I try to not hunch, and imagine a straight line from my head to my butt. I'll rotate my pelvis forward and basically let my joints do the bending instead of my spine, if you catch my drift.

An opposite example was another BF'er who posted pictures of himself looking for posture advice. His lower back, from his tailbone up through the first few vertebrae, was almost vertical, and his forward lean came almost entirely from his stomach area. It just looked really uncomfortable to me.

There's some yoga-like sensibility to how I try to set my posture. The more I can keep my body in balance, the more comfortable I feel, and the longer I can last doing whatever I'm doing.