Lumbar muscle stiffness is different in individuals with low back pain than asymptomatic controls and is associated with pain and disability, but not common physical examination findings

The role of muscle function and pointe shoe characteristics in Arabesque movement among ballet dancers with non-specific low back pain

This study aimed to investigate posterior chain muscle function and the influence of pointe shoes in ballet dancers with and without low back pain (LBP) in the Arabesque. Twenty-nine young professional ballet dancers (17 with LBP and 12 healthy controls) were recruited. Muscle strength and mechanical properties of the erector spinae and hamstrings were assessed. The displacement of centre of mass (COM) during Arabesque under different shoe conditions (R-class, Chacott, and own shoes) was measured with a motion capture system. The LBP group exhibited greater dynamic stiffness and decreased mechanical stress relaxation time in the lateral hamstring compared to the control group. During Arabesque, the LBP group demonstrated significantly greater anterior-posterior displacement of the COM and a larger percentage of time to achieve maximal trunk extension angle. The COM displacement in vertical and medial-lateral directions was smaller in the R-class than in their own shoes. LBP impacts muscle mechanical properties, particularly in the lateral hamstring. The compromised muscle function resulted in a longer time to spinal extension during Arabesque, signifying that reduced trunk control contributed to greater COM displacement. Hence, it is essential to emphasise that evaluating muscle properties and dynamic postural control is imperative for dancers experiencing LBP.

Trunk muscles' characteristics in adolescent gymnasts with low back pain: a pilot study on the effects of a physiotherapy intervention including a postural reeducation program

BACKGROUND

Trunk muscles' function and characteristics are of great importance for both static and dynamic tasks in different sports, and abnormalities of trunk flexors and extensors might be associated with low back pain (LBP). The aim of this study was to provide a comprehensive evaluation of the functional, morphological and contractile properties in trunk flexors and extensors of young gymnasts with and without LBP.

METHODS

Young gymnasts (14/25 females, 14-18 y) were screened for the presence of chronic LBP. Abdominal and lumbar muscles were tested for function (McGill's endurance tests), thickness (ultrasound), and contractile responses (tensiomyography). An 8-sessions physiotherapy intervention including postural reeducation was performed by a subsample of 10 subjects with LBP.

RESULTS

LBP was found to be associated to higher flexors-to-extensors endurance ratio (OR 11.250, 95% CI: 1.647-76.849, p = 0.014), reduced mean lumbar multifidus thickness (OR 16.500, 95% CI: 2.246-121.228, p = 0.006), and reduced mean erector spinae radial displacement (OR 16.500, 95% CI: 2.246-121.228, p = 0.006). The physiotherapy intervention was found to reduce LBP symptoms and it was associated with a significant improvement in the flexors-to-extensors ratio (p < 0.001).

CONCLUSIONS

This study provides preliminary evidence of functional, morphological, and contractile trunk muscles' alterations associated with chronic LBP in young gymnasts, and presents the effects of a postural reeducation program on symptoms and muscles' functional properties.

Targeted multifidus muscle activation reduces fibrosis of multifidus muscle following intervertebral disc injury

PURPOSE

Aerobic exercise produces beneficial outcomes in patients with low back pain and partially attenuates the fibrotic changes to the multifidus in a model of intervertebral disc (IVD) degeneration. More targeted exercise might be required to fully attenuate these fibrotic alterations. This study aimed to investigate whether activation of the multifidus induced by neurostimulation could reduce fibrosis of the multifidus in a model of IVD degeneration in sheep.

METHODS

IVD degeneration was induced in 18 merino sheep via a partial thickness unilateral annulus fibrosus lesion to the L1/2 and L3/4 IVDs. All sheep received an implantable neurostimulation device that provides stimulation of the L2 medial branch of the dorsal ramus. Three months after surgery, the animals were assigned to Injury or Activated groups. Activated animals received neurostimulation and the Injury group received no stimulation. Six months after surgery, the multifidus was harvested at L2 and L4. Van Gieson's, Sirius Red and immunofluorescence staining for Collagen-I and -III and quantitative PCR was used to examine fibrosis. Muscle harvested from a previous study without IVD injury was used as a control.

RESULTS

Neurostimulation of the multifidus attenuated IVD degeneration dependent increases in the connective tissue, including Collagen-I but not Collagen-III, compared to the Injury group at L4. No measures of the multifidus muscle at L2, which received no stimulation, differed between the Injury and Activated groups.

CONCLUSIONS

These data reveal that targeted activation of the multifidus muscle attenuates IVD degeneration dependent fibrotic alterations to the multifidus.

Lumbar multifidus layers stiffness at L5-S1 level in prone and sitting posture measured by shear wave elastography

BACKGROUND

Multifidus is an important lumbar muscle with distinct superficial and deep fibers responsible for torque production and stabilization, respectively. Its mechanical properties change when transitioning from lying to sitting positions, necessitating enhanced stability. It holds crucial clinical relevance to assess these layers separately, especially in the sitting posture, which demands increased neuromuscular control compared to the prone position.

OBJECTIVE

To compare lumbar multifidus stiffness in lying versus sitting postures, analyzing both superficial and deep layers.

METHODS

Supersonic Shear Imaging captured elastographic images from 26 asymptomatic volunteers in prone and seated positions.

RESULTS

Left multifidus shear modulus in lying: 5.98 ± 1.80/7.96 ± 1.59 kPa (deep/superficial) and sitting: 12.58 ± 4.22/16.04 ± 6.65 kPa. Right side lying: 6.08 ± 1.97/7.80 ± 1.76 kPa and sitting: 13.25 ± 4.61/17.95 ± 7.12 kPa. No side differences (lying p= 0.99, sitting p= 0.43). However, significant inter-postural differences occurred.

CONCLUSION

Lumbar multifidus exhibits increased stiffness in sitting, both layers affected, with superior stiffness in superficial versus deep fibers. Applying these findings could enhance assessing multifidus stiffness changes, for classifying tension-induced low back pain stages.

Is musculoskeletal pain associated with increased muscle stiffness? Evidence map and critical appraisal of muscle measurements using shear wave elastography

INTRODUCTION AND AIMS

Approximately 21% of the world's population suffers from musculoskeletal conditions, often associated with sensations of stiff muscles. Targeted therapy requires knowing whether typically involved muscles are objectively stiffer compared to asymptomatic individuals. Muscle stiffness is quantified using ultrasound shear wave elastography (SWE). Publications on SWE-based comparisons of muscle stiffness between individuals with and without musculoskeletal pain are increasing rapidly. This work reviewed and mapped the existing evidence regarding objectively measured muscle stiffness in musculoskeletal pain conditions and surveyed current methods of applying SWE to measure muscle stiffness.

METHODS

A systematic search was conducted in PubMed and CINAHL using the keywords "muscle stiffness", "shear wave elastography", "pain", "asymptomatic controls" and synonyms. The search was supplemented by a hand search using Google Scholar. Included articles were critically appraised with the AXIS tool, supplemented by items related to SWE methods. Results were visually mapped and narratively described.

RESULTS

Thirty of 137 identified articles were included. High-quality evidence was missing. The results comprise studies reporting lower stiffness in symptomatic participants, no differences between groups and higher stiffness in symptomatic individuals. Results differed between pain conditions and muscles, and also between studies that examined the same muscle(s) and pathology. The methods of the application of SWE were inconsistent and the reporting was often incomplete.

CONCLUSIONS

Existing evidence regarding the objective stiffness of muscles in musculoskeletal pain conditions is conflicting. Methodological differences may explain most of the inconsistencies between findings. Methodological standards for SWE measurements of muscles are urgently required.

Low back pain and biomechanical characteristics of back muscles in firefighters

Firefighters often experience low back pain (LBP), but their back muscle characteristics are not well studied. This study aimed to 1) compare the biomechanical characteristics of back muscles and self-reported back disabilities in frontline firefighters with and without LBP history, and 2) examine the relationships between back disability and biomechanical measurements. We recruited 42 male firefighters and assessed their perceived pain and disabilities, maximum isometric back extension strength, passive stiffness, and fatigability of the longissimus. 54.8% of the participants experienced LBP within the past year. Those indicating higher pain intensity also had greater disability as indicated by the Oswestry Disability Index. There were no significant differences in strength, stiffness or fatigability of the back muscles between firefighters with and without LBP history. Multiple linear regression analysis revealed no significant relationship between the back disability and any biomechanical or demographic measures, likely due to the high functional abilities of the participants.

Scapular muscle dynamic stiffness of asymptomatic subjects and subjects with chronic shoulder pain, at rest and isometric contraction conditions

Muscle stiffness had a crucial role in joint stability, particularly, at the shoulder complex. Although changes in upper trapezius muscle stiffness have been described for shoulder pain, contradictory findings have been obtained. Also, existing data regarding scapular muscles are, majorly, about trapezius. Myotonometry is a method used to assess stiffness; however, the reliability values of scapular muscle stiffness through this method have not been assessed in shoulder pain conditions. The present study aims to compare scapular muscles' stiffness (trapezius, serratus anterior, and levator scapulae) between subjects with and without chronic shoulder pain and to evaluate the related test-retest reliability. Twenty-two symptomatic and twenty-two asymptomatic subjects participated in a cross-sectional study. The dynamic muscular stiffness of scapular muscles, at rest and during an isometric contraction, was measured bilaterally with myotonometry, in two moments. The differences in bilateral averaged values between symptomatic and asymptomatic subjects and the effect of the group (group presenting pain in the dominant or non-dominant side, and asymptomatic group) and of the limb (unilateral painful or asymptomatic limb, and bilateral asymptomatic limbs) were investigated. Test-retest intra-rater reliability was determined. An effect of the group was observed at rest, for middle trapezius stiffness, and during contraction, for middle and lower trapezius stiffness. For middle trapezius, increased values were observed in the group presenting pain in non-dominant side comparing to both groups or to group presenting pain in dominant side. The intraclass correlation coefficient, majorly, ranged between 0.775 and 0.989. Participants with pain in the non-dominant side presented an increased middle trapezius' stiffness. Globally, high reliability was observed for scapular muscles dynamic stiffness.

Changes of trunk muscle stiffness in individuals with low back pain: a systematic review with meta-analysis

BACKGROUND

Low back pain (LBP) is one of the most common musculoskeletal conditions. People with LBP often display changes of neuromuscular control and trunk mechanical properties, including trunk stiffness. Although a few individual studies have examined back muscle stiffness in individuals with LBP, a synthesis of the evidence appears to be lacking. Therefore, the aim of this systematic review with meta-analysis was to synthesize and evaluate the available literature investigating back muscle stiffness in association with LBP.

METHODS

We conducted a systematic review of the literature according to the PRISMA guidelines. We searched Pubmed, Scopus, Web of Science and ScienceDirect for studies, that compared back muscle stiffness, measured either by ultrasound-based elastography or myotonometry, between individuals with and without LBP. Pooled data of the included studies were presented descriptively. Additionally, we performed two meta-analyses to calculate the standardized mean difference between the two groups for resting stiffness of the multifidus and erector spinae muscle. For both meta-analyses, the random effect model was used and the weight of individual studies was calculated using the inverse-variance method. The quality of the included studies was assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Analytical Cross-Sectional studies. Furthermore, the certainty of evidence was evaluated using the GRADE approach.

RESULTS

Nine studies were included in our systematic review. Our results suggest that individuals with LBP have higher stiffness of the multifidus (SMD = 0.48, 95% CI: 0.15 - 0.81, p < 0.01; I2 = 48 %, p = 0.11) and erector spinae at rest (SMD = 0.37, 95% CI: 0.11 - 0.62, p < 0.01; I2 = 39 %, p = 0.14) compared to asymptomatic controls. On the other hand, the evidence regarding muscle stiffness during submaximal contractions is somewhat contradictory.

CONCLUSIONS

Based on the findings of this systematic review we conclude that people with LBP may have higher back muscle stiffness compared to asymptomatic controls. Addressing muscle stiffness might represent an important goal of LBP treatment. Nevertheless, our findings should be interpreted with extreme caution due to a limited quality of evidence, small number of included studies and differences in measurement methodology.

BackMov: Individualized Motion Capture-Based Test to Assess Low Back Pain Mobility Recovery after Treatment

Low back pain (LBP) is a common issue that negatively affects a person's quality of life and imposes substantial healthcare expenses. In this study, we introduce the (Back-pain Movement) BackMov test, using inertial motion capture (MoCap) to assess lumbar movement changes in LBP patients. The test includes flexion-extension, rotation, and lateralization movements focused on the lumbar spine. To validate its reproducibility, we conducted a test-retest involving 37 healthy volunteers, yielding results to build a minimal detectable change (MDC) graph map that would allow us to see if changes in certain variables of LBP patients are significant in relation to their recovery. Subsequently, we evaluated its applicability by having 30 LBP patients perform the movement's test before and after treatment (15 received deep oscillation therapy; 15 underwent conventional therapy) and compared the outcomes with a specialist's evaluations. The test-retest results demonstrated high reproducibility, especially in variables such as range of motion, flexion and extension ranges, as well as velocities of lumbar movements, which stand as the more important variables that are correlated with LBP disability, thus changes in them may be important for patient recovery. Among the 30 patients, the specialist's evaluations were confirmed using a low-back-specific Short Form (SF)-36 Physical Functioning scale, and agreement was observed, in which all patients improved their well-being after both treatments. The results from the specialist analysis coincided with changes exceeding MDC values in the expected variables. In conclusion, the BackMov test offers sensitive variables for tracking mobility recovery from LBP, enabling objective assessments of improvement. This test has the potential to enhance decision-making and personalized patient monitoring in LBP management.

Differential Effects of Classical vs. Sports Massage on Erector Spinae and Upper Trapezius Muscle Stiffness: A Shear-Wave Elastography Study in Young Women

Classical and sports massages are commonly used interventions, but their comparative effects on muscle stiffness remain unclear. Classical massage is more general and uses light to moderate pressure, and its main purpose is relaxation. Sports massage, on the other hand, is more specialized and targets the unique needs of massaged individuals using moderate to firm pressure. This study aimed to evaluate the impacts of classical and sports massages on the stiffness of the erector spinae (ES) and upper trapezius (UT) muscles. Fifteen recreationally active young women, aged 22.9 ± 1.2 years, underwent a randomized cross-over study (with three conditions). Participants received either a five-minute classical or sports massage or a passive rest as a control on distinct days. Muscle stiffness was assessed using shear-wave elastography. The ES shear modulus displayed a significant time effect (p < 0.001; η2 = 0.515) without noticeable differences between the conditions, and the time × massage-type interactions approached statistical significance (F = 2.014; p = 0.073). There was also a large and statistically significant effect of the time on the UT (F = 11.127; p < 0.001; η2 = 0.443). We could not prove that classical and sports massages reduced muscle stiffness. The absence of significant differences might be attributed to the specific intervention parameters (massage duration of 5 min) and the small, only young women sample size. Given some tendencies towards significant effects, larger sample sizes are needed to further investigate this research question.

Physically Active Adults with Low Back Pain do not Demonstrate Altered Deadlift Mechanics: A Novel Application of Myotonometry to Estimate Inter-Muscular Load Sharing

Background

Rehabilitation clinicians that work with physically active populations are challenged with how to safely return patients back to performing deadlift movements following low back injury. Application of reliable and valid tests and measures to quantify impairments related to low back pain (LBP) enhances clinical decision making and may affect outcomes. Myotonometry is a non-invasive method to assess muscle stiffness which has demonstrated significant associations with physical performance and musculoskeletal injury.

Hypothesis/Purpose

The purpose of this study was to compare the stiffness of trunk (lumbar multifidus [LM] and longissimus thoracis [LT]) and lower extremity (vastus lateralis [VL] and biceps femoris [BF]) muscles between individuals with and without LBP during the lying, standing, and deadlifting body positions.

Study Design

Cross-sectional cohort comparison.

Methods

Muscle stiffness measures were collected in the VL, BF, LM, and LT muscles with participants in lying (supine and prone), standing, and the trap bar deadlift position. Separate analyses of covariance were conducted to compare absolute and relative muscle stiffness between the groups for each muscle and condition.

Results

Sixty-eight participants (41 female, 21.3 years, 34 LBP) volunteered for the study. Within the deadlift condition there was a significantly greater increase in the percent-muscle stiffness change in the VL (p = .029, 21.9%) and BF (p = .024, 11.2%) muscles in the control group than in the LBP group. There were no differences in percent-muscle stiffness changes for the standing condition nor were there any absolute muscle stiffness differences between the two groups for the three conditions.

Conclusion

No differences in muscle stiffness were identified in the lying, standing, or deadlifting conditions between participants with and without LBP. Differences in percent stiffness changes were noted between groups for the deadlift position, however the differences were modest and within measurement error. Future studies should investigate the utility of myotonometry as a method to identify LBP-related impairments that contribute to chronic and/or recurrent low back injury.

Level of Evidence

Level 3.

Evaluation of the Reproducibility of MR Elastography Measurements of the Lumbar Back Muscles

BACKGROUND

MR elastography (MRE) may provide quantitative imaging biomarkers of lumbar back muscles (LBMs), complementing MRI in spinal diseases by assessing muscle mechanical properties. However, reproducibility analyses for MRE of LBM are lacking.

PURPOSE

To assess technical failure, within-day and inter-day reproducibility, robustness with the excitation source positioning, and inter-observer agreement of MRE of muscles.

STUDY TYPE

Prospective.

SUBJECTS

Seventeen healthy subjects (mean age 28 ± 4 years; 11 females).

FIELD STRENGTH/SEQUENCE

1.5 T, gradient-echo MRE, T1-weighted turbo spin echo.

ASSESSMENT

The pneumatic driver was centered at L3 level. Four MRE were performed during two visits, 2-4 weeks apart, each consisting of two MRE with less than 10 minutes inter-scan interval. At Visit 1, after the first MRE, the coil and driver were removed, then reinstalled. The MRE was repeated. At Visit 2, following the first MRE, only the driver was moved down 5 cm. The MRE was repeated. Two radiologists segmented the multifidus and erector spinae muscles.

STATISTICAL TESTS

Paired t-test, analysis of variance, intraclass correlation coefficients (ICCs). P-values <0.05 were considered statistically significant.

RESULTS

Mean stiffness of LBM ranged from 1.44 to 1.60 kPa. Mean technical failure rate was 2.5%. Inter-observer agreement was excellent (ICC ranging from 0.82 [0.64-0.96] to 0.99 [0.98-0.99] in the multifidus, and from 0.85 [0.69-0.92] to 0.99 [0.97-0.99] in the erector spinae muscles). Within-day reproducibility was fair in the multifidus (ICC: 0.53 [0.47-0.77]) and good in the erector spinae muscles (ICC: 0.74 [0.48-0.88]). Reproducibility after moving the driver was excellent in both multifidus (ICC: 0.85 [0.69-0.93]) and erector spinae muscles (ICC: 0.84 [0.67-0.92]). Inter-day reproducibility was excellent in the multifidus (ICC: 0.76 [0.48-0.89]) and poor in the erector spinae muscles (ICC: 0.23 [-0.61 to 0.63]).

DATA CONCLUSION

MRE of LBM provides measurements of stiffness with fair to excellent reproducibility and excellent inter-observer agreement. However, inter-day reproducibility in the multifidus muscles indicated that the herein used MRE protocol may not be optimal for this muscle.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Which muscles exhibit increased stiffness in people with chronic neck pain? A systematic review with meta-analysis

Introduction

Chronic neck pain (CNP) substantially impacts quality of life, posing both personal challenges and economic strains. This systematic review sought to discern muscle-specific stiffness differences between CNP patients and individuals without CNP.

Methods

We searched the PubMed, Scopus, and PEDro databases for studies using ultrasound elastography or myotonometry to compare muscle stiffness between CNP patients and asymptomatic controls. Using a meta-analysis with a random-effects model, we derived the pooled effect as standardized mean difference (SMD).

Results

Out of the six studies selected, the adjusted Newcastle-Ottawa rating scale for cross-sectional studies denoted three as moderate-quality and three as high-quality. Our findings indicate that the upper trapezius (UT) stiffness was elevated in CNP patients compared to their counterparts without CNP (SMD = 0.39, 95% CI = 0.05 to 0.74; p = 0.03; small effect size). The data for other muscles remained inconclusive.

Discussion

Given the case-control design of all reviewed studies, a direct causative link between UT stiffness and CNP is yet to be confirmed. As such, recommending a reduction in trapezius muscle stiffness as a primary rehabilitation strategy for CNP patients is still inconclusive and further research is needed.

Effects of a Myofascial Technique on the Stiffness and Thickness of the Thoracolumbar Fascia and Lumbar Erector Spinae Muscles in Adults with Chronic Low Back Pain: A Randomized before-and-after Experimental Study

The thoracolumbar fascia (TLF) may be a pain generator, given its rich innervation. Structural and biomechanical changes have also been documented in adults with chronic non-specific low back pain (LBP). Myofascial techniques (MFTs) are commonly used in manual therapy and are hypothesized to reduce tissue stiffness and pain. However, evidence for these effects is limited. The objective of this study was to evaluate the immediate effects of a standardized MFT compared to a simulated MFT on: (1) the stiffness of the TLF and erector spinae muscles (shear-wave sonoelastography), (2) the thickness of the TLF (B-mode ultrasound), and (3) pain intensity (numerical rating scale). Forty-nine participants with chronic non-specific LBP were included in a randomized before-and-after experimental study. Outcome measures were collected before (T0) and immediately after the intervention (T1). Pain intensity was also assessed on day two (T2) and seven (T7). The MFT group showed a significant decrease in left erector spinae muscle stiffness and left TLF thickness compared to the simulated group. In addition, there was a significant reduction in pain intensity in the MFT group compared to the simulated group at T1 and T2. The results of this study suggest that MFT results in immediate tissue changes and transient pain reduction in patients with LBP.

Preliminary investigation of the effects of sitting with and without short active breaks on muscle stiffness assessed with shear-wave elastography

Purpose

The purpose of this preliminary study was to compare the effects of 1-h sitting with and without short active breaks on muscle stiffness as measured by shear-wave elastography (SWE).

Methods

The participants (7 females, 3 males; age: 24.9 ± 1.2 years) completed two (with and without active breaks) 1-h sitting exposures on separate days. Active breaks (2–3 min) were performed at 20 min and 40 min time marks and comprised simple stretching and activation exercises. Before, during (30 min) and after (1 h) of sitting, shear modulus of upper trapezius, lumbar region of erector spinae and rectus femoris muscles was measured with SWE.

Results

Statistically significant effects of sitting exposure in erector spinae muscle stiffness were noted (p = 0.041; η2 = 0.38). There were no other statistically significant effects of sitting exposure or condition (with/without breaks).

Conclusions

Although few statistically significant effects were detected, the trends in this preliminary trial suggest that prolonged sitting increases muscle stiffness and warrants further investigation of short active breaks with larger sample sizes.

Women with Chronic Pelvic Pain Demonstrate Increased Lumbopelvic Muscle Stiffness Compared to Asymptomatic Controls

Background: Although lumbopelvic muscle stiffness is commonly clinically assessed in women with chronic pelvic pain (CPP), it has not been objectively quantified in this population, and its association with other pain-related impairments has not yet been established. Objective: To compare superficial lumbopelvic muscle stiffness in women with and without CPP. In addition, pressure pain threshold (PPT) was compared between groups and the associations between muscle stiffness and PPT were assessed in women with CPP. Study Design: Case-control. Methods: Muscle stiffness and PPT of 11 lumbopelvic muscles were assessed in 149 women with CPP and 48 asymptomatic women. Subjective outcome measures, including pelvic floor function, health history, and psychosocial outcomes, were collected before muscle stiffness and PPT measurements. Analysis of covariance was used to compare muscle stiffness differences between groups, and independent t-tests were used to compare PPT between groups. Associations between measurements of PPT and muscle stiffness were calculated using correlation analysis. Results: Five of the 11 muscles measured were significantly stiffer in women with CPP than those without CPP (p < 0.05). PPT was significantly decreased in all muscles measured in women with CPP; however, there was not a significant association between muscle stiffness and PPT in women with CPP. Conclusion: The study identified the abdominal lumbopelvic muscles that have increased stiffness in women with CPP compared to asymptomatic women. In addition, muscle stiffness and PPT are two distinct impairments within this population. The results suggest that women with CPP have peripheral muscle impairments, which may be addressed without intravaginal or intrarectal intervention. Clinical Trial Registration: NCT04851730.

The Effects of Isometric Fatigue on Trunk Muscle Stiffness: Implications for Shear-Wave Elastography Measurements

Muscle stiffness has been implicated as a possible factor in low back pain risk. There are few studies on the effects of isometric fatigue on the shear modulus of trunk muscles. This study aimed to investigate the effects of trunk isometric fatigue on the passive and active (during low and high-level contractions) shear moduli of the erector spinae (ES) and superficial and deep multifidus (MF) muscles. We assessed passive and active shear modulus using shear-wave elastography in healthy young participants (n = 22; 11 males, 11 females), before and after an isometric trunk extension fatigue protocol. Maximal voluntary force decreased from 771.2 ± 249.8 N before fatigue to 707.3 ± 204.1 N after fatigue (-8.64%; p = 0.003). Passive shear modulus was significantly decreased after fatigue in the MF muscle (p = 0.006-0.022; Cohen's d = 0.40-46), but not the ES muscle (p = 0.867). Active shear modulus during low-level contraction was not affected by fatigue (p = 0.697-0.701), while it was decreased during high-level contraction for both muscles (p = 0.011; d = 0.29-0.34). Sex-specific analysis indicated the decrease in ES shear modulus was significant in males (p = 0.015; d = 0.31), but not in females (p = 0.140). Conversely, the shear modulus in superficial MF had a statistically significant decrease in females (p = 0.002; d = 0.74) but not in males (p = 0.368). These results have important implications for further investigations of the mechanistic interaction between physical workloads, sex, muscle stiffness (and other variables affecting trunk stability and neuromuscular control), and the development/persistence of low back pain.

Effects of Different Long-Term Exercise Modalities on Tissue Stiffness

Stiffness is a fundamental property of living tissues, which may be modified by pathologies or traumatic events but also by nutritional, pharmacological and exercise interventions. This review aimed to understand if specific forms of exercise are able to determine specific forms of tissue stiffness adaptations. A literature search was performed on PubMed, Scopus and Web of Science databases to identify manuscripts addressing adaptations of tissue stiffness as a consequence of long-term exercise. Muscular, connective, peripheral nerve and arterial stiffness were considered for the purpose of this review. Resistance training, aerobic training, plyometric training and stretching were retrieved as exercise modalities responsible for tissue stiffness adaptations. Differences were observed related to each specific modality. When exercise was applied to pathological cohorts (i.e. tendinopathy or hypertension), stiffness changed towards a physiological condition. Exercise interventions are able to determine tissue stiffness adaptations. These should be considered for specific exercise prescriptions. Future studies should concentrate on identifying the effects of exercise on the stiffness of specific tissues in a broader spectrum of pathological populations, in which a tendency for increased stiffness is observed.

Associations between Deformation of the Thoracolumbar Fascia and Activation of the Erector Spinae and Multifidus Muscle in Patients with Acute Low Back Pain and Healthy Controls: A Matched Pair Case-Control Study

Background: The thoracolumbar fascia (TLF) is thought to play a role in the development of LBP, but it is not yet clear which factor of TLF changes is a cause and which is an effect. Therefore, some studies used the cross-correlation function (CCR) to reveal time-dependent relationships between biomechanical and neuromotor factors. Methods: Ten patients with acute low back pain (aLBP) were matched to healthy controls. Simultaneous recording of surface electromyography (sEMG) of the erector spinae and multifidus muscle (ESM) and dynamic ultrasound (US) images of TLF deformation were performed during trunk extension. CCR functions and Granger causality (GC) were used to describe the relationship between the two measures. Results: CCR time lags were significant higher in the aLBP group (p = 0.04). GC showed a direct effect of TLF deformation on ESM activation only in the aLBP group (p < 0.03). Conclusions: The results suggest that in aLBP, ESM activity is significantly affected by TLF, whereas this relationship is completely random in healthy subjects studied with CCR and GC comparisons of dynamic US imaging and sEMG data signals. Fascia-related disturbances in neuromotor control, particularly due to altered muscle spindle functions, are suspected as a possible mechanism behind this.

Functional versus conventional strength and conditioning programs for back injury prevention in emergency responders

Back pain and back-related injuries are common complaints among emergency responders. The purpose of this study was to compare the effectiveness of two strength and conditioning programs in improving back muscle characteristics and disabilities in emergency responders (firefighters/paramedics). Participants (n = 24) were randomized into two groups to complete 16 weeks of supervised exercise intervention: 1) Functional training used unilateral movements that mimicked the asymmetrical nature of emergency operations, 2) Conventional training performed bilaterally loaded exercises. Outcome measures were maximum isometric back extension strength, passive muscle stiffness, lumbar extensor fatigability, and revised Oswestry Low Back Pain Questionnaire. A mixed model Analysis of Variance with repeated measures was performed to compare the difference over time and between groups. While the training effects were similar between groups, both programs improved isometric back extension strength (+21.3% functional, +20.3% conventional, p &lt; 0.001, ηp2 = 0.625) and lumbar extensor muscle fatigability (+17.4% functional, +9.5% conventional, p = 0.009, ηp2 = 0.191). Bilateral symmetry in muscle stiffness was improved as indicated by reduction in symmetry index (-7.1% functional, -11.8% conventional, p = 0.027, ηp2 = 0.151). All self-reported pain and disability scores fell within the category of “minimum functional limitation” throughout the intervention and 6-month follow-up periods. For frontline firefighters and paramedics, both functional and conventional strength training are effective for improving back muscle characteristics.

The effect of phasic versus combined neuromuscular electrical stimulation using the StimaWELL 120MTRS system on multifidus muscle morphology and function in patients with chronic low back pain: a randomized controlled trial protocol

Background

Neuromuscular electrical stimulation (NMES) is used to improve muscle strength clinically when rehabilitating various musculoskeletal disorders. However, the effects of NMES on muscle morphology and function in individuals with non-specific chronic low back pain (CLBP) have scarcely been investigated. Although research links deficits in the paraspinal musculature with subjective reports of pain and disability, it is unknown if treatment with NMES can help reverse these deficits. Therefore, the primary aim of this study is to compare the effects of two muscle therapy protocols with a medium-frequency electrotherapy device (the StimaWELL 120MTRS system) on multifidus muscle morphology and function in CLBP patients. The secondary aims are to determine the effects of these protocols subjective reports of pain intensity, pain interference, disability, and catastrophizing.

Methods

A total of 30 participants with non-specific CLBP, aged 18–60, will be recruited from local orthopedic clinics and databases. Participants will be randomized (1:1) to either the phasic or combined (phasic + tonic) muscle therapy protocols on the StimaWELL 120MTRS system. Participants will undergo 20 supervised electrotherapy treatments over a 10-week period. The primary outcomes will be multifidus morphology (e.g. cross-sectional area (CSA), fat infiltration) and function (e.g., contraction measured via %thickness change from a rested to contracted state, and stiffness at rest and during contraction). Secondary outcomes will include pain intensity, interference, disability, and catastrophizing. Both primary and secondary outcomes will be obtained at baseline and at 11-weeks; secondary outcomes measured via questionnaires will also be obtained at 6-weeks, while LBP intensity will be measured before and after each treatment. Paired t-tests will be used to assess within-group changes for all primary outcome measures. A two-way repeated-measures analysis of variance will be used to assess changes in secondary outcomes over time.

Discussion

The results of this trial will help clarify the role of medium-frequency NMES on lumbar multifidus morphology and function.

Trial Registration

NCT04891692, registered retrospectively on May 18, 2021.

The relationships between physical activity, lumbar multifidus muscle morphology, and low back pain from childhood to early adulthood: a 12-year longitudinal study

We investigated the longitudinal associations between physical activity (PA), lumbar multifidus morphology, and impactful low back pain (LBP) in young people. Nine-year-old children were recruited from 25 primary schools and followed up at age 13, 16, and 21 years. We measured PA with accelerometers at age 9, 13, and 16; quantified patterns of lumbar multifidus intramuscular adipose tissue (IMAT) change from 13 to 16 years using magnetic resonance imaging; and recorded LBP and its impact with standardised questionnaires and interviews. Associations were examined with crude and adjusted logistic or multinomial models and reported with odds ratios (OR) or relative risk ratios (RRR). We included data from 364 children (mean[SD] age = 9.7[.4] years). PA behaviour was not associated with LBP. Having persistently high IMAT levels at age 13 and 16 was associated with greater odds of LBP (OR[95% CI] = 2.98[1.17 to 7.58]). Increased time in moderate and vigorous intensity PA was associated with a lower risk of higher IMAT patterns (RRR[95% CI] = .67[.46 to .96] to .74[.55 to 1.00]). All associations became non-significant after adjusting for sex and body mass index (BMI). Future studies investigating the relationships between PA behaviour, lumbar multifidus IMAT, and impactful LBP should account for potential confounding by sex and BMI.

Assessment of selected muscles reactivity in the lower spinal segment

Background: Lumbar spine pain is now a common affliction. In 90% of cases, the pain is of ambiguous and multicausal etiology, described as non-specific lower back pain (NLBP). Various models of this dysfunction were examined. The most popular model presents the pain as a result of an insult and secondary to changes in tension and lumbar muscles degeneration. There is no unequivocal solution concerning the cause of lumbar spine pain in the literature. Aim of the study: To examine the differences in muscles reactivity in the lumbar region in cases who suffer from lumbar spine pain in comparison to otherwise healthy controls. Material and methods: In total, 50 participants (24 men and 26 women) aged 18–45, including 24 people with pain, and 26 without ailments were included in the study. The visual analogue scale was used to measure pain intensity. The participants were assessed to determine the reactivity of the soft tissues of the lumbar part of the body. Selected muscles of this area were examined using a myotonometer, which shows five parameters relevant to viscoelastic tissues. Results: There were significant differences in the level of the pain (p<0.001), hypokinesia of the left abdominal rectus (p<0.05), asymmetry indicators for the creep parameter of the erector spinalis and abdominal external oblique muscle, and the stiffness of abdominal rectus (p<0.05). No significant differences for the remaining parameters were found. Conclusions: Tissue reactivity of selected muscles of the lumbar spine shows slight differences because of pain afflictions occurring in this area.

[Feeling stiff…but what does it mean objectively? : Can you measure muscle tension?]

Almost everyone is familiar with "tense muscles", but what is muscle tension physiologically behind? Are tense muscles more active; do they have problems relaxing? Are they harder or stiffer than asymptomatic muscles? In this work, current evidence regarding the activity and stiffness of tense neck muscles is presented. Further, measurement methods and their limitations are explained. These limitations reveal the shortcomings of the current knowledge and the need for further research. Finally, a recently funded research project on the measurement of tense muscles is presented.

Modulation in the Stiffness of Specific Muscles of the Quadriceps in Patients With Knee Osteoarthritis and Their Relationship With Functional Ability

Deficits in the flexibility of the quadriceps are one of the risk factors for developing knee joint disorders. No studies have investigated the changes in the stiffness of the quadriceps muscle among patients with knee osteoarthritis (OA). Therefore, the purpose of this study was to investigate changes in the stiffness of specific-muscle of the quadriceps in patients with knee OA and their relationship with functional ability. Twenty-five patients with knee OA and 25 healthy, asymptomatic subjects were recruited in this study. The stiffness of the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) in all participants was evaluated using MyotonPRO at 60° and 90° flexion of the knee joint. The results of this study showed a greater VL stiffness in patients with knee OA than in healthy subjects at both 60° and 90° of knee flexion (p &lt; 0.05). Significant differences in VL, VM and RF stiffness were obtained at different knee joint angles in individuals with and without knee OA (p &lt; 0.05). In addition, there was a positive correlation between VL stiffness and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores in patients with Knee OA (60° of knee flexion: r = 0.508, p = 0.010; 90° of knee flexion: r = 0.456, p = 0.022). These results indicate that there is an increase in VL stiffness in patients with knee OA compared with healthy, asymptomatic subjects, and the quadriceps stiffness was increased with knee flexion in both healthy subjects and patients with knee OA. VL stiffness is associated with WOMAC scores in patients with knee OA.

Are Morphometric and Biomechanical Characteristics of Lumbar Multifidus Related to Pain Intensity or Disability in People With Chronic Low Back Pain After Considering Psychological Factors or Insomnia?

INTRODUCTION

Lumbar multifidus muscle (LMM) dysfunction is thought to be related to pain and/or disability in people with chronic low back pain (CLBP). Although psychosocial factors play a major role in pain/disability, they are seldom considered as confounders in analyzing the association between LMM and CLBP.

OBJECTIVES

This study aimed to determine: (1) differences in psychological factors, insomnia, and LMM characteristics between people with and without CLBP; (2) associations between psychological factors, insomnia, or LMM characteristics and low back pain (LBP) intensity or LBP-related disability in people with CLBP; and (3) whether LMM characteristics are related to LBP symptoms in people with CLBP after considering confounders.

METHODS

Seventy-eight volunteers with CLBP and 73 without CLBP provided sociodemographic information, filled the 11-point numeric pain rating scale and Roland-Morris disability questionnaire (RMDQ). They completed the Hospital Anxiety and Depression Scale (HADS), Pain Catastrophizing Scale (PCS), Fear Avoidance Belief Questionnaire (FAB), and Insomnia Severity Index Scale (ISI). Resting and contracted thickness of LMM at L4-S1 levels were measured from brightness-mode ultrasound images. Percent thickness changes of LMM at L4-S1 levels during contraction were calculated. Resting LMM stiffness at L4-S1 was measured by shear wave elastography. Associations among LMM, psychosocial or insomnia parameters and clinical outcomes were analyzed by univariate and multivariate analyses.

RESULTS

People with CLBP demonstrated significantly higher LBP-intensity, RMDQ, HADS, FAB, PCS, and ISI scores than asymptomatic controls (p < 0.05). The former also had significantly smaller percent thickness changes of LMM at L4/L5 during contraction. LBP-intensity was positively related to scores of PCS-total, PCS-helplessness, FAB-total, FAB-work, and ISI in people with CLBP (p < 0.05). RMDQ scores were positively associated with the scores of HADS-total, HADS-depression, PCS-total, FAB-total, FAB-physical activity, PCS-helplessness, and ISI in people with CLBP (p < 0.05). FAB-work and ISI scores together explained 24% of LBP-intensity. FAB-total scores alone explained 34% of variance of LBP-related disability in people with CLBP.

CONCLUSION

More fear-avoidance belief or insomnia is related to greater LBP-intensity and/or LBP-related disability in people with CLBP. Although people with CLBP were thought to have aberrant LMM morphometry/function, no LMM characteristics were related to LBP-intensity or LBP-related disability after considering other confounders.

Effect of dry needling on lumbar muscle stiffness in patients with low back pain: A double blind, randomized controlled trial using shear wave elastography

Background: Dry needling treatment focuses on restoring normal muscle function in patients with musculoskeletal pain; however, little research has investigated this assertion. Shear wave elastography (SWE) allows quantification of individual muscle function by estimating both resting and contracted muscle stiffness.Objective: To compare the effects of dry needling to sham dry needling on lumbar muscle stiffness in individuals with low back pain (LBP) using SWE.Methods: Sixty participants with LBP were randomly allocated to receive one session of dry needling or sham dry needling treatment to the lumbar multifidus and erector spinae muscles on the most painful side and spinal level. Stiffness (shear modulus) of the lumbar multifidus and erector spinae muscles was assessed using SWE at rest and during submaximal contraction before treatment, immediately after treatment, and 1 week later. Treatment effects were estimated using linear mixed models.Results: After 1 week, resting erector spinae muscle stiffness was lower in individuals who received dry needling than those that received sham dry needling. All other between-groups differences in muscle stiffness were similar, but non-significant.Conclusion: Dry needling appears to reduce resting erector spinae muscle following treatment of patients with LBP. Therefore, providers should consider the use of dry needling when patients exhibit aberrant stiffness of the lumbar muscles.

Implementing Ultrasound Imaging for the Assessment of Muscle and Tendon Properties in Elite Sports: Practical Aspects, Methodological Considerations and Future Directions

Ultrasound (US) imaging has been widely used in both research and clinical settings to evaluate the morphological and mechanical properties of muscle and tendon. In elite sports scenarios, a regular assessment of such properties has great potential, namely for testing the response to training, detecting athletes at higher risks of injury, screening athletes for structural abnormalities related to current or future musculoskeletal complaints, and monitoring their return to sport after a musculoskeletal injury. However, several practical and methodological aspects of US techniques should be considered when applying this technology in the elite sports context. Therefore, this narrative review aims to (1) present the principal US measures and field of applications in the context of elite sports; (2) to discuss, from a methodological perspective, the strengths and shortcomings of US imaging for the assessment of muscle and tendon properties; and (3) to provide future directions for research and application.

Examination of pelvic floor muscle elasticity in patients with interstitial cystitis/bladder pain syndrome using real-time tissue elastography

INTRODUCTION AND HYPOTHESIS

The aim was to compare pelvic floor muscle (PFM) elasticity between interstitial cystitis/bladder pain syndrome (IC/BPS) patients and healthy women using real-time tissue elastography.

METHODS

The subjects were 17 IC/BPS female patients (IC/BPS group; age 34-84 years), 10 healthy middle-aged women (middle-aged group; 50-80 years), and 17 healthy young adult women (young group; 23-37 years). The target sites of elastography were the striated urethral sphincter (SUS) and adipose tissue as the reference site; muscle elasticity was calculated as the strain ratio (SR) of the SUS to the reference site. Evaluations were performed at rest and during PFM contraction. The IC/BPS group completed lower urinary tract symptom and pain questionnaires. SUS SR was compared among the three groups. SUS SR at rest and during PFM contraction was compared among the three groups with the t-test and the Wilcoxon test. Associations between questionnaire results and SUS SR were evaluated by correlation analysis.

RESULTS

There was no significant difference in age between the IC/BPS and middle-aged groups, but the young group was significantly younger than the other groups (p < 0.001). SUS SR at rest was significantly higher in the IC/BPS group than in the middle-aged (p = 0.014) and young groups (p = 0.002). Furthermore, in the IC/BPS group, there was no significant difference in SUS SR between at rest and during PFM contraction. SUS SR was not significantly correlated with questionnaire results for lower urinary tract symptoms.

CONCLUSIONS

SUS SR at rest was significantly higher in the IC/BPS group than in the young and middle-aged groups.

Shear modulus of multifidus and longissimus muscles measured using shear wave elastography correlates with muscle activity, but depends on image quality

Shear wave elastography (SWE) estimates shear modulus in muscle. This is interpreted as an index of muscle stiffness, but depends on muscle characteristics. This study evaluated relationship between shear modulus and myoelectric activity of lumbar multifidus and longissimus muscles to assess its validity. Intramuscular electromyography (EMG) of multifidus (deep [DM], superficial [SM] fibres) at L4/5, longissimus [LG] at L2, were recorded in nine healthy participants. Participants performed isometric trunk extension in side-lying from 0 to 30% maximal voluntary contraction (MVC) with EMG amplitude feedback. Using SWE, two regions of interest (ROI) were investigated in each muscle. Generally, shear modulus was moderately correlated with root mean squared (RMS) EMG (r = 0.50-0.78). Univariate and multiple regression analyses showed ultrasound/SWE features of 'B-mode quality' (24.5%), '%Void pixels' (17.9%) and 'Connective tissue' (16.2%) explained most variation in the shear modulus/EMG relationship. Regression prediction scores generated using imaging features were correlated with r-coefficients of shear modulus/EMG relationship. When analysis was restricted to high quality data (i.e., regression prediction score above an a priori defined threshold), the shear modulus/EMG relationship increased to r = 0.70-0.96. Although a linear relationship between shear modulus/EMG was confirmed, supporting validity of SWE measures in anatomically distinct back muscles, this depends on image quality.

Impact of nonsurgical spinal decompression on paraspinal muscle morphology and mechanical properties in young adults with low back pain

Objective

The mechanism underlying the benefit of nonsurgical spinal decompression (NSSD) on low back pain is unclear. This study was performed to investigate the immediate impact of NSSD on the mechanical properties and morphology of the paraspinal muscles.

Methods

Participants with low back pain were recruited. NSSD therapy was provided on one occasion. A myotonometer was placed perpendicularly on the skin surface over the paraspinal muscle at the level of L₃/L₄ to measure the mechanical muscle properties. The multifidus thickness was measured using B-mode ultrasound and defined as the distance between the transverse process and subcutaneous tissue fascia. The difference between before and after NSSD was analyzed by a paired t-test.

Results

Thirty participants (mean age, 20.9 ± 0.8 years; 9 male, 21 female) were recruited. No significant difference was observed in the muscle mechanical properties or morphology between before and after the intervention.

Conclusions

NSSD intervention did not induce immediate changes in the paraspinal muscle mechanical properties or multifidus thickness in young adults with low back pain. NSSD might produce benefits by stimulating mechanical receptors rather than inducing morphological changes or mechanical property alterations of the muscle fibers. These parameters may not be suitable outcome measures for NSSD intervention.