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Irving Rosenberg is credited to have coined the term sarcopenia (from the Greek roots – sarx = flesh and ‐penia = low, meaning “poverty of flesh”) in 1988 to describe the striking age‐related decline in lean body mass and its potential functional significance [1].

Methods to estimate muscle mass (or lean body mass) were increasingly available, as were epidemiological studies using such techniques. Based on these parameters, sarcopenia was operationally defined as a gradual loss of muscle mass. For instance, Baumgartner used a definition based on appendicular skeletal muscle mass estimated by dual‐energy x‐ray absorptiometry (DXA), corrected for height, and defined sarcopenia as being two standard deviations below sex‐specific means of healthy young persons (18–40 years) of a reference population [2]. Longitudinal studies confirmed that a progressive reduction in muscle mass was present in both males and females [3]. Muscle mass declines at approximately 1–2% per year after the age of 50 years. Sarcopenia, when defined as a severe muscle mass loss (two standard deviations below healthy young populations), is present in 5–13% of persons of 60–70 years old and 11–50% of those over 80 years [4].

While the definition of sarcopenia based on a reduced muscle mass alone served the scientific community fairly well, it was less satisfying for clinicians, the pharmaceutical industry, and regulatory agencies. Unlike bone mineral density, measures of muscle mass have not been widely adopted by clinicians. Regulatory agencies have failed to accept that restoration of muscle mass is a valid reason to allow a drug to be approved for use. Also, many crucial aspects of sarcopenia are missed by the simplistic use of muscle mass as a measure, which has shown to be a weak predictor of outcomes; and the link between muscle mass, muscle function (defined by muscle strength and power), physical performance, and other downstream outcomes is not linear [5–8]. The fact that all clinical measures of muscle mass are in fact estimations and have a wide range of measurement error may partially explain this situation [9]. Research has also showed that loss of muscle strength is two to five times faster than loss of muscle mass and is associated with changes in muscle quality (defined as intramuscular fat) and is more predictive of outcomes [3, 8].