Round versus concave back

Hey guys!

I was wondering if anyone has good video or pictures that exemplifies round versus concave (engaged) back at the trot on a western-tacked horse. I am trying to be able to spot the difference and it's tough, especially looking at videos of me where my pad extends back over the areas I'm trying to see! Ha.

Thanks. :)

Ash

I have no pics, but just look at the horse's back behind the saddle in the Lumbar-sacral area before the croup. If it's up, he's round. If it's dipped, he's hollow.