In addition, in the young muscle, mRNA expression of a gene involved in proteolysis [17], Atrogin1, was significantly increased due to the reduction of the muscle fiber area in the H group compared with that in the IH group, and mRNA expression of myostatin, which is involved in the promotion of proteolysis and inhibition of muscle formation [18], was significantly increased in the IH group. This evidence concerns the gene MSTN and isolated hemihyperplasia.