[Pathological state or cause of sarcopenia.]

Skeletal muscle atrophy by aging(Sarcopenia)is more likely to occur in lower limbs rather than upper ones, and in the thigh rather than in the lower leg, and in the anterior side of thigh rather than posterior, faster in men than in women. It differs from disuse muscle atrophy in that it occurs slowly and gradually, hard to be recovered, or fast twitch fibers are mainly involved. Many factors or phenomena are known to contribute to proceed sarcopenia. In the aged skeletal muscle tissue, the number of satellite cells or motor neurons decrease and the function of the neuro-muscular junction declines. Oxidative stress and chronic inflammation increase as aging which relate with sarcopenia. Inflammatory cytokines, such IL-6, TNF-α, IL-5 play the roles Muscle protein breakdown is up regulated through ubiquitin-dependent proteolysis. Oxidative stress influences mitochondrial dysfunction or induces apoptosis. Also as aging, anabolic factors which are preferable to protein synthesis, such as IGF-1, sex hormones, vitamin D, or branched chain amino acid.