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CHAPTER 2 Epidemiology of Muscle Mass Loss with Age
Marjolein Visser
Department of Health Sciences, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
INTRODUCTION
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 originally 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 age‐related 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.
MUSCLE MASS DIFFERENCES AMONG AGE GROUPS
Comparisons among young and older men and women with regard to muscle size have been made in several small studies starting in the 1980s. The results showed that healthy women in their 70s had a 33% smaller quadriceps cross‐sectional area as obtained by compound ultrasound imaging compared with women in their 20s [2]. Using the same methodology and age groups, healthy older men had a 25% smaller quadriceps cross‐sectional area [3]. In a study investigating thigh composition using five computed tomography (CT) scans of the total thigh, smaller muscle cross‐sectional areas were observed in older men compared with younger men even though their total thigh cross‐sectional area was similar. The older men had a 13% smaller total muscle cross‐sectional area, 25.4% smaller quadriceps, and 17.9% smaller hamstring cross‐sectional area [4]. Using magnetic resonance imaging of the leg anterior compartment, muscle area was measured in young and older men and women [5]. The older persons had a smaller area of contractile tissue, 11.5% less in women and 19.2% less in men, compared with the young persons. These data, obtained by different body composition technologies, clearly showed a smaller muscle size in older persons compared with young persons. The observed differences in muscle size between age 20 and age 70 suggested a loss of skeletal muscle mass of about 0.26–0.56% per year.