FROM THE CHICAGO MEETINGS Sarcopenia JOHN E. MORLEY, RICHARD N. BAUMGARTNER, RONENN ROUBENOFF, JEAN MAYER, and K. SREEKUMARAN NAIR ST. LOUIS, MISSOURI, ALBUQUERQUE, NEW MEXICO, BOSTON, MASSACHUSETTS, and ROCHESTER, MINNESOTA Sarcopenia is a term utilized to define the loss of muscle mass and strength that occurs with aging. Sarcopenia is believed to play a major role in the pathogen- esis of frailty and functional impairment that occurs with old age. Progressive muscle wasting occurs with aging. The prevalence of clinically significant sarcope- nia is estimated to range from 8.8% in young old women to 17.5% in old old men. Persons who are obese and sarcopenic (the “fat frail”) have worse outcomes than those who are sarcopenic and non-obese. There is a disproportionate atrophy of type IIa muscle fibers with aging. There is also evidence of an age-related decrease in the synthesis rate of myosin heavy chain proteins, the major anabolic protein. Motor units innervating muscle decline with aging, and there is increased irregularity of muscle unit firing. There are indications that cytokines—especially interleukin-1β, tumor necrosis factor-α, and interleukin-6—play a role in the pathogenesis of sarcopenia. Similarly, the decline in anabolic hormones—name- ly, testosterone, dehydroepiandrosterone growth hormone, and insulin-like growth factor-I—is also implicated in the sarcopenic process. The role of the physiologic anorexia of aging remains to be determined. Decreased physical activity with aging appears to be the key factor involved in producing sarcopenia. An increased research emphasis on the factors involved in the pathogenesis of sar- copenia is needed. (J Lab Clin Med 2001;137:231-43) Abbreviations: CRP = C-reactive protein; DXA = dual energy x-ray absorptiometry; IGF-1 = insulin-like growth factor-1; IL-1 = interleukin-1; IL-1Rα = IL-1 receptor antagonist; MHC = myosin heavy chain; PBMC = peripheral blood mononuclear cell; RSMI = relative skeletal muscle mass; TNF-α = tumor necrosis factor-α 231 From the Division of Geriatric Medicine, Saint Louis University School of Medicine; the Division of Epidemiology and Preventive Medicine, University of New Mexico School of Medicine, Albu- querque; the Nutrition, Exercise Physiology, and Sarcopenia Labora- tory, USDA Human Nutrition Research Center on Aging, Tufts Uni- versity, Boston; and the Division of Endocrinology, Metabolism, Nutrition and Internal Medicine, Mayo Clinic, Rochester. Supported in part by USDA Cooperative Agreement 58-1950-9-001 and National Institutes of Health Grant AG15797. The contents of this publication do not necessarily reflect the views or policies of the US Department of Agriculture, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government. Presented at the Seventy-third Meeting of the Central Society for Clinical Research, Sept 21 through 23, 2000, Chicago, IL. Submitted for publication August 15, 2000; revision submitted November 17, 2000; accepted November 27, 2000. Reprint requests: John E. Morley, MB, BCh, Department of Medi- cine/Geriatrics, Saint Louis University School of Medicine, 1402 South Grand, Room M-238, St Louis, MO 63104. 5/1/113504 doi:10.1067/mlc.2001.113504