolism in patients with large burns.

Way of solution This is a pragmatic cross-over study in patients with burns of 20 % TBSA or more in the early acute phase of the burn disease, who are expected to be hospitalized for 35 days or more. Patients meeting the inclusion criteria will be divided into two groups, A (n = 10) and B (n = 10). Group C will consist of healthy volunteers (n = 10).

The study will start after patient's basic cardiopulmonary stabilization, which usually corresponds to days 3-5 after the injury.

Group A: Early illusory movements Phase 1: A patient enrolled in group A will have standard rehabilitation according to the instructions of the attending surgeon and performed by an independent physiotherapist from the start of the study (Day 1), and also FPS performed by a study nurse will take place for 30 minutes twice a day, 2 hours or more after the end of standard rehabilitation, for 14 days (Day 15).

Phase 2: From Day 16 onwards, the patient will undergo standard rehabilitation only according to the instructions of the attending surgeon and performed by an independent physiotherapist for 14 days (Day 30).

Group B: Deferred illusory movements Phase 1: A patient enrolled in group B will have standard rehabilitation according to the instructions of the attending surgeon and performed by an independent physiotherapist, from the start of the study (Day 1) for 14 days (Day 15).

Phase 2: Then, from Day 16 onwards, in addition to standard physiotherapy, FPS performed by a study nurse will take place for 30 minutes twice a day, 2 hours or more after the end of standard rehabilitation, for 14 days (Day 30).

Group C: Illusory movements in healthy individuals This group will consist of 10 healthy volunteers in whom REE will be measured before and after 30 minutes of FPS.

c) Medical, social and economic rationale of this study Large burns are often the cause of neuromyopathy and disability of the injured [30]. Hypercatabolism and enormous muscle loss increase the morbidity and mortality of patients, prolong treatment and greatly increase the overall cost of medical care [31]. Early rehabilitation using illusory movements could reduce the extent of muscle devastation in otherwise immobile patients and improve the effect of standard rehabilitation by maintaining functional brain maps. This should lead to an earlier return of the injured to their normal activities a improve quality of life.

In addition, if the positive effects of illusory movements are proved, there are many critically ill patients outside the burns who could benefit from this form of physiotherapy.

d) Methodology Nutrition support will be provided in accordance with European Society of Parenteral and Enteral Nutrition recommendations.

During the study, the following parameters will be measured, and the following examinations will be performed in addition to standard biochemical, haematological and imaging examinations of Group A and B:

• Nitrogen balance;
• Resting Energy Expenditure using indirect calorimetry;

On Days 1, 15 and 30:

• Patient weight;
• APACHE II score;
• Muscle biopsy (from m. vastus lateralis);
• BMR;
• Glucose disposal using a hyperinsulinaemic euglycaemic clamp;
• Degree of insulin resistance according to Homeostasis Model Assessment;
• Muscle mitochondrial respiratory capacity and coupling with the Oxygraph-2K;
• Mitochondrial mass determination and dynamics in myocytes with MitoTracker ;
• Plasmatic levels of myokinins ;
• Ultrasound measurement of the rectus femoris diameter measured by an independent sonographer.