MSTN and obesity due to melanocortin 4 receptor deficiency: Postnatal inhibition of myostatin signaling in mice with diet-induced obesity will be necessary to directly compare these two muscle hypertrophy models to determine whether the reduction in adipose tissue mass in HFD-fed constitutively active Akt1 mice is caused by hypertrophy of fast glycolytic fibers, by increasing the activation of the Akt signaling pathways, or both.