What causes sarcopenia?

In the case of primary sarcopenia, there is a wide range of factors that contribute to the development of the condition, which are not entirely understood and largely thought to be natural consequences of aging.^[1] These include decreased type II muscle fiber size, loss of motor units (i.e., a motor neuron and the muscle fibers it innervates), hormonal changes (i.e., a decline in serum levels of anabolic hormones like testosterone and insulin-like growth factor 1), anorexia (i.e., decreased or loss of appetite), decreased physical activity, anabolic resistance (i.e., a blunted muscle protein synthesis response to dietary protein and resistance exercise), systemic inflammation, insulin resistance, and increased body fat.^[2]