Epidemiology of Muscle Mass Loss with Age

The development of new body composition methods in the early 1970s and 1980s led to more research on this topic, including the study of differences in body composition between young and older persons. These initial studies were followed by much larger studies covering a wide age range investigating how body composition varied across the life span. Variations in lean body mass and fat-free mass were described between age groups. These studies served as the important scientific basis for developing the concept Sarcopenia. Sarcopenia was defined as the age-related loss of muscle mass [1]. The term is derived from the Greek words sarx (flesh) and penia (loss). The development of this concept further stimulated research in this specific body composition area. More recently, large-scale studies among older persons have included accurate and precise measurements of skeletal muscle mass. Moreover, these measurements have been repeated over time, enabling the sarcopenia process to be studied. This chapter will discuss the results of epidemiological studies investigating the agerelated loss of skeletal muscle mass. First, several cross-sectional studies will be presented comparing the body composition between younger and older persons. Then prospective studies will be discussed investigating the change in body composition with aging. The chapter will conclude with the results of more recent, prospective studies that precisely measured change in skeletal muscle mass in large samples of older persons.