“…Although their diagnostic criteria are similar, sarcopenia is characterised by a progressive muscle loss associated with ageing, in contrast to myopenia that may, at least in part, be developmental or "intrinsic." 8,9,23,37,50,51,[54][55][56][57] Fontan-associated myopenia is likely due to a myriad of factors, which are poorly characterised. These factors include, but are not limited to, physical inactivity, increased protein turnover in the myocardium and skeletal muscle, increased energy requirements of the peripheral pump with exercise, metabolic alteration of substrates (i.e., glucose, lipids, amino acids) secondary to body composition changes, inadequate dietary intake compared to nutritional requirements, malabsorption, nutrition-impact symptoms, feeding difficulties during childhood, and reduced appetite secondary to low levels of the appetite hormone ghrelin.…”