Differences among skeletal muscle mass indices derived from height-, weight-, and body mass index-adjusted models in assessing sarcopenia

Abstract

Aging processes are inevitably accompanied by structural and functional changes in vital organs. Skeletal muscle, which accounts for 40% of total body weight, deteriorates quantitatively and qualitatively with aging. Skeletal muscle is known to play diverse crucial physical and metabolic roles in humans. Sarcopenia is a condition characterized by significant loss of muscle mass and strength. It is related to subsequent frailty and instability in the elderly population. Because muscle tissue is involved in multiple functions, sarcopenia is closely related to various adverse health outcomes. Along with increasing recognition of the clinical importance of sarcopenia, several international study groups have recently released their consensus on the definition and diagnosis of sarcopenia. In practical terms, various skeletal muscle mass indices have been suggested for assessing sarcopenia: appendicular skeletal muscle mass adjusted for height squared, weight, or body mass index. A different prevalence and different clinical implications of sarcopenia are highlighted by each definition. The discordances among these indices have emerged as an issue in defining sarcopenia, and a unifying definition for sarcopenia has not yet been attained. This review aims to compare these three operational definitions and to introduce an optimal skeletal muscle mass index that reflects the clinical implications of sarcopenia from a metabolic perspective.

Keywords: Appendicular skeletal muscle mass; Frailty; Muscle mass; Muscle mass index; Sarcopenia.

Figure 1.

Age trends in skeletal muscle mass indices in (A, B) men and (C, D) women. ASM, appendicular skeletal muscle mass; ht², height squared; wt, weight; BMI, body mass index.

Figure 2.

Prevalence rates of sarcopenia in (A) men and women aged 65 years or older and in each age group stratified by 5-year intervals for (B) men and (C) women according to three different operational methods. Class I and class II sarcopenia were defined when their values were within –1.0 to –2.0 standard deviation (SD) or below –2.0 SD of the sex-specific mean of a young reference group (20 to 29 years old), respectively. ASM, appendicular skeletal muscle mass; ht², height squared; wt, weight; BMI, body mass index.