How do you breathe during a session?

The wiki suggests two types of breathing:

  1. Deep breathing to relax, which I think is consciously breathing into the lower chest

  2. 'Valley' breathing, to "stimulate the abdominal and pelvic areas". I've done a bit of research but can't quite understand what this is. Does anyone do it?

I've tried deep breathing during a session but found it a bit of a frustration because the consistent conscious effort took my concentration away from other sensations.

Does anyone else pay attention to breathing? What do you do?