Effects of experimental muscle pain on shoulder-abduction force steadiness and muscle activity in healthy subjects

The Effect of Experimentally Induced Pain in the Cervical, Shoulder, or Orofacial Regions on Cervical Neuromuscular and Kinematic Features: A Systematic Review and Meta-analysis

In this systematic review, we synthesize the literature investigating the effect of experimentally induced pain in the cervical, shoulder, or orofacial regions on cervical neuromuscular and kinematic features. Databases were searched up to November 1, 2023. A total of 29 studies using hypertonic saline injection (n = 27) or glutamate injection (n = 2) as experimental pain models were included. Meta-analyses revealed reduced upper trapezius activation during shoulder flexion/abduction when pain was induced in the upper trapezius (standardized mean difference: -.90, 95% confidence interval: [-1.29; -.51]), splenius capitis (-1.03 [-1.44; -.63]), and supraspinatus (-.63 [-1.25; -.01]), but not in the subacromial space (.22 [-.16; .60]). Furthermore, experimentally induced pain caused a caudal redistribution of activation within the upper trapezius (.96 [.58; 1.34]) but did not change the mediolateral distribution (.11 [-.22; .42]). None of these adaptations persisted after pain resolution. Low-quality evidence supported the absence of an effect of experimental pain on upper trapezius muscle activation during manual dexterity and cervical flexion/extension tasks, as well as on cervical flexor and extensor muscle activation during cervical and jaw tasks. Inconsistent and limited evidence, attributed to the large heterogeneity of task and outcomes, precluded drawing meaningful conclusions about the effects of experimentally induced pain in the cervical region on cervical kinematics. Overall, cervical muscle activation tended to decrease in response to experimentally induced pain, and the decrease of muscle activation depended on the location of the painful stimulus. These adaptations are only partially representative of muscle activation patterns observed in clinical populations. PERSPECTIVE: This systematic review and meta-analysis revealed a reduced or unchanged muscle activation during experimental pain in the cervical, shoulder, or orofacial regions, depending on the task and location of nociceptive stimulation. There was inconsistent evidence on cervical kinematics. These findings enhance our understanding of neuromuscular adaptations to acute experimental pain.

The influence of pain and kinesiophobia on motor control of the upper limb: how pointing task paradigms can point to new avenues of understanding

ABSTRACT

People experiencing kinesiophobia are more likely to develop persistent disabilities and chronic pain. However, the impact of kinesiophobia on the motor system remains poorly understood. We investigated whether kinesiophobia could modulate shoulder pain-induced changes in (1) kinematic parameters and muscle activation during functional movement and (2) corticospinal excitability. Thirty healthy, pain-free subjects took part in the study. Shoulder, elbow, and finger kinematics, as well as electromyographic activity of the upper trapezius and anterior deltoid muscles, were recorded while subjects performed a pointing task before and during pain induced by capsaicin at the shoulder. Anterior deltoid cortical changes in excitability were assessed through the slope of transcranial magnetic stimulation input-output curves obtained before and during pain. Results revealed that pain reduced shoulder electromyographic activity and had a variable effect on finger kinematics, with individuals with higher kinesiophobia showing greater reduction in finger target traveled distance. Kinesiophobia scores were also correlated with the changes in deltoid corticospinal excitability, suggesting that the latter can influence motor activity as soon as the motor signal emerges. Taken together, these results suggest that pain and kinesiophobia interact with motor control adaptation.

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

BACKGROUND AND OBJECTIVE

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

DATABASES AND DATA TREATMENT

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

RESULTS

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

CONCLUSIONS

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

SIGNIFICANCE STATEMENT

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

Spatiotemporal characterization of an experimental model of muscle pain in humans based on short-wave diathermy

BACKGROUND

Commonly used models for eliciting muscle pain involve the injection of algesic substances or the induction of delayed onset muscle soreness. The former require invasive procedures, and the time frame for pain induction and subsidence in the latter can be inconvenient. This study presents a detailed spatiotemporal characterization of a new experimental model of muscle pain based on short-wave diathermy (SWD), developed to overcome the limitations of existing models.

METHODS

The shoulder was selected as target site and the effects of the model were tested in two sessions to assess its reliability. Pain intensity profiles were recorded during the application of SWD, and changes in pressure pain threshold (PPT) in the infraspinatus muscle, together with pain intensity, duration, and quality were assessed 30 min after induction.

RESULTS

SWD-induced pain intensity scores averaged 4 points on a visual analogue scale, whereas PPT showed a consistent decrease of about 25% relative to baseline values. Pain was localized in the shoulder area, and was described as continuous, dull, well-delimited, heavy, and bearable. Pain lasted for an average of 145 min without requiring reinduction and was reliably elicited in both experimental sessions.

CONCLUSION

SWD can be used to elicit experimental muscle pain in a non-invasive, long-lasting, and reliable way and allows for repeated within- and between-session testing in the shoulder.

SIGNIFICANCE STATEMENT

SWD produces deep heating in muscles by converting electromagnetic energy to thermal energy. It was previously shown that it can be used to elicit experimental pain in the forearm muscles, and the present study demonstrates that this can be reliably generalized to other body sites, such as the shoulder. Furthermore, SWD application is non-invasive and presents a convenient time frame for pain induction and subsidence, thus overcoming limitations associated with traditional muscle pain models.

Comparison of the physiotherapy with and without focus on the scapulothoracic joint on pain, range of motion, functional disability, quality of life, and treatment effectiveness of patients after arthroscopic shoulder rotator cuff tendon repair: A randomized controlled trial with short-term follow-up

BACKGROUND

Rotator cuff tears are prevalent shoulder injuries, significantly affecting shoulder stabilization and patient quality of life. Despite rehabilitation efforts post-arthroscopic surgery, the efficacy of scapular-focused exercises remains uncertain with limited supportive evidence.

PURPOSE

This study aimed to compare the immediate and short-term effects of emphasizing scapulothoracic joint rehabilitation in addition to conventional physiotherapy on pain, range of motion (ROM), function, quality of life, and treatment effectiveness in patients after shoulder arthroscopic rotator cuff tendon repair (ARCR).

STUDY DESIGN

Two arms, parallel-group, randomized controlled trial, with concealed allocation METHODS: This parallel-group randomized controlled trial, with concealed allocation, was conducted in a clinic setting on 28 participants aged 30-75 years, exhibiting progressive degenerative full-thickness tears of rotator cuff muscles and undergoing ARCR, provided the tear size was small or medium. Participants were randomly allocated to receive 21 sessions of conventional rehabilitation (n = 14) or comprehensive rehabilitation (with a focus on scapula training; n = 14) in 12 weeks (reporting of intervention complied with Consensus on Exercise Reporting Template (CERT) and Template for Intervention Description and Replication (TIDieR) Guideline). Pain (as primary outcome), ROM, functional disability, quality of life, and treatment effectiveness were assessed both pre- and post-intervention, along with a 3-month follow-up. Participants, assessors, and statistician were blinded to group assignment. For the reporting of the RCT, the Consolidated Standards of Reporting Trials (CONSORT) has been used.

RESULTS

Trial was completed with 28 participants and no dropouts. The analysis of variance revealed statistically significant group-by-time interaction (p < 0.05) for all outcome measures except for active ROMs (p > 0.05). Multiple comparison analysis showed statistically significant between-group differences (p < 0.05) at 3-month follow-up with large effect size (>0.8 Hedges' g) for all outcomes (mean differences: visual analog scale: 1.3, American Shoulder and Elbow Surgeons: -17.3, Shoulder Pain and Disability Index: 17.6, Western Ontario Rotator Cuff: -19.5, QuickDASH: 17.8), except for extension ROM (passive ROM: confidence interval = -25.4 to 0.56; active ROM: confidence interval = -20.0 to 6.0). The differences in American Shoulder and Elbow Surgeons and Western Ontario Rotator Cuff were also clinically significant based on their minimally clinical important difference cutoff points. For the Global Rating of Change scale, more participants stated "much improved" in the comprehensive group than in the conventional. No adverse effects were reported.

CONCLUSIONS

Comprehensive rehabilitation, compared to conventional physiotherapy, has shown a statistically and clinically significant difference in improving pain, ROM, functional disability, quality of life, and treatment effectiveness in patients after ARCR.

Experimentally Induced Pain Results in Reduced Activity of the Rotator Cuff Muscles in Healthy Subjects

Shoulder pain is a complex, prevalent problem that is multifactorial in nature. While there are many potential causes, one common suspect is the rotator cuff musculature. The purpose of the present study was to induce pain in the supraspinatus muscle of healthy subjects and observe the resulting changes in muscle activity. Eight muscles on 23 subjects were assessed using electromyography: anterior, middle, and posterior deltoid; pectoralis major; upper trapezius; latissimus dorsi; serratus anterior; supraspinatus; and infraspinatus. It was hypothesized that the rotator cuff muscles would display reduced activity during pain, and that reductions in activity would remain after the pain had dissipated. Both of the rotator cuff muscles measured did indeed display reduced activity in a majority of the dynamic, isometric, and maximal contractions. Many of those reductions remained after the pain had subsided.

Comparing the effect of physiotherapy and physiotherapy plus corticosteroid injection on pain intensity, disability, quality of life, and treatment effectiveness in patients with Subacromial Pain Syndrome: a randomized controlled trial

PURPOSE

To compare the short and medium-term effects of physiotherapy plus corticosteroid injection (combined) with physiotherapy alone on pain intensity, disability, Quality of Life (QoL), and treatment effectiveness in patients with Subacromial Pain Syndrome (SAPS).

METHODS

In this double-blind, parallel Randomized Controlled Trial (RCT), 50 patients with SAPS were randomly assigned into combined (N = 25, a single injection 3-6 days before physiotherapy) and physiotherapy alone group (N = 25). Pain, disability, QoL, and treatment-effectiveness were measured at pre-intervention, post-intervention, and 3 and 6-month follow-up with Visual Analog Scale (VAS), Shortened Disability of the Arm, Shoulder, and Hand (Quick-DASH), Shoulder Pain and Disability Index (SPADI) (primary outcome measure), Western Ontario Rotator Cuff (WORC), and Global Rating of Change (GRC) respectively. A 2 × 4 (group × time) mixed model analysis of variance (ANOVA) was applied for analysis.

RESULTS

The ANOVA revealed statistically significant group-in-time interaction for all outcome measures (p-value < 0.05). The independent t-test showed more effectiveness in the combined group at medium-term, as the mean scores of almost all outcome measures were substantially lesser (p < 0.01). Moreover, in short-time, despite a greater number of patients stating "completely recovered" in the combined group, there was no statistically significant difference between groups.

CONCLUSIONS

Effects of physiotherapy plus corticosteroid injection could be more long-lasting than physiotherapy alone in improving pain intensity, disability, QoL, and treatment effectiveness in patients with SAPS.

TRIAL REGISTRATION NUMBER

IRCT20201010048980N1.IMPLICATIONS FOR REHABILITATIONShoulder pain is common, persistent, and predominantly results from subacromial pain syndrome (SAPS).Physiotherapy and corticosteroid injections are effective interventions for this condition.Comprehensive physiotherapy alone can be as effective as corticosteroid injection combined with physiotherapy in the short term.A combined approach versus physiotherapy alone may have more medium-term effects on SAPS patients' pain, disability, quality of life, and treatment effectiveness.

Mid-term effects of two different Kinesio tape treatments in female patients with subacromial impingement syndrome: Randomized controlled ultrasonographic study

STUDY DESIGN

Randomized controlled study.

PURPOSE OF THE STUDY

To evaluate the effect of Kinesio Tape (KT) applied differently in patients diagnosed with Subacromial Impingement Syndrome (SIS) on acromiohumeral distance (AHD) and supraspinatus tendon (SsT) thickness using ultrasound (US) and its effect on pain, upper limb functional status and hand grip muscle strength in the short and mid-term.

METHODS

The 90 patients diagnosed with unilateral SIS by clinical examination were randomized into 3 groups. In addition to exercise therapy, the deltoid in group 1 and the supraspinatus muscle in group 2 were taped from insertion to origin. Group 3, which was the control group, was applied 9 sessions of sham taping for 3 weeks. Cases were evaluated for AHD and SsT thickness, pain was evaluated with the Visual Analog Scale (VAS), function with the Disabilities of the arm, shoulder and hand (DASH) and the Western Ontario Rotator Cuff Index (WORC), and hand grip strength (HGS) using a dynamometer before, and 3rd week and 3rd month after the KT application.

RESULTS

There was a significant improvement in all parameters in the short and mid-term intra group comparisons in Group 1 and 2 after taping (P < .05). In intergroup comparisons, significant improvement was achieved in all parameters in Group 1 and Group 2 in the mid and short term compared to the control group (P < .05). In comparison of Group 1 and Group 2, HGS in the short term (p: 0.07) and the SsT thickness in the short and mid-term (p: 0.36, p: 0.85) did not exhibit any difference. The improvement in all other parameters in group 1 was statistically significant.

CONCLUSION

The findings of our study provide definitive evidence for the effectiveness of KT treatment depending on the method of tape application employed.

Kinematic, electromyographic and isokinetic measurements for the management of shoulder subacromial pain syndrome: A systematic review

BACKGROUND

Subacromial shoulder pain syndrome is a very common and challenging musculoskeletal disorder. Kinematics, electromyographic muscle activity and isokinetic dynamometry are promising non-invasive movement analysis tools to improve understanding of this condition. No review has combined their results to provide a better understanding of the effects of subacromial pain syndrome on shoulder movement. This systematic review aimed to synthesise the associations between exposure to shoulder pain due to subacromial pain syndromes or subacromial impingement and changes in shoulder movement measures.

METHODS

The databases were Scholar google, Pubmed, Science Direct, Scopus and the Cochrane Library. We included studies that observed the association of the presence of subacromial pain syndromes or subacromial impingement with changes in shoulder motion measures.

FINDINGS

Seventeen studies with 943 participants were included. The main kinematic change was a lower scapular posterior during abduction in the subacromial pain syndrome group with a "low" level of evidence (standardised mean difference = -0.61, 95% confidence interval [-0.80; -0.43]). The main electromyographic change was an earlier onset of activation of the upper trapezius in the subacromial pain syndrome group, with a "moderate" level of evidence (standardised mean difference = 1.01, 95% confidence interval: [-2.97; 0.96]). The main isokinetic change was a lower peak internal rotator torque in the subacromial pain syndrome group, with a 'low' level of evidence (standardised mean difference = -0.41, 95% confidence interval: [-0.53; -0.29]).

INTERPRETATION

The variables measured during movement are associated with subacromial pain syndrome or subacromial impingement syndrome. Consistency between the results supports the importance of scapula biomechanics measurements in these conditions.

People with chronic low back pain display spatial alterations in high-density surface EMG-torque oscillations

We quantified the relationship between spatial oscillations in surface electromyographic (sEMG) activity and trunk-extension torque in individuals with and without chronic low back pain (CLBP), during two submaximal isometric lumbar extension tasks at 20% and 50% of their maximal voluntary torque. High-density sEMG (HDsEMG) signals were recorded from the lumbar erector spinae (ES) with a 64-electrode grid, and torque signals were recorded with an isokinetic dynamometer. Coherence and cross-correlation analyses were applied between the filtered interference HDsEMG and torque signals for each submaximal contraction. Principal component analysis was used to reduce dimensionality of HDsEMG data and improve the HDsEMG-based torque estimation. sEMG-torque coherence was quantified in the δ(0–5 Hz) frequency bandwidth. Regional differences in sEMG-torque coherence were also evaluated by creating topographical coherence maps. sEMG-torque coherence in the δ band and sEMG-torque cross-correlation increased with the increase in torque in the controls but not in the CLBP group (p = 0.018, p = 0.030 respectively). As torque increased, the CLBP group increased sEMG-torque coherence in more cranial ES regions, while the opposite was observed for the controls (p = 0.043). Individuals with CLBP show reductions in sEMG-torque relationships possibly due to the use of compensatory strategies and regional adjustments of ES-sEMG oscillatory activity.

Coordinate activity of the quadratus lumborum posterior layer, lumbar multifidus, erector spinae, and gluteus medius during single-leg forward landing

This study aimed to clarify the differences in electromyographic activity between the quadratus lumborum anterior (QL-a) and posterior layers (QL-p), and the relationship among trunk muscles and gluteus medius (GMed) activities during forward landing. Thirteen healthy men performed double-leg and single-leg (ipsilateral or contralateral sides as the electromyography measurement of trunk muscles) forward landings from a 30 cm-height-box. The onset of electromyographic activity in pre-landing and the electromyographic amplitude of the unilateral QL-a, QL-p, abdominal muscles, lumbar multifidus (LMF), erector spinae (LES), and bilateral GMed were recorded. Two-way ANOVA was used to compare the onset of electromyographic activity (3 landing leg conditions × 10 muscles) and electromyographic amplitude among (3 landing leg conditions × 2 phases). The onset of QL-p was significantly earlier in contralateral-leg landing than in the double-leg and ipsilateral-leg landings. The onset of LMF and LES was significantly earlier than that of the abdominal muscles in contralateral-leg landing. QL-p activity and GMed activity on the contralateral leg side in the pre-landing were significantly higher in contralateral-leg landing than in the other leg landings. To prepare for pelvic and trunk movements after ground contact, LMF, LES, QL-p on non-support leg side, and GMed on support leg side showed early or high feedforward activation before ground contact during single-leg forward landing.

The impact of experimental pain on shoulder movement during an arm elevated reaching task in a virtual reality environment

BACKGROUND

People with chronic shoulder pain have been shown to present with motor adaptations during arm movements. These adaptations may create abnormal physical stress on shoulder tendons and muscles. However, how and why these adaptations develop from the acute stage of pain is still not well-understood.

OBJECTIVE

To investigate motor adaptations following acute experimental shoulder pain during upper limb reaching.

METHODS

Forty participants were assigned to the Control or Pain group. They completed a task consisting of reaching targets in a virtual reality environment at three time points: (1) baseline (both groups pain-free), (2) experimental phase (Pain group experiencing acute shoulder pain induced by injecting hypertonic saline into subacromial space), and (3) Post experimental phase (both groups pain-free). Electromyographic (EMG) activity, kinematics, and performance data were collected.

RESULTS

The Pain group showed altered movement planning and execution as shown by a significant increased delay to reach muscles EMG peak and a loss of accuracy, compared to controls that have decreased their mean delay to reach muscles peak and improved their movement speed through the phases. The Pain group also showed protective kinematic adaptations using less shoulder elevation and elbow flexion, which persisted when they no longer felt the experimental pain.

CONCLUSION

Acute experimental pain altered movement planning and execution, which affected task performance. Kinematic data also suggest that such adaptations may persist over time, which could explain those observed in chronic pain populations.

Changes in electromyographic activity of deltoid muscles in women with shoulder pain during a functional task

BACKGROUND

Shoulder pain is one of the most common complaints of patients with musculoskeletal disorders in the shoulder and is usually caused by the Subacromial Impact Syndrome. Muscle imbalances can contribute to this syndrome leading to disorders that cause changes in muscle activity. The aim of this study was to determine whether pain causes changes in the electromyographic activity of the shoulder girdle muscles during an isometric task of arm elevation in the scapular plane.

METHOD

This is a comparative observational study using a simple convenience sampling method, composed of 22 women aged (44 ± 10) who were divided into two groups: 11 women with shoulder pain and 11 women without shoulder pain. The muscle activity evaluation was performed using surface electromyography of the muscles: anterior deltoid, middle deltoid, upper trapezius and middle trapezius, during an isometric task of arm elevation in the scapular plane. Independent Samples t-Test was used to analyze and compare the normalized electromyography data.

RESULTS

Results revealed a significant increase in the activity of the anterior and middle deltoid muscles in women with shoulder pain compared to women without shoulder pain in the isometric task of arm elevation.

CONCLUSION

It was concluded that the shoulder pain of the women evaluated caused changes in the activity of the anterior and middle deltoid muscles.

Does pain influence force steadiness? A protocol for a systematic review

INTRODUCTION

Performing contractions with minimum force fluctuations is essential for everyday life as reduced force steadiness impacts on the precision of voluntary movements and functional ability. Several studies have investigated the effect of experimental or clinical musculoskeletal pain on force steadiness but with conflicting findings. The aim of this systematic review is to summarise the current literature to determine whether pain, whether it be clinical or experimental, influences force steadiness.

METHODS AND ANALYSIS

This protocol for a systematic review was informed and reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols and the Cochrane Handbook for Systematic Reviews of Interventions. Key databases will be searched from inception to 31 August 2020, including MEDLINE, EMBASE, PubMed, CINAHL Plus, ZETOC and Web of Science. Grey literature and key journals will be also reviewed. Risk of bias will be assessed with the Newcastle-Ottawa tool, and the quality of the cumulative evidence assessed with the Grading of Recommendations, Assessment, Development and Evaluation guidelines. If homogeneity exists between groups of studies, meta-analysis will be conducted. Otherwise, a narrative synthesis approach and a vote-counting method will be used, while the results will be presented as net increases or decreases of force steadiness.

ETHICS AND DISSEMINATION

The findings will be presented at conferences and the review will be also submitted for publication in a refereed journal. No ethical approval was required.

PROSPERO REGISTRATION NUMBER

CRD42020196479.

Quantitative response of healthy muscle following the induction of capsaicin: an exploratory randomized controlled trial

Background

Myofascial pain syndrome (MPS) is a prevalent chronic pain disorder primarily characterized by myofascial trigger points (MTrPs). There is limited knowledge on the pathophysiology and mechanisms underlying MTrP and its development. Research has previously demonstrated the identification of MTrPs using ultrasound and vibration sonoelastography, although there is some contradictory evidence regarding if MTrPs present as hyper or hypoechoic regions. Electromyography (EMG) investigations of MTrP have demonstrated that MTrPs are usually located proximal to innervation zones where the peak surface EMG signals are obtained from. Central sensitization has been proposed as the primary mechanism underlying MTrP development. Central sensitization is associated with hyperexcitability of neuronal responses to normal or noxious stimuli. There is a need for a study that measures ultrasound image textural changes and motor unit activity responses in the muscle following sensitization. The purpose of this study is to determine whether sensitizing healthy muscle using capsaicin induces a regional change in image texture variables within the specific and surrounding muscles, as well as the motor unit frequency and amplitude changes that accompany them. This is an exploratory trial that aims to provide preliminary evidence on whether central sensitization is a direct cause of taut band and MTrP development.

Methods

Ethical approval was obtained from the University Health Network (UHN) Research Ethics Board. This proposed study is a single centered, factorial, randomized placebo-controlled trial with two independent variables, depth of capsaicin application and dose of capsaicin, for a total of six treatment arms and three control treatment groups.

Discussion

This will be the first study that assesses the B-mode ultrasound image texture of induced sensitized muscles and will provide more evidence on muscle motor unit activity and regional changes of central sensitization. Findings from this study may support one of few hypotheses proposed delineating the involvement of central sensitization in the development of trigger points.

Trial registration

National Institutes of Health ClinicalTrials.gov NCT03944889. Registered on May 07, 2019

Does Motor Cortex Engagement During Movement Preparation Differentially Inhibit Nociceptive Processing in Patients with Chronic Whiplash Associated Disorders, Chronic Fatigue Syndrome and Healthy Controls? An Experimental Study

BACKGROUND

Patients with chronic fatigue syndrome (CFS) and chronic whiplash associated disorders (cWAD) present a reduced ability to activate central descending nociceptive inhibition after exercise, compared to measurements before exercise. It was hypothesised that a dysfunctional motor-induced inhibition of nociception partly explains this dysfunctional exercise-induced hypoalgesia. This study investigates if engagement of the motor system during movement preparation inhibits nociception-evoked brain responses in these patients as compared to healthy controls (HC).

METHODS

The experiment used laser-evoked potentials (LEPs) during three conditions (no task, mental task, movement preparation) while recording brain activity with a 32-channel electroencephalogram in 21 patients with cWAD, 20 patients with CFS and 18 HC. Two-factor mixed design Analysis of variance were used to evaluate differences in LEP amplitudes and latencies.

RESULTS

No differences in N1, N2, N2P2, and P2 LEP amplitudes were found between the HC, CFS, and cWAD groups. After nociceptive stimulation, N1, N2 (only at hand location), N2P2, and P2 LEP amplitudes significantly decreased during movement preparation compared to no task (within group differences).

CONCLUSION

Movement preparation induces a similar attenuation of LEPs in patients with CFS, patients with cWAD and HC. These findings do not support reduced motor-induced nociceptive inhibition in these patients.

The effect of experimental shoulder pain on contralateral muscle force and activation

Inhibition of rotator cuff activation and force after local experimental pain has been previously shown. Clinically, strength is often indexed to the uninvolved side in order to quantify deficits during injury and recovery. This study assessed the effect of experimental subacromial pain on contralateral shoulder external rotation (ER) force and activation. We hypothesized that subacromial pain would not affect contralateral shoulder external rotation force and voluntary activation (VA) of the contralateral infraspinatus because we believe that the effects of acute experimental pain will largely exert an ipsilateral, spinal segmental effect. Twenty healthy adults were tested. External rotation force and VA were tested while participants performed maximum voluntary isometric contractions of shoulder external rotation, during which a brief electrical stimulus was applied to the infraspinatus muscle at an intensity that maximized external rotation force. To elicit pain, 1.5 ml of 5% hypertonic saline was injected into the contralateral subacromial space. Mean (SD) pain immediately after injection was 6.3/10 (0.85) resulting in a 7.6% decline in contralateral external rotation force (p < .01) and 3.3% decline in infraspinatus muscle VA (p = .48). A subset of participants (n = 9) showed a more substantial decline in both force (15.4%; p < .000001; d = -3.53) and VA (8.7%; p = .045; d = -0.98). Experimental shoulder pain had a modest effect on contralateral ER force and VA in a subset of participants; therefore, it may be important to index or compare strength bilaterally throughout rehabilitation to capture this bilateral effect as pain resolves.

Reorganized Force Control in Elbow Pain Patients During Isometric Wrist Extension

INTRODUCTION

Reorganized force control may be an important adaptation following painful traumas. In this study, force control adaptations were assessed in elbow pain patients. Increasing the contraction demand may overcome pain interference on the motor control and as such act as an internal control. It was hypothesized that elbow pain patients compared with controls would present greater change in the direction of force when increasing the demand of the motor task.

METHODS

Elbow pain patients (n=19) and asymptomatic participants (n=21) performed isometric wrist extensions at 5% to 70% of maximum voluntary contraction. Pressure pain thresholds were recorded at the lateral epicondyle and tibialis anterior muscle. Contraction force was recorded using a 3-directional force transducer. Participants performed contractions according to visual feedback of the task-related force intensity (main direction of wrist extension) and another set of contractions with feedback of the 3 force directions. Going from the simple to the detailed force feedback will increase the demand of the motor task. Force steadiness in all 3 dimensions and force directions were extracted.

RESULTS

Compared with controls, elbow pain patients presented lower pressure pain thresholds at both sites (P<0.05). Force steadiness was not significantly different between groups or feedback methods. The change in force direction when providing simple visual feedback in contrast with feedback of all force components at all contraction levels was greater for patients compared with controls (P<0.05).

CONCLUSION

The larger change in force direction in pain patients implies redistribution of loads across the arm as an associated effect of pain.

Increased co-contraction of arm adductors is associated with a favorable course in subacromial pain syndrome

BACKGROUND

Enhancement of arm adductor activity during abduction (ie, adductor co-contraction), may be effective in the treatment of subacromial pain syndrome (SAPS). We assessed whether an increase of adductor co-contraction is associated with a favorable course of SAPS.

METHODS

At baseline and after nearly 4 years of follow-up, electromyography of the latissimus dorsi (LD), teres major (TM), pectoralis major, and deltoid muscle was obtained during isometric abduction and adduction tasks in 26 patients with SAPS. Changes in co-contraction were assessed with change in the activation ratio (ΔAR). The AR ranges between -1 and 1, where lower values indicate more co-contraction. Clinical course was determined from an anchor question (reduced, persistent, or increased complaints), the visual analog scale for pain (VAS), and the Western Ontario Rotator Cuff score (WORC).

RESULTS

In patients indicating persistent complaints (31%), the VAS and WORC remained stable. In patients who indicated reduced complaints (69%), the VAS reduced (z score, -3.4; P = .001) and WORC increased (z score, 3.6; P < .001). Unchanged ARs associated with complaints persistence, whereas decreased AR of the LD (ΔAR_LD, -0.21; 95% confidence interval [CI], -0.36 to -0.06) and TM (ΔAR_TM, -0.17; 95% CI, -0.34 to -0.00) coincided with reduced complaints. There was a significant between-group difference in ΔAR_LD (-0.35; 95% CI, -0.60 to 0.10) and ΔAR_TM (-0.36; 95% CI, -0.66 to -0.05).

CONCLUSIONS

Increased co-contraction of the LD and TM is associated with a favorable course of SAPS. This may be explained by widening of the subacromial space accomplished by adductor co-contraction.

Three Months of Progressive High-Load Versus Traditional Low-Load Strength Training Among Patients With Rotator Cuff Tendinopathy: Primary Results From the Double-Blind Randomized Controlled RoCTEx Trial

Background:

Progressive high-load exercise (PHLE) has led to positive clinical results in patients with patellar and Achilles tendinopathy. However, its effects on rotator cuff tendinopathy still need to be investigated.

Purpose:

To assess the clinical effects of PHLE versus low-load exercise (LLE) among patients with rotator cuff tendinopathy.

Study Design:

Randomized controlled trial; Level of evidence, 1.

Methods:

Patients with rotator cuff tendinopathy were recruited and randomized to 12 weeks of PHLE or LLE, stratified for concomitant administration of corticosteroid injection. The primary outcome measure was change from baseline to 12 weeks in the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire, assessed in the intention-to-treat population.

Results:

A total of 100 patients were randomized to PHLE (n = 49) or LLE (n = 51). Mean changes in the DASH questionnaire were 7.11 points (95% CI, 3.07-11.16) and 8.39 points (95% CI, 4.35-12.44) in the PHLE and LLE groups, respectively; this corresponded to a statistically nonsignificant adjusted mean group difference of −1.37 points (95% CI, −6.72 to 3.99; P = .61). Similar nonsignificant results were seen for pain, range of motion, and strength. However, a significant interaction effect was found between the 2 groups and concomitant corticosteroid use (P = .028), with the largest positive change in DASH in favor of PHLE for the group receiving concomitant corticosteroid.

Conclusion:

The study results showed no superior benefit from PHLE over traditional LLE among patients with rotator cuff tendinopathy. Further investigation of the possible interaction between exercise type and corticosteroid injection is needed to establish optimal and potentially synergistic combinations of these 2 factors.

Registration:

NCT01984203 (ClinicalTrials.gov identifier): Rotator Cuff Tendinopathy Exercise Trial (RoCTEx).

The influence of induced shoulder muscle pain on rotator cuff and scapulothoracic muscle activity during elevation of the arm

BACKGROUND

Altered recruitment of rotator cuff and scapulothoracic muscles has been identified in patients with subacromial impingement syndrome. To date, however, the cause-consequence relationship between pain and altered muscle recruitment has not been fully unraveled.

METHODS

The effect of experimental shoulder pain induced by injection of hypertonic saline in the supraspinatus on the activity of the supraspinatus, infraspinatus, subscapularis, trapezius, and serratus anterior activity was investigated during the performance of an elevation task by use of muscle functional magnetic resonance imaging in 25 healthy individuals. Measurements were taken at 4 levels (C6-C7, T2-T3, T3-T4, and T6-T7) at rest and after the elevation task performed without and with experimental shoulder pain.

RESULTS

During arm elevation, experimentally induced pain caused a significant activity reduction, expressed as reduction in T2 shift of the IS (P = .029). No significant changes in T2 shift values were found for the other rotator cuff muscles or the scapulothoracic muscles.

CONCLUSIONS

This study demonstrates that acute experimental shoulder pain has an inhibitory effect on the activity of the IS during arm elevation. Acute experimental shoulder pain did not seem to influence the scapulothoracic muscle activity significantly. The findings suggest that rotator cuff muscle function (infraspinatus) should be a consideration in the early management of patients with shoulder pain.

Effects of Prolonged and Acute Muscle Pain on the Force Control Strategy During Isometric Contractions

Musculoskeletal pain is associated with multiple adaptions in movement control. This study aimed to determine whether changes in movement control acquired during acute pain are maintained over days of pain exposure. On day 0, the extensor carpi radialis brevis muscle of healthy participants was injected with nerve growth factor (NGF) to induce persistent movement-evoked pain (n = 13) or isotonic saline as a control (n = 13). On day 2, short-lasting pain was induced by injection of hypertonic saline into extensor carpi radialis brevis muscles of all participants. Three-dimensional force components were recorded during submaximal isometric wrist extensions on day 0, day 4, and before, during, and after saline-induced pain on day 2. Standard deviation (variation of task-related force) and total excursion of center of pressure (variation of force direction) were assessed. Maximal movement-evoked pain was 3.3 ± .4 (0-10 numeric scale) in the NGF-group on day 2 whereas maximum saline-induced pain was 6.8 ± .3 cm (10-cm visual analog scale). The difference in centroid position of force direction relative to day 0 was greater in the NGF group than in the control group (P < .05) on day 2 (before saline-induced pain) and day 4, reflecting changes in tangential force direction used to achieve the task. During saline-induced pain in both groups, tangential and task-related force variation was greater than before and after saline-induced pain (P < .05).

PERSPECTIVE

Persistent movement-evoked pain changes force direction from the pain-free direction. Acute pain leads to increased variation in force direction irrespective of persistent movement-evoked pain preceding the acutely painful event. These differences provide novel insight into the search for and consolidation of new motor strategies in the presence of pain.

Exercise therapy after ultrasound-guided corticosteroid injections in patients with subacromial pain syndrome: a randomized controlled trial

Background

Subacromial pain syndrome (SAPS) accounts for around 50 % of all cases of shoulder pain. The most commonly used treatments are glucocorticosteroid (steroid) injections and exercise therapy; however, despite treatment SAPS patients often experience relapse of their symptoms. Therefore the clinical effect of combining steroid and exercise therapy is highly relevant to clarify. The aim of this randomized controlled trial was to investigate if exercise therapy added to steroid injection in patients with SAPS will improve the effect of the injection therapy on shoulder pain.

Methods

In this two-arm randomized trial running over 26 weeks, patients with unilateral shoulder pain (> 4 weeks) and thickened subacromial bursa (> 2 mm on US) were included. At baseline all participants received two steroid injections into the painful shoulder with an interval of one week. Subsequently they were randomized (1:1) to either 10 weeks exercise of the involved shoulder (intervention group) or exercise of the uninvolved shoulder (control group). The patients were re-examined after the exercise program (at week 13) and again at week 26. The primary outcome assessed after 26 weeks was change in shoulder pain analyzed using the intention-to-treat principle (non-responder imputation).

Results

Ninety-nine SAPS patients (58 female) participated (49 intervention/50 control). At both follow up visits (week 13 and 26) no statistically significant between-group differences in pain changes on a visual analog scale (mm) were seen (13 weeks: pain at rest 1.7 (95 % CI –3.6 to 7.0; P = 0.53); pain in activity 2.2 (95 % CI –6.5 to 10.9; P = 0.61), 26 weeks: rest 5.6 (95 % CI –0.9 to 12.1; P = 0.09); activity 2.2 (95 % CI –6.8 to 11.2; P = 0.62). The reduction in pain was most evident in the control group at all four pain measurements. The only difference between groups was seen by US examination at week 13, where fewer participants with impingement were observed in the intervention group compared with the controls (9 vs. 19 participants; P = 0.03).

Conclusion

Exercise therapy in the painful shoulder in SAPS patients did not improve the effectiveness of steroid injections for shoulder pain in patients with unilateral SAPS and enlarged subacromial bursa on US examination.

Trial registration

ClinicalTrials.gov (NCT01506804). Registration date 5 May 2011.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1002-5) contains supplementary material, which is available to authorized users.

Experimental Muscle Pain Impairs the Synergistic Modular Control of Neck Muscles

A motor task can be performed via different patterns of muscle activation that show regularities that can be factorized in combinations of a reduced number of muscle groupings (also referred to as motor modules, or muscle synergies). In this study we evaluate whether an acute noxious stimulus induces a change in the way motor modules are combined to generate movement by neck muscles. The neck region was selected as it is a region with potentially high muscular redundancy. We used the motor modules framework to assess the redistribution of muscular activity of 12 muscles (6 per side) in the neck region of 8 healthy individuals engaged in a head and neck aiming task, in non-painful conditions (baseline, isotonic saline injection, post pain) and after the injection of hypertonic saline into the right splenius capitis muscle. The kinematics of the task was similar in the painful and control conditions. A general decrease of activity was noted for the injected muscle during the painful condition together with an increase or decrease of the activity of the other muscles. Subjects did not adopt shared control strategies (motor modules inter subject similarity at baseline 0.73±0.14); the motor modules recorded during the painful condition could not be used to reconstruct the activation patterns of the control conditions, and the painful stimulus triggered a subject-specific redistribution of muscular activation (i.e., in some subjects the activity of a given muscle increased, whereas in other subjects it decreased with pain). Alterations of afferent input (i.e., painful stimulus) influenced motor control at a multi muscular level, but not kinematic output. These findings provide new insights into the motor adaptation to pain.

Experimental knee pain impairs submaximal force steadiness in isometric, eccentric, and concentric muscle actions

INTRODUCTION

Populations with knee joint damage, including arthritis, have noted impairments in the regulation of submaximal muscle force. It is difficult to determine the exact cause of such impairments given the joint pathology and associated neuromuscular adaptations. Experimental pain models that have been used to isolate the effects of pain on muscle force regulation have shown impaired force steadiness during acute pain. However, few studies have examined force regulation during dynamic contractions, and these findings have been inconsistent. The goal of the current study was to examine the effect of experimental knee joint pain on submaximal quadriceps force regulation during isometric and dynamic contractions.

METHODS

The study involved fifteen healthy participants. Participants were seated in an isokinetic dynamometer. Knee extensor force matching tasks were completed in isometric, eccentric, and concentric muscle contraction conditions. The target force was set to 10 % of maximum for each contraction type. Hypertonic saline was then injected into the infrapatella fat pad to generate acute joint pain. The force matching tasks were repeated during pain and once more 5 min after pain had subsided.

RESULTS

Hypertonic saline resulted in knee pain with an average peak pain rating of 5.5 ± 2.1 (0-10 scale) that lasted for 18 ± 4 mins. Force steadiness significantly reduced during pain across all three muscle contraction conditions. There was a trend to increased force matching error during pain but this was not significant.

CONCLUSION

Experimental knee pain leads to impaired quadriceps force steadiness during isometric, eccentric, and concentric contractions, providing further evidence that joint pain directly affects motor performance. Given the established relationship between submaximal muscle force steadiness and function, such an effect may be detrimental to the performance of tasks in daily life. In order to restore motor performance in people with painful arthritic conditions of the knee, it may be important to first manage their pain more effectively.

Influence of obstructive sleep apnea syndrome in the fluctuation of the submaximal isometric torque of knee extensors in patients with early-grade osteoarthritis

OBJECTIVE

The aim of this study was to investigate whether obstructive sleep apnea (OSA) alters the fluctuation of submaximal isometric torque of the knee extensors in patients with early-grade osteoarthritis (OA).

METHOD

The study included 60 male volunteers, aged 40 to 70 years, divided into four groups: Group 1 (G1) - Control (n=15): without OA and without OSA; Group 2 (G2) (n=15): with OA and without OSA; Group 3 (G3) (n=15): without OA and with OSA; and Group 4 (G4) (n=15) with OA and with OSA. Five patients underwent maximal isometric contractions of 10 seconds duration each, with the knee at 60° of flexion to determine peak torque at 60°. To evaluate the fluctuation of torque, 5 submaximal isometric contractions (50% of maximum peak torque) of 10 seconds each, which were calculated from the standard deviation of torque and coefficient of variation, were performed.

RESULTS

Significant differences were observed between groups for maximum peak torque, while G4 showed a lower value compared with G1 (p=0.005). Additionally, for the average torque exerted, G4 showed a lower value compared to the G1 (p=0.036). However, no differences were found between the groups for the standard deviation (p=0.844) and the coefficient of variation (p=0.143).

CONCLUSION

The authors concluded that OSA did not change the parameters of the fluctuation of isometric submaximal torque of knee extensors in patients with early-grade OA.

Experimental muscle pain increases variability of neural drive to muscle and decreases motor unit coherence in tremor frequency band

It has been observed that muscle pain influences force variability and low-frequency (<3 Hz) oscillations in the neural drive to muscle. In this study, we aimed to investigate the effect of experimental muscle pain on the neural control of muscle force at higher frequency bands, associated with afferent feedback (alpha band, 5-13 Hz) and with descending cortical input (beta band, 15-30 Hz). Single-motor unit activity was recorded, in two separate experimental sessions, from the abductor digiti minimi (ADM) and tibialis anterior (TA) muscles with intramuscular wire electrodes, during isometric abductions of the fifth finger at 10% of maximal force [maximum voluntary contraction (MVC)] and ankle dorsiflexions at 25% MVC. The contractions were repeated under three conditions: no pain (baseline) and after intramuscular injection of isotonic (0.9%, control) and hypertonic (5.8%, painful) saline. The results showed an increase of the relative power of both the force signal and the neural drive at the tremor frequency band (alpha, 5-13 Hz) between the baseline and hypertonic (painful) conditions for both muscles (P < 0.05) but no effect on the beta band. Additionally, the strength of motor unit coherence was lower (P < 0.05) in the hypertonic condition in the alpha band for both muscles and in the beta band for the ADM. These results indicate that experimental muscle pain increases the amplitude of the tremor oscillations because of an increased variability of the neural control (common synaptic input) in the tremor band. Moreover, the concomitant decrease in coherence suggests an increase in independent input in the tremor band due to pain.

Spatial reorganisation of muscle activity correlates with change in tangential force variability during isometric contractions

The aim of this study was to quantify the effects of spatial reorganisation of muscle activity on task-related and tangential components of force variability during sustained contractions. Three-dimensional forces were measured from isometric elbow flexion during submaximal contractions (50s, 5-50% of maximal voluntary contraction (MVC)) and total excursion of the centre of pressure was extracted. Spatial electromyographic (EMG) activity was recorded from the biceps brachii muscle. The centroids of the root mean square (RMS) EMG and normalised mutual information (NMI) maps were computed to assess spatial muscle activity and spatial relationship between EMG and task-related force variability, respectively. Result showed that difference between the position of the centroids at the beginning and at the end of the contraction of the RMS EMG and the NMI maps were different in the medial-lateral direction (P<0.05), reflecting that muscle regions modulate their activity without necessarily modulating the contribution to the task-related force variability over time. Moreover, this difference between shifts of the centroids was positively correlated with the total excursion of the centre of pressure at the higher levels of contractions (>30% MVC, R(2)>0.30, P<0.05), suggesting that changes in spatial muscle activity could impact on the modulation of tangential forces. Therefore, within-muscle adaptations do not necessarily increase force variability, and this interaction can be quantified by analysing the RMS EMG and the NMI map centroids.

Shoulder muscle function in frozen shoulder syndrome patients following manipulation under anesthesia: a 6-month follow-up study

INTRODUCTION

The present study evaluates changes in shoulder muscle function in patients with frozen shoulder syndrome (FSS) following manipulation under general anesthesia (MUA).

PATIENTS AND METHODS

Fifteen FSS patients with mean (±SD) age of 53.6±9.7 years were included in this study. Isometric endurance of the shoulder muscles was characterized by time and net impulse (NI), which were assessed with the patient holding a weight in the hand until exhaustion. Fatigability of the deltoid and trapezius muscles during isometric endurance test was assessed by electromyogram power spectrum median frequency (MF) slope per minute. Patients were also screened for daytime pain. Data were collected before MUA, and at 1 and 6 months postoperatively.

RESULTS

Six months postoperatively, the MF slope for the trapezius and deltoid muscles of the involved and uninvolved shoulders did not differ (P>0.05), whereas NI remained lower and endurance time was longer (P<0.05). Shoulder pain was reduced as compared to preoperative levels (on visual analog scale) 1 and 6 months postoperatively (P<0.05).

DISCUSSION

In patients with FSS, the fastest improvements in shoulder muscle NI, fatigability and pain take place in the first month after MUA; 6 months after MUA, however, NI and endurance time remained impaired for the involved shoulder. Physiotherapy should pay more attention to muscle function recovery.

LEVEL OF EVIDENCE

Level III, prospective follow-up study.

Shoulder internal and external rotations torque steadiness in overhead athletes with and without impingement symptoms

OBJECTIVES

This study aimed to investigate torque steadiness of shoulder internal and external rotations in regularly training overhead athletes with and without impingement symptoms.

DESIGN

Cross-sectional laboratory study.

METHODS

Three groups were evaluated: athletes with impingement symptoms (n=21), asymptomatic athletes (n=25) and non-athletes (n=21). To assess torque steadiness, the participants performed 3 submaximal contractions (35% of peak torque) for 10s each, with the arm at 90° of shoulder abduction and 90° of external rotation. The standard deviation, coefficient of variation, mean exerted torque and time to stability were measured from the steadiness trials.

RESULTS

The standard deviation of internal rotation was higher in asymptomatic athletes than in non-athletes (p<0.01); however, there was no difference between the athletes with impingement symptoms and the other groups. The other variables presented no differences among the groups.

CONCLUSIONS

Higher torque fluctuation of shoulder internal rotation in asymptomatic athletes may point to neuromuscular adaptations related to throwing training. However, the steadiness patterns of athletes with impingement symptoms did not differ from those of asymptomatic athletes or non-athletes.

The impact of rotator cuff tendinopathy on proprioception, measuring force sensation

BACKGROUND

The impact of rotator cuff tendinopathy and related impingement on proprioception is not well understood. Numerous quantitative and qualitative changes in shoulder muscles have been shown in patients with rotator cuff tendinopathy. These findings suggest that control of force might be affected. This investigation wants to evaluate force sensation, a submodality of proprioception, in patients with rotator cuff tendinopathy.

METHODS

Thirty-six patients with rotator cuff tendinopathy and 30 matched healthy subjects performed force reproduction tests to isometric external and internal rotation to investigate how accurately they could reproduce a fixed target (50% MVC). Relative error, constant error, and force steadiness were calculated to evaluate respectively magnitude of error made during the test, direction of this error (overshoot or undershoot), and fluctuations of produced forces.

RESULTS

Patients significantly overshoot the target (mean, 6.04% of target) while healthy subjects underestimate the target (mean, -5.76% of target). Relative error and force steadiness are similar in patients with rotator cuff tendinopathy and healthy subjects. Force reproduction tests, as executed in this study, were found to be highly reliable (ICC 0.849 and 0.909). Errors were significantly larger during external rotation tests, compared to internal rotation.

CONCLUSION

Patients overestimate the target during force reproduction tests. This should be taken into account in the rehabilitation of patients with rotator cuff tendinopathy; however, precision of force sensation and steadiness of force exertion remains unaltered. This might indicate that control of muscle force is preserved.

Determinants of co-contraction during walking before and after arthroplasty for knee osteoarthritis

BACKGROUND

Knee osteoarthritis patients co-contract in knee-related muscle pairs during walking. The determinants of this co-contraction remain insufficiently clear.

METHODS

A heterogeneous group of 14 patients was measured before and one year after knee arthroplasty, and compared to 12 healthy peers and 15 young subjects, measured once. Participants walked on a treadmill at several imposed speeds. Bilateral activity of six muscles was registered electromyographically, and co-contraction time was calculated as percentage of stride cycle time. Local dynamic stability and variability of sagittal plane knee movements were determined. The surgeon's assessment of alignment was used. Pre-operatively, multivariate regressions on co-contraction time were used to identify determinants of co-contraction. Post-operatively it was assessed if predictor variables had changed in the same direction as co-contraction time.

FINDINGS

Patients co-contracted longer than controls, but post-operatively, differences with the healthy peers were no longer significant. Varus alignment predicted co-contraction time. No patient had post-operative varus alignment. The patients' unaffected legs were more unstable, and instability predicted co-contraction time in both legs. Post-operatively, stability normalised. Longer unaffected side co-contraction time was associated with reduced affected side kinematic variability. Post-operatively, kinematic variability had further decreased.

INTERPRETATIONS

Varus alignment and instability are determinants of co-contraction. The benefits of co-contraction in varus alignment require further study. Co-contraction probably increases local dynamic stability, which does not necessarily decrease the risk of falling. Unaffected side co-contraction contributed to decreasing affected side variability, but other mechanisms than co-contraction may also have played a role in decreasing variability.

Nociception affects motor output: a review on sensory-motor interaction with focus on clinical implications

OBJECTIVES

Research has provided us with an increased understanding of nociception-motor interaction. Nociception-motor interaction is most often processed without conscious thoughts. Hence, in many cases neither patients nor clinicians are aware of the interaction. It is aimed at reviewing the scientific literature on nociception-motor interaction, with emphasis on clinical implications.

METHODS

Narrative review.

RESULTS

Chronic nociceptive stimuli result in cortical relay of the motor output in humans, and a reduced activity of the painful muscle. Nociception-induced motor inhibition might prevent effective motor retraining. In addition, the sympathetic nervous system responds to chronic nociception with enhanced sympathetic activation. Not only motor and sympathetic output pathways are affected by nociceptive input, afferent pathways (proprioception, somatosensory processing) are influenced by tonic muscle nociception as well.

DISCUSSION

The clinical consequence of the shift in thinking is to stop trying to restore normal motor control in case of chronic nociception. Activation of central nociceptive inhibitory mechanisms, by decreasing nociceptive input, might address nociception-motor interactions.

The effectiveness of therapeutic exercise for painful shoulder conditions: a meta-analysis

BACKGROUND

Shoulder pain is the third leading musculoskeletal complaint seen by general practitioners. Physical therapy is often the first line of intervention in this population; however, there is limited description of what constitutes effective physical therapy treatment. No study has examined the effectiveness of therapeutic exercise across all painful shoulder conditions. Our purpose was to examine the effectiveness of therapeutic exercise as an intervention across all pathoanatomic mechanisms of shoulder pain in terms of range of motion (ROM), pain, and function.

METHODS

Medline via Ovid, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials were searched from 1997 through March 2011. Randomized controlled trials comparing physical therapist-prescribed exercises against any other type of intervention were included. Articles were qualitatively evaluated by use of the Physiotherapy Evidence Database scale by 5 separate reviewers. Data from included studies were extracted and synthesized with respect to the primary outcomes of ROM, pain, and function. Individual effect sizes were calculated with a standard formula, and overall effect was calculated by use of random- and fixed-effects models.

RESULTS

We qualitatively reviewed 19 articles; 17 achieved the criterion of 6 or better on the Physiotherapy Evidence Database scale. Significant heterogeneity in reporting among included studies limited quantitative assessment. Overall, therapeutic exercise has a positive effect on pain and function above all other interventions. The findings for ROM were inconclusive.

CONCLUSION

Therapeutic exercise is an effective intervention for the treatment of painful shoulder conditions; however, subsequent research is necessary for translation into clinical practice.

Low-frequency oscillations of the neural drive to the muscle are increased with experimental muscle pain

We investigated the influence of nociceptive stimulation on the accuracy of task execution and motor unit spike trains during low-force isometric contractions. Muscle pain was induced by infusion of hypertonic saline into the abductor digiti minimi muscle of 11 healthy men. Intramuscular EMG signals were recorded from the same muscle during four isometric contractions of 60-s duration at 10% of the maximal force [maximal voluntary contraction (MVC)] performed before injection (baseline), after injection of isotonic (control) or hypertonic saline (pain), and 15 min after pain was no longer reported. Each contraction was preceded by three 3-s ramp contractions from 0% to 10% MVC. The low-frequency oscillations of motor unit spike trains were analyzed by the first principal component of the low-pass filtered spike trains [first common component (FCC)], which represents the effective neural drive to the muscle. Pain decreased the accuracy of task performance [coefficient of variation (CoV) for force: baseline, 2.8 ± 1.8%, pain, 3.9 ± 1.8%; P < 0.05] and reduced motor unit discharge rates [11.6 ± 2.3 pulses per second (pps) vs. 10.7 ± 1.7 pps; P < 0.05]. Motor unit recruitment thresholds (2.2 ± 1.2% MVC vs. 2.4 ± 1.6% MVC), interspike interval variability (18.4 ± 4.9% vs. 19.1 ± 5.4%), strength of motor unit short-term synchronization [common input strength (CIS) 1.02 ± 0.44 vs. 0.83 ± 0.22], and strength of common drive (0.47 ± 0.08 vs. 0.47 ± 0.06) did not change across conditions. The FCC signal was correlated with force (R = 0.45 ± 0.06), and the CoV for FCC increased in the painful condition (5.69 ± 1.29% vs. 7.83 ± 2.61%; P < 0.05). These results indicate that nociceptive stimulation increased the low-frequency variability in synaptic input to motoneurons.

The association between submaximal quadriceps force steadiness and the knee adduction moment during walking in patients with knee osteoarthritis

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

To investigate the relationship between quadriceps force steadiness and knee adduction moment during walking in patients with knee osteoarthritis (OA).

BACKGROUND

Studies have shown that quadriceps force steadiness is impaired in patients with knee OA. Furthermore, patients with knee OA, compared to healthy controls, have also demonstrated a significantly higher external knee adduction moment during walking. However, no studies have examined the relationship between quadriceps force steadiness and the peak knee adduction moment during walking in this population.

METHODS

Forty-one patients with knee OA (34 females and 7 males) were included in the study. Submaximal isometric quadriceps force steadiness was measured during a force target-tracking task. Peak knee adduction moments during ambulation were measured using a 3-dimensional gait analysis system, and knee pain was assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) pain subscale and a visual analog scale.

RESULTS

Regression analyses showed that quadriceps force steadiness did not predict the peak knee adduction moment (adjusted R2 = 0.05, P = .41). Inclusion of covariates did not change the outcome.

CONCLUSION

No statistically significant association between submaximal isometric quadriceps force steadiness and peak knee external adduction moments during walking was found. It could be speculated that submaximal isometric quadriceps muscle force steadiness and knee joint loads during walking represent 2 distinctive pathways and may have independent influences on knee OA pathogenesis.

Experimental muscle pain challenges the postural stability during quiet stance and unexpected posture perturbation

Musculoskeletal pain impairs postural control and stability. Nine subjects stood as quietly as possible on a moveable force platform before, during, and after experimental pain in the right leg muscles. A moveable force platform was used to measure the center of pressure and provided unexpected perturbations. Lower limb muscle activity, joint angles, and foot pressure distributions were measured. Hypertonic saline was used to induce pain in the vastus lateralis, vastus medialis, or biceps femoris muscle of the right leg. Compared to baseline and control sessions, pain in the knee extensor muscles during quiet standing evoked: 1) larger sway area, greater medial-lateral center of pressure displacement and higher speed (P < .05); 2) increased sway displacement in the anterior-posterior direction (P < .05); and 3) increased electromyography (EMG) activity for left tibialis anterior and left erector spinae muscles (P < .05). Pain provoked longer time to return to an equilibrium posture after forward EMG activity for, and pain in vastus medialis muscle decreased the time for the maximum hip flexion during this perturbation (P < .05). These results show that muscle pain impairs postural stability during quiet standing and after unexpected perturbation, which suggest that people suffering from leg muscle pain are more vulnerable to falls.

PERSPECTIVE

This article presents the acute responses to leg muscle pain on the postural control. This measure could potentially help clinicians who seek to assess how pain responses may contribute to patient's postural control and stability during quiet standing and after recovering from unexpected perturbations.

Kinetic strategies of patients with shoulder impingement syndrome

Our aim was to determine whether subjects with shoulder impingement syndrome (SIS) have abnormal multijoint torque patterns compared to healthy subjects during normalized isometric force along specific directions. Subjects had to generate an isometric force corresponding to 40% of the maximal pain-free force. Eight targets were displayed on a monitor (0, 45, 90, 135, 180, 225, 270, and 315 degrees ). We calculated shoulder and elbow torques (kinetic strategies) using a biomechanical model. Regardless of the target location, the SIS group succeeded in reaching the target; however, when compared to the healthy subjects, they needed more time to do so, suggesting that SIS may slow down the execution of the kinetic strategies. Moreover, the SIS group produced lower shoulder external/internal torque to reach the targets located at 0 degrees and 225 degrees, and they generated greater abduction/adduction torque for targets located at 0, 135, and 180 degrees. In addition, they had lower elbow extension/flexion torque for the target located at 315 degrees. The investigation of atypical kinetic strategies is essential to provide an understanding of the pathomechanics of the SIS and to develop more effective treatment strategies.