I was wondering what are quadriplegic muscles?

Guessing your intent. There are no such things as quadriplegic muscles. What I am guessing you are trying to ask is the meaning of "quadriplegia or quadriplegic?" so the term quadriplegia means "muscle paralysis in 4 limbs." in practical terms you've probably heard the statement, "paralyzed from the neck down." that's quadriplegia. You don't need to include the word "muscle" along with the term.