Conceptual and operational definitions of sarcopenia and its measurement limitations

Skeletal muscle mass declines by approximately 1% per year after the age of 30 years, with an overall decline of 20–30% between the ages of 20 and 80 years. Although this age-related loss of muscle mass had been considered as a physiological aging, previous studies revealed that excessive muscle decline in older adults was associated with adverse health outcomes. Based on these backgrounds, the concept of sarcopenia was proposed to distinguish pathological muscle loss from normal aging. Sarcopenia is now defined as age-related muscle loss and dysfunction. Since the European Working Group on Sarcopenia in Older People proposed diagnostic criteria in 2010, several definitions have been developed and updated by consensus groups including those in Asia (Asian Working Group for Sarcopenia). While all criteria include skeletal muscle mass, muscle strength, or physical function, the combinations and priorities among these criteria differ, and a consensus has yet to be established. This review aims to summarize the conceptual and operational evolution of sarcopenia definitions and to compare the differences of definitions among consensus groups. Moreover, we discuss the measurement methods and its limitations related to skeletal muscle mass, muscle strength, and physical function.