FNDC5 and sarcopenia: One key mechanism of irisin action is its influence on mitochondrial homeostasis: it stimulates mitochondrial biogenesis via PGC-1α activation, improves mitochondrial dynamics, activates mitophagy to remove damaged mitochondria, and reduces oxidative stress, which is critical for preventing age-related mitochondrial dysfunction—a key mechanism in the development of sarcopenia [109].