the posterior surface of the iliac crest, the iliopsoas ligament

the twelfth rib, the transverse processes of L1-L4

Unilaterally : lateral flexion
Bilaterally : back extension

Quadratus lumborum is one of bilateral muscles that compose the posterior abdominal wall along with psoas major, iliacus. It plays a significant role in the stabilization of the lumbar spines and pelvis, and it is easy to be weakened. It is one of the causes for chronic lower back pain. Patients may experience a stiff back pain during a prolonged sitting, and difficulty in lateral flexion and rotation of the back; the intervertebral disc lesions may be accompanied.

Erector Spinae, Gluteus Minimus

Apply the base of the Y strip to PSIS.
With the patient's body flexed forward in order to fully stretch the muscle, tape it towards the twelfth rib.