Vastus Lateralis Motor Unit Firing Rate Is Higher in Women With Patellofemoral Pain

Does pain influence control of muscle force? A systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

In the presence of pain, whether clinical or experimentally induced, individuals commonly show impairments in the control of muscle force (commonly known as force steadiness). In this systematic review and meta-analysis, we synthesized the available evidence on the influence of clinical and experimental pain on force steadiness.

DATABASES AND DATA TREATMENT

MEDLINE, EMBASE, PubMed, CINAHL Plus and Web of Science databases were searched from their inception to 19 December 2023, using MeSH terms and pre-selected keywords related to pain and force steadiness. Two independent reviewers screened studies for inclusion and assessed their methodological quality using a modified Newcastle-Ottawa risk of bias tool.

RESULTS

In total, 32 studies (19 clinical pain and 13 experimental pain) were included. Meta-analyses revealed reduced force steadiness in the presence of clinical pain as measured by the coefficient of variation (CoV) and standard deviation (SD) of force (standardized mean difference; SMD = 0.80, 95% CI = 0.31-1.28 and SMD = 0.61, 95% CI = 0.11-1.11). These findings were supported by moderate and low strength of evidence respectively. In the presence of experimental pain, meta-analyses revealed reductions in force steadiness when measured by the CoV of force but not by the SD of force (SMD = 0.50, 95% CI = 0.01-0.99; and SMD = 0.44, 95% CI = -0.04 to 0.92), each supported by very low strength of evidence.

CONCLUSIONS

This work demonstrates that pain, particularly clinical pain, impairs force steadiness. Such impairments likely have clinical relevance and could become targets for treatment when managing people experiencing musculoskeletal pain.

SIGNIFICANCE STATEMENT

This systematic review and meta-analyses enhances our understanding of motor impairments observed in people experiencing musculoskeletal pain. It underscores the significance of incorporating force steadiness assessment when managing individuals experiencing musculoskeletal pain. Additionally, it suggests that future research should explore the potential benefits of force steadiness training in alleviating patients' symptoms and enhancing their functional performance. This could potentially lead to the development of innovative therapeutic approaches for individuals suffering from musculoskeletal pain.

Quadriceps muscle contraction causes medial patellofemoral ligament elongation by intermeshed fibers of vastus medialis oblique muscle

The first aim of this study was to compare the medial patellofemoral length between contracted and relaxed quadriceps muscle and second to assess the importance of the intermeshed vastus medialis oblique fibers. After a priori power analysis (α = 0.05, power [1-β] = 0.95), 35 healthy males aged 18-30 were prospectively examined with a 3.0-T magnetic resonance imaging (MRI) scanner in 10-15° of knee flexion. Two axial MRI sequences (25 s each) were made with relaxed and contracted quadriceps. Two blinded, independent raters measured twice medial patellofemoral ligament length (curved line) and attachment-to-attachment length (straight line). Mean medial patellofemoral ligament length and attachment-to-attachment length with relaxed quadriceps was: 65.5 mm (SD = 3.7), 59.7 mm (SD = 3.6), and after contraction, it increased to 68.7 mm (SD = 5.3), 61.2 mm (SD = 4.7); p < 0.01 and <0.001, respectively. Intraclass correlation coefficients for intra- and inter-rater reliabilities ranged from 0.55 (moderate) to 0.97 (excellent). Mean medial patellofemoral ligament length elongation after quadriceps contraction was significantly greater (3.2 mm, SD = 3.9) than mean attachment-to-attachment length elongation (1.6 mm, SD = 2.8); p < 0.001. Contraction of quadriceps muscle causes elongation of the medial patellofemoral ligament to the extent greater than the elongation of distance between its attachments. This confirms that medial patellofemoral ligament elongation after quadriceps contraction results not only from movement of its patellar attachment but also directly from intermeshed vastus medialis oblique fibers pulling medial patellofemoral ligament in a different direction creating a bow-like construct in agreement with the "pull-and-guide mechanism" proposed in the literature.

Activation, strength, and resistance: Which variables predict the kinematics of women with and without patellofemoral pain?

INTRODUCTION

Investigating the possible relationship between neuromuscular changes and movement alterations could help to describe the mechanisms underlying patellofemoral pain (PFP).

OBJECTIVE

To investigate whether activation and muscle strength of the trunk and lower limb and muscle resistance of the trunk predict the knee frontal and trunk sagittal kinematics in women with and without PFP.

METHOD

Sixty women (PFP, n = 30; asymptomatic, n = 30) underwent the single-leg squat test to collect electromyographic and kinematic data. Activation of transversus abdominis/internal oblique, gluteus medius (GMed), and vastus medialis oblique (VMO); knee frontal and trunk sagittal angles were analyzed. Participants also underwent maximal isometric tests to determine lateral trunk, hip abductor, and knee extensor torques and performed a lateral trunk resistance test. Multiple regression was used to determine predictive models.

RESULTS

In the PFP group, knee frontal angle (R2 = 0.39, p = 0.001) was predicted by GMed activation (β = 0.23, p = 0.000) and hip abductor torque (β = 0.08, p = 0.022). No variable was able to predict trunk sagittal kinematics in this group. In the asymptomatics, knee frontal angle (R2 = 0.16, p = 0.029) was predicted by hip abductor torque (β = 0.07, p = 0.029), while trunk sagittal angle (R2 = 0.24, p = 0.024) was predicted by VMO activation (β = 0.12, p = 0.016).

CONCLUSION

Kinematics is predicted by the muscles acting in the respective planes, such that hip abductors capacities are related to the knee frontal alignment in both groups, and that of the VMO is related to the trunk sagittal alignment only in asymptomatic women.

Lower motor unit discharge rates in gastrocnemius lateralis, but not in gastrocnemius medialis or soleus, in runners with Achilles tendinopathy: a pilot study

OBJECTIVES

Deficits in muscle performance could be a consequence of a reduced ability of a motor neuron to increase the rate in which it discharges. This study aimed to investigate motor unit (MU) discharge properties of each triceps surae muscle (TS) and TS torque steadiness during submaximal intensities in runners with Achilles tendinopathy (AT).

METHODS

We recruited runners with (n = 12) and without (n = 13) mid-portion AT. MU discharge rate was analysed for each of the TS muscles, using high-density surface electromyography during 10 and 20% isometric plantar flexor contractions.

RESULTS

MU mean discharge rate was lower in the gastrocnemius lateralis (GL) in AT compared to controls. In AT, GL MU mean discharge rate did not increase as torque increased from 10% peak torque, 8.24 pps (95% CI 7.08 to 9.41) to 20%, 8.52 pps (7.41 to 9.63, p = 0.540); however, in controls, MU discharge rate increased as torque increased from 10%, 8.39 pps (7.25-9.53) to 20%, 10.07 pps (8.89-11.25, p < 0.001). There were no between-group difference in gastrocnemius medialis (GM) or soleus (SOL) MU discharge rates. We found no between-group differences in coefficient of variation of MU discharge rate in any of the TS muscles nor in TS torque steadiness.

CONCLUSION

Our data demonstrate that runners with AT may have a lower neural drive to GL, failing to increase MU discharge rate to adjust for the increase in torque demand. Further research is needed to understand how interventions focussing on increasing neural drive to GL would affect muscle function in runners with AT.

Alterations in peripheral joint muscle force control in adults with musculoskeletal disease, injury, surgery, or arthroplasty: A systematic review and meta-analysis

PURPOSE

To systematically review and analyse whether musculoskeletal conditions affect peripheral joint muscle force control (i.e. magnitude and/or complexity of force fluctuations).

METHODS

A literature search was conducted using MEDLINE, CINAHL and SPORTDiscus databases (from inception-8th April 2021) for studies involving: 1) participants with musculoskeletal disease, injury, surgery, or arthroplasty in the peripheral joints of the upper/lower limb; 2) comparison with an unaffected control group or unaffected contralateral limb; and 3) measures of the magnitude and/or complexity of force fluctuations during targeted isometric contractions. The methodological quality of studies was evaluated using a modified Downs and Black Quality Index. Studies were combined using the standardized mean difference (SMD) in a random-effects model.

RESULTS

14 studies (investigating 694 participants) were included in the meta-analysis. There was a significant effect of musculoskeletal conditions on peripheral joint muscle force coefficient of variation (CV; SMD = 0.19 [95 % CI 0.06, 0.32]), whereby individuals with musculoskeletal conditions exhibited greater CV than controls. Subgroup analyses revealed that CV was only greater: 1) when comparison was made between symptomatic and asymptomatic individuals (rather than between affected and contralateral limbs; SMD = 0.22 [95 % CI 0.07, 0.38]); 2) for conditions of the knee (SMD = 0.29 [95 % CI 0.14, 0.44]); and 3) for ACL injury post-surgery (SMD = 0.56 [95 % CI 0.36, 0.75]).

CONCLUSION

Musculoskeletal conditions result in an increase in peripheral joint muscle force CV, with this effect dependent on study design, peripheral joint, and surgical status. The greater force CV is indicative of decreased force steadiness and could have implications for long-term tissue health/day-to-day function.

SPATIAL DISTRIBUTION PATTERN OF THE ELECTROMYOGRAPHIC POTENTIAL IN THE VASTUS MEDIALIS AND LATERALIS MUSCLES FOR THREE KNEE FLEXION ANGLES DURING ISOMETRIC KNEE EXTENSION

Understanding the function of the vastus lateralis (VL) and vastus medialis (VM) muscles is important since these muscles are essential for daily and sport activities. The association between the knee flexion angle and spatial muscle activation is controversial. This study compares the distribution patterns of multi-channel electromyographic activities of the VL and VM muscles at three knee flexion angles for three intensities of isometric contraction. Sixteen men performed isometric knee extensions at 30%, 50% and 70% maximal voluntary contraction (MVC), at [Formula: see text], [Formula: see text] and [Formula: see text] knee flexion. Alterations in the spatial electromyographic potential distribution were determined by the root mean square (RMS), modified entropy, and coefficient of variation in the spatial electromyographic potential. Modified entropy and the coefficient of variation showed differences in the VM muscle between [Formula: see text] and [Formula: see text] knee flexion. The RMS at the three angles was similar between the VL and VM muscles, with no differences in contraction intensities at 30%, 50%, or 70% MVC. The VL and VM muscle function differed among knee flexion angles, as did activity in the distal and proximal VM muscles. These findings suggest the need for functional evaluation of the VL and VM muscles at each knee flexion angle.

Relationship between vastus medialis Hoffmann reflex excitability and knee extension biomechanics during different tasks in women with patellofemoral pain

BACKGROUND

Impaired knee extension biomechanics and spinal excitability have been reported in women with patellofemoral pain, but their relationship has not been explored. A significant relationship between them could indicate the need for investigating the potential benefits of disinhibitory interventions for women with patellofemoral pain. Thus, this study aimed to investigate the relationship between vastus medialis Hoffmann reflex and (1) maximal isometric, concentric and eccentric knee extensor strength and rate of torque development; (2) knee extensor torque steadiness; and (3) knee extensor moment during functional tasks; in women with patellofemoral pain.

METHODS

Spinal excitability of twenty-four participants was assessed by the amplitude of maximal vastus medialis Hoffmann reflex. Knee extensor strength, rate of torque development and torque steadiness were assessed using an isokinetic dynamometer. Knee extensor moment during step-down and stair descent tasks were obtained using a three-dimensional motion analysis system.

FINDINGS

A moderate negative relationship was found between vastus medialis Hoffmann reflex and knee extensor torque steadiness (r = -0.35; p = 0.05); whereas a moderate positive relationship was found with maximal isometric knee extensor strength (r = 0.37; p = 0.044). No significant relationships were found between vastus medialis Hoffmann reflex and the other variables.

INTERPRETATION

Our findings provide insight on the relationship between spinal excitability and neuromuscular control of maximal and submaximal isometric torque production in women with patellofemoral pain. Conversely, spinal excitability does not seem to be related with dynamic torques and moments of the knee extensors in women with patellofemoral pain.

The effect of experimental and clinical musculoskeletal pain on spinal and supraspinal projections to motoneurons and motor unit properties in humans: A systematic review

BACKGROUND AND OBJECTIVE

Numerous studies have examined the influence of pain on spinal reflex excitability, motor unit behaviour and corticospinal excitability. Nevertheless, there are inconsistencies in the conclusions made. This systematic review sought to understand the effect of pain on spinal and supraspinal projections to motoneurons and motor unit properties by examining the influence of clinical or experimental pain on the following three domains: H-reflex, corticospinal excitability and motor unit properties.

DATABASES AND DATA TREATMENT

MeSH terms and preselected keywords relating to the H-reflex, motor evoked potentials and motor unit decomposition in chronic and experimental pain were used to perform a systematic literature search using Cumulative Index of Nursing and Allied Health Literature (CINAHL), Excerpta Medica dataBASE (EMBASE), Web of Science, Medline, Google Scholar and Scopus databases. Two independent reviewers screened papers for inclusion and assessed the methodological quality using a modified Downs and Black risk of bias tool; a narrative synthesis and three meta-analyses were performed.

RESULTS

Sixty-one studies were included, and 17 different outcome variables were assessed across the three domains. Both experimental and clinical pain have no major influence on measures of the H-reflex, whereas experimental and clinical pain appeared to have differing effects on corticospinal excitability. Experimental pain consistently reduced motor unit discharge rate, a finding which was not consistent with data obtained from patients. The results indicate that when in tonic pain, induced via experimental pain models, inhibitory effects on motoneuron behaviour were evident. However, in chronic clinical pain populations, more varied responses were evident likely reflecting individual adaptations to chronic symptoms.

SIGNIFICANCE

This is a comprehensive systematic review and meta-analysis which synthesizes evidence on the influence of pain on spinal and supraspinal projections to motoneurons and motor unit properties considering measures of the H-reflex, corticospinal excitability and motor unit behaviour. The H-reflex is largely not influenced by the presence of either clinical or experimental pain. Whilst inhibitory effects on corticospinal excitability and motor unit behaviour were evident under experimental pain conditions, more variable responses were observed for people with painful musculoskeletal disorders.

A task-relevant experimental pain model to target motor adaptation

KEY POINTS

Motor adaptation is thought to be a strategy to avoid pain. Current experimental pain models do not allow for consistent modulation of pain perception depending on movement. We showed that low-frequency sinusoidal stimuli delivered at painful intensity result in minimal habituation of pain perception (over 60 s) and minimal stimulation artefacts on electromyographic signals. When the amplitude of the low-frequency sinusoidal stimuli was modulated based on the vertical force participants applied to the ground with their right leg while standing upright, we demonstrated a strong association between perceived pain and motor adaptation. By enabling task-relevant modulation of perceived pain intensity and the recording electromyographic signals during electrical painful stimulation, our novel pain model will permit direct experimental testing of the relationship between pain and motor adaptation.

ABSTRACT

Contemporary pain adaptation theories predict that motor adaptation occurs to limit pain. Current experimental pain models, however, do not allow for pain intensity modulation according to one's posture or movements. We developed a task-relevant experimental pain model using low-frequency sinusoidal electrical stimuli applied over the infrapatellar fat pad. In fourteen participants, we compared perceived pain habituation and stimulation-induced artefacts in vastus medialis electromyographic recordings elicited by sinusoidal (4, 10, 20 and 50 Hz) and square electrical waveforms delivered at constant peak stimulation amplitude. Next, we simulated a clinical condition where perceived knee pain intensity is proportional to the load applied on the leg by controlling sinusoidal current amplitude (4 Hz) according to the vertical force the participants applied with their right leg to the ground while standing upright. Pain ratings habituated over a 60 s period for 50 Hz sinusoidal and square waveforms but not for low-frequency sinusoidal stimuli (P < 0.001). EMG filters removed most stimulation artefacts for low-frequency sinusoidal stimuli (4 Hz). While balancing upright, participants' pain ratings were correlated with the force applied by the right leg (R²  = 0.65), demonstrating task-relevant changes in perceived pain intensity. Low-frequency sinusoidal stimuli can induce knee pain of constant intensity for 60 s with minimal EMG artefacts while enabling task-relevant pain modulation when controlling current amplitude. By enabling task-dependent modulation of perceived pain intensity, our novel experimental model replicates key temporal aspects of clinical musculoskeletal pain while allowing quantification of neuromuscular activation during painful electrical stimulation. This approach will enable researchers to test the predicted relationship between movement strategies and pain.

Effects of Trigger Point Dry Needling on Neuromuscular Performance and Pain of Individuals Affected by Patellofemoral Pain: A Randomized Controlled Trial

Purpose

To investigate the effects of trigger point dry needling (TrP-DN) on exercise-induced patellofemoral pain syndrome (PFPS).

Patients and Methods

In this randomized, single-blind, parallel-group trial, 50 patients with PFPS were randomly allocated to the following two groups: the TrP-DN group (n = 25) and the Sham needling group (n = 25). Patients in both groups were asked to perform a stretching exercise of the quadriceps daily after needling. The needling group received a single session of TrP-DN to trigger points (TrPs) in the vastus medialis oblique (VMO), vastus lateralis (VL), and rectus femoris muscles (once a week for 6 weeks), and the Sham group received placebo needling. Visual analogue scale (VAS) for pain intensity and Kujala questionnaire for the functional status were assessed before treatment, 3 and 6 weeks after treatment, and at the 3-month follow-up. The ratio of the myoelectric amplitude of the vastus medialis oblique and vastus lateralis muscles (VMO/VL) was assessed before treatment and 6 weeks after treatment.

Results

There was no significant difference in the general data between the two groups. The VAS scores and Kujala scores in the TrP-DN group were significantly improved and increased at the 3-week treatment visit, 6-week treatment visit, and 3-month follow-up compared to the scores before treatment; and the scores in the Sham group were only significantly improved at the 3-week treatment visit, and 6-week treatment visit. VAS scores in the TrP-DN group were significantly lower and Kujala scores were significantly higher at the 6-week treatment visit and the 3-month follow-up compared to those in the Sham group. The VMO/VL ratio in the TrP-DN group was significantly increased at the 6-week treatment visit compared to that before treatment.

Conclusion

TrP-DN at the quadriceps combined with stretch can reduce the pain, and improves the clinical symptoms and function, the VMO/VL ratio, and the coordination of VMO and VL in patients with PFPS.

Targeted Treatment Protocol in Patellofemoral Pain: Does Treatment Designed According to Subgroups Improve Clinical Outcomes in Patients Unresponsive to Multimodal Treatment?

BACKGROUND

Targeted intervention for subgroups is a promising approach for the management of patellofemoral pain.

HYPOTHESIS

Treatment designed according to subgroups will improve clinical outcomes in patients unresponsive to multimodal treatment.

STUDY DESIGN

Prospective crossover intervention.

LEVEL OF EVIDENCE

Level 3.

METHODS

Patients with patellofemoral pain (PFP; n = 61; mean age, 27 ± 9 years) were enrolled. Patients with PFP received standard multimodal treatment 3 times a week for 6 weeks. Patients not responding to multimodal treatment were then classified into 1 of 3 subgroups (strong, weak and tight, and weak and pronated foot) using 6 simple clinical tests. They were subsequently administered 6 further weeks of targeted intervention, designed according to subgroup characteristics. Visual analog scale (VAS), perception of recovery scale (PRS), 5-Level European Quality 5 Dimensions (EQ-5D-5L), and self-reported version of the Leeds Assessment of Neuropathic Symptoms and Signs scale (S-LANSS) were used to assess pain, knee function, and quality of life before and after the interventions.

RESULTS

In total, 34% (n = 21) of patients demonstrated recovery after multimodal treatment. However, over 70% (n = 29/40) of nonresponders demonstrated recovery after targeted treatment. The VAS, PRS, S-LANSS, and EQ-5D-5L scores improved significantly after targeted intervention compared with after multimodal treatment (P < 0.001). The VAS score at rest was significantly lower in the "weak and pronated foot" and the "weak and tight" subgroups (P = 0.011 and P = 0.008, respectively). Posttreatment pain intensity on activity was significantly lower in the "strong" subgroup (P = 0.006).

CONCLUSION

Targeted treatment designed according to subgroup characteristics improves clinical outcomes in patients unresponsive to multimodal treatment.

CLINICAL RELEVANCE

Targeted intervention could be easily implemented after 6 simple clinical assessment tests to subgroup patients into 1 of 3 subgroups (strong, weak and tight, and weak and pronated foot). Targeted interventions applied according to the characteristics of these subgroups have more beneficial treatment effects than a current multimodal treatment program.