The progressive loss of skeletal muscle mass, strength, and function that occurs with aging. Sarcopenia typically accelerates after age 50, with muscle mass declining at roughly 1–2% per year and muscle strength declining even faster. It is recognized as a distinct medical condition with ICD-10 diagnostic coding.

Sarcopenia increases the risk of falls, fractures, disability, hospitalization, and death. Its causes are multifactorial: declining anabolic hormones (growth hormone, IGF-1, testosterone), chronic inflammation, mitochondrial dysfunction, physical inactivity, and inadequate protein intake. Multiple peptide classes are studied in this context—GH secretagogues (tesamorelin, MK-677), myostatin inhibitors (follistatin), and mitochondrial-targeted peptides (SS-31)—though no peptide is currently approved specifically for sarcopenia treatment.