The painful point can be felt as a nodule or band in the muscle, and a twitch response can be elicited on stimulation of the trigger point.
Palpation of the trigger point reproduces the patient's complaint of pain, and the pain radiates in a distribution typical of the specific muscle harboring the trigger point.
Travell and Simons' seminal work on the subject, Myofascial Pain and Dysfunction: The Trigger Point Manual,[1] states the following:
Around 75% of pain clinic patients have a trigger point as the sole source of their pain.
Arthritis is often cited as the cause for pain even though pain is not always concomitant with arthritis. The real culprit may be a trigger point, normally activated by a certain activity involving the muscles used in the motion, by chronically bad posture, bad mechanics, repetitive motion, structural deficiencies such as a lower limb length inequality or a small hemipelvis, or nutritional deficiencies.