Anatomy Trains Superficial Back Line collection. Note: this collection contains dissection imagery and may not be suitable for all viewers. The Superficial Back Line (SBL) connects and protects the entire posterior surface of the body like a carapace from the bottom of the foot to the top of the head in two pieces - toes to knees and knees to brow. When the knees are extended, as in standing, the SBL functions as one continuous line of integrated myofascia.