How Common Are Latent Myofascial Trigger Points in the Scapular Positioning Muscles?

Short-term effect of frequency specific intramuscular electrical stimulation on post dry needling soreness of upper fibers of trapezius: A randomized controlled trial

OBJECTIVES

The purpose of this study was to compare the effect of frequency specific intramuscular electrical stimulation on post trigger point dry needling soreness.

BACKGROUND

Dry needling (DN) with intramuscular electrical stimulation (DN/IMES) has been shown to be effective in reducing post needling soreness. The effect of frequency specific intramuscular electrical stimulation on post needling soreness has not been studied abundantly, but initial results are favorable. This study investigated the effect of frequency specific intramuscular electrical stimulation on post needling soreness.

METHODS

A convenience sample of 45 (α = 0.05, power = 95%) subjects was recruited for this study and randomly assigned to DN (n = 15), DN/IMES [f-2Hz] (n = 15) and DN/IMES [f-100Hz] (n = 15) groups. Pain Pressure Threshold (PPT) and Numeric Pain Rating Scale (NPRS) were measured before and 24 hours after the intervention.

RESULT

Both DN/IMES [f-2Hz and 100 Hz] groups showed statistically significant improvement in NPRS (p = 0.001 and 0.00005, respectively) and PPT (p = 0.004 and 0.0002, respectively). No statistically significant changes were observed in DN group in NPRS (p = 0.726) and PPT (p = 0.238).

CONCLUSION

Both dry needling with Intramuscular electrical stimulation (DN/IMES [f-2Hz and 100Hz]) groups demonstrated statistically significant improvement in soreness as compared to DN group, but DN/IMES [f-100 Hz] group showed more significant improvement as compared to DN/IMES [f-2 Hz] group in reducing post needling soreness.

High Medial Longitudinal Arch of the Foot and Latent Trigger Points in Lower Limb Muscles

Background: The objective was to evaluate the prevalence of latent trigger points (LTrPs) in lower limb muscles in participants with a high medial longitudinal arch (MLA) of the foot compared to controls. Methods: Participants with a navicular drop test of 4-9 mm were included in the control group; the high MLA group included navicular drop test values of ≤4 mm. The presence of LTrPs was assessed by palpation techniques. The muscles evaluated were medial gastrocnemius (LTrP1), lateral gastrocnemius (LTrP2), soleus (LTrP1), peroneus longus, peroneus brevis, tibialis anterior, extensor digitorum longus, flexor digitorum longus, rectus femoris, vastus medialis (LTrP1 and LTrP2), and the vastus lateralis of the quadriceps (LTrP1 and LTrP2). Results: Thirty-seven participants with high MLA and thirty-seven controls were included in the study. Twenty-nine (78.4%) participants in the high MLA group had at least 1 LTrP, compared to twenty-three (62.2%) in the control group. No statistical difference (p < 0.05) was found in the total number of LTrPs between groups (4.46 ± 3.78 vs. 3.24 ± 3.85). There were more participants (p < 0.05) with LTrPs in the tibialis anterior, extensor digitorum longus, and vastus lateralis (LTrP1 and LTrP2) in the high MLA group than in the control group. Conclusion: Although no differences were found in the number of total LTrPs between groups, the prevalence was statistically significantly higher in the tibialis anterior, extensor digitorum longus, and vastus lateralis of the participants with high MLA of the foot.

Association between myofascial trigger point therapy and conditioned pain modulation

INTRODUCTION

Myofascial trigger point therapy (MTrP) is a widely used therapeutic approach, although the underlying mechanisms remain unclear. Mechanisms discussed include peripheral involvement of muscles as well as central pain modulating processes such as the conditioned pain modulation (CPM). The aim of this study was to investigate whether the analgesic response of MTrP and the analgesic response of CPM correlate in asymptomatic participants in order to identify shared underlying mechanisms of MTrP and CPM.

METHOD

Both, CPM and MTrP protocols consisted of heat-based test stimuli (heat pain thresholds before and after the intervention) and pressure-based (conditioning) stimuli. Asymptomatic participants (n = 94) were randomly assigned to receive either mild, intense or no pressure stimuli (between-group design) to both the fingernail and the MTrP of the infraspinatus muscle (within-group design). Pressure stimuli at both locations (fingernail, MTrP) were applied with a pressure algometer for 120 s and continuously adjusted to maintain a constant pain intensity of mild or intense pain. All thermal stimuli were applied on the lower leg with a thermal stimulator.

RESULTS

A significant correlation was shown between the analgesic effect of CPM and MTrP therapy for mild (r = 0.53, p = 0.002) and intensive stimuli (r = 0.73, p < 0.001). 17.3% of the variance of the MTrP effect were explained by CPM after mild stimulation, and 47.1% after intense stimulation. Pain-related characteristics did not explain the variance within the analgesic response using a regression analysis.

CONCLUSIONS

Between the analgesic responses following MTrP and CPM paradigms, a moderate to strong correlation was observed, suggesting shared underlying mechanisms.

Identifying and Managing Nociplastic Pain in Individuals With Rheumatic Diseases: A Narrative Review

Chronic pain is a burdensome and prevalent symptom in individuals with rheumatic disease. The International Association for the Study of Pain classifies pain into 3 descriptive categories: nociceptive, neuropathic, and nociplastic. These categories are intended to provide information about the mechanisms underlying the pain, which can then serve as targets for drug or non-drug treatments. This review describes the 3 types of pain as they relate to patients seen by rheumatology health care providers. The focus is on identifying individuals with nociplastic pain, which can either occur in isolation as in fibromyalgia, or as a comorbidity in individuals with primary autoimmune conditions, such as rheumatoid arthritis and systemic lupus erythematosus. Practical information about how rheumatology health care providers can approach and manage chronic pain is also provided.

Effects of Trigger Point Dry Needling on Strength Measurements and Activation Levels of the Gluteus Medius: A Quasi-Experimental Randomized Control Study

Background

Latent trigger points have been identified as a source of impaired muscle function giving rise to a reduction in force production and alterations in muscle activation patterns and movement efficiency. There is limited investigation into the effectiveness of a treatment in reducing these clinical manifestations.

Purpose

To investigate whether the application of trigger point dry needling (TDN) to latent trigger points within the gluteus medius musculature affected strength measurements and muscle activation levels immediately following intervention.

Design

Quasi experimental, single group, pretest-posttest, randomized control study.

Methods

A control and an intervention side were randomly assigned for each participant (N = 39). Hand held dynamometer (HHD) force measurements and raw surface electromyography (sEMG) amplitude readings were recorded during maximal volitional isometric contractions of the gluteus medius in two separate positions before and after application of TDN. Comparison of within and between group data were conducted.

Results

A statistically significant interaction between time (pre-TDN to post-TDN) and groups (intervention side and control side), p < 0.001 was found for HHD measurements in both positions. Post hoc analysis revealed a statistically significant difference (p < 0.001) for all comparisons in the side lying neutral (SL0) position, while statistically significant differences (p < 0.001) were found for pre and post-TDN measurements within intervention side as well as between the intervention and control side for post-TDN measurements in the side lying internal rotation (SLIR) position. For sEMG amplitude measurements, statistically significant differences were found only in the SL0 position for within group comparisons on the intervention side (p = 0.009) and for between group comparisons for post-TDN measurements (p = 0.002).

Conclusion

Application of TDN to latent trigger points within the gluteus medius can significantly increase gluteus muscle force production immediately following intervention while reducing the level of muscle activation required during contraction.

Level of Evidence

Level 2.

Pain threshold in selected trigger points of superficial muscles of the back in young adults

BACKGROUND

Monitoring of pain threshold is the basis for verification of the effectiveness of therapy or assessment of the patient's condition. This study aimed to determine the pain threshold of selected superficial muscles of the back taking into account trigger point activity in young and healthy males and females, with the evaluation of intrarater reliability of algometric measurements.

MATERIAL AND METHODS

The study examined 30 young adult participants (15 males and 15 females) aged 26.23 ± 3.21, and BMI of 23.80 ± 3.43. The Pain Test FPX Algometer (Wagner) was used for the study. Trigger points on the levator scapulae and trapezius muscles (superior and inferior portion) on both sides were examined. It was also verified whether the trigger points studied are active or inactive. Furthermore, an author's survey questionnaire was used.

RESULTS

Within the trigger points of the right (p = 0.04) and left (p = 0.02) superior trapezius muscle and the left (p = 0.04) levator scapulae muscle, the pain threshold values were higher in the male group. There was a statistically significantly higher number of active trigger points in the female group compared to that in the male group (2.49 ± 1.51 vs. 1.07 ± 1.16, respectively), p = 0.01. For all muscles tested, mean pain threshold values were significantly higher for inactive trigger points. A greater number of active trigger points is associated with lower pain thresholds at these points (left: the superior trapezius, r = -0.597, the inferior trapezius, r = -0.609; the levator scapulae, r = -0.746; right: the superior trapezius, r = -0.610, the inferior trapezius, r = -0.604; the levator scapulae, r = -0.747). The evaluation of the intrarater reliability showed excellent agreement between the first and second measurements, ICC > 0.987 for all examined trigger points.

CONCLUSIONS

(1) Women who reported pain more than once a week in the studied muscles showed a greater number of active trigger points. (2) A greater number of active trigger points in female is related to a lower pain threshold (which is associated with greater pain sensitivity) in female than in male. (3) A sample size of 30 people seems sufficient to detect variations in the pain threshold at active and inactive trigger points of selected back muscles, especially when the frequency of occurrence of both types of points is comparable.

Acute Effects of Static Self-Stretching Exercises and Foam Roller Self-Massaging on the Trunk Range of Motions and Strength of the Trunk Extensors

Although the effectiveness of static self-stretching exercises (SSSEs) and foam roller self-massaging (FRSM) in joint range of motion and muscle strength of the lower limbs has been extensively investigated, little is known about their effectiveness on the posterior trunk muscles. The present study aimed to investigate the acute effects of two 7-min SSSEs and FRSM intervention protocols on the range of trunk movements and the strength of the trunk extensors. Twenty-five healthy active males (n = 14) and females (n = 11) performed each intervention separately, one week apart. The range of motion (ROM) of the trunk-hip flexion (T-HF), the ROM of the trunk side-flexion (TSF) and rotation (TR) bilaterally, as well as the isometric maximum strength (TESmax) and endurance (TESend) of the trunk extensors were measured before and after each intervention. The ROMs of T-HF, TSF, and TR were significantly increased following both SSSEs and FRSM. The TESmax and TESend were also significantly increased after FRSM, but decreased following SSSEs. While both interventions were effective in increasing the range of motion of the trunk, a single 7-min session of FRSM presented more advantages over a similar duration SSSEs protocol due to the increase in the strength of the trunk extensors it induced.

Hypoalgesic and Motor Effects of Neural Mobilisation versus Soft-Tissue Interventions in Experimental Craniofacial Hyperalgesia: A Single-Blinded Randomised Controlled Trial

Objective: The present trial aimed to compare the effects of the mobilisation of the nervous system (NS) to those of a soft-tissue intervention in subjects exposed to an experimentally induced hyperalgesia of the masticatory muscles. Methods: The study was a single-blinded randomised controlled trial. A total of 49 participants (mean ± SD age: 41 ± 11 years; 61% female) with latent myofascial trigger points (LMTrPs) in the craniofacial region were randomly assigned to one of three groups: neural mobilisation (NM), soft-tissues techniques and stretching (STT-S), and control group (CG). An initial assessment (baseline) was performed before the provocation chewing masticatory test. The pre-treatment measurements were registered 24 h later. Next, the randomised intervention was applied, and afterwards, post-treatment data were obtained. Outcome measures included pain-free maximum mouth opening (MMO), pressure pain thresholds (PPTs) in the trigeminal and cervical region, and trigeminal and cervical two-point discrimination (TPD). Results: ANOVA revealed significant differences for the time × group interaction for pain-free MMO and PPTs. The results showed an improvement in the MMO and the PPTs for NM and STT-S groups but not for the CG. There were no differences between the NM and STT-S groups. However, the effect sizes were large for the NM and medium for the STT-S. No differences were found for TDP between groups nor over time. Conclusions: The results show that with NM and STT-S techniques, we could influence motor and sensory variables in asymptomatic subjects with LMTrPs after a masticatory provocation test. Both techniques increased MMO and PPTs in the short term. These beneficial effects lead us to consider the importance of including these methods in clinical practice.

Ischemic Pressure vs Postisometric Relaxation for Treatment of Rhomboid Latent Myofascial Trigger Points: A Randomized, Blinded Clinical Trial

OBJECTIVE

The purpose of this study was to investigate the effects of ischemic pressure (IP) vs postisometric relaxation (PIR) on rhomboid-muscle latent trigger points (LTrPs).

METHODS

Forty-five participants with rhomboid-muscle LTrPs were randomly assigned into 3 groups and received 3 weeks of treatment-group A: IP and traditional treatment (infrared radiation, ultrasonic therapy, and transcutaneous electrical nerve stimulation); group B: PIR and traditional treatment; and group C: traditional treatment. Shoulder pain and disability, neck pain and disability, and pressure pain threshold (PPT) of 3 points on each side were measured before and after treatment.

RESULTS

Multivariate analysis of variance indicated a statistically significant Group × Time interaction (P = .005). The PPT for the right lower point was increased in group A more than in groups B or C. Neck pain was reduced in group B more than in group C. Moreover, shoulder and neck disability were reduced in both groups A and B more than in group C. The PPTs of the left lower and middle points were increased in group B compared with groups A and C. The PPT of the left upper point was increased in group A more than in group C. There were significant changes in all outcomes in the 2 experimental groups (P < .05). No changes were found in the control group except in pain intensity, shoulder disability, and PPT of the left lower point.

CONCLUSION

This study found that IP may be more effective than PIR regarding PPT, but both techniques showed changes in the treatment of rhomboid-muscle LTrPs.

The impact of internet addiction on depression, physical activity level and trigger point sensitivity in Turkish university students

BACKGROUND AND OBJECTIVES

Internet addiction (IA), defined as excessive, time consuming, uncontrollable use of the internet, has become a widespread problem. In this study, we investigated the impact of internet addiction on depression, physical activity level, and latent trigger point sensitivity in Turkish university students.

METHODS

A total of 215 university students (155 females and 60 males) who were between 18-25 years of age participated in the study. Using the Addiction Profile Index Internet Addiction Form (APIINT), we identified 51 people as non-internet-addicted (non-IA) (Group 1: 10 male/41 female) and 51 as internet-addicted (IA) (Group 2: 7 male/44 female). APIINT, International Physical Activity Questionnaire-Short-Form (IPAQ), Beck Depression Inventory (BDI), and Neck Disability Index (NDI) were administered to both groups, and the pressure-pain threshold (PPT) in upper/middle trapezius latent trigger points area was measured.

RESULTS

The internet addiction rate was 24.3% in our students. Compared with the non-IA group, the daily internet use time and BDI and NDI scores were higher (all p< 0.05), while the IPAQ walking (p< 0.01), IPAQ total (p< 0.05), and PPT values (p< 0.05) were lower in the IA group.

CONCLUSIONS

IA is a growing problem. This addiction may lead to musculoskeletal problems and can have consequences involving the level of physical activity, depression, and musculoskeletal disorders, particularly in the neck.

Presence of Latent Myofascial Trigger Points and Determination of Pressure Pain Thresholds of the Shoulder Girdle in Healthy Children and Young Adults: A Cross-sectional Study

OBJECTIVE

The primary objective of this study was to compare the number of myofascial trigger points (MTPs) and the pressure pain thresholds (PPTs) in the shoulder girdle, on the dominant and nondominant sides, between healthy children and adults. The secondary aim was to assess the correlations between the number of MTPs and the PPTs in these populations.

METHODS

A cross-sectional study was performed. Thirty-five children (aged 9.1 ± 1.7 years) and 35 adults (aged 23.4 ± 3.4 years) with no history of shoulder or cervical pathology were included. All participants were examined for MTPs in the shoulder muscles and assessed for PPTs in the neck, shoulder, and tibialis anterior. Parametric and nonparametric tests, effect sizes, and odds ratios were used to determine the differences between groups and sides. Spearman's σ test was used to assess correlations between latent MTPs (LTPs) and PPTs in each group.

RESULTS

Children had fewer LTPs than adults did (P = .03). The upper trapezius was the muscle with the largest number of LTPs, affecting 13 adults on the dominant side. Children had lower PPTs compared with adults (P < .05). Correlations between the number of LTPs (on both sides and in total) and PPTs were observed only in adults.

CONCLUSIONS

Healthy children have fewer LTPs and lower PPTs in the shoulder girdle than healthy adults. A relationship was observed between sensitivity to pressure and the presence of LTPs in adults, in whom lower PPT was associated with more LTPs. This relationship was not detected in children.

The immediate effect of multiple mechanical impulses on electromyography and pressure pain threshold of lumbar latent trigger points: an experimental study

BACKGROUND

Myofascial pain is a common syndrome, which has not been studied extensively in the low back. Despite a variety of manual and instrument assisted interventions available, little work has targeted the possible effects of fast mechanical impulses on myofascial trigger points (MTrPs) on its sensitivity and electrical activity. The purpose of this experimental study was to quantify the immediate effect of one session of mechanical impulses to lumbar latent MTrPs and to normal muscle tissue with pressure pain threshold (PPT) and surface electromyography (sEMG) as outcome measures.

METHODS

During the autumn of 2009, in 41 asymptomatic subjects between 17-40 years of age the lumbar musculature was searched for a latent MTrP by a trained clinician. Using 3 disposable pre-gelled electrodes bilaterally, sEMG was recorded continuously from muscle containing either latent or no MTrP. Both the trigger point group and control group received the intervention and were blinded to group allocation. The immediate effects of mechanical impulses were assessed by sEMG and PPT before and after intervention using Wilcoxon matched-pairs signed-ranks test, Mann-Whitney U test and paired t-tests.

RESULTS

The PPT increased significantly across both groups (p < 0.01) after intervention. The proportionate increase (14.6 %) was comparable in both MTrP and control groups. The electrical activity on the MTrP side was not significantly higher in the MTrP group compared to the contralateral side. The decrease of resting electrical activity after intervention was significant in the MTrP group on the side of the latent MTrP (P = 0.001) as well as the contralateral side (p=0.022), and not significant in the control group on either side (p=0.33 and p=0.93).

CONCLUSION

In this study, the immediate effect of one session of mechanical impulses was associated with a significant increase in PPT for both groups and a significant decrease in the resting electrical activity of the lumbar muscles only in the MTrP group. It is unknown if these effects have clinical significance.

Prevalence of Myofascial Pain Syndrome in Chronic Non-Specific Neck Pain: A Population-Based Cross-Sectional Descriptive Study

BACKGROUND

Chronic non-specific neck pain is a frequent complaint. It is a recognized medical and socioeconomic problem and a frequent cause of job absenteeism. In recent years, case reports about myofascial pain syndrome (MPS) are emerging among patients suffering from pain. MPS is a regional pain syndrome characterized by myofascial trigger points (MTrP) in palpable taut bands of skeletal muscle that refer pain to a distance, and that can cause distant motor and autonomic effects.

OBJECTIVE

To assess the prevalence of active and latent MTrPs in subjects suffering from chronic non-specific neck pain.

DESIGN

A population-based cross-sectional descriptive study was carried out from January 2012 to December 2014.

SETTING

Three primary healthcare centers in Alcalá de Henares, Madrid (Spain).

SUBJECTS

Two hundred and twenty-four participants diagnosed by their family doctor with chronic non-specific neck pain.

METHODS

Participants were examined by a physical therapist to determine the presence of MPS. Pain descriptions from the subjects and pain body diagrams guided the physical examination. The subjects were not given any information concerning MPS or other muscle pain syndromes.

RESULTS

All participants presented with MPS. MTrPs of the trapezius muscles were the most prevalent, in 93.75% of the participants. The most prevalent active MTrPs were located right (82.1%) and left (79%) in the nearly-horizontal fibers of the upper trapezius muscle. Furthermore, active MTrPs in the levator scapulae, multifidi, and splenius cervicis muscles reached a prevalence of 82.14%, 77.68%, and 62.5%, respectively.

CONCLUSIONS

MPS is a common source of pain in subjects presenting chronic non-specific neck pain.

Differential activation of scapular muscles, during arm elevation, with and without trigger points

BACKGROUND

Latent Myofascial Trigger Points (LMTrPs) are defined as certain pain-free hyperirritable spots in a muscle taut band which lead to muscle activation pattern alternation in both loaded and unloaded conditions during scaption. The current study aimed to investigate the onset of upward scapular rotator muscle activations during rapid arm elevation in three planes of movement in patients with upper trapezius LMTrPs compared to healthy control participants.

METHOD

Three planes of scapular movement were evaluated. The onset of Deltoid (DEL) was considered as the starting point in marking the onset of Upper Trapezius (UT) and Serratus Anterior (SA) muscle activations.

RESULTS

There were significant differences in the relative muscle latencies between the LMTrPs and the control group. Those with LMTrPs showed a delayed and inconsistent activity of UT during all three planes of elevation (p < 0.05) and the same pattern happened for SA during flexion (p < 0.05).

CONCLUSIONS

Both hosted and synergistic muscles experience delay in muscle activation and alterations in their recruitment pattern during rapid arm elevation in all planes of movement. These changes may serve as adaptive motor control strategies due to the presence of LMTrPs in UT muscles.

Clinical implication of latent myofascial trigger point

Myofascial trigger points (MTrPs) are hyperirritable points located within a taut band of skeletal muscle or fascia, which cause referred pain, local tenderness and autonomic changes when compressed. There are fundamental differences between the effects produced by the two basic types of MTrPs (active and latent). Active trigger points (ATrPs) usually produce referred pain and tenderness. In contrast, latent trigger points (LTrPs) are foci of hyperirritability in a taut band of muscle, which are clinically associated with a local twitch response, tenderness and/or referred pain upon manual examination. LTrPs may be found in many pain-free skeletal muscles and may be "activated" and converted to ATrPs by continuous detrimental stimuli. ATrPs can be inactivated by different treatment strategies; however, they never fully disappear but rather convert to the latent form. Therefore, the diagnosis and treatment of LTrPs is important. This review highlights the clinical implication of LTrPs.

Effect of latent myofascial trigger points on strength measurements of the upper trapezius: a case-controlled trial

PURPOSE

The purpose of this article was to determine whether strength is altered in the upper trapezius in the presence of latent myofascial trigger points (MTrP).

METHODS

This study was case controlled and used convenience sampling. The sample recruited was homogeneous with respect to age, sex, height, and body mass. Participants were assessed for the presence of latent MTrP in the upper trapezius and placed into two groups: an experimental group that had latent MTrP in the upper trapezius and a control group that did not. Eighteen women (mean age 21.4 y, SD 1.89; mean height 156.9 cm, SD 4.03; and mean body mass 51.7 kg, SD 5.84) made up the experimental group, and 19 women (mean age 20.3 y, SD 1.86; mean height 158.6 cm, SD 3.14; and mean body mass 53.2 kg, SD 5.17) made up the control group. We obtained strength measurements of the non-dominant arm using a handheld dynamometer and compared them between the two groups.

RESULTS

The difference in the strength measurements between the two groups was not statistically significant (p=0.59).

CONCLUSIONS

The presence of latent MTrPs may not affect the strength of the upper trapezius.

Muscle activation patterns in the scapular positioning muscles during loaded scapular plane elevation: the effects of Latent Myofascial Trigger Points

BACKGROUND

Latent Myofascial Trigger Points are pain-free neuromuscular lesions that have been found to affect muscle activation patterns in the unloaded state. The aim was to extend these observations to loaded motion by investigating muscle activation patterns in upward scapular rotator muscles (upper and lower trapezius and serratus anterior) hosting Latent Myofascial Trigger Points simultaneously with lesion-free synergists for shoulder abduction (infraspinatus and middle deltoid). This approach allowed examination of the effects of these lesions on both their hosts and their lesion-free synergists in order to understand their effects on the performance of shoulder abduction.

METHODS

Surface electromyography was employed to measure the timing of onset of muscle activation of the upper and lower trapezius and serratus anterior (upward scapular rotators), infraspinatus (rotator cuff) and middle deltoid (abductor of the arm) initially without load and then with light (1-4 kg) dumbbells. Comparisons were made between control (no Latent Trigger Points; n=14) and Latent Trigger Point (n=28) groups.

FINDINGS

The control group displayed a relatively stable sequence of muscle activation that was significantly different in timing and variability to that of the Latent Trigger Point group in all muscles except middle deltoid (all P<0.05). The Latent Trigger Point group muscle activation pattern under load was inconsistent, with the only common feature being the early activation of the infraspinatus.

INTERPRETATION

The presence of Latent Trigger Points in upward scapular rotators alters the muscle activation pattern during scapular plane elevation, potentially predisposing to overuse conditions including impingement syndrome, rotator cuff pathology and myofascial pain.

The impact of latent trigger points on regional muscle function

To date, most investigation of latent myofascial trigger points (LTrPs) has occurred in pain populations. Many have thought that LTrPs are clinically relevant as -potential precursors to developing active myofascial trigger points and spontaneous pain. Nociceptive substances have been found in greater concentrations at LTrP sites compared with non-TrP sites, indicating the potential for group III and IV afferent fibers to provide input to the central nervous system from affected peripheral sites. Fatigue and neurophysiologic studies provide evidence as to the pathways via which group III and IV afferents can alter activity of the motoneuron pool and therefore affect muscle activation and performance. This article offers suggestions as to the mechanisms via which LTrP-related pathophysiology may explain the clinical examination findings associated with LTrP-containing and functionally related muscles.