The first reports of accurate skeletal muscle mass measurement in human subjects appeared at about the same time as introduction of the sarcopenia concept in the late 1980s. Since then these methods, computed tomography and MRI, have been used to gain insights into older (i.e. anthropometry and urinary markers) and more recently developed and refined methods (ultrasound, bioimpedance analysis and dual-energy X-ray absorptiometry) of quantifying regional and total body skeletal muscle mass. The objective of this review is to describe the evolution of these methods and their continued development in the context of sarcopenia evaluation and treatment. Advances in these technologies are described with a focus on additional quantifiable measures that relate to muscle composition and ‘quality’. The integration of these collective evaluations with strength and physical performance indices is highlighted with linkages to evaluation of sarcopenia and the spectrum of related disorders such as sarcopenic obesity, cachexia and frailty. Our findings show that currently available methods and those in development are capable of non-invasively extending measures from solely ‘mass’ to quality evaluations that promise to close the gaps now recognised between skeletal muscle mass and muscle function, morbidity and mortality. As the largest tissue compartment in most adults, skeletal muscle mass and aspects of muscle composition can now be evaluated by a wide array of technologies that provide important new research and clinical opportunities aligned with the growing interest in the spectrum of conditions associated with sarcopenia.

This study reports the metabolic and morphological characteristics of bovine intermuscular adipose tissue (AT) throughout foetal growth. Our hypothesis was that the histological and molecular features of intermuscular AT would be different from those previously reported for foetal perirenal AT, based on its anatomical location near the muscle and the recent identification of two distinct adipocyte precursors in mouse AT depending on their locations. To address this question, intermuscular AT was sampled from Charolais and Blond d'Aquitaine foetuses at 180, 210 and 260 days post conception (dpc). The two bovine breeds were chosen because of the higher adiposity of Charolais than Blond d'Aquitaine cattle during the postnatal life. Regardless of the breed, adipocyte volume increased slightly (+38%, P < 0.01) with increasing foetal age. This was concomitant with a decrease (P < 0.05) in the activity of enzymes involved in de novo fatty acid (FA) synthesis (FA synthase and glucose-6-phosphate dehydrogenase) and FA esterification (glycerol-3-phosphate dehydrogenase) when expressed per million adipocytes, and with an increase (P ⩽ 0.01) in mRNA abundances for uncoupling protein 1, adiponectin and leptin (LEP) between 180 and 260 dpc. No difference was observed in the adipocyte volume between breeds, which was consistent with the lack of major between-breed differences in mRNA abundances or activities of enzymes involved in lipid metabolism. The mRNA abundance of lipoprotein lipase was maintained across ages, suggesting a storage of circulating FA rather than of FA synthesized de novo. Plasma LEP increased with foetal age, but only in the Charolais breed (+71%, P ⩽ 0.01), and was two- to threefold higher in Charolais than Blond d'Aquitaine foetuses. Regardless of the breed, bovine intermuscular AT contained predominantly unilocular adipocytes believed to be white adipocytes that were larger at 260 dpc than at 180 dpc. These data thus challenge current concepts of the largely brown nature of bovine foetal AT (based on histological and metabolic features of perirenal AT as previously reported a few days before or after birth).