What is the primary issue observed in active trigger points?

Active trigger points are characterized by their ability to reproduce pain spontaneously and limit muscle function, particularly muscle lengthening. When a trigger point is active, it generates pain that can be felt in the local area as well as in referred regions, which can significantly affect the individual's range of motion and overall functionality. These trigger points often lead to discomfort during both rest and muscle movement due to the sustained contraction of the muscle, causing tightness and stiffness.

The other options highlight attributes that are not representative of active trigger points. For instance, active trigger points do indeed cause muscle tightness and cannot be considered asymptomatic, as they are defined by their pain-producing characteristics. Furthermore, they do not solely exist in the absence of a mechanical stimulus; active trigger points can be present regardless of whether an external stimulus is applied. Understanding these characteristics helps in the identification and treatment of muscle pain and dysfunction in a clinical setting.