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Introduction
The term sarcopenia, derived from two ancient Greek words (sarcos and penia, i.e., 'flesh' and ‘loss'), was used for the first time in 1989 by Rosenberg [1] to describe the loss of muscle mass correlated with aging. Since then, the term sarcopenia defined a syndrome characterized by a progressive and generalized loss of skeletal muscle mass and muscle strength, which is accompanied by a reduction in the quality of life and increased risk of disability and death [2,3]. This definition of sarcopenia has been developed in 2010 by the European Working Group on Sarcopenia in Older People (EWGSOP) that suggests a different classification staging as: ‘pre-sarcopenia', ‘sarcopenia' and ‘severe sarcopenia' [4]. However, the growing elderly population and the increasing incidence of obesity in Western societies require more accurate studies to evaluate the prevalence of sarcopenia in this group and its related risks. Moreover, the prevalence of sarcopenic obesity is rising in obese adults due to an imbalance between lean mass, excess body fat and total body size that appears earlier in life, because of the disproportion between the even conserved lean mass when compared to fat mass and exceeding body weight that lean mass could support [5].
Most of the literature focuses on the obesity/poor muscle mass combination, usually defined as sarcopenic obesity. Sarcopenic obesity was defined for the first time in 1996 by Heber et al. [6] as the combination of reduced fat free mass (FFM) evaluated by bioimpedance analysis (BIA) and fat mass excess, expressed as percent of body weight. In a recent review, criteria adopted by different authors partially overlapped. One of the main obstacles is represented by the definition of sarcopenic obesity and especially whether it should be based only on criteria of body composition or functional criteria should also be taken into account [7].
Changes in body composition typically occur during the aging process: lean body mass tends to decline with age, accompanied by a relative increase of total adipose tissue with fat infiltration of muscles [8]. Moreover, engagement in sedentary activities as well as unhealthy dieting may lead to the development of phenotypic aspects of sarcopenic obesity even in younger subjects [9]. Chronic inflammation induced by obesity is the main factor accounting for additional depletion of muscle mass...