Described by Blanco et al as an advancement of the classical TAP block.
QLB1: Block performed at the anterolateral border of the quadratus lumborum muscle where it adjoins the aponeurosis of the transversus abdominis
QLB2: Block performed posterior to the quadratus lunborum muscle
QLB 3 or Transmuscular QLB block performed between quadratus lumborum and psoas muscle, under the transversalis fascia

Useful read
http://www.respond2articles.com/ANA/f...

http://bja.oxfordjournals.org/forum/t...

http://cdn.intechopen.com/pdfs/38231/...

http://www.ncbi.nlm.nih.gov/pmc/artic...

Still in its early stages, trials are ongoing of its clinical utility

https://clinicaltrials.gov/ct2/show/N...
Quadratus Lumborum Block vs Tranversus Abdominis Plane Block for Cesarean Section

https://clinicaltrials.gov/ct2/show/N...
Transmuscular Quadratus Lumborum Block for Laparoscopic Cholecystectomy (TQL)