noun

• (pathology) Gradual loss of skeletal muscle due to aging, immobility, illness, or combinations thereof.
  "Now, let me stop here to make a sort of plea. No decline with age is more dramatic or potentially more functionally significant than the decline in lean body mass. […] Think of the implication of this decrease in lean body mass in respect to the physical behavior of elderly subjects. There may be no single feature of age-related decline that could more dramatically affect ambulation, mobility, calorie intake, and overall nutrient intake and status, independence, breathing, etc. Why have we not given it more attention? Perhaps it needs a name derived from the Greek. I'll suggest a couple: sarcomalacia or sarcopenia. We might study more about the relationship between this decline and exercise; such studies are being done in some of the laboratories at our center. We know that elders can build and rebuild muscle mass. Even the frail elderly can recover function remarkably. I think this is am opportunity for some new attention that would pay off handsomely in maintaining the health and vigor that we described as a goal of our work."