When performing a post isometric relaxation stretch the target muscle is lengthened until a mild stretch is felt. At that point the target muscle is contracted and then relaxed so the muscle can lengthen further. This is an example of innervating this proprioceptor:

The MBLEx is a standardized certification exam produced by the Federation of State Massage Therapy Boards (United States) and is used by many states to license or certify massage therapists. The massage board exam covers these topics:
Anatomy & Physiology, Kinesiology, Pathology & Contraindications: Physiological Effects of Massage, Client Assessment,Ethics, Boundaries, Laws & Regulations and Guidelines for Professional Practice.