Latent Myofascial Trigger Points

A latent myofascial trigger point (MTP) is defined as a focus of hyperirritability in a muscle taut band that is clinically associated with local twitch response and tenderness and/or referred pain upon manual examination. Current evidence suggests that the temporal profile of the spontaneous electrical activity at an MTP is similar to focal muscle fiber contraction and/or muscle cramp potentials, which contribute significantly to the induction of local tenderness and pain and motor dysfunctions. This review highlights the potential mechanisms underlying the sensory-motor dysfunctions associated with latent MTPs and discusses the contribution of central sensitization associated with latent MTPs and the MTP network to the spatial propagation of pain and motor dysfunctions. Treating latent MTPs in patients with musculoskeletal pain may not only decrease pain sensitivity and improve motor functions, but also prevent latent MTPs from transforming into active MTPs, and hence, prevent the development of myofascial pain syndrome.     

Identification and quantification of myofascial taut bands with magnetic resonance elastography

Chen Q, Bensamoun S, Basford JR, Thompson JM, An K-N. Identification and quantification of myofascial taut bands with magnetic resonance elastography.

Objective

To explore the feasibility of using a new magnetic resonance imaging (MRI) technique—magnetic resonance elastography (MRE)—to identify and quantitate the nature of myofascial taut bands.

Design

This investigation consisted of 3 steps. The first involved proof of concept on gel phantoms, the second involved numeric modeling, and the third involved a pilot trial on 2 subjects. Imaging was performed with a 1.5T MRI machine. Shear waves were produced with a custom-developed acoustically driven pneumatic transducer with gradient-echo image collection gated to the transducer’s motion. Shear wave propagation were imaged by MRE.

Setting

An MRI research laboratory.

Participants

Two women, one with a 3-year history of myofascial pain and the other serving as the control.

Interventions

Not applicable.

Main Outcome Measures

MRE images, finite element analysis calculations, and tissue and phantom stiffness determinations.

Results

Results of the phantom measurements, finite element calculations, and study patients were all consistent with the concept that taut bands are detectable and quantifiable with MRE imaging. The findings in the subjects suggest that the stiffness of the taut bands (9.0±0.9KPa) in patients with myofascial pain may be 50% greater than that of the surrounding muscle tissue.

Conclusions

Our findings suggest that MRE can quantitate asymmetries in muscle tone that could previously only be identified subjectively by examination.     

The evaluation of electrodermal properties in the identification of myofascial trigger points

OBJECTIVES: To determine whether skin resistance measurements can objectively identify the location of myofascial trigger points (MTPs) and to differentiate between 3 states. DESIGN: Static group comparison. SETTING: Climate-controlled laboratory. PARTICIPANTS: Forty-nine participants (age, 20.5+/-2.6 y) were assigned to 1 of 3 groups based on clinical examination result: absent (n=21), latent (n=16), or active (n=12) MTP. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Skin resistance (in kilo-ohms). RESULTS: The 16 data points were divided into 3 categories for analysis: MTP site, surrounding tissue proximal to the MTP (first ring), and area furthest from the MTP (second ring). There was a significant increase in skin resistance between the MTP (403.64+/-124.73 kOmega), first ring (419.66+/-123.04 kOmega), and second ring (454.61+/-163.19 kOmega) (P<.01). The measurements did not differ significantly between the 3 MTP states. CONCLUSIONS: The changes in skin resistance between the MTP and the surrounding tissue support the inclusion of this technique to help identify MTPs. The similarity between MTP states warrants investigation into the physiologic differences at specific anatomic locations.     

Endplate potentials are common to midfiber myofacial trigger points

OBJECTIVES: To compare the prevalence of motor endplate potentials (noise and spikes) in active central myofascial trigger points, endplate zones, and taut bands of skeletal muscle to assess the specificity of endplate potentials to myofascial trigger points. DESIGN: This nonrandomized, unblinded needle examination of myofascial trigger points compares the prevalence of three forms of endplate potentials at one test site and two control sites in 11 muscles of 10 subjects. The endplate zone was independently determined electrically. Active central myofascial trigger points were identified by spot tenderness in a palpable taut band of muscle, a local twitch response to snapping palpation, and the subject's recognition of pain elicited by pressure on the tender spot. RESULTS: Endplate noise without spikes occurred in all 11 muscles at trigger-point sites, in four muscles at endplate zone sites outside of trigger points (P = 0.024), and did not occur in taut band sites outside of an endplate zone (P = 0.000034). CONCLUSIONS: Endplate noise was significantly more prevalent in myofascial trigger points than in sites that were outside of a trigger point but still within the endplate zone. Endplate noise seems to be characteristic of, but is not restricted to, the region of a myofascial trigger point.     

Myofascial trigger points

Painful conditions of the musculoskeletal system, including myofascial pain syndrome, constitute some of the most important chronic problems encountered in a clinical practice. A myofascial trigger points is a hyperirritable spot, usually within a taut band of skeletal muscle, which is painful on compression and can give rise to characteristic referred pain, motor dysfunction, and autonomic phenomena. Trigger points may be relieved through noninvasive measures, such as spray and stretch, transcutaneous electrical stimulation, physical therapy, and massage. Invasive treatments for myofascial trigger points include injections with local anesthetics, corticosteroids, or botulism toxin or dry needling. The etiology, pathophysiology, and treatment of myofascial trigger points are addressed in this article.     

Myofascial Trigger Points: An Evidence-Informed Review

Abstract

This article provides a best evidence-informed review of the current scientific understanding of myofascial trigger points with regard to their etiology, pathophysiology, and clinical implications. Evidence-informed manual therapy integrates the best available scientific evidence with individual clinicians' judgments, expertise, and clinical decision-making. After abrief historical review, the clinical aspects of myofascial trigger points, the interrater reliability for identifying myofascial trigger points, and several characteristic features are discussed, including the taut band, local twitch response, and referred pain patterns. The etiology of myofascial trigger points is discussed with a detailed and comprehensive review of the most common mechanisms, including low-level muscle contractions, uneven intramuscular pressure distribution, direct trauma, unaccustomed eccentric contractions, eccentric contractions in unconditioned muscle, and maximal or sub-maximal concentric contractions. Many current scientific studies are included and provide support for considering myofascial trigger points in the clinical decision-making process. The article concludes with a summary of frequently encountered precipitating and perpetuating mechanical, nutritional, metabolic, and psychological factors relevant for physical therapy practice. Current scientific evidence strongly supports that awareness and working knowledge of muscle dysfunction and in particular myofascial trigger points should be incorporated into manual physical therapy practice consistent with the guidelines for clinical practice developed by the International Federation of Orthopaedic Manipulative Therapists. While there are still many unanswered questions in explaining the etiology of myofascial trigger points, this article provides manual therapists with an up-to-date evidence-informed review of the current scientific knowledge.     

Myofacial trigger point

Myofascial trigger points are one of the most common causes of acute and chronic musculoskeletal pain. Contrary to popular belief, myofascial trigger points can be primary, and not just secondary due to other non-muscular pathology. The main criteria, for which the interrater reliability has been established, include the presence of a taut band, a local twitch response, an exquisite tender point within the taut band, and typical referred pain patterns. During the past few years, the actual existence and high prevalence of myofascial trigger points are supported by worldwide research findings. The “energy crisis theory” describes the peripheral pathophysiologic events of myofascial trigger points. In most cases myofascial trigger points can be treated successfully both in acute and chronic pain syndromes. Several treatment options are available including manual therapy, injections, dry needling, and electrotherapeutic modalities. In some cases neuroplastic changes in the spinal dorsal horn and sympathetic-afferent coupling play a role in the development of chronic pain syndromes and complicate the treatment.      

Current studies on myofascial pain syndrome

Recent studies have clarified the nature of myofascial trigger points (MTrPs). In an MTrP region, multiple hyperirritable loci can be found. The sensory components of the MTrP locus are sensitized nociceptors that are responsible for pain, referred pain, and local twitch responses. The motor components are dysfunctional endplates that are responsible for taut band formation as a result of excessive acetylcholine (ACh) leakage. The concentrations of pain- and inflammation-related substances are increased in the MTrP region. It has been hypothesized that excessive ACh release, sarcomere shortening, and release of sensitizing substances are three essential features that relate to one another in a positive feedback cycle. This MTrP circuit is the connection among spinal sensory (dorsal horn) neurons responsible for the MTrP phenomena. Recent studies suggest that measurement of biochemicals associated with pain and inflammation in the MTrP region, the sonographic study of MTrPs, and the magnetic resonance elastography for taut band image are potential tools for the diagnosis of MTrPs. Many methods have been used to treat myofascial pain, including laser therapy, shockwave therapy, and botulinum toxin type A injection.     

Myofasziale Triggerpunkte

Myofascial trigger points are one of the most common causes of pain in the musculoskeletal system. They are characterized by a palpable nodule-like thickening in skeletal muscle within a taut band and a pain projection area. The etiology of myofascial trigger points is not fully understood but they are probably based on an interaction of increased local muscle tension close to neuromuscular junctions and an inflammatory component. Postural abnormalities and abnormal movement patterns also play a role. For the treatment of trigger points many techniques are available but systematic studies to prioritize or sequence the different treatment approaches are lacking. Following pragmatic considerations preference should first be given to non-invasive techniques, such as local postisometric relaxation, followed by dry needling and ultrasound. If the neurogenic inflammation component predominates the use of a local anesthetic or botulinum toxin can be considered. Each trigger point therapy should be integrated in manual-medical concepts including consideration of possible chain reactions.     

Ability of magnetic resonance elastography to assess taut bands

BACKGROUND: Myofascial taut bands are central to diagnosis of myofascial pain. Despite their importance, we still lack either a laboratory test or imaging technique capable of objectively confirming either their nature or location. This study explores the ability of magnetic resonance elastography to localize and investigate the mechanical properties of myofascial taut bands on the basis of their effects on shear wave propagation. METHODS: This study was conducted in three phases. The first involved the imaging of taut bands in gel phantoms, the second a finite element modeling of the phantom experiment, and the third a preliminary evaluation involving eight human subjects-four of whom had, and four of whom did not have myofascial pain. Experiments were performed with a 1.5 T magnetic resonance imaging scanner. Shear wave propagation was imaged and shear stiffness was reconstructed using matched filtering stiffness inversion algorithms. FINDINGS: The gel phantom imaging and finite element calculation experiments supported our hypothesis that taut bands can be imaged based on its outstanding shear stiffness. The preliminary human study showed a statistically significant 50-100% (P=0.01) increase of shear stiffness in the taut band regions of the involved subjects relative to that of the controls or in nearby uninvolved muscle. INTERPRETATION: This study suggests that magnetic resonance elastography may have a potential for objectively characterizing myofascial taut bands that have been up to now detectable only by the clinician's fingers.     

Latent Myofascial Trigger Points Are Associated With an Increased Intramuscular Electromyographic Activity During Synergistic Muscle Activation

The aim of this study was to evaluate intramuscular muscle activity from a latent myofascial trigger point (MTP) in a synergistic muscle during isometric muscle contraction. Intramuscular activity was recorded with an intramuscular electromyographic (EMG) needle inserted into a latent MTP or a non-MTP in the upper trapezius at rest and during isometric shoulder abduction at 90° performed at 25% of maximum voluntary contraction in 15 healthy subjects. Surface EMG activities were recorded from the middle deltoid muscle and the upper, middle, and lower parts of the trapezius muscle. Maximal pain intensity and referred pain induced by EMG needle insertion and maximal pain intensity during contraction were recorded on a visual analog scale. The results showed that higher visual analog scale scores were observed following needle insertion and during muscle contraction for latent MTPs than non-MTPs (P < .01). The intramuscular EMG activity in the upper trapezius muscle was significantly higher at rest and during shoulder abduction at latent MTPs compared with non-MTPs (P < .001). This study provides evidence that latent MTPs are associated with increased intramuscular, but not surface, EMG amplitude of synergist activation. The increased amplitude of synergistic muscle activation may result in incoherent muscle activation pattern of synergists inducing spatial development of new MTPs and the progress to active MTPs.PerspectiveThis article presents evidence of increased intramuscular, but not surface, muscle activity of latent MTPs during synergistic muscle activation. This incoherent muscle activation pattern may overload muscle fibers in synergists during muscle contraction and may contribute to spatial pain propagation.     

Ultrasound Imaging of Embedded Shrapnel Facilitates Diagnosis and Management of Myofascial Pain Syndrome

Trigger points can result from a variety of inciting events including muscle overuse, trauma, mechanical overload, and psychological stress. When the myofascial trigger points occur in cervical musculature, they have been known to cause headaches. Ultrasound imaging is being increasingly used for the diagnosis and interventional management of various painful conditions. A veteran was referred to the pain clinic for management of his severe headache following a gunshot wound to the neck with shrapnel embedded in the neck muscles a few years prior to presentation. He had no other comorbid conditions. Physical examination revealed a taut band in the neck. An ultrasound imaging of the neck over the taut band revealed the deformed shrapnel located within the levator scapulae muscle along with an associated trigger point in the same muscle. Ultrasound guided trigger point injection, followed by physical therapy resolved his symptoms. This is a unique report of embedded shrapnel and coexisting myofascial pain syndrome revealed by ultrasound imaging. The association between shrapnel and myofascial pain syndrome requires further investigation.     

Symptomatology and clinical pathophysiology of myofascial pain

Myofascial pain syndromes, fibromyalgia, and articular dysfunctions may all be contributing to our patients' ubiquitous musculoskeletal pain problems that generally are poorly understood and poorly managed. Thepectoralis minor myofascial pain syndrome, for example, results from trigger points (TrPs) activated by stress overload of the muscle. Symptoms of pain referred to the shoulder and ulnar aspect of the arm and forearm, and of pain on reaching around and behind the body, are characteristic. Findings include restricted stretch range of motion and some weakness of the muscle, taut bands of muscle fibers, and focal trigger point tenderness of each taut band on palpation. Snapping palpation at the TrP elicits a local twitch response (LTR). The increased muscle tension of a pectoralis minor syndrome commonly entraps the lower trunk of the brachial plexus, producing symptoms of a cervical radiculopathy.     

Latent Myofascial Trigger Points are Associated With an Increased Antagonistic Muscle Activity During Agonist Muscle Contraction

The aim of this study was to evaluate motor unit activity from a latent myofascial trigger point (MTP) in an antagonist muscle during isometric agonist muscle contraction. Intramuscular activity was recorded with an intramuscular electromyographic (EMG) needle inserted into a latent MTP or a non-MTP in the posterior deltoid muscle at rest and during isometric shoulder flexion performed at 25% of maximum voluntary contraction in 14 healthy subjects. Surface EMGs were recorded from the anterior and posterior deltoid muscles. Maximal pain intensity and referred pain induced by EMG needle insertion were recorded on a visual analogue scale. The results showed that higher local pain was observed following needle insertion into latent MTPs (4.64 ± .48 cm) than non-MTPs (2.35 ± .43 cm, P < .005). Referred pain was reported in 6/14 subjects following needle insertion into latent MTPs, but none into the non-MTPs. The intramuscular EMG activity, but not surface EMG activity, in the antagonist muscle was significantly higher at rest and during shoulder flexion at latent MTPs than non-MTPs (P < .05). The current study provides the first evidence that increased motor unit excitability is associated with reduced antagonist reciprocal inhibition.

Perspective

This study shows that MTPs are associated with reduced efficiency of reciprocal linhibition, which may contribute to the delayed and incomplete muscle relaxation following exercise, disordered fine movement control, and unbalanced muscle activation. Elimination of latent MTPs and/or prevention of latent MTPs from becoming active may improve motor functions.     

Myofascial trigger points in early life

OBJECTIVE: To determine whether latent myofascial trigger points (MTPs) can be identified in healthy infants and in healthy adult subjects. DESIGN: Blind comparison. SETTING: Ambulatory. PARTICIPANTS: A convenience sample of 60 healthy adults and 60 infants (age range, 0-12mo). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: An algometer was used to measure the pressure pain threshold (PPT) on 3 different sites, including a midpoint (assumed to be the MTP site) in the brachioradialis muscle. RESULTS: The mean PPT values at the MTP site were significantly lower than the other sites in the adult muscles. However, no significant differences in PPT values among these 3 sites were found in the infants. Taut bands were found in all the adult muscles but none in the infants. CONCLUSIONS: In the adult subjects, the midpoint of brachioradialis muscle was significantly more irritable than other sites and the midpoint was probably a latent MTP. However, in the infants younger than 1 year old, such a phenomenon could not be observed in this study. It is very likely that the latent MTPs might not exist in early life, but develop in later life.     

Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points

Shah JP, Danoff JV, Desai MJ, Parikh S, Nakamura LY, Phillips TM, Gerber LH. Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.

Objectives

To investigate the biochemical milieu of the upper trapezius muscle in subjects with active, latent, or absent myofascial trigger points (MTPs) and to contrast this with that of the noninvolved gastrocnemius muscle.

Design

We used a microanalytic technique, including needle insertions at standardized locations in subjects identified as active (having neck pain and MTP), latent (no neck pain but with MTP), or normal (no neck pain, no MTP). We followed a predetermined sampling schedule; first in the trapezius muscle and then in normal gastrocnemius muscle, to measure pH, bradykinin, substance P, calcitonin gene-related peptide, tumor necrosis factor alpha, interleukin 1β (IL-1β), IL-6, IL-8, serotonin, and norepinephrine, using immunocapillary electrophoresis and capillary electrochromatography. Pressure algometry was obtained. We compared analyte concentrations among groups with 2-way repeated-measures analysis of variance.

Setting

A biomedical research facility.

Participants

Nine healthy volunteer subjects.

Interventions

Not applicable.

Main Outcome Measures

Preselected analyte concentrations.

Results

Within the trapezius muscle, concentrations for all analytes were higher in active subjects than in latent or normal subjects (P<.002); pH was lower (P<.03). At needle insertion, analyte concentrations in the trapezius for the active group were always higher (pH not different) than concentrations in the gastrocnemius muscle. At all times within the gastrocnemius, the active group had higher concentrations of all analytes than did subjects in the latent and normal groups (P<.05); pH was lower (P<.01).

Conclusions

We have shown the feasibility of continuous, in vivo recovery of small molecules from soft tissue without harmful effects. Subjects with active MTPs in the trapezius muscle have a biochemical milieu of selected inflammatory mediators, neuropeptides, cytokines, and catecholamines different from subjects with latent or absent MTPs in their trapezius. These concentrations also differ quantitatively from a remote, uninvolved site in the gastrocnemius muscle. The milieu of the gastrocnemius in subjects with active MTPs in the trapezius differs from subjects without active MTPs.     

Central modulation of pain evoked from myofascial trigger point

OBJECTIVES: Low-intensity low-frequency electrostimulation delivered within a myofascial trigger point (MTP) has been used as intervention to deactivate MTPs. The therapeutic effect has been suggested to be due to peripheral mechanisms. However, nonpainful stimuli are also known to reduce simultaneous pain through central effects. The primary objective of the present study was to assess if central pain modulation occurs after intervention with low-intensity electrostimulation within an MTP. We hypothesized that intervention induces pain inhibition via the periaqueductal gray (PAG). METHODS: Twenty-four patients with myofascial pain syndrome participated in the study. During functional magnetic resonance scanning, painful (high-intensity) intramuscular electrostimulation was delivered at random intervals (mean interstimulus interval=10.2 s) within an MTP of the upper left trapezius muscle. In-between scanning sessions, intervention (intramuscular electrostimulation, low-intensity, interstimulus interval=0.5 s) was applied to the same area. Patients were divided into responders and nonresponders according to their change in pressure pain thresholds relative to intervention. In addition to a whole brain search, a region of interest approach was also implemented to test the effect of intervention on PAG signal change. RESULTS: The main findings were: (1) intervention modulated PAG activity to painful stimuli more in responders than in nonresponders, (2) change in PAG activity from the whole patient population correlated with change in pressure pain threshold, and (3) a network known to regulate affective qualities of the pain experience was (subsignificantly) engaged more in responders than in nonresponders. DISCUSSION: The applied intervention most likely involves supraspinal pain control mechanisms related to both antinociception and regulation of pain affect.     

Uncovering the biochemical milieu of myofascial trigger points using in vivo microdialysis: An application of muscle pain concepts to myofascial pain syndrome

This article discusses muscle pain concepts in the context of myofascial pain syndrome (MPS) and summarizes microdialysis studies that have surveyed the biochemical basis of this musculoskeletal pain condition. Though MPS is a common type of non-articular pain, its pathophysiology is only beginning to be understood due to its enormous complexity. MPS is characterized by the presence of myofascial trigger points (MTrPs), which are defined as hyperirritable nodules located within a taut band of skeletal muscle. MTrPs may be active (spontaneously painful and symptomatic) or latent (non-spontaneously painful). Painful MTrPs activate muscle nociceptors that, upon sustained noxious stimulation, initiate motor and sensory changes in the peripheral and central nervous systems. This process is called sensitization. In order to investigate the peripheral factors that influence the sensitization process, a microdialysis technique was developed to quantitatively measure the biochemical milieu of skeletal muscle. Biochemical differences were found between active and latent MTrPs, as well as in comparison with healthy muscle tissue. In this paper we relate the findings of elevated levels of sensitizing substances within painful muscle to the current theoretical framework of muscle pain and MTrP development.     

Novel Applications of Ultrasound Technology to Visualize and Characterize Myofascial Trigger Points and Surrounding Soft Tissue

Sikdar S, Shah JP, Gebreab T, Yen R-H, Gilliams E, Danoff J, Gerber LH. Novel applications of ultrasound technology to visualize and characterize myofascial trigger points and surrounding soft tissue.

Objective

To apply ultrasound (US) imaging techniques to better describe the characteristics of myofascial trigger points (MTrPs) and the immediately adjacent soft tissue.

Design

Four sites in each patient were labeled based on physical examination as active myofascial trigger points (A-MTrPs; spontaneously painful), latent myofascial trigger points (L-MTrPs; nonpainful), or normal myofascial tissue. US examination was performed on each subject by a team blinded to the physical findings. A 12∼5MHz US transducer was used. Vibration sonoelastography (VSE) was performed by color Doppler variance imaging while simultaneously inducing vibrations (∼92Hz) with a handheld massage vibrator. Each site was assigned a tissue imaging score as follows: 0, uniform echogenicity and stiffness; 1, focal hypoechoic region with stiff nodule; 2, multiple hypoechoic regions with stiff nodules. Blood flow in the neighborhood of MTrPs was assessed using Doppler imaging. Each site was assigned a blood flow waveform score as follows: 0, normal arterial flow in muscle; 1, elevated diastolic flow; 2, high-resistance flow waveform with retrograde diastolic flow.

Setting

Biomedical research center.

Participants

Subjects (N=9) meeting Travell and Simons' criteria for MTrPs in a taut band in the upper trapezius.

Interventions

Not applicable.

Main Outcome Measures

MTrPs were evaluated by (1) physical examination, (2) pressure algometry, and (3) three types of US imaging including gray-scale (2-dimensional [2D] US), VSE, and Doppler.

Results

MTrPs appeared as focal, hypoechoic regions on 2D US, indicating local changes in tissue echogenicity, and as focal regions of reduced vibration amplitude on VSE, indicating a localized, stiff nodule. MTrPs were elliptical, with a size of .16±.11cm². There were no significant differences in size between A-MTrPs and L-MTrPs. Sites containing MTrPs were more likely to have a higher tissue imaging score compared with normal myofascial tissue (P<.002). Small arteries (or enlarged arterioles) near A-MTrPs showed retrograde flow in diastole, indicating a highly resistive vascular bed. A-MTrP sites were more likely to have a higher blood flow score compared with L-MTrPs (P<.021).

Conclusions

Preliminary findings show that, under the conditions of this investigation, US imaging techniques can be used to distinguish myofascial tissue containing MTrPs from normal myofascial tissue (lacking trigger points). US enables visualization and some characterization of MTrPs and adjacent soft tissue.     

Spatial pain propagation over time following painful glutamate activation of latent myofascial trigger points in humans

The aim of this present study was to test the hypothesis that tonic nociceptive stimulation of latent myofascial trigger points (MTPs) may induce a spatially enlarged area of pressure pain hyperalgesia. Painful glutamate (.2 mL, 1M) stimulation of latent MTPs and non-MTPs in the forearm was achieved by an electromyography-guided procedure. Pain intensity (as rated on the visual analog scale [VAS]) and referred pain area following glutamate injections were recorded. Pressure pain threshold (PPT) was measured over 12 points in the forearm muscles and at the mid-point of tibialis anterior muscle before and at .5 hour, 1 hour, and 24 hours after glutamate injections. The results showed that maximal pain intensity, the area under the VAS curve, and referred pain area were significantly higher and larger following glutamate injection into latent MTPs than non-MTPs (all, P < .05). A significantly lower PPT level was detected over time after glutamate injection into latent MTPs at .5 hour (at 4 points), 1 hour (at 7 points), and 24 hours (at 6 points) in the forearm muscles. However, a significantly lower PPT was observed only at 24 hours after glutamate injection into non-MTPs in the forearm muscles (at 4 points, P < .05) when compared to the pre-injection PPT. PPT at the mid-point of the tibialis anterior was significantly decreased at 1 hour only as compared to the pre-injection PPT in both groups (< .05). The results of the present study indicate that nociceptive stimulation of latent MTPs is associated with an early onset of locally enlarged area of mechanical hyperalgesia. PERSPECTIVE: This study shows that MTPs are associated with an early occurrence of a locally enlarged area of pressure hyperalgesia associated with spreading central sensitization. Inactivation of MTPs may prevent spatial pain propagation.