Sarcopenia

Sarcopenia is the accelerated loss of skeletal muscle mass and function commonly, but not exclusively, associated with advancing age, and it can lead to decline in physical function and mobility as well as increased risk of falls, fractures and premature mortality. ^[1] The term 'sarcopenia' was coined after Rosenberg in 1989 emphasized the importance of the loss of skeletal muscle mass that occurs with aging. ^[2] Originally characterised as loss of muscle mass, the definition has evolved to focus on loss of skeletal muscle function, particularly strength. ^[3]

Loss of muscle mass with aging is largely due to the progressive loss of motoneurons and is associated with reduced muscle fiber number and size, with muscle function declining because motoneuron loss is not adequately compensated by reinnervation. ^[4] In the elderly a lack of exercise, malnutrition and hormonal changes lead to neuromuscular junction insufficiency, reduced repair and regeneration capacity, inflammatory cell infiltration and oxidative stress, resulting in muscle protein degradation exceeding synthesis. ^[2] Mitochondrial dysfunction causes metabolic abnormalities such as insulin resistance, which may contribute to the quantitative and qualitative skeletal-muscle changes seen in sarcopenia. ^[2]

For the diagnosis of sarcopenia, the European Working Group on Sarcopenia in Older People (EWGSOP) recommends using the presence of both low muscle mass and low muscle function (strength or performance), and suggests a case-finding algorithm based on gait speed, grip strength and muscle mass. ^[5] The Global Leadership Initiative in Sarcopenia (GLIS) reached strong consensus that muscle mass, muscle strength and muscle-specific strength should all be components of the conceptual definition, whereas impaired physical performance was accepted as an outcome rather than a component of sarcopenia. ^[6] Even using a conservative approach the prevalence of sarcopenia is between 5% and 10% in the general population, and in a systematic review it was estimated to affect 10% to 16% of the elderly worldwide. ^{[1] [7]} In a global meta-analysis the prevalence of sarcopenia varied between 10% and 27% depending on the classification and cut-off point used, while severe sarcopenia ranged from 2% to 9%. ^[8]

Sarcopenia is associated with increased morbidity, mortality and health-care expenditure yet remains under-recognized and poorly managed in routine clinical practice, in part due to a lack of available diagnostic testing and uniform diagnostic criteria. ^[9] Resistance exercise is currently the mainstay of treatment, and there are no pharmacologic agents approved for the treatment of sarcopenia. ^{[1] [9]} Sarcopenia can be a primary component of physical frailty, and its presence is closely related to falls and the need for nursing care in the elderly. ^[2] In older people with sarcopenia, resistance training significantly improves muscle strength and gait speed compared with control, making it a powerful intervention against sarcopenic muscle loss ^[10].