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.