The study will consist of three groups of subjects. Ten young male subjects (18-30 years) will lie supine for 21 days, 10 older male subjects (65+ years) will lie supine for 10 days, and a third group of 10 older male subjects (65+ years) will also lie supine for 10 days but will receive interventions (see below) to counteract the physical changes caused by supine lying. All three groups will be bedridden in the premises of Izola General Hospital. Subjects will be housed in 5-bed rooms at the hospital and will receive 24-hour medical care, proper hygiene, nutrition, passive exercise, Internet, a relaxing environment, and visits. After their stay, subjects return home but receive 21 days of care at local fitness centers. Rehabilitation consists of interval training, in which subjects perform high-intensity exercise for 4 times 5 minutes. A number of important health parameters are measured before, during, and after bed rest. Some of these measurements will be invasive (blood and muscle sampling), for which appropriate medical personnel, sterile instruments, and environment will be available. Measurements will include normal voluntary efforts (indoor cycling, various jumps, short stretches) and electrically evoked muscle contractions (electrical stimulation with single impulses). All tests are normal tests and come from normal lifestyles and routine medical examinations.

Inclusion Criteria:

• age: for young arm (18-35), for old arm (65-75)
• BMI: 22 in 32 kg/m2
• appendicular muscle mass > 7,23 kg/m2

Exclusion Criteria:

• serious acute or chronic diseases: skeletal, cancer, cardiovascular, metabolic, neuromuscular and psychiatric;
• cardiovascular disease detected on ECG examination;
• allergies to the active substances used in the study;
• problems with digestion of the active substances;
• frequent diarrhea and vomiting;
• arterial hypertension (>140/90 mmHg);
• psychological problems;
• susceptibility to deep vein thrombosis (D-dimer < 500 μg/L)
• poor orthostatic tolerance (frequent dizziness when changing position, especially when rising from a supine position);
• venous abnormalities that would cause difficulty in drawing blood;
• a large blood volume (more than 300 ml) in the last 3 months prior to the start of the project;
• problems with excessive consumption of alcoholic beverages;
• active smoking;
• Previous participation in any biomedical research in the last 3 months prior to the start of this study;
• a communicable disease before the start of the project;
• any ferromagnetic implant.