Trigger Point Therapy
Trigger Point Therapy is a modality that fits under the umbrella of NMT, or PNMT. Aside from massage therapists, it is popular in many diverse medical circles; Chiropractic, Osteopathic, and Physio/Physical Therapy all teach some version of this approach. One can also easily draw correlations between trigger points and acupressure, shiatsu, and many other traditional massage approaches. As far as modalities go, it has been very heavily researched, but experts are no where near agreeing on what that research suggests. You can find believers and skeptics, and many folks in the middle (like me) waiting for a compelling conclusion.
The basic premise for trigger points is simple, which makes for a good story. When muscle tissue gets damaged in a particular way, usually an overly demanding eccentric activity, bands within that muscle get locked into a contracted state. These bands are hard, like a "muscle knot" but they are usually much smaller and hyper localized. Within a 3-6 millimeter span, if you apply direct pressure on one, there will be sharp pain which refers along quasi-well-documented patterns. Agreement beyond these basic ideas is hard to find