Muscles do not run simply from origin of one bone to insertion on another. All muscles function in chains, or slings, connecting to each other to form more powerful movers. Some muscles attach more to the next muscle in the chain, than they do to the bone that they cross! There is probably one sling that is more famous than any other, not that it’s more important, but that it’s so large and visible in dissection. The Thoraco-Lumbar Fascia cross our entire lower back region, and is a key component in connecting the opposite shoulder to hip. The largest two muscles are the Glute Max and the Latisimus Dorsi, and we use this sling CONSTANTLY. So go prone young men and women and work that Thoraco !!!