Writing with Arm?

I've recently learned that you're supposed to write with your arm instead of your wrist, and I've been coming across some issues trying to implement that. I'm not sure whether it's because I'm doing it wrong or if it's normal. Trying to write with my arm, I've found that not only is my writing more messy and less controlled, but also that my shoulder/upper arm tenses up quite a bit and starts to cramp. Is this a normal thing or is there something I'm doing wrong, and how do I correct it?