Hi.
I've been looking into sway-back posture recently & I found some quite useful info in the book "Muscles, Testing and Functions with Posture and Pain" (5th ed), by Kendall, et al (ISBN: 0781747805).

You can look at & search in the book online by going to google books & searching for it there. (I haven’t posted here enough to be allowed to insert URLs).

Also, there will be links there to other, related books e.g. "Management of Common Musculoskeletal Disorders: Physical Therapy Principles and Methods" by Kessler & Hertling (ISBN: 0781736269)

I hope this helps,

Jeff