This is a single-center, prospective, randomized, double-blind (pharmacotherapy), placebo-controlled, and comprehensive physiotherapy and nutritional intervention phase II clinical trial to determine the usefulness of nandrolone decanoate in a new indication (sarcopenia).

Patients will be randomized 1:1 to receive nandrolone decanoate (50 mg intramuscular injection over four visits every 3 weeks) or placebo (1 ml volume equivalent to 50 mg intramuscular nandrolone decanoate dose) for 12 weeks (83-85 days ). Both groups will receive comprehensive physiotherapy and nutritional intervention.

There will be 5 outpatient visits to the research center. The procedures and assessments performed as part of the study are listed in the study schedule.

It is planned to include 168 patients in the study, which, assuming a 10% level of non-completion of the program, will result in the examination of 152 patients (76 in each arm). The study will cover people aged over 60 to 99 years of age with confirmed muscle weakness measured with a hand dynamometer (< 27 kg for men and 16 kg for women) and with a decrease in: muscle mass of upper and lower limbs (ASMM) (7.0 kg/m2 height in men and 5.5 kg/m2 in women) or total muscle mass of the upper and lower extremities (< 20 kg in men and < 15 kg in women) by densitometry.

Inclusion Criteria:

1. individuals aged 60 years or older through 99 years of age.

2. Patients meeting the following criteria diagnosed with sarcopenia based on EWGSOP 2 criteria from 2019:

   • weakness of muscle strength measured by hand dynamometer ( < 27 kg for men and 16 kg for women) and

   • reduction in densitometry:

     • upper and lower limb muscle mass (ASMM)(below 7.0 kg/m2 height in men and 5.5 kg/m2 in women) or
     • total muscle mass of the arms and legs in men less than 20 kg and less than 15 kg in women).

Exclusion Criteria:

1. Mini-Mental State Examination (MMSE) score less than 24;
2. malignant neoplasm, lymphoproliferative or myeloproliferative disorders requiring oncologic or palliative treatment and the period before: 5 years in the case of: malignant melanoma, leukemia, Hodgkin's disease, malignant lymphomas, kidney tumors, 12 months in the case of other malignant neoplasms after the completion of surgery, chemotherapy or radiotherapy;
3. history of oncologic diagnosis of focal lesions in the prostate gland;
4. acute and chronic inflammatory diseases of the gastrointestinal tract that present with malabsorption (celiac disease, ulcerative colitis, Crohn's disease, etc.);
5. uncompensated hyper- or hypothyroidism;
6. recent history of myocardial infarction or stroke (up to 4 weeks prior to study entry); history of thromboembolism (up to 6 months prior to study entry) or recurrent thromboembolism;
7. poorly controlled hypertension;
8. liver impairment (AST and/or ALT > 3x normal: AST> 111 U/l and ALT> 123 U/l); 9 Acute kidney injury and/or chronic kidney disease (stage G4 and G5);

10. nephrotic syndrome, acute or chronic glomerulonephritis; 11. advanced circulatory failure (NYHA stages III and IV); 12. Acute and chronic respiratory failure requiring oxygen therapy; 13. Amyotrophic lateral sclerosis, multiple sclerosis, myasthenia gravis, dystrophies, spinal muscular atrophy type IV, primary muscular disorders (ICD-10 G71), toxic-field myopathies, myopathies in the course of infectious and parasitic diseases. Epilepsy; 14. need for treatment during the study period:

• systemic corticosteroids for more than 3 weeks at a dose equivalent to greater than or equal to 5 mg prednisone;
• hormone replacement therapy,
• 5-alpha reductase inhibitors,
• aromatase inhibitors,
• anti-estrogenic hormonal drugs with anabolic effects other than nandrolone decanoate,
• megestrol. 15. Lack of informed consent for participation in the study.