What is Sarcopenia?
Muscle, also called lean body mass (LBM) can be lost at any age as the result of injury, disease, emotional stress, diet and any other number of factors. Despite the cause, muscle loss is clinically significant because it erodes strength, endurance, health and vitality. In contrast to LBM loss resulting from individual adverse circumstances, sarcopenia is a condition characterized by muscle atrophy that affects everyone as the result of aging. Surprisingly, muscle loss begins early in life; upon completion of development and as early as twenty or twenty-five years of age. Clinical studies have shown that the excretion of urinary creatinine, which is a measure of muscle creatine content and total muscle mass, decreases by nearly 50% between the ages of 20 and 70 years. These measurements indicate that degradation of muscle exceeds its synthesis after young adulthood is past. This decline is clearly evident as loss of speed, strength and endurance in middle-aged athletes, which is presumably less than in non-athletes.
A large component of involuntary weight loss during aging occurs in fat-free mass. In other words, by age thirty, body weight gain begins to be preferentially accrued as fat instead of muscle and this process that underlies loss of LBM continues unabated thereafter. However, the lost muscle is usually not noticed by affected individuals, because it is replaced in subtle ways such as by padding areas of loss with extra fat. After forty years of age, muscle loss proceeds at a rate of about 0.5 - 2% per year or 8% per decade on average. This rate accelerates noticeably after age 60 and is highest in physically inactive persons along with a parallel decline in their muscle strength. From age 60 and for each decade thereafter, the rate of muscle loss doubles.
Loss of age-associated muscle mass is accompanied by diminished dynamic, static, and isokinetic muscle strength. The result of such age-related LBM loss is a decline in function such that up to 65% of older men and women report that they are unable to lift ten pounds with their arms.
Since maintaining muscle mass is essential to supporting whole-body protein metabolism, wound healing, physical strength, organ function, skin integrity and immune function, sarcopenia can be debilitating. Consequences of age-related muscle loss include: