The term Trigger Points (TrPs) is often used by therapists to describe localised tender spots that may refer pain to other areas when stimulated. Whilst there seems to be less argument about whether they exist or not there is more about what they might be and there are major issues with being able to find them, perhaps 50/50 at best, and the reproducibility of actually being able to find them, 18%. In fact in 1992 a, admittedly small, blind study
was carried out on them using using both those with Myofascial TrP's and fibromyalgia. Yet the best of the best of Trigger Point specialists including Simons, of Travell and Simons writers of the Trigger Point bible, and 3 others couldn't find or agree on any where they were given as much time as required to find them.
For myself they were never a good fit in any treatment I was trying to carry out as the treatment of them seemed to be the polar opposite of what I was trying to do otherwise, that is relieve pain not cause more pain. The treatment of TrP's for most manual therapists seems to revolve around pressing hard on something that is already sore and use the symptoms to help understand what the underlying problem may be and treat that not the symptoms, I've always felt that they were symptoms of an issue elsewhere rather than a problem in and of themselves.
There is certainly more evidence to suggest that TrP's may be a sensitization of the nervous system, possibly centrally. This carries even more weight when you consider that the areas that the referred pain cover are very similar to the path of the peripheral nerves. There is a great short piece over at the HumanAntiGravitySuit
giving a couple of lovely diagrams of how the idea of TrP's may be more about nerves.