Skeletal muscle loss: cachexia, sarcopenia, and inactivity

Loss of skeletal muscle mass occurs during aging (sarcopenia), dis-ease (cachexia), or inactivity (atrophy).This article contrasts andcom-pares the metabolic causes of loss of muscle resulting from these conditions. An understanding of the underlying causes of muscle loss is critical for the development of strategies and therapies to preserve musclemass and function.Loss of skeletalmuscle protein results from an imbalance between the rate of muscle protein synthesis and deg-radation. Cachexia, sarcopenia, and atrophy due to inactivity are char-acterized by a loss of muscle mass. Each of these conditions results in a metabolic adaptation of increased protein degradation (cachexia), decreased rate ofmuscle protein synthesis (inactivity), or an alteration in both (sarcopenia). The clinical consequences of bedrestmaymimic those of cachexia, including rapid loss of muscle, insulin resistance, and weakness. Prophylaxis against bedrest-induced atrophy includes nutrition support with an emphasis on high-quality protein. Nutri-tional supplementation alone may not prevent muscle loss secondary to cachexia, but, in combination with the use of an anabolic agent, it may slow or prevent muscle loss. Am J Clin Nutr doi: 10. 3945/ajcn.2010.28608A