Trigger Points: Effects on Muscle Function by Dr. Hinkeldey
In his first article on HealthPath, Dr. Hinkeldey discusses the role of trigger points on muscle function and resolving dysfunctional movement patterns.
Manual therapy continues to garner more and more momentum throughout the healthcare continuum. Interventions like manipulation, Myofascial release, trigger point injections, and massage have been prominent topics within the literature and amongst physicians dealing with pain management. This blog will dissect some of the current literature regarding the muscular and fascial systems. Most notable to any physician will be the effect that trigger points can have on muscle function and performance. It is my hope that by the end of these posts, you will have a better understanding of: 1.The difference between active and latent trigger points. 2.The effect latent trigger points have on synergistic muscle function. 3.The effect that latent trigger points have on antagonistic muscle function. 4.The effect that latent trigger points have on muscle fatigability.
Trigger points have been known pain generators for quite some time. Travell and Simons identified these lesions as active pain generators years ago, but recently this topic has been prevalent within the current literature. Trigger points are described as either active or latent. Today’s selection will concentrate on the effect that latent trigger points have on the neuromuscular system.
Active Trigger Points vs. Latent Trigger Points
Latent trigger points are described as “a focus of hyperirritability in a muscle taut band that is clinically associated with a local twitch response and tenderness and/or referred pain upon manual examination (1).” Active trigger points share the above qualities with the exception that manual examination is not necessary to produce the pain response. While there is still much to learn about the latter, it is known that latent trigger points, when biopsied, do not possess the bradykinin, Substance P, calcitonin gene-related peptide, TNF-a, IL-1,6,and 8, serotonin, and norepinephrine which have all been associated with the inflammatory response, which is likely why active trigger points produce pain without manual provocation. The latter study examined active trigger points within the trapezius vs. latent or no trigger points. Even more interesting is that uninvolved sites far from the trapezius (gastrocnemius) also illustrated higher concentrations of inflammatory mediators in the active trigger point population, suggesting some systemic involvement. The latter may provide the rationale for why the active trigger point produces the pain response without manual examination (2).
Latent Trigger Point and Synergistic Muscle Function
Latent trigger points, while non-painful without manual examination, do still have a negative effect on muscle function. Ge Hy et al have examined intermuscular and surface EMG activity within individuals with latent trigger points in the trapezius muscle and compared the results to the opposite side without the latent trigger point. They found that the trapezius with the latent trigger point illustrated greater intermuscular EMG activity. Failure to correct the latter may result in spatial summation and transition of the latent trigger point to an active trigger point (3). Regardless of whether or not the lesion becomes active or not, increased muscle activation of the trapezius may result in early elevation of the scapula which could eventually result in shoulder impingement. Therefore, reducing this latent (non-symptomatic) trigger point could hypothetically assist in restoring normal shoulder function and prevent shoulder impingement from occurring. While the latter would not constitute “medically necessary care” as determined by insurance companies, it would be an argument for preventative treatment especially from a sports medicine perspective.
Latent Trigger Points and Antagonistic Muscle Function
In addition to the effect that latent trigger points have on synergistic muscle function, latent trigger points also have an effect on antagonistic muscle function. Throughout the physician education, many different theories regarding muscle facilitation and inhibition are introduced. The concept of agonistic and antagonistic muscle function is well understood, and within rehabilitation, the concept of reciprocal inhibition is utilized to inhibit over facilitated musculature. When analyzed, latent trigger points are associated with:
Reduced efficiency of reciprocal inhibition, which may contribute to the delayed and incomplete muscle relaxation following exercise, disordered fine movement control, and unbalanced muscle activation. Elimination of latent trigger points and/or prevention of latent trigger points from becoming active may improve motor functions (4).
Latent Trigger Points and Muscle Performance
It is quite clear that latent trigger points have an effect on the synergistic and antagonistic muscle function. As a result, latent trigger points also have an effect on muscle performance and fatigability. According to EMG studies, latent trigger points accelerate the development of muscle fatigue. As a result, the fatigue results in overload of the active motor units adjacent to the trigger point which accelerates fatigue of the respective motor units. The latter is important as today’s current society is centered on increasing performance and endurance. Reducing latent trigger points may increase the patient’s ability to do more.
An Argument for Trigger Point Therapy
Hopefully, the above makes it quite clear that it is of the utmost importance when treating a dysfunctional movement pattern to first resolve the trigger point whether it is active or latent. It also effectively makes the argument that it is important to evaluate and treat the entire body even if pain is not present. Latent trigger points result in altered synergist, antagonist, and fatigability of muscle function; therefore, it is important to identify these lesions and treat them before they become active or result in other debilitating conditions.