Stalking Sarcopenia

Among the most dramatic biological markers of increasing age are changes in body composition. Although weight may remain stable or increase somewhat throughout adulthood, fat-free mass steadily decreases and fat mass as a percentage of body weight therefore increases [1]. This age-related change is even more impressive if the decrease in muscle mass is measured rather than the decrease in lean body mass or fat-free mass, which includes viscera and bone. The rate of decline by decade is particularly great after age 70 years; this can be confirmed by direct regional assessments of the cross-sectional area of skeletal muscle in images produced by computed tomography. At the mid-thigh level, for example, muscle accounts for 90% of the cross-sectional area in active young men but only 30% of that area in frail elderly women. The average woman's lean body mass is always smaller than that of men at the same age, but the decline is striking nonetheless. Some studies, including the report by Poehlman and colleagues in this issue [2], have shown an accelerated decline associated with menopause. One large study, which combined both cross-sectional and longitudinal data and used total body potassium levels as the most reliable current measure of body cell mass, showed a 1.2% decline in total body potassium levels per year for each of 3 years around menopause [3]. We refer to this age-related loss of skeletal muscle mass as sarcopenia (literally, lack of flesh) to describe a condition that has profound physiologic and clinical consequences and therefore greatly warrants further attention and study [4].