A muscle head is someone who spends all their energy with their head in a book.
Muscle heads are the guys who you do not like in high school who end up making six figures after you graduate. Brain always wins over Brawn! You go muscleheads!
The musclehead stayed home from the party while we had fun.
Male (or female) body builder whose only concern in life is bigger muscles. Usually implies little-no brain activity.
John is a complete muscle head, nice to look at but nothing upstairs.