Step-by-step explanation:
There are no such things as muscles of desire in medical terminology but there is a condition that is referring to the desire for muscles and it is called Bigorexia.
When somebody has Bigorexia they are always checking themselves in the mirror, they are eating more proteins, and they are always wanting to gain more weight by working out. They want their muscles to look big and they are always seeing themselves like not big enough or small.