The main muscle that allows you to turn your palm up is called the supinator. Motor weakness of the supinator can be caused by pressure on the posterior interosseous nerve at the elbow. If this nerve is involved, you may be having some weakness lifting up (extending) the wrist and fingers.

There are many possible causes of nerve pressure. Sometimes a fibrous band of connective tissue grows over or around the nerve. A ganglion cyst or tumor may be the cause of these symptoms. Repetitive use of the arm may be a factor. It's best to have a doctor examine your arm and find out the exact cause.