Sarcopenia is progressive loss of skeletal muscle mass, strength, and function with age. Starts at 30, accelerates after 50, becomes critical after 65.
Mechanism — Driven by anabolic resistance (cells respond less to amino acids and resistance), motor unit loss (especially fast-twitch), satellite cell decline, inflammaging, and chronic disuse. Type II fibers atrophy preferentially.
Use case — Resistance training 3-4x/week with progressive overload. Protein intake 1.6-2.2 g/kg/day, with emphasis on leucine-rich sources at each meal. Vitamin D, creatine, omega-3s as supportive.
Caveats — Sarcopenia is preventable but not reliably reversible. Start training early — the cost of starting at 70 is much higher than at 40. Hospitalization and bedrest accelerate it dramatically.