I assume you mean academic warm-up and not physical?
There are pros and cons to this method. As a tutor I have students who get really nervous reviewing their material before an exam. Me personally I always studied before the exam for last minute cramming and refresher.
That being said, with verbal it's different. It's not like bio or chem where a last-minute review will give you a formula or term to remember. It's just reading.
So, I would think it can be confusing reading something unrelated before the exam and having that stuck in your head. Again, just my opinion.
With something like verbal you're better off building a long-term strategy. Read every day, do practice every day, and get your brain thinking the right way in the long term.
As for actual warming up. Yes exercise and stretching has been proven (don't remember where) to increase test-taking ability