Sarcopenia is a type of muscle loss (muscle atrophy) that occurs with aging and/or immobility. It is characterized by the degenerative loss of skeletal muscle mass, quality, and strength. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors. The muscle loss is related to changes in muscle synthesis signalling pathways. It is distinct from cachexia, in which muscle is degraded through cytokine-mediated degradation, although both conditions may co-exist. Sarcopenia is considered a component of frailty syndrome. Sarcopenia can lead to reduced quality of life, falls, fracture, and disability.Sarcopenia is a factor in changing body composition associated with aging populations; and certain muscle regions are expected to be affected first, specifically the anterior thigh and abdominal muscles. In population studies, body mass index (BMI) is seen to decrease in aging populations while bioelectrical impedance analysis (BIA) shows body fat proportion rising.The term sarcopenia is from Greek σάρξ sarx, "flesh" and πενία penia, "poverty". This was first proposed by Rosenberg in 1989, who wrote that "there may be no single feature of age-related decline that could more dramatically affect ambulation, mobility, calorie intake, and overall nutrient intake and status, independence, breathing, etc." Signs and symptoms
The hallmark sign of sarcopenia is loss of lean muscle mass, or muscle atrophy. The change in body composition may be difficult to detect due to obesity, changes in fat mass, or edema. Changes in weight, limb or waist circumference are not reliable indicators of muscle mass changes.
In the elderly, this often leads to decreased biological reserve and increased vulnerability to stressors known as the "frailty syndrome". Loss of lean body mass is also associated with increased risk of infection, decreased immunity, and poor wound healing. The weakness that accompanies muscle atrophy leads to higher risk of falls, fractures, physical disability, need for institutional care, reduced quality of life, increased mortality, and increased healthcare costs. This represents a significant personal and societal burden and its public health impact is increasingly recognized. Research directions
There are significant opportunities to better understand the causes and consequences of sarcopenia and help guide clinical care. This includes elucidation of the molecular and cellular mechanisms of sarcopenia, further refinement of reference populations by ethnic groups, validation of diagnostic criteria and clinical tools, as well as tracking of incidence of hospitalization admissions, morbidity, and mortality. Identification and research on potential therapeutic approaches and timing of interventions is also needed.New pharmaceutical therapies in clinical development include myostatin and the selective androgen receptor modulators (SARMs). Nonsteriodal SARMs are of particular interest, given they exhibit significant selectivity between the anabolic effects of testosterone on muscle, but with little to no evidence of androgenic effects (such as prostate stimulation in men). See also
Cachexia
Ageing
Frailty syndrome
Geriatrics
Dynapenia

References
Further reading
Fujita S, Volpi E (January 2006). "Amino acids and muscle loss with aging". The Journal of Nutrition (Review). 136 (1 Suppl): 277S–80S. doi:10.1093/jn/136.1.277S. PMC 3183816. PMID 16365098. Roubenoff R (December 2007). "Physical activity, inflammation, and muscle loss". Nutrition Reviews. 65 (12 Pt 2): S208-12. doi:10.1111/j.1753-4887.2007.tb00364.x. PMID 18240550.