肌肉减少症(Sarcopenia)，来自希腊语σάρξ “肉体”和πενία“减少症”，是指肌肉体在质量和强度上随着年龄产生退化性损失。肌肉减少症是老化过程，50岁以后每年有0.5-1％的损失。可以通过病理和行为因素如营养不足加速。肌肉减少症是脆弱综合征frailty syndrome的一个组成部分。它也可以是恶病质（如癌症）的组成部分。

Sarcopenia (from Greek σάρξ sarx, "flesh" and πενία penia, "poverty") is the degenerative loss of skeletal muscle mass (0.5–1% loss per year after the age of 50), quality, and strength associated with aging. Sarcopenia is a component of the frailty syndrome. It is often a component of cachexia. It can also exist independently of cachexia; whereas cachexia includes malaise and is secondary to an underlying pathosis (such as cancer), sarcopenia may occur in healthy people and does not necessarily include malaise.