Myostatin is a protein belonging to the myokine class, the family of transforming growth factors β (TGF-β). The review article, based on the analysis of literature data, shows the key role of myostatin in the development of senile sarcopenia and cachexia in various pathological conditions, such as cancer, chronic heart failure, chronic renal failure, COPD, etc. The article discusses the structure of myostatin, provides a detailed diagram of the synthesis and activation of myostatin, the ways of implementing the mechanism of action as a negative regulator of muscle growth and differentiation in these pathological conditions. The main physiological properties and clinical significance are highlighted. Exogenous and endogenous factors regulating myostatin expression and possible mechanisms of their action are considered.