Achilles tendon morpho-mechanical parameters are related to triceps surae motor unit firing properties.

Recent studies combining high-density surface electromyography (HD-sEMG) and ultrasound imaging have yielded valuable insights into the relationship between motor unit activity and muscle contractile properties. However, limited evidence exists on the relationship between motor unit firing properties and tendon morpho-mechanical properties. This study aimed to determine the relationship between triceps surae motor unit firing properties and the morpho-mechanical properties of the Achilles tendon (AT). Motor unit firing properties (i.e. mean discharge rate (DR) and coefficient of variation of the interspike interval (COVisi)) and motor unit firing-torque relationships (cross-correlation between cumulative spike train (CST) and torque, and the delay between motor unit firing and torque production (neuromechanical delay)) of the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SO) muscles were assessed using HD-sEMG during isometric plantarflexion contractions at 10% and 40% of maximal voluntary contraction (MVC). The morpho-mechanical properties of the AT (i.e. length, thickness, cross-sectional area and resting stiffness) were determined using B-mode ultrasonography and shear-wave elastography. Multiple linear regression analysis showed that at 10% MVC, the DR of the triceps surae muscles explained 41.7% of the variance in resting AT stiffness. Additionally, at 10% MVC, COVisi SO predicted 30.4% of the variance in AT length. At 40% MVC, COVisi MG and COVisi SO explained 48.7% of the variance in AT length. Motor unit-torque relationships were not associated with any morpho-mechanical parameter. This study provides novel evidence of a contraction-intensity dependent relationship between motor unit firing parameters of the triceps surae muscle and the morpho-mechanical properties of the AT.

Unraveling the Mechanisms Behind the Short-Term Effects of Dry Needling: New Insights From a Mediation Analysis With Repeatedly Measured Mediators and Outcomes.

OBJECTIVE: To explore the causal pathways underlying the short-term effects of deep dry needling (DDN) in people with chronic neck pain. DESIGN: Explanatory longitudinal mediation analysis with repeatedly measured mediators and outcomes. SETTING: Primary care setting. PARTICIPANTS: Patients (N=128) with chronic neck pain. INTERVENTIONS: Participants were randomized into 2 groups; DDN of the neck muscles combined with stretching (n=64) and stretching alone (n=64). MAIN OUTCOME MEASURES: Two outcomes (pain intensity and neck pain-related disability) and 3 candidate mediators (local pressure pain thresholds [PPTs], cervical range of motion [ROM], and neck muscle strength) were included. Pain intensity was also included as a competing mediator in the mediation analysis for disability. Mediators and outcomes were measured at 3 time points: after intervention and at 2- and 4-week follow-up. Age, sex, and the baseline values of the outcome and mediators were included as pretreatment mediator-outcome confounders. RESULTS: Reductions in pain intensity strongly mediated the short-term effects of DDN on disability, from after intervention to 4-week follow-up. In addition, the attenuation of local hypersensitivity (via increasing PPTs) moderately mediated reductions in pain intensity at each time point. On the other hand, gains in cervical ROM contributed to reducing neck pain-related disability. Changes in muscle strength did not lead to better outcomes. CONCLUSIONS: This novel study demonstrated that DDN effect on neck pain-related disability is strongly driven by the analgesic effects of this physical therapy modality. Increasing PPTs and cervical ROM seem to be also part of the mechanisms behind DDN's effect.

Effect of movement-evoked and tonic experimental pain on muscle force production.

INTRODUCTION: When performing an exercise or a functional test, pain that is evoked by movement or muscle contraction could be a stronger stimulus for changing how individuals move compared to tonic pain. We investigated whether the decrease in muscle force production is larger when experimentally-induced knee pain is directly associated to the torque produced (movement-evoked) compared to a constant painful stimulation (tonic). METHODS: Twenty-one participants performed three isometric knee extension maximal voluntary contractions without pain (baseline), during pain, and after pain. Knee pain was induced using sinusoidal electrical stimuli at 10 Hz over the infrapatellar fat pad, applied continuously or modulated proportionally to the knee extension torque. Peak torque and contraction duration were averaged across repetitions and normalized to baseline. RESULTS: During tonic pain, participants reported lower pain intensity during the contraction than at rest (p < 0.001), whereas pain intensity increased with contraction during movement-evoked pain (p < 0.001). Knee extension torque decreased during both pain conditions (p < 0.001), but a larger reduction was observed during movement-evoked compared to tonic pain (p < 0.001). Participants produced torque for longer during tonic compared to movement-evoked pain (p = 0.005). CONCLUSION: Our results indicate that movement-evoked pain was a more potent stimulus to reduce knee extension torque than tonic pain. The longer contraction time observed during tonic pain may be a result of a lower perceived pain intensity during muscle contraction. Overall, our results suggest different motor adaptation to tonic and movement-evoked pain and support the notion that motor adaptation to pain is a purposeful strategy to limit pain. This mechanistic evidence suggests that individuals experiencing prevalently tonic or movement-evoked pain may exhibit different motor adaptations, which may be important for exercise prescription.

Measurement properties of cervical joint position error in people with and without neck pain: a systematic review and narrative synthesis.

INTRODUCTION: Proprioception can be impaired in people with neck pain. The cervical joint position sense test, which measures joint position error (JPE), is the most common test used to assess neck proprioception. The aim of this systematic review was to assess the measurement properties of this test for the assessment of people with and without neck pain. METHODS: This systematic review was registered prospectively on Prospero (CRD42020188715). It was designed using the COSMIN guidelines and reported in line with the PRISMA checklist. Two reviewers independently searched Medline, Embase, SportDiscus, and CINAHL Plus databases from inception to the 24th July 2022 with an update of the search conducted until 14th of October 2023. The COSMIN risk of bias checklist was used to assess the risk of bias in each study. The updated criteria for good measurement properties were used to rate individual studies and then the overall pooled results. The level of evidence was rated by two reviewers independently using a modified GRADE approach. RESULTS: Fifteen studies were included in this review, 13 reporting absolute JPE and 2 reporting constant JPE. The measurement properties assessed were reliability, measurement error, and validity. The measurement of JPE showed sufficient reliability and validity, however, the level of evidence was low/very low for both measurement properties, apart from convergent validity of the constant JPE, which was high. CONCLUSION: The measure of cervical JPE showed sufficient reliability and validity but with low/very low levels of evidence. Further studies are required to investigate the reliability and validity of this test as well as the responsiveness of the measure.

Biomechanical Posture Analysis in Healthy Adults with Machine Learning: Applicability and Reliability.

Posture analysis is important in musculoskeletal disorder prevention but relies on subjective assessment. This study investigates the applicability and reliability of a machine learning (ML) pose estimation model for the human posture assessment, while also exploring the underlying structure of the data through principal component and cluster analyses. A cohort of 200 healthy individuals with a mean age of 24.4 ± 4.2 years was photographed from the frontal, dorsal, and lateral views. We used Student's t-test and Cohen's effect size (d) to identify gender-specific postural differences and used the Intraclass Correlation Coefficient (ICC) to assess the reliability of this method. Our findings demonstrate distinct sex differences in shoulder adduction angle (men: 16.1° ± 1.9°, women: 14.1° ± 1.5°, d = 1.14) and hip adduction angle (men: 9.9° ± 2.2°, women: 6.7° ± 1.5°, d = 1.67), with no significant differences in horizontal inclinations. ICC analysis, with the highest value of 0.95, confirms the reliability of the approach. Principal component and clustering analyses revealed potential new patterns in postural analysis such as significant differences in shoulder-hip distance, highlighting the potential of unsupervised ML for objective posture analysis, offering a promising non-invasive method for rapid, reliable screening in physical therapy, ergonomics, and sports.

Pain chronification impacts whole-brain functional connectivity in women with hip osteoarthritis during pain stimulation.

OBJECTIVE: Previous neuroimaging studies have shown that patients with chronic pain display altered functional connectivity across distributed brain areas involved in the processing of nociceptive stimuli. The aim of the present study was to investigate how pain chronification modulates whole-brain functional connectivity during evoked clinical and tonic pain. METHODS: Patients with osteoarthritis of the hip (n = 87) were classified into 3 stages of pain chronification (Grades I-III, Mainz Pain Staging System). Electroencephalograms were recorded during 3 conditions: baseline, evoked clinical hip pain, and tonic cold pain (cold pressor test). The effects of both factors (recording condition and pain chronification stage) on the phase-lag index, as a measure of neuronal connectivity, were examined for different frequency bands. RESULTS: In women, we found increasing functional connectivity in the low-frequency range (delta, 0.5-4 Hz) across pain chronification stages during evoked clinical hip pain and tonic cold pain stimulation. In men, elevated functional connectivity in the delta frequency range was observed in only the tonic cold pain condition. CONCLUSIONS: Across pain chronification stages, we found that widespread cortical networks increase their synchronization of delta oscillations in response to clinical and experimental nociceptive stimuli. In view of previous studies relating delta oscillations to salience detection and other basic motivational processes, our results hint at these mechanisms playing an important role in pain chronification, mainly in women.

Predictors of poor outcome following lumbar spinal fusion surgery: a prospective observational study to derive two clinical prediction rules using British Spine Registry data.

PURPOSE: Lumbar spinal fusion surgery (LSFS) is common for lumbar degenerative disorders. The objective was to develop clinical prediction rules to identify which patients are likely to have a favourable outcome to inform decisions regarding surgery and rehabilitation. METHODS: A prospective observational study recruited 600 (derivation) and 600 (internal validation) consecutive adult patients undergoing LSFS for degenerative lumbar disorder through the British Spine Registry. Definition of good outcome (6 weeks, 12 months) was reduction in pain intensity (Numerical Rating Scale, 0-10) and disability (Oswestry Disability Index, ODI 0-50) > 1.7 and 14.3, respectively. Linear and logistic regression models were fitted and regression coefficients, Odds ratios and 95% CIs reported. RESULTS: Lower BMI, higher ODI and higher leg pain pre-operatively were predictive of good disability outcome, higher back pain was predictive of good back pain outcome, and no previous surgery and higher leg pain were predictive of good leg pain outcome; all at 6 weeks. Working and higher leg pain were predictive of good ODI and leg pain outcomes, higher back pain was predictive of good back pain outcome, and higher leg pain was predictive of good leg pain outcome at 12 months. Model performance demonstrated reasonable to good calibration and adequate/very good discrimination. CONCLUSIONS: BMI, ODI, leg and back pain and previous surgery are important considerations pre-operatively to inform decisions for surgery. Pre-operative leg and back pain and work status are important considerations to inform decisions for management following surgery. Findings may inform clinical decision making regarding LSFS and associated rehabilitation.

Determining the level of cervical radiculopathy: Agreement between visual inspection of pain drawings and magnetic resonance imaging.

BACKGROUND AND AIMS: Pain drawings are commonly used in the clinical assessment of people with cervical radiculopathy. This study aimed to assess (1) the agreement of clinical interpretation of pain drawings and MRI findings in identifying the affected level of cervical radiculopathy, (2) the agreement of these predictions based on the pain drawing among four clinicians from two different professions (i.e., physiotherapy and surgery) and (3) the topographical pain distribution of people presenting with cervical radiculopathy (C4-C7). METHODS: Ninety-eight pain drawings were obtained from a baseline assessment of participants in a randomized clinical trial, in which single-level cervical radiculopathy was determined using MRI. Four experienced clinicians independently rated each pain drawing, attributing the pain distribution to a single nerve root (C4-C7). A post hoc analysis was performed to assess agreement. OUTCOME MEASURES: Percentage agreement and kappa values were used to assess the level of agreement. Topographic pain frequency maps were created for each cervical radiculopathy level as determined by MRI. RESULTS: The radiculopathy level determined from the pain drawings showed poor overall agreement with MRI (mean = 35.7%, K = -0.007 to 0.139). The inter-clinician agreement ranged from fair to moderate (K = 0.212-0.446). Topographic frequency maps revealed that pain distributions were widespread and overlapped markedly between patients presenting with different levels cervical radiculopathy. CONCLUSION: This study revealed a lack of agreement between the segmental level affected determined from the patient's pain drawing and the affected level as identified on MRI. The large overlap of pain and non-dermatomal distribution of pain reported by patients likely contributed to this result.

Higher Neck Pain Intensity and the Presence of Psychosocial Factors Are More Likely When Headache is Present after a Whiplash Injury: A Case-Control Study.

BACKGROUND: Several factors such as neck pain intensity, disability, anxiety, depression, female sex, or a previous history of headache are associated with post-whiplash headache. However, the possible role of psychosocial factors contributing to the presence of headache or worsening of headache after a whiplash trauma remains unclear. To address this gap in knowledge, there is the need to assess psychosocial factors concerning headache shortly after a whiplash injury. OBJECTIVE: To evaluate psychological features, pain and disability in people with acute whiplash associated disorders (WAD) and compare these features between those with and without headache. DESIGN: Case-control study. SETTING: A secondary care traumatology center. METHODS: Forty-seven people with acute WAD were recruited; 28 with headache, and 19 without. All participants completed self-reported questionnaires including Visual Analogue Scale (VAS) for neck pain intensity, the Neck Disability Index (NDI), Pain Catastrophizing Scale (PCS), Tampa Scale Kinesiophobia-11 (TSK-11), and State-Trait Anxiety Inventory. RESULTS: Neck pain intensity (P < .001), neck disability (P < 0.001), pain catastrophizing (P < .001), kinesiophobia (P < .001), and anxiety state (P = .007) and trait (P = .05) were higher in those with headache when compared to those without. In addition, high levels of neck pain (P = .025), moderate levels of neck disability (P < .001), moderate levels of pain catastrophizing (P = .015), and moderate (P = .002) and severe (P = .016) levels of kinesiophobia were related to the presence of headache. CONCLUSIONS: The level of neck pain intensity and disability, kinesiophobia, catastrophizing, and anxiety were all greater in people with acute WAD who presented with a headache compared to those without headache.

Immediate Effects of Dry Needing or Manual Pressure Release of Upper Trapezius Trigger Points on Muscle Activity During the Craniocervical Flexion Test in People with Chronic Neck Pain: A Randomized Clinical Trial.

OBJECTIVE: To compare the effects of dry needling or manual pressure release on an active trigger point in the upper trapezius on craniocervical flexion test performance, pressure pain thresholds, and cervical range of motion in chronic neck pain. DESIGN: A parallel randomized clinical trial. SETTING: Physical therapy service. SUBJECTS: Individuals with chronic neck pain. METHODS: Subjects were randomized to receive dry needling (n = 25) or manual trigger point pressure release (n = 25) on upper trapezius active trigger points. Surface electromyography from the upper trapezius, splenius capitis, sternocleidomastoid, and scalene muscles during performance of the craniocervical flexion test was assessed before and immediately after the intervention as the primary outcome. Neck pain intensity, range of motion, and pressure pain thresholds were the secondary outcomes. RESULTS: A decrease in sternocleidomastoid activity at all stages of the craniocervical flexion test (time effect, P < 0.001) was found in both groups after the interventions, with no significant between-group difference. Pressure pain thresholds measured over the cervical spine and second metacarpal increased after dry needling when compared with manual trigger point pressure release (P < 0.05). Pain intensity decreased immediately after both treatments with moderate to large effect sizes, whereas cervical range of motion increased for both groups but with small effect sizes. CONCLUSION: A single session of dry needling or manual pressure release over upper trapezius active trigger points promotes limited effects on muscle performance during the craniocervical flexion test, pressure pain thresholds, and cervical range of motion in patients with chronic neck pain.

Digital pain extent is associated with pain intensity but not with pain-related cognitions and disability in people with chronic musculoskeletal pain: a cross-sectional study.

BACKGROUND: To evaluate whether digital pain extent is associated with an array of psychological factors such as optimism, pessimism, expectations of recovery, pain acceptance, and pain self-efficacy beliefs as well as to analyse the association between digital pain extent and pain intensity and pain-related disability in people with chronic musculoskeletal pain. METHODS: A descriptive cross-sectional study conducted in a primary health care setting was carried out including 186 individuals with chronic musculoskeletal pain. Patient-reported outcomes were used to assess psychological factors, pain intensity, and pain-related disability. Digital pain extent was obtained from pain drawings shaded using a tablet and analysed using novel customized software. Multiple linear regression models were conducted to evaluate the association between digital pain extent and the aforementioned variables. RESULTS: Digital pain extent was statistically significantly associated with pain intensity. However, digital pain extent was not associated with any psychological measure nor with pain-related disability. DISCUSSION: The results did not support an association between digital pain extent and psychological measures.

Cervical spine and muscle adaptation after spaceflight and relationship to herniation risk: protocol from 'Cervical in Space' trial.

BACKGROUND: Astronauts have a higher risk of cervical intervertebral disc herniation. Several mechanisms have been attributed as causative factors for this increased risk. However, most of the previous studies have examined potential causal factors for lumbar intervertebral disc herniation only. Hence, we aim to conduct a study to identify the various changes in the cervical spine that lead to an increased risk of cervical disc herniation after spaceflight. METHODS: A cohort study with astronauts will be conducted. The data collection will involve four main components: a) Magnetic resonance imaging (MRI); b) cervical 3D kinematics; c) an Integrated Protocol consisting of maximal and submaximal voluntary contractions of the neck muscles, endurance testing of the neck muscles, neck muscle fatigue testing and questionnaires; and d) dual energy X-ray absorptiometry (DXA) examination. Measurements will be conducted at several time points before and after astronauts visit the International Space Station. The main outcomes of interest are adaptations in the cervical discs, muscles and bones. DISCUSSION: Astronauts are at higher risk of cervical disc herniation, but contributing factors remain unclear. The results of this study will inform future preventive measures for astronauts and will also contribute to the understanding of intervertebral disc herniation risk in the cervical spine for people on Earth. In addition, we anticipate deeper insight into the aetiology of neck pain with this research project. TRIAL REGISTRATION: German Clinical Trials Register, DRKS00026777. Registered on 08 October 2021.

Trunk Muscle Coactivation in People with and without Low Back Pain during Fatiguing Frequency-Dependent Lifting Activities.

Lifting tasks are manual material-handling activities and are commonly associated with work-related low back disorders. Instrument-based assessment tools are used to quantitatively assess the biomechanical risk associated with lifting activities. This study aims at highlighting different motor strategies in people with and without low back pain (LBP) during fatiguing frequency-dependent lifting tasks by using parameters of muscle coactivation. A total of 15 healthy controls (HC) and eight people with LBP performed three lifting tasks with a progressively increasing lifting index (LI), each lasting 15 min. Bilaterally erector spinae longissimus (ESL) activity and rectus abdominis superior (RAS) were recorded using bipolar surface electromyography systems (sEMG), and the time-varying multi-muscle coactivation function (TMCf) was computed. The TMCf can significantly discriminate each pair of LI and it is higher in LBP than HC. Collectively, our findings suggest that it is possible to identify different motor strategies between people with and without LBP. The main finding shows that LBP, to counteract pain, coactivates the trunk muscles more than HC, thereby adopting a strategy that is stiffer and more fatiguing.

Effectiveness of manual therapy applied to craniomandibular structures in temporomandibular disorders: A systematic review.

BACKGROUND: Within physical therapy, manual therapy is known to be effective for managing temporomandibular disorders (TMDs). However, manual therapy is a broad term including different approaches applied to different body regions. AIMS: This is the first systematic review that aims to evaluate the effectiveness of manual therapy applied specifically to the craniomandibular structures (Cranio-Mandibular Manual Therapy [CMMT]) on pain and maximum mouth opening in people with TMD. MATERIAL AND METHODS: This systematic review was developed based on a pre-determined published protocol which was prospectively registered with PROSPERO (CRD42019160213). A search of MEDLINE, Embase, CINAHL, ZETOC, Web of Science, SCOPUS, PEDro, PubMed, Cochrane Library and Best Evidence, EBM reviews-Cochrane Central Register of Controlled Trials, Index to Chiropractic Literature ChiroAccess and Google Scholar databases was conducted from inception until October 2020. Randomised controlled trials comparing the effect of CMMT on pain and maximum mouth opening versus other types of treatment in TMDs were included. Two reviewers independently screened articles for inclusion, extracted data, assessed risk of bias with the revised Cochrane risk of bias tool for randomised trials and evaluated the overall quality of evidence with the Grading of Recommendations, Assessment, Development and Evaluations. RESULTS: A total of 2720 records were screened, of which only 6 (293 participants) satisfied the inclusion criteria. All studies showed some concerns in risk of bias, except for one, which was high risk of bias. The overall quality of evidence was very low for all outcomes because of high heterogeneity and small sample sizes. All studies showed a significant improvement in pain and maximum mouth opening for CMMT from baseline in the mid-term, but only two showed superiority compared to other interventions. Given the high heterogeneity and small sample sizes of the included studies, a quantitative synthesis was not performed. DISCUSSION AND CONCLUSION: There is the need for future high methodology research investigating different manual therapy techniques applied to different regions and different populations (e.g., chronic versus acute TMD) to determine what is most effective for pain and maximum mouth opening in patients with TMDs.

Deficit in knee extension strength following anterior cruciate ligament reconstruction is explained by a reduced neural drive to the vasti muscles.

The persistence of quadriceps weakness represents a major concern following anterior cruciate ligament reconstruction (ACLR). The underlying adaptations occurring in the activity of spinal motoneurons are still unexplored. This study examined the discharge patterns of large populations of motor units (MUs) in the vastus lateralis (VL) and vastus medialis muscles following ACLR. Nine ACLR individuals and 10 controls performed unilateral trapezoidal contractions of the knee extensor muscles at 35%, 50% and 70% of the maximal voluntary isometric force (MVIF). High-density surface electromyography (HDsEMG) was used to record the myoelectrical activity of the vasti muscles in both limbs. HDsEMG signals were decomposed with a convolutive blind source separation method and MU properties were extracted and compared between sides and groups. The ACLR group showed a lower MVIF on the reconstructed side compared to the contralateral side (28.1%; P < 0.001). This force deficit was accompanied by reduced MU discharge rates (∼21%; P < 0.05), lower absolute MU recruitment and derecruitment thresholds (∼22% and ∼22.5%, respectively; P < 0.05) and lower input-output gain of motoneurons (27.3%; P = 0.009). Deficits in MU discharge rates of the VL and in absolute recruitment and derecruitment thresholds of both vasti MUs were associated with deficits in MVIF (P < 0.05). A strong between-side correlation was found for MU discharge rates of the VL of ACLR individuals (P < 0.01). There were no significant between-group differences (P > 0.05). These results indicate that mid- to long-term strength deficits following ACLR may be attributable to a reduced neural drive to vasti muscles, with potential changes in excitatory and inhibitory synaptic inputs. KEY POINTS: Impaired expression and control of knee extension forces is common after anterior cruciate ligament reconstruction and is related to high risk of a second injury. To provide novel insights into the neural basis of this impairment, the discharge patterns of motor units in the vastus lateralis and vastus medialis were investigated during voluntary force contractions. There was lower knee extensor strength on the reconstructed side with respect to the contralateral side, which was explained by deficits in motor unit discharge rate and an altered motoneuronal input-output gain. Insufficient excitatory inputs to motoneurons and increased inhibitory afferent signals potentially contributed to these alterations. These results further our understanding of the neural underpinnings of quadriceps weakness following anterior cruciate ligament reconstruction and can help to develop effective rehabilitation protocols to regain muscle strength and reduce the risk of a second injury.

Regional changes in muscle activity do not underlie the repeated bout effect in the human gastrocnemius muscle.

The repeated bout effect (RBE) confers protection following exercise-induced muscle damage. Typical signs of this protective effect are significantly less muscle soreness and faster recovery of strength after the second bout. The aim of this study was to compare regional changes in medial gastrocnemius (MG) muscle activity and mechanical hyperalgesia after repeated bouts of eccentric exercise. Twelve healthy male participants performed two bouts of eccentric heel drop exercise (separated by 7 days) while wearing a vest equivalent to 20% of their body weight. High-density MG electromyographic amplitude maps and topographical pressure pain sensitivity maps were created before, two hours (2H), and two days (2D) after both exercise bouts. Statistical parametric mapping was used to identify RBE effects on muscle activity and mechanical hyperalgesia, using pixel-level statistics when comparing maps. The results revealed a RBE, as a lower strength loss (17% less; P < .01) and less soreness (50% less; P < .01) were found after the second bout. However, different muscle regions were activated 2H and 2D after the initial bout but not following the repeated bout. Further, no overall changes in EMG distribution or mechanical hyperalgesia were found between bouts. These results indicate that muscle activation is unevenly distributed during the initial bout, possibly to maintain muscle function during localized mechanical fatigue. However, this does not reflect a strategy to confer protection during the repeated bout by activating undamaged/non-fatigued muscle areas.

Self-efficacy beliefs mediate the association between pain intensity and pain interference in acute/subacute whiplash-associated disorders.

PURPOSE: To evaluate whether a set of pre-accident demographic, accident-related, post-accident treatment and psychosocial factors assessed in people with acute/subacute whiplash-associated disorders (WAD) mediate the association between pain intensity and: (1) pain interference and (2) expectations of recovery, using Bayesian networks (BNs) analyses. This study also explored the potential mediating pathways (if any) between different psychosocial factors. METHODS: This was a cross-sectional study conducted on a sample of 173 participants with acute/subacute WAD. Pain intensity, pain interference, pessimism, expectations of recovery, pain catastrophizing, and self-efficacy beliefs were assessed. BN analyses were conducted to analyse the mediating effects of psychological factors on the association between pain intensity and pain-related outcomes. RESULTS: The results revealed that self-efficacy beliefs partially mediated the association between pain intensity and pain interference. Kinesiophobia partially mediated the association between self-efficacy and pain catastrophizing. Psychological factors did not mediate the association between pain intensity and expectations of recovery. CONCLUSION: These results indicate that individuals with acute/subacute WAD may present with lesser pain interference associated with a determined pain intensity value when they show greater self-efficacy beliefs. As the cross-sectional nature of this study limits firm conclusions on the causal impact, researchers are encouraged to investigate the role that patient's self-efficacy beliefs play in the transition to chronic WAD via longitudinal study designs.

Does the Score on the MRC Strength Scale Reflect Instrumented Measures of Maximal Torque and Muscle Activity in Post-Stroke Survivors?

It remains unknown whether variation of scores on the Medical Research Council (MRC) scale for muscle strength is associated with operator-independent techniques: dynamometry and surface electromyography (sEMG). This study aimed to evaluate whether the scores of the MRC strength scale are associated with instrumented measures of torque and muscle activity in post-stroke survivors with severe hemiparesis both before and after an intervention. Patients affected by a first ischemic or hemorrhagic stroke within 6 months before enrollment and with complete paresis were included in the study. The pre- and post-treatment assessments included the MRC strength scale, sEMG, and dynamometry assessment of the triceps brachii (TB) and biceps brachii (BB) as measures of maximal elbow extension and flexion torque, respectively. Proprioceptive-based training was used as a treatment model, which consisted of multidirectional exercises with verbal feedback. Each treatment session lasted 1 h/day, 5 days a week for a total 15 sessions. Nineteen individuals with stroke participated in the study. A significant correlation between outcome measures for the BB (MRC and sEMG p = 0.0177, ρ = 0.601; MRC and torque p = 0.0001, ρ = 0.867) and TB (MRC and sEMG p = 0.0026, ρ = 0.717; MRC and torque p = 0.0001, ρ = 0.873) were observed post intervention. Regression models revealed a relationship between the MRC score and sEMG and torque measures for both the TB and BB. The results confirmed that variation on the MRC strength scale is associated with variation in sEMG and torque measures, especially post intervention. The regression model showed a causal relationship between MRC scale scores, sEMG, and torque assessments.

Digital pain drawings are a useful and reliable tool for assessing patients with temporomandibular disorders.

BACKGROUND: Temporomandibular disorders (TMD) are characterised by complex symptomatology and their assessment can be enhanced using pain drawings (PD). OBJECTIVES: To evaluate the location and extent of pain in people TMD using digital PD, and to explore their association with clinical features. Reliability of pain extent and pain location using PD was also assessed. METHODS: Forty volunteers with TMD completed two consecutive digital PDs. Clinical features were captured from self-reported questionnaire. Additionally, secondary hyperalgesia was measured using the pressure pain threshold (PPT). The correlation between pain extent and clinical features was investigated using Spearman rank correlation coefficients. Reliability of pain extent was evaluated using intraclass correlation coefficient (ICC) and Bland-Altman plots. The Jaccard index was computed to assess the reliability of pain location. RESULTS: Analysis of the PDs indicated that people with TMD commonly experience pain in other body regions including the neck, the shoulder and the low back. Except for PPT and pain catastrophising, all other clinical features were significantly correlated with pain extent. The ICCs of pain extent for all body charts were very high (ICCs 95% CI from 0.73 to 0.96), and Bland-Altman plots showed mean biases close to zero with narrow limits of agreement. The reliability of pain location was also supported by Jaccard index mean scores above 0.68. CONCLUSIONS: People with TMD showed widespread pain, and pain extent was associated with pain intensity, neck and headache-related disability, depression, anxiety, hyperventilation and central sensitivity. The reliability of measuring pain extent and pain location was confirmed.

Divergent response of low- versus high-threshold motor units to experimental muscle pain.

KEY POINTS: The neural strategies behind the control of force during muscle pain are not well understood as previous research has been limited in assessing pain responses only during low-force contractions. Here we compared, for the first time, the behaviour of motor units recruited at low and high forces in response to pain. The results showed that motor units activated at low forces were inhibited while those recruited at higher forces increased their activity in response to pain. When analysing lower- and higher-threshold motor unit behaviour at high forces we observed differential changes in discharge rate and recruitment threshold across the motor unit pool. These adjustments allow the exertion of high forces in acutely painful conditions but could eventually lead to greater fatigue and stress of the muscle tissue. ABSTRACT: During low-force contractions, motor unit discharge rates decrease when muscle pain is induced by injecting nociceptive substances into the muscle. Despite this consistent observation, it is currently unknown how the central nervous system regulates motor unit behaviour in the presence of muscle pain at high forces. For this reason, we analysed the tibialis anterior motor unit behaviour at low and high forces. Surface EMG signals were recorded from 15 healthy participants (mean age (SD) 26 (3) years, six females) using a 64-electrode grid while performing isometric ankle dorsiflexion contractions at 20% and 70% of the maximum voluntary force (MVC). Signals were decomposed and the same motor units were tracked across painful (intramuscular hypertonic saline injection) and non-painful (baseline, isotonic saline, post-pain) contractions. At 20% MVC, discharge rates decreased significantly in the painful condition (baseline vs. pain: 12.7 (1.1) Hz to 11.5 (0.9) Hz, P < 0.001). Conversely, at 70% MVC, discharge rates increased significantly during pain (baseline vs. pain: 19.7 (2.8) Hz to 21.3 (3.5) Hz, p = 0.029) and recruitment thresholds decreased (baseline vs. pain: 59.0 (3.9) %MVC to 55.9 (3.2) %MVC, p = 0.02). These results show that there is a differential adjustment between low- and high-threshold motor units during painful conditions. An increase in excitatory drive to high-threshold motor units is likely required to compensate for the inhibitory influence of nociceptive afferent inputs on low-threshold motor units. These differential mechanisms allow the force output to be maintained during acute pain but this strategy could lead to increased muscle fatigue and symptom aggravation in the long term.