Especially if you have carpal tunnel or tendonitis tendencies. But also using your arms can complicate those - you still have to avoid tension in the wrist, which can be just as bad as moving your wrist a lot.

My hands are small the size of a 7th, to make it worse my R.H's 5th finger is damaged.

everyday, to start off, I practise chopin's etude op.25 no.10 "Octaves" and I find that it really helps.

remember that when you play octaves, use your eyes to guide your hands and lift your wrists up. Shape your hands like you are holding an orange and you can't let go of that shape.

The other day my teacher actually placed a pomelo on my hand to let me grasp the idea.