When you do the vertical solo Sun ba gua exercise why do you arch your back so much?

also, when you were running the Shen Wu Academy when did your students do bag work to develop kicking and punching power? Did you allot time during your mma classes or did they come on their own time to do that?

It's important to practice back arching exercises not only to condition your back and spine to bend backwards (for health, strength and flexibility), but also because, sometimes, you'll have to arch back when you are fighting, and it's very important to be able to arch correctly so you can maintain your balance and still have access to whole body power.

In my old school, we hit mitts and pads almost every class.

Tim,

Are you against toe to heel stepping in Sun ba gua as opposed to the heel to toe you teach?

There is no toe to heel stepping in Sun Style Baguazhang.