Changes in excitability of corticomotor inputs to the trunk muscles during experimentally-induced acute low back pain

Measurement of voluntary activation of abdominal flexors using transcranial magnetic stimulation

BACKGROUND

Transcranial magnetic stimulation (TMS) has been used to assess voluntary activation (VA) of limb and back muscles, however its ability to assess abdominal muscle VA is unknown. The assessment of abdominal muscle VA using TMS could be applied to patients with trunk dysfunction to enable further understanding of the neurophysiology of trunk control, inform practice and enable the development and monitoring of rehabilitation programmes.

AIM

The aim of this study was to investigate use of TMS and the twitch interpolation technique to measure voluntary activation of abdominal muscles.

METHODS

Twenty healthy participants performed sets of isometric abdominal contractions of varying levels, during which TMS was applied to the primary motor cortex. The evoked twitches were measured as torque, while simultaneous surface electromyographic (EMG) activity was recorded bilaterally from rectus abdominis, erector spinae, tensor fasciae latae, and rectus femoris. VA was calculated as: (1 - superimposed twitch amplitude/estimated resting twitch amplitude) x 100. Estimated resting twitch amplitude was calculated by extrapolation using linear regression of superimposed twitch amplitude against torque for contraction strengths 50-100 % maximum voluntary contraction (MVC).

RESULTS

There was a strong linear relationship between voluntary torque of 50-100 % MVC and TMS-evoked twitch amplitude (r2 = 0.994, p = 0.035), and voluntary torque between 50-100 % MVC and VA (r2 = 0.997, p = 0.025). VA at a target torque of 100 % MVC was less than 100 % (86.20 ± 2.29 %).

CONCLUSIONS

VA of abdominal muscles can be assessed with twitch interpolation using TMS. VA has been shown to be submaximal during maximum voluntary contractions, and it has been demonstrated that superimposed twitch amplitude decreases in a linear fashion with increasing contraction intensity. Using this technique to explore trunk muscle function could help to improve understanding of the neurophysiology of trunk control, including the sites on any deficit in drive and also improve monitoring of the efficacy of treatment regimes for clinical conditions associated with dysfunctions in trunk control e.g. low back pain.

The reliability and validity of rapid transcranial magnetic stimulation mapping for muscles under active contraction

Rapid mapping is a transcranial magnetic stimulation (TMS) mapping method which can significantly reduce data collection time compared to traditional approaches. However, its validity and reliability has only been established for upper-limb muscles during resting-state activity. Here, we determined the validity and reliability of rapid mapping for non-upper limb muscles that require active contraction during TMS: the masseter and quadriceps muscles. Eleven healthy participants attended two sessions, spaced two hours apart, each involving rapid and 'traditional' mapping of the masseter muscle and three quadriceps muscles (rectus femoris, vastus medialis, vastus lateralis). Map parameters included map volume, map area and centre of gravity (CoG) in the medial-lateral and anterior-posterior directions. Low to moderate measurement errors (%SEMeas = 10-32) were observed across muscles. Relative reliability varied from good-to-excellent (ICC = 0.63-0.99) for map volume, poor-to-excellent (ICC = 0.11-0.86) for map area, and fair-to-excellent for CoG (ICC = 0.25-0.8) across muscles. There was Bayesian evidence of equivalence (BF's > 3) in most map outcomes between rapid and traditional maps across all muscles, supporting the validity of the rapid mapping method. Overall, rapid TMS mapping produced similar estimates of map parameters to the traditional method, however the reliability results were mixed. As mapping of non-upper limb muscles is relatively challenging, rapid mapping is a promising substitute for traditional mapping, however further work is required to refine this method.

Sensorimotor Integration in Chronic Low Back Pain

OBJECTIVE

Chronic low back pain (CLBP) impacts on spine movement. Altered sensorimotor integration can be involved. Afferents from the lumbo-pelvic area might be processed differently in CLBP and impact on descending motor control. This study aimed to determine whether afferents influence the corticomotor control of paravertebral muscles in CLBP. Fourteen individuals with CLBP (11 females) and 13 pain-free controls (8 females) were tested with transcranial magnetic stimulation (TMS) to measure the motor-evoked potential [MEP] amplitude of paravertebral muscles. Noxious and non-noxious electrical stimulation, and magnetic stimulation in the lumbo-sacral area were used as afferent stimuli and triggered 20 to 200 ms prior to TMS. EMG modulation elicited by afferent stimulation alone was measured to control net motoneuron excitability. MEP/EMG ratio was used as a measure of corticospinal excitability with control of net motoneuron excitability. MEP/EMG ratio was larger at 60, 80 and 100-ms intervals in CLBP compared to controls, and afferent stimulations alone reduced EMG amplitude greater in CLBP than controls at 100 ms. Our results suggest alteration in sensorimotor integration in CLBP highlighted by a greater facilitation of the descending corticospinal input to paravertebral muscles. Our results can help to optimise interventions by better targeting mechanisms.

Effects of pain on cortical homeostatic plasticity in humans: a systematic review

Homeostatic plasticity (HP) is a negative feedback mechanism that prevents excessive facilitation or depression of cortical excitability (CE). Cortical HP responses in humans have been investigated by using 2 blocks of noninvasive brain stimulation with a no-stimulation block in between. A healthy HP response is characterized by reduced CE after 2 excitatory stimulation blocks and increased CE when using inhibitory stimulation. Conversely, impaired HP responses have been demonstrated in experimental and chronic pain conditions. Therefore, this systematic review aimed to provide an overview of the effect of pain on cortical HP in humans. Scopus, Embase, and PubMed were searched from inception until November 20, 2023. The included studies (1) compared experimental or clinical pain conditions with healthy controls, (2) induced HP using 2 blocks of stimulation with a no-stimulation interval, and (3) evaluated CE measures such as motor-evoked potentials. Four studies were included, consisting of 5 experiments and 146 participants, of whom 63 were patients with chronic pain and 48 were subjected to an experimental pain model. This systematic review found support for an HP impairment in pain compared with that in pain-free states, reflected by a lack of CE reduction after excitatory-excitatory HP induction over the primary motor cortex. Inhibitory-inhibitory HP induction did not produce a consistent HP response across studies, independent of pain or pain-free states. Standardization of HP induction protocols and outcome calculations is needed to ensure reproducibility and study comparison. Future HP studies may consider investigating sensory domains including nociception, which would further our understanding of abnormal HP regulation in pain conditions.

Acute pain impairs retention of locomotor learning

Despite abundant evidence that pain alters movement performance, considerably less is known about the potential effects of pain on motor learning. Some of the brain regions involved in pain processing are also responsible for specific aspects of motor learning, indicating that the two functions have the potential to interact, yet it is unclear if they do. In experiment 1, we compared the acquisition and retention of a novel locomotor pattern in young, healthy individuals randomized to either experience pain via capsaicin and heat applied to the lower leg during learning or no stimulus. On day 1, participants learned a new asymmetric walking pattern using distorted visual feedback, a paradigm known to involve mostly explicit re-aiming processes. Retention was tested 24 h later. Although there were no differences in day 1 acquisition between groups, individuals who experienced pain on day 1 demonstrated reduced retention on day 2. Furthermore, the degree of forgetting between days correlated with pain ratings during learning. In experiment 2, we examined the effects of a heat stimulus alone, which served as a control for (nonpainful) cutaneous stimulation, and found no effects on either acquisition or retention of learning. Thus, pain experienced during explicit, strategic locomotor learning interferes with motor memory consolidation processes and does so most likely through a pain mechanism and not an effect of distraction. These findings have important implications for understanding basic motor learning processes and for clinical rehabilitation, in which painful conditions are often treated through motor learning-based interventions.NEW & NOTEWORTHY Pain is a highly prevalent and burdensome experience that rehabilitation practitioners often treat using motor learning-based interventions. Here, we showed that experimental acute pain, but not a heat stimulus, during locomotor learning impaired 24-h retention of the newly learned walking pattern. The degree of retention loss was related to the perceived pain level during learning. These findings suggest important links between pain and motor learning that have significant implications for clinical rehabilitation.

Combined transcranial magnetic stimulation and electroencephalography reveals alterations in cortical excitability during pain

Transcranial magnetic stimulation (TMS) has been used to examine inhibitory and facilitatory circuits during experimental pain and in chronic pain populations. However, current applications of TMS to pain have been restricted to measurements of motor evoked potentials (MEPs) from peripheral muscles. Here, TMS was combined with electroencephalography (EEG) to determine whether experimental pain could induce alterations in cortical inhibitory/facilitatory activity observed in TMS-evoked potentials (TEPs). In Experiment 1 (n=29), multiple sustained thermal stimuli were administered to the forearm, with the first, second, and third block of thermal stimuli consisting of warm but non-painful (pre-pain block), painful (pain block) and warm but non-painful (post-pain block) temperatures, respectively. During each stimulus, TMS pulses were delivered while EEG (64 channels) was simultaneously recorded. Verbal pain ratings were collected between TMS pulses. Relative to pre-pain warm stimuli, painful stimuli led to an increase in the amplitude of the frontocentral negative peak ~45 ms post-TMS (N45), with a larger increase associated with higher pain ratings. Experiments 2 and 3 (n=10 in each) showed that the increase in the N45 in response to pain was not due to changes in sensory potentials associated with TMS, or a result of stronger reafferent muscle feedback during pain. This is the first study to use combined TMS-EEG to examine alterations in cortical excitability in response to pain. These results suggest that the N45 TEP peak, which indexes GABAergic neurotransmission, is implicated in pain perception and is a potential marker of individual differences in pain sensitivity.

Trunk Muscle Activities during Ergometer Rowing in Rowers with and without Low Back Pain

This study aimed to determine the differences in trunk muscle activity during rowing at maximal effort between rowers with and without low back pain (LBP). Ten rowers with LBP and 12 rowers without LBP were enrolled in this study. All rowers performed a 500-m trial using a rowing ergometer at maximal effort. The amplitudes of the activities of the thoracic erector spinae (TES), lumbar erector spinae (LES), latissimus dorsi (LD), rectus abdominis (RA), and external oblique (EO) muscles were analyzed using a wireless surface electromyography (EMG) system. EMG data at each stroke were converted into 10-time series data by recording averages at every 10% in the 100% stroke cycle and normalized by maximum voluntary isometric contraction in each muscle. Two-way repeated measures analysis of variance was performed. Significant interactions were found in the activities of the TES and LES (P < 0.001 and P = 0.047, respectively). In the post hoc test, the TES activity in the LBP group was significantly higher than that in the control group at the 10% to 20% and 20% to 30% stroke cycles (P = 0.013 and P = 0.007, respectively). The LES activity in the LBP group was significantly higher than that in the control group at the 0% to 10% stroke cycle (P < 0.001). There was a main group effect on the LD activity, with significantly higher activity in the LBP group than in the control group (P = 0.023). There were no significant interactions or main effects in the EO and RA activities between the groups. The present study showed that rowers with LBP compared with those without LBP exhibited significantly higher TES, LES, and LD muscle activities. This indicates that rowers with LBP exhibit excessive back muscle activity during rowing under maximal effort.

Contribution of neural circuits tested by transcranial magnetic stimulation in corticomotor control of low back muscle: a systematic review

Introduction

Transcranial magnetic stimulation (TMS) is widely used to investigate central nervous system mechanisms underlying motor control. Despite thousands of TMS studies on neurophysiological underpinnings of corticomotor control, a large majority of studies have focused on distal muscles, and little is known about axial muscles (e.g., low back muscles). Yet, differences between corticomotor control of low back and distal muscles (e.g., gross vs. fine motor control) suggest differences in the neural circuits involved. This systematic review of the literature aims at detailing the organisation and neural circuitry underlying corticomotor control of low back muscles tested with TMS in healthy humans.

Methods

The literature search was performed in four databases (CINAHL, Embase, Medline (Ovid) and Web of science) up to May 2022. Included studies had to use TMS in combination with EMG recording of paraspinal muscles (between T12 and L5) in healthy participants. Weighted average was used to synthesise quantitative study results.

Results

Forty-four articles met the selection criteria. TMS studies of low back muscles provided consistent evidence of contralateral and ipsilateral motor evoked potentials (with longer ipsilateral latencies) as well as of short intracortical inhibition/facilitation. However, few or no studies using other paired pulse protocols were found (e.g., long intracortical inhibition, interhemispheric inhibition). In addition, no study explored the interaction between different cortical areas using dual TMS coil protocol (e.g., between primary motor cortex and supplementary motor area).

Discussion

Corticomotor control of low back muscles are distinct from hand muscles. Our main findings suggest: (i) bilateral projections from each single primary motor cortex, for which contralateral and ipsilateral tracts are probably of different nature (contra: monosynaptic; ipsi: oligo/polysynaptic) and (ii) the presence of intracortical inhibitory and excitatory circuits in M1 influencing the excitability of the contralateral corticospinal cells projecting to low back muscles. Understanding of these mechanisms are important for improving the understanding of neuromuscular function of low back muscles and to improve the management of clinical populations (e.g., low back pain, stroke).

The Effect of Acute and Sustained Pain on Corticomotor Excitability: A Systematic Review and Meta-Analysis of Group and Individual Level Data

Pain alters motor function. This is supported by studies showing reduced corticomotor excitability in response to experimental pain lasting &lt;90 minutes. Whether similar reductions in corticomotor excitability are present with pain of longer durations or whether alterations in corticomotor excitability are associated with pain severity is unknown. Here we evaluated the evidence for altered corticomotor excitability in response to experimental pain of differing durations in healthy individuals. Databases were systematically searched for eligible studies. Measures of corticomotor excitability and pain were extracted. Meta-analyses were performed to examine: (1) group-level effect of pain on corticomotor excitability, and (2) individual-level associations between corticomotor excitability and pain severity. 49 studies were included. Corticomotor excitability was reduced when pain lasted milliseconds-seconds (hedges g's = -1.26 to -1.55) and minutes-hours (g's = -0.55 to -0.9). When pain lasted minutes-hours, a greater reduction in corticomotor excitability was associated with lower pain severity (g = -0.24). For pain lasting days-weeks, there were no group level effects (g = -0.18 to 0.27). However, a greater reduction in corticomotor excitability was associated with higher pain severity (g = 0.229). In otherwise healthy individuals, suppression of corticomotor excitability may be a beneficial short-term strategy with long-term consequences. PERSPECTIVE: This systematic review synthesised the evidence for altered corticomotor excitability in response to experimentally induced pain. Reduced corticomotor excitability was associated with lower acute pain severity but higher sustained pain severity, suggesting suppression of corticomotor excitability may be a beneficial short-term adaptation with long-term consequences.

Neuromuscular Consequences of Lumbopelvic Dysfunction: Research and Clinical Perspectives

Injuries involving the lumbopelvic region (ie, lumbar spine, pelvis, hip) are common across the lifespan and include pathologies such as low back pain, femoroacetabular impingement syndrome, labrum tear, and osteoarthritis. Joint injury is known to result in an arthrogenic muscle response which contributes to muscle weakness and altered movement patterns. The purpose of this manuscript is to summarize the arthrogenic muscle response that occurs across lumbopelvic region pathologies, identify methods to quantify muscle function, and propose suggestions for future research. While each lumbopelvic region pathology is unique, there are a few common impairments and a relative consistent arthrogenic muscle response that occurs across the region. Hip muscle weakness and hip joint range of motion limitations occur with both lumbar spine and hip pathologies, and individuals with low back pain are known to demonstrate inhibition of the transversus abdominis and multifidus. Assessment of muscle inhibition is often limited to research laboratory settings, but dynamometers, ultrasound imaging, and electromyography offer clinical capacity to quantify muscle function and inform treatment pathways. Future studies should systematically determine the arthrogenic muscle response across multiple muscle groups and the timeline for changes in muscle function and determine whether disinhibitory modalities improve functional outcomes beyond traditional treatment approaches.

The influence of experimental low back pain on neural networks involved in the control of lumbar erector spinae muscles

INTRODUCTION

Low back pain (LBP) often modifies spine motor control, but the neural origin of these motor control changes remains largely unexplored. This study aimed to determine the impact of experimental low back pain on the excitability of cortical, subcortical, and spinal networks involved in the control of back muscles.

METHOD

Thirty healthy subjects were recruited and allocated to Pain (capsaicin and heat) or Control (heat) groups. Corticospinal excitability (motor-evoked potential-MEP) and intracortical networks were assessed by single- and paired-pulse transcranial magnetic stimulation, respectively. Electrical vestibular stimulation was applied to assess vestibulospinal excitability (vestibular MEP-VMEP), and the stretch reflex for excitability of the spinal or supraspinal loop (R1 and R2, respectively). Evoked back motor responses were measured before, during and after pain induction. Nonparametric rank-based ANOVA determined if pain modulated motor neural networks.

RESULTS

A decrease of R1 amplitude was present after the pain disappearance (p=0.01) whereas an increase was observed in the control group (p=0.03) compared to the R1 amplitude measured at pre-pain and pre-heat period, respectively (Group x Time interaction - p<0.001). No difference in MEP and VMEP amplitude was present during and after pain (p>0.05).

CONCLUSION

During experimental LBP, no change in cortical, subcortical, or spinal networks was observed. After pain disappearance, the reduction of the R1 amplitude without modification of MEP and VMEP amplitude suggest a reduction in spinal excitability potentially combined with an increase in descending drives. The absence of effect during pain needs to be further explored.

Can training of a skilled pelvic movement change corticomotor control of back muscles? Comparison of single and paired-pulse transcranial magnetic stimulation

Evidence suggests excitability of the motor cortex (M1) changes in response to motor skill learning of the upper limb. Few studies have examined immediate changes in corticospinal excitability and intra‐cortical mechanisms following motor learning in the lower back. Further, it is unknown which transcranial magnetic stimulation (TMS) paradigms are likely to reveal changes in cortical function in this region. This study aimed to (1) compare corticospinal excitability and intra‐cortical mechanisms in the lower back region of M1 before and after a single session of lumbopelvic tilt motor learning task in healthy people and (2) compare these measures between two TMS coils and two methods of recruitment curve (RC) acquisition. Twenty‐eight young participants (23.6 ± 4.6 years) completed a lumbopelvic tilting task involving three 5‐min blocks. Single‐pulse (RC from 70% to 150% of active motor threshold) and paired‐pulse TMS measures (ICF, SICF and SICI) were undertaken before (using 2 coils: figure‐of‐8 and double cone) and after (using double cone coil only) training. RCs were also acquired using a traditional and rapid method. A significant increase in corticospinal excitability was found after training as measured by RC intensities, but this was not related to the RC slope. No significant differences were found for paired‐pulse measures after training. Finally, there was good agreement between RC parameters when measured with the two different TMS coils or different acquisition methods (traditional vs. rapid). Changes in corticospinal excitability after a single session of lumbopelvic motor learning task are seen, but these changes are not explained by changes in intra‐cortical mechanisms.

Effects of different modalities of afferent stimuli of the lumbo-sacral area on control of lumbar paravertebral muscles

Somatosensory feedback to the central nervous system is essential to plan, perform and refine spine motor control. However, the influence of somatosensory afferent input from the trunk on the motor output to trunk muscles has received little attention. The objective was to compare the effects of distinct modalities of afferent stimulation on the net motoneuron and corticomotor excitability of paravertebral muscles. Fourteen individuals were recruited. Modulation of corticospinal excitability (motor-evoked potential [MEP]) of paravertebral muscles was measured when afferent stimuli (cutaneous noxious and non-noxious, muscle contraction) were delivered to the trunk at 10 intervals prior to transcranial magnetic stimulation. Each peripheral stimulation was applied alone, and subsequent EMG modulation was measured to control for net motoneuron excitability. MEP modulation and MEP/EMG ratio were used as measures of corticospinal excitability with and without control of net motoneuron excitability, respectively. MEP and EMG modulation were smaller after evoked muscle contraction than after cutaneous noxious and non-noxious stimuli. MEP/EMG ratio was not different between stimulation types. Both MEP and EMG amplitudes were reduced after evoked muscle contraction, but not when expressed as MEP/EMG ratio. Noxious and non-noxious stimulation had limited impact on all variables. Distinct modalities of peripheral afferent stimulation of the lumbo-sacral area differently modulated responses of paravertebral muscles, but without an influence on corticospinal excitability with control of net motoneuron excitability. Muscle stimulation reduced paravertebral activity and was best explained by spinal mechanisms. The impact of afferent stimulation on back muscles differs from the effects reported for limb muscles.

Characterisation of motor cortex organisation in patients with different presentations of persistent low back pain

Persistence of low back pain is thought to be associated with different underlying pain mechanisms, including ongoing nociceptive input and central sensitisation. We hypothesised that primary motor cortex (M1) representations of back muscles (a measure of motor system adaptation) would differ between pain mechanisms, with more consistent observations in individuals presumed to have an ongoing contribution of nociceptive input consistently related to movement/posture. We tested 28 participants with low back pain sub-grouped by the presumed underlying pain mechanisms: nociceptive pain, nociplastic pain and a mixed group with features consistent with both. Transcranial magnetic stimulation was used to study M1 organisation of back muscles. M1 maps of multifidus (deep and superficial) and longissimus erector spinae were recorded with fine-wire electromyography and thoracic erector spinae with surface electromyography. The nociplastic pain group had greater variability in M1 map location (centre of gravity) than other groups (p < .01), which may suggest less consistency, and perhaps relevance, of motor cortex adaptation for that group. The mixed group had greater overlap of M1 representations between deep/superficial muscles than nociceptive pain (deep multifidus/longissimus: p = .001, deep multifidus/thoracic erector spinae: p = .008) and nociplastic pain (deep multifidus/longissimus: p = .02, deep multifidus/thoracic erector spinae: p = .02) groups. This study provides preliminary evidence of differences in M1 organisation in subgroups of low back pain classified by likely underlying pain mechanisms. Despite the sample size, differences in cortical re-organisation between subgroups were detected. Differences in M1 organisation in subgroups of low back pain supports tailoring of treatment based on pain mechanism and motor adaptation.

Task- and Intensity-Dependent Modulation of Arm-Trunk Neural Interactions in the Corticospinal Pathway in Humans

Most human movements require coordinated activation of multiple muscles. Although many studies reported associations between arm, leg, and trunk muscles during functional tasks, their neural interaction mechanisms still remain unclear. Therefore, the aim of our study was to investigate arm-trunk or arm-leg neural interactions in the corticospinal tract during different arm muscle contractions. Specifically, we examined corticospinal excitability of the erector spinae (ES; trunk extensor), rectus abdominis (RA; trunk flexor), and tibialis anterior (TA; leg) muscles while participants exerted: (1) wrist flexion and (2) wrist extension isometric contraction at various contraction intensity levels ranging from rest to 50% of maximal voluntary contraction (MVC) effort. Corticospinal excitability was assessed using motor evoked potentials (MEPs) elicited through motor cortex transcranial magnetic stimulation (TMS). Results showed that ES MEPs were facilitated even at low contractions (>5% MVC) during wrist flexion and extension, while stronger contractions (>25% MVC) were required to facilitate RA MEPs. The extent of facilitation of ES MEPs depended on contraction intensity of wrist extension, but not flexion. Moreover, TA MEPs were facilitated at low contractions (>5% MVC) during wrist flexion and extension, but contraction intensity dependence was only shown during stronger wrist extension contractions (>25% MVC). In conclusion, trunk extensor corticospinal excitability seems to depend on the task and the intensity of arm contraction, while this is not true for trunk flexor and leg muscles. Our study therefore demonstrated task- and intensity-dependent neural interactions of arm-trunk connections, which may underlie anatomic and/or functional substrates of these muscle pairs.

Understanding the role of patient preference in the treatment algorithm for chronic low back pain: results from a survey-based study

Aims: Interventional pain treatments range from injections to established radiofrequency ablation techniques and finally neuromodulation. In addition to safety, efficacy and cost dominance, patient preference for type of treatment is important. Methods: Chronic pain patients (n = 129) completed a preference scale to determine which interventional pain management procedures they would prefer from among radiofrequency ablation, temporary (60-day) peripheral nerve stimulation (PNS), conventional PNS and spinal cord stimulation/dorsal root ganglion stimulation. A second survey (n = 347) specific to assessing the preference for radiofrequency ablation or temporary PNS treatment was completed by patients with low back pain. Results: On the basis of mean rank, temporary PNS percutaneously implanted for up to 60 days was the most preferred treatment compared with the other options presented (p = 0.002). Conclusions: Patient preference should be unbiased and considered as an independent variable for physician discussion in treatment options and future research.

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

BACKGROUND AND OBJECTIVE

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

DATABASES AND DATA TREATMENT

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

RESULTS

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

SIGNIFICANCE

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

Hindlimb Somatosensory Information Influences Trunk Sensory and Motor Cortices to Support Trunk Stabilization

Sensorimotor integration in the trunk system is poorly understood despite its importance for functional recovery after neurological injury. To address this, a series of mapping studies were performed in the rat. First, the receptive fields (RFs) of cells recorded from thoracic dorsal root ganglia were identified. Second, the RFs of cells recorded from trunk primary sensory cortex (S1) were used to assess the extent and internal organization of trunk S1. Finally, the trunk motor cortex (M1) was mapped using intracortical microstimulation to assess coactivation of trunk muscles with hindlimb and forelimb muscles, and integration with S1. Projections from trunk S1 to trunk M1 were not anatomically organized, with relatively weak sensorimotor integration between trunk S1 and M1 compared to extensive integration between hindlimb S1/M1 and trunk M1. Assessment of response latency and anatomical tracing suggest that trunk M1 is abundantly guided by hindlimb somatosensory information that is derived primarily from the thalamus. Finally, neural recordings from awake animals during unexpected postural perturbations support sensorimotor integration between hindlimb S1 and trunk M1, providing insight into the role of the trunk system in postural control that is useful when studying recovery after injury.

Mapping Responses of Lumbar Paravertebral Muscles to Single-Pulse Cortical TMS Using High-Density Surface Electromyography

Motor evoked potential (MEP), which was elicited by transcranial magnetic stimulation (TMS), has been widely used to detect corticospinal projection from TMS cortical site to trunk muscles. It can help to find the stimulation hotspot in the scalp. However, it fails to precisely describe coordinated activities of trunk muscle groups with only single-channel myoelectric signal. In this study, we aimed to use high-density surface electromyography (sEMG) to explore the effect of cortical TMS on lumbar paravertebral muscles in healthy subjects. The cortical site at 1 cm anterior and 4 cm lateral to vertex was chosen to simulate using a single-pulse TMS with different intensities and forward-bending angles. A high-density electrode array (45 channels) was placed on the surface of lumbar paravertebral muscles to record sEMG signals during a TMS experiment. MEP signals elicited by TMS were extracted from 45-channel recordings and one topographic map of the MEP amplitudes with six spatial features was constructed at each sampling point. The results showed TMS could successfully evoke an oval area with high intensity in the MEP topographic map, while this area mainly located in ipsilateral side of the TMS site. Intensity features related to the high intensity area rose significantly with TMS intensity and forward-bending angle increasing, but location features showed no change. The optimal stimulation parameters were 80% of maximum stimulator output (MSO) for TMS intensity and 30/60 degree for forward-bending angle. This study provided a potentially effective mapping tool to explore the hotspot for transcranial stimulation on trunk muscles.

Effects of exercise therapy plus manual therapy on muscle activity, latency timing and SPADI score in shoulder impingement syndrome

PURPOSE

The study aimed to compare the effects of exercise therapy plus manual therapy (ET plus MT) and exercise therapy (ET) alone on muscle activity, muscle onset latency timing and shoulder pain and disability index-Hindi (SPADI-H) score in athletes with shoulder impingement syndrome (SIS).

MATERIALS AND METHOD

Overhead male athletes diagnosed with SIS were randomly allocated into ET plus MT group(n = 40) and ET group(n = 40). Muscle activity, muscle onset latency timings and SPADI-H score were assessed. Both the groups performed 8 weeks of intervention and were evaluated at baseline, 4th and 8th weeks.

RESULT

ET plus MT group was more effective in increasing muscle activity, optimising latency timings and decreasing SPADI score when compared to ET group alone(p < 0.05). After treatment muscle activity and SPADI-H improved in both groups (p < 0.05).

CONCLUSION

ET plus MT was superior for improving muscle activity, muscle onset latency timing and SPADI score compared to ET alone.

Correlation Between Central Sensitization and Remote Muscle Performance in Individuals With Chronic Low Back Pain

OBJECTIVE

The purpose of this study was to examine associations between the degree of central sensitization (CS) and remote muscle performance in people with chronic low back pain (CLBP).

METHODS

The 2011 fibromyalgia (FM) criteria and severity scales (2011 FM survey) were used as a surrogate measure of CS to divide the participants into 2 groups: FM-positive CLBP and FM-negative CLBP. Measures related to central sensitization included the 2011 FM survey and pressure pain threshold of the thumbnail. Measures related to muscle performance included neck flexor muscle strength and endurance and plantar flexor muscle strength. Between-groups and correlation analyses were performed.

RESULTS

Sixty people with CLBP were enrolled (30 FM-positive, 30 FM-negative). There was no significant difference between the subgroups in age, sex, or pain duration (P > .05). The FM-positive CLBP group showed poorer neck flexor muscle endurance (P = .01) and plantar flexor muscle strength (P = .002) than the FM-negative CLBP group, whereas neck flexor muscle strength was not different between the groups (P = .175). Scores for FM and values for pressure pain thresholds of the thumbnail were associated with neck flexor muscle strength (respectively, r = -0.320, P = .013, and r = 0.467, P < .001), endurance (r = -0.242, P < .001, and r = 0.335, P = .009), and plantar flexor muscle strength (r = -0.469, P < .001, and r = 0.500, P < .001).

CONCLUSION

We found associations between the degree of CS and remote muscle strength and endurance, suggesting that poor remote muscle performance is possibly a clinical sign of CS in people with CLBP.

Assessing sensorimotor control of the lumbopelvic-hip region using task-based functional MRI

Recent brain imaging studies have suggested that cortical remodeling within sensorimotor regions are associated with persistent low back pain and may be a driving mechanism for the impaired neuromuscular control associated with this condition. This paper outlines a new approach for investigating cortical sensorimotor integration during the performance of small-amplitude lumbopelvic movements with functional MRI. Fourteen healthy right-handed participants were instructed in the lumbopelvic movement tasks performed during fMRI acquisition. Surface electromyography (EMG) collected on 8 lumbopelvic and thigh muscles captured organized patterns of muscle activation during the movement tasks. fMRI data were collected on 10 of 14 participants. Sensorimotor cortical activation across the tasks was identified using a whole brain analysis and further explored with regional analyses of key components of the cortical sensorimotor network. Head motion had low correlation to the tasks (r = -0.101 to 0.004) and head translation averaged 0.98 (0.59 mm) before motion correction. Patterns of activation of the key lumbopelvic and thigh musculature (average amplitude normalized 2-17%) were significantly different across tasks (P > 0.001). Neuroimaging demonstrated activation in key sensorimotor cortical regions that were consistent with motor planning and sensory feedback needed for performing the different tasks. This approach captures the specificity of lumbopelvic sensorimotor control using goal-based tasks (e.g., "lift your hip" vs. "contract your lumbar multifidus to 20% of maximum") performed within the confines of the scanner. Specific patterns of sensorimotor cortex activation appear to capture differences between bilateral and unilateral tasks during voluntary control of multisegmental movement in the lumbopelvic region.NEW & NOTEWORTHY We demonstrated the feasibility of using task-based functional magnetic resonance imaging (fMRI) protocols for acquiring the blood oxygen level-dependent (BOLD) response of key sensorimotor cortex regions during voluntary lumbopelvic movements. Our approach activated lumbopelvic muscles during small-amplitude movements while participants were lying supine in the scanner. Our data supports these tasks can be done with limited head motion and low correlation of head motion to the task. The approach provides opportunities for assessing the role of brain changes in persistent low back pain.

Electromyographic Biofeedback in Motor Function Recovery After Peripheral Nerve Injury: An Integrative Review of the Literature

Electromyographic biofeedback (EMG-BF) has been applied to treat different types of peripheral nerve injuries (PNI). However, despite the clinical practice widespread use its evidence is controversial. With the objective of summarize the available evidence on the electromyographic biofeedback effectiveness and efficacy to help motor function recovery after PNI an integrative review was performed. A secondary objective was to identify the conceptual framework and strategies of EMG-BF intervention, and the quality of technical description of EMG-BF procedures. To conduct this integrative review a systematic search of the literature was performed between October 2013 and July 2018, in PUBMED, ISI and COCHRANE databases for EMG-BF original studies in PNI patients of any etiology, in English, Portuguese, Spanish or French, published after 1990. Exclusion criteria were poor description of EMG-BF treatment, associated treatment that could impair EMG-BF effect, inclusion of non-PNI individuals and case studies design. The PEDro scale was used to evaluate study quality of randomized clinical trials (RCTs) included. This resulted in 71 potential articles enrolled to full reading, although only nine matched the inclusion criteria. PNI included facial paralysis, acute sciatic inflammation and carpal tunnel syndrome. The average quality score of the included RCTs was five, corresponding to low methodological quality. Due to the small number of included articles, low quality studies and heterogeneity of interventions, outcomes and population we concluded that there is limited evidence of EMG-BF effectiveness and efficacy for motor function recovery in PNI patients.

Electrical Stimulation of Back Muscles Does Not Prime the Corticospinal Pathway

OBJECTIVES

To investigate whether peripheral electrical stimulation (PES) of back extensor muscles changes excitability of the corticospinal pathway of the stimulated muscle and synergist trunk muscles.

METHODS

In 12 volunteers with no history of low back pain (LBP), intramuscular fine-wire electrodes recorded electromyography (EMG) from the deep multifidus (DM) and longissimus muscles. Surface electrodes recorded general EMG from the erector spinae and abdominal muscles. Single- and paired-pulse transcranial magnetic stimulation (TMS) paradigms tested corticospinal excitability, short-interval intracortical inhibition (SICI-2 and 3 ms), and intracortical facilitation (ICF) optimized for recordings of DM. Active motor threshold (aMT) to evoke a motor-evoked potential (MEP) in DM was determined and stimulation was applied at 120% of this intensity. PES was provided via electrodes placed over the right multifidus. The effect of 20-min PES (ramped motor activation) was studied.

RESULTS

Mean aMT for DM was 42.7 ± 10% of the maximal stimulator output. No effects of PES were found on MEP amplitude (single-pulse TMS) for any trunk muscles examined. There was no evidence for changes in SICI or ICF; that is, conditioned MEP amplitude was not different between trials after PES.

CONCLUSION

Results indicate that, unlike previous reports that show increased corticospinal excitability of limb muscles, PES of back muscles does not modify the corticospinal excitability. This difference in response of the motor pathway of back muscles to PES might be explained by the lesser importance of voluntary cortical drive to these muscles and the greater role of postural networks. Whether PES influences back muscle training remains unclear, yet the present results suggest that potential effects are unlikely to be explained by the effects of PES at corticospinal level with the parameters used in this study.

Neuroplasticity of Sensorimotor Control in Low Back Pain

Low back pain (LBP) is an important medical and socioeconomic problem. Impaired sensorimotor control has been suggested to be a likely mechanism underlying development and/or maintenance of pain. Although early work focused on the structural and functional abnormalities within the musculoskeletal system, in the past 20 years there has been an increasing realization that patients with LBP might also have extensive neuroplastic changes within the central nervous system. These include changes related to both the structure (eg, gray matter changes) and function (eg, organization of the sensory and motor cortices) of the nervous system as related to processing of pain and nociception and to motor and somatosensory systems. Moreover, clinical interventions increasingly aim to drive neuroplasticity with treatments to improve pain and sensorimotor function. This commentary provides a contemporary overview of neuroplasticity of the pain/nociceptive and sensorimotor systems in LBP. This paper addresses (1) defining neuroplasticity in relation to control of the spine and LBP, (2) structural and functional nervous system changes as they relate to nonspecific LBP and sensorimotor function, and (3) related clinical implications. Individuals with recurrent and persistent LBP differ from those without LBP in several markers of the nervous system's function and structure. Neuroplastic changes may be addressed by top-down cognitive-based interventions and bottom-up physical interventions. An integrated clinical approach that combines contemporary pain neuroscience education, cognition-targeted sensorimotor control, and physical or function-based treatments may lead to better outcomes in patients with recurrent and persistent LBP. This approach will need to consider variation among individuals, as no single finding/mechanism is present in all individuals, and no single treatment that targets neuroplastic changes in the sensorimotor system is likely to be effective for all patients with LBP. J Orthop Sports Phys Ther 2019;49(6):402-414. doi:10.2519/jospt.2019.8489.

Motor cortex representation of deep and superficial neck flexor muscles in individuals with and without neck pain

Sensorimotor control of neck muscles differs between individuals with and without pain. Differences in the primary motor cortex (M1) maps of these muscles may be involved. This study compared M1 representations of deep (DNF) and superficial (SNF) neck flexor muscles between 10 individuals with neck pain (NP) and 10 painfree controls. M1 organisation was studied using transcranial magnetic stimulation (TMS) applied to a grid over the skull and surface electromyography of DNF (pharyngeal electrode) and SNF. Three-dimensional maps of M1 representation of each muscle were generated. Peaks in the SNF map that represented the sternocleidomastoid (SCM) and platysma muscles were identified. Unique centre of gravity (CoG)/map peaks were identified for the three muscles. In comparison to painfree controls, NP participants had more medial location of the CoG/peak of DNF, SCM, and platysma, greater mediolateral variation in DNF CoG (p = 0.02), fewer SNF and DNF map peaks (p = 0.01). These data show that neck flexor muscle M1 maps relate to trunk, neck, and face areas of the motor homunculus. Differences in M1 representation in NP have some similarities and some differences with observations for other musculoskeletal pain conditions. Despite the small sample size, our data did reveal differences and is comparable to other similar studies. The results of this study should be interpreted with consideration of methodological issues.

Effects of Repetitive Peripheral Magnetic Stimulation on Patients With Acute Low Back Pain: A Pilot Study

Objective

To investigate the effects of real repetitive peripheral magnetic stimulation (rPMS) treatment compared to sham rPMS treatment on pain reduction and functional recovery of patients with acute low back pain.

Methods

A total of 26 patients with acute low back pain were randomly allocated to the real rPMS group and the sham rPMS group. Subjects were then administered a total of 10 treatment sessions. Visual analogue scale (VAS) was assessed before and after each session. Oswestry Disability Index (ODI) and Roland-Morris Disability Questionnaire (RMDQ) were employed to assess functional recovery at baseline and after sessions 5 and 10.

Results

Real rPMS treatment showed significant pain reduction immediately after each session. Sustained and significant pain relief was observed after administering only one session in the real rPMS group. Significant functional improvement was observed in the real rPMS group compared to that in the sham rPMS group after sessions 5 and 10 based on ODI and after session 5 based on RMDQ.

Conclusion

Real rPMS treatment has immediate effect on pain reduction and sustained effect on pain relief for patients with acute low back pain compared to sham rPMS.

Effectiveness of extrinsic feedback for management of non-specific low back pain: a systematic review protocol

INTRODUCTION

Low back pain is the greatest cause of years lived with disability worldwide and is linked with high societal and economic burden. Neuromuscular control impairments are a common clinical presentation in patients with non-specific low back pain. Musculoskeletal physiotherapists commonly use feedback as a part of the management of low back disorders. This systematic review will aim to assess the effectiveness of extrinsic biofeedback for reducing pain, disability and recurrence of pain in patients with non-specific low back pain.

METHODS AND ANALYSIS

Systematic searches will be performed in CINAHL, Embase, Medline, PsycInfo, Scopus and Web of Science. We will include randomised controlled trial studies, if the study recruited patients with non-specific low back pain; compared extrinsic feedback versus either placebo or control; another intervention; or in addition to an intervention versus that intervention alone; and have used pain, disability scores or low back pain recurrence as outcome measures. We will exclude studies with designs other than randomised controlled trials. We will assess the risk of bias within included studies using the PEDro scale, and the strength of evidence using the Grades of Recommendation, Assessment, Development and Evaluation approach.

ETHICS AND DISSEMINATION

Ethical approval and patient consent are not required since this is a systematic review based on published studies. The results of this study will be published in an international peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42017077888.

Effect of Cutaneous Heat Pain on Corticospinal Excitability of the Tibialis Anterior at Rest and during Submaximal Contraction

Previous studies have shown that pain can interfere with motor control. The neural mechanisms underlying these effects remain largely unknown. At the upper limb, mounting evidence suggests that pain-induced reduction in corticospinal excitability is involved. No equivalent data is currently available at the lower limb. The present study therefore examined the effect of thermal pain on the corticospinal drive to tibialis anterior (TA) at rest and during an isometric submaximal dorsiflexion. Transcranial magnetic stimulation was used to induce motor-evoked potentials (MEPs) in the TA at rest and during contraction in the presence or absence of cutaneous heat pain induced by a thermode positioned above the TA (51°C during 1 s). With similar pain ratings between conditions (3.9/10 at rest and 3.6/10 during contraction), results indicate significant decreases in MEP amplitude during both rest (−9%) and active conditions (−13%) (main effect of pain, p = 0.02). These results therefore suggest that cutaneous heat pain can reduce corticospinal excitability in the TA muscle and that such reduction in corticospinal excitability could contribute to the interference of pain on motor control/motor learning.

Shoulder Taping and Neuromuscular Control

CONTEXT

  Scapular taping can offer clinical benefit to some patients with shoulder pain; however, the underlying mechanisms are unclear. Understanding these mechanisms may guide the development of treatment strategies for managing neuromusculoskeletal shoulder conditions.

OBJECTIVE

  To examine the mechanisms underpinning the benefits of scapular taping.

DESIGN

  Descriptive laboratory study.

SETTING

  University laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 15 individuals (8 men, 7 women; age = 31.0 ± 12.4 years, height = 170.9 ± 7.6 cm, mass = 73.8 ± 14.4 kg) with no history of shoulder pain.

INTERVENTION(S)

  Scapular taping.

MAIN OUTCOME MEASURE(S)

  Surface electromyography (EMG) was used to assess the (1) magnitude and onset of contraction of the upper trapezius (UT), lower trapezius (LT), and serratus anterior relative to the contraction of the middle deltoid during active shoulder flexion and abduction and (2) corticomotor excitability (amplitude of motor-evoked potentials from transcranial magnetic stimulation) of these muscles at rest and during isometric abduction. Active shoulder-flexion and shoulder-abduction range of motion were also evaluated. All outcomes were measured before taping, immediately after taping, 24 hours after taping with the original tape on, and 24 hours after taping with the tape removed.

RESULTS

  Onset of contractions occurred earlier immediately after taping than before taping during abduction for the UT (34.18 ± 118.91 milliseconds and 93.95 ± 106.33 milliseconds, respectively, after middle deltoid contraction; P = .02) and during flexion for the LT (110.02 ± 109.83 milliseconds and 5.94 ± 92.35 milliseconds, respectively, before middle deltoid contraction; P = .06). These changes were not maintained 24 hours after taping. Mean motor-evoked potential onset of the middle deltoid was earlier at 24 hours after taping (tape on = 7.20 ± 4.33 milliseconds) than before taping (8.71 ± 5.24 milliseconds, P = .008). We observed no differences in peak root mean square EMG activity or corticomotor excitability of the scapular muscles among any time frames.

CONCLUSIONS

  Scapular taping was associated with the earlier onset of UT and LT contractions during shoulder abduction and flexion, respectively. Altered corticomotor excitability did not underpin earlier EMG onsets of activity after taping in this sample. Our findings suggested that the optimal time to engage in rehabilitative exercises to facilitate onset of trapezius contractions during shoulder movements may be immediately after tape application.

Cortical contributions to anticipatory postural adjustments in the trunk

KEY POINTS

Increases in activity of trunk muscles that occur prior to, or concurrent with, a voluntary limb movement are termed anticipatory postural adjustments (APAs). APAs are important for maintaining postural stability in response to perturbations but the neural mechanisms underlying APAs remain unclear. Our results showed that corticospinal excitability of erector spinae (ES) muscle increased at 40 ms prior to rapid shoulder flexion, with a reduction in intracortical inhibition and no change in spinal excitability. Changes in corticospinal excitability were observed in ES, with similar excitability profiles between standing and lying positions, but were not observed in rectus abdominis. We suggest that the neural control of postural adjustments involves changes at a cortical level, which in part are due to reduced inhibition.

ABSTRACT

Voluntary limb movements are associated with increases in trunk muscle activity, some of which occur within a time window considered too fast to be induced by sensory feedback; these increases are termed anticipatory postural adjustments (APAs). Although it is known that the function of APAs is to maintain postural stability in response to perturbations, excitability of the corticospinal projections to the trunk muscles during the APAs remains unclear. Thirty-four healthy subjects performed rapid shoulder flexion in response to a visual cue in standing and lying positions. Transcranial magnetic stimulation (TMS) was delivered over the trunk motor cortex to examine motor evoked potentials (MEPs) in erector spinae (ES) and in rectus abdominis (RA) muscles at several time points prior to the rise in electromyographic activity (EMG) of anterior deltoid (AD) muscle. TMS was also used to assess short-interval intracortical inhibition (SICI) and cervicomedullary MEPs (CMEPs) in ES in the standing position. MEPs in ES were larger at time points closer to the rise in AD EMG in both standing and lying positions, whereas MEPs in RA did not differ over the time course examined. Notably, SICI was reduced at time points closer to the rise in AD EMG, with no change in CMEPs. Our results demonstrate that increasing excitability of corticospinal projections to the trunk muscles prior to a voluntary limb movement is likely to be cortical in origin and is muscle specific.

Improved compensatory postural adjustments of the deep abdominals following exercise in people with chronic low back pain

The purpose of this study was to determine if 8 weeks of exercise affects motor control in people with chronic low back pain (CLBP), measured by anticipatory (APAs) and compensatory postural adjustments (CPAs). APAs and CPAs were measured prior to and following 8 weeks in two groups of people with CLBP: an exercise group (n=12) who attended three exercise sessions per week for 8 weeks; and a non-exercise control group (n=12) who were advised to continue their usual activities for the duration of the study. APAs and CPAs were recorded during unilateral arm flexion, bilaterally from rectus abdominis (RA), transverse abdominis/internal oblique (TA/IO), and erector spinae (ES) via surface electromyography. Analysis of muscle onsets and APA amplitudes suggests APAs did not change for either group. Ipsi-lateral TA/IO CPAs increased for the exercise group and ipsi-lateral TA/IO CPAs decreased for the control group. Only exercise promoted a pattern of TA/IO activity during CPAs similar to healthy individuals, suggesting improved control of rotational torques. These results show motor control improvement following exercise in people with CLBP, highlighted by improved side specific control of TA/IO.

A random-perturbation therapy in chronic non-specific low-back pain patients: a randomised controlled trial

The purpose of the study was to assess the effectiveness of a specific rehabilitation therapy for chronic non-specific low-back pain patients, based on a random/irregular functional perturbation training induced by force disturbances to the spine. Forty patients (20 controls and 20 in the perturbation-based group) finished the whole experimental design. A random-perturbation exercise, which included variable and unpredictable disturbances, was implemented in the therapy of the perturbation-based group (13 weeks, two times per week and 1.5 h per session). The participants of the control group did not receive any specific training. Low-back pain, muscle strength, and neuromuscular control of spine stability were investigated before and after the therapy using the visual analog scale, maximal isometric and isokinetic contractions, nonlinear time series analysis, and by determining the stiffness and damping of the trunk after sudden perturbations. The perturbation-based therapy reduced patient's low-back pain (35%), increased muscle strength (15-22%), and trunk stiffness (13%), while no significant changes were observed in the control group. It can be concluded that the proposed therapy has the potential to enhance trunk muscle capability as well as sensory information processing within the motor system during sudden loading and, as a consequence, improve the stabilization of the trunk.

Correlation between lumbar dysfunction and fat infiltration in lumbar multifidus muscles in patients with low back pain

Background

Lumbar multifidus muscles (LMM) are important for spinal motion and stability. Low back pain (LBP) is often associated with fat infiltration in LMM. An increasing fat infiltration of LMM may lead to lumbar dysfunction. The purpose of this study was to investigate whether there is a correlation between the severity of lumbar dysfunction and the severity of fat infiltration of LMM.

Methods

In a cross-sectional study, 42 patients with acute or chronic LBP were recruited. Their MRI findings were visually rated and graded using three criteria for fat accumulation in LMM: Grade 0 (0–10%), Grade 1 (10–50%) and Grade 2 (>50%). Lumbar sagittal range of motion, dynamic upright and seated posture control, sagittal movement control, body awareness and self-assessed functional disability were measured to determine the patients’ low back dysfunction.

Results

The main result of this study was that increased severity of fat infiltration in the lumbar multifidus muscles correlated significantly with decreased range of motion of lumbar flexion (p = 0.032). No significant correlation was found between the severity of fat infiltration in LMM and impaired movement control, posture control, body awareness or self-assessed functional disability.

Conclusion

This is the first study investigating the relationship between the severity of fat infiltration in LMM and the severity of lumbar dysfunction. The results of this study will contribute to the understanding of the mechanisms leading to fat infiltration of LMM and its relation to spinal function. Further studies should investigate whether specific treatment strategies are effective in reducing or preventing fat infiltration of LMM.

Effects of Vojta method on trunk stability in healthy individuals

Vojta reflex locomotion is important to main upright posture through stimulation of breast zone to patient with cerebral palsy. However, application in other diseases is no investigated. So, we determined the effects of stimulation of the breast zone on trunk stability in healthy individuals. Fourteen young healthy adults (7 males and 7 females) voluntarily participated in this study. The subjects were randomly divided into an experimental group (breast zone) and control group (arbitrary point). All groups were stimulated for 5 min on the left and right sides, respectively, for a total 10 times. We used the thickness of the external oblique abdominal muscle (EO), the internal oblique abdominal muscle, the transversus abdominis muscle (TrA), and the rectus abdominis muscles, as well as the area of the diaphragm by using ultrasonography. In the experimental group, the thickness of the TrA significantly increased during stimulation (P<0.05) while the thickness of the EO significantly decreased (P<0.05). Also, the area of diaphragm in inspiration was significantly different (P<0.05). Therefore, stimulation of the breast zone may be effective to improve trunk stability through activation of the TrA muscle and the diaphragm.

Influence of paravertebral muscles training on brain plasticity and postural control in chronic low back pain

BACKGROUND AND PURPOSE

Isometric activation (ISOM) of deep multifidi muscles (MF) can influence postural adjustments and primary motor cortex (M1) function in chronic low back pain (CLBP). In order to better understand how ISOM impacts on CLBP condition, the present study contrasted ISOM after-effects on M1 function, MF postural activation and pain with another training, the global activation of paravertebral muscles (GLOB, hip extension). The main objective of this study was to compare the effects of ISOM and GLOB (3-week training each) on MF postural activation and M1 function in a CLBP population.

METHODS

Twenty-four people with CLBP were randomly allocated to ISOM and GLOB groups for a 3-week daily practice. Pre/post-training after-effects were assessed by the onset of superficial MF (MF-S) activation during ballistic limb movements (bilateral shoulder flexion in standing; unilateral hip extension in prine lying), MF-S corticomotor control tested by transcranial magnetic stimulation of M1, and assessment of pain, kinesiophobia and disability by standardized questionnaires.

RESULTS

Both ISOM and GLOB improved pain and disability. However, only ISOM influenced M1 function (decreased corticospinal excitability and increased intracortical inhibition), fastened MF-S postural activation and decreased kinesiophobia.

CONCLUSIONS

Changes of corticospinal excitability and of MF-S postural adjustments suggest that ISOM better influenced brain plasticity. Future studies should further test whether our novel findings relate to an influence of the exercises on the lumbopelvic control of different muscles and on cognitive function. Clinically, individual's evaluation remains warranted before prescribing one or the other of these two conventional exercises for reducing pain.

IMPLICATIONS

This original study presents how motor control exercises can influence brain plasticity and postural control in chronic low back pain. This knowledge will impact on the decision of clinicians to prescribe specific exercises with a view of improving motor control in this musculoskeletal condition.

Does experimental low back pain change posteroanterior lumbar spinal stiffness and trunk muscle activity? A randomized crossover study

BACKGROUND

While some patients with low back pain demonstrate increased spinal stiffness that decreases as pain subsides, this observation is inconsistent. Currently, the relation between spinal stiffness and low back pain remains unclear. This study aimed to investigate the effects of experimental low back pain on temporal changes in posteroanterior spinal stiffness and concurrent trunk muscle activity.

METHOD

In separate sessions five days apart, nine asymptomatic participants received equal volume injections of hypertonic or isotonic saline in random order into the L3-L5 interspinous ligaments. Pain intensity, spinal stiffness (global and terminal stiffness) at the L3 level, and the surface electromyographic activity of six trunk muscles were measured before, immediately after, and 25-minute after injections. These outcome measures under different saline conditions were compared by generalized estimating equations.

FINDINGS

Compared to isotonic saline injections, hypertonic saline injections evoked significantly higher pain intensity (mean difference: 5.7/10), higher global (mean difference: 0.73N/mm) and terminal stiffness (mean difference: 0.58N/mm), and increased activity of four trunk muscles during indentation (P<0.05). Both spinal stiffness and trunk muscle activity returned to baseline levels as pain subsided.

INTERPRETATION

While previous clinical research reported inconsistent findings regarding the association between spinal stiffness and low back pain, our study revealed that experimental pain caused temporary increases in spinal stiffness and concurrent trunk muscle co-contraction during indentation, which helps explain the temporal relation between spinal stiffness and low back pain observed in some clinical studies. Our results substantiate the role of spinal stiffness assessments in monitoring back pain progression.

Corticospinal Excitability of Trunk Muscles during Different Postural Tasks

Evidence suggests that the primary motor cortex (M1) is involved in both voluntary, goal-directed movements and in postural control. Trunk muscles are involved in both tasks, however, the extent to which M1 controls these muscles in trunk flexion/extension (voluntary movement) and in rapid shoulder flexion (postural control) remains unclear. The purpose of this study was to investigate this question by examining excitability of corticospinal inputs to trunk muscles during voluntary and postural tasks. Twenty healthy adults participated. Transcranial magnetic stimulation was delivered to the M1 to examine motor evoked potentials (MEPs) in the trunk muscles (erector spinae (ES) and rectus abdominis (RA)) during dynamic shoulder flexion (DSF), static shoulder flexion (SSF), and static trunk extension (STE). The level of background muscle activity in the ES muscles was matched across tasks. MEP amplitudes in ES were significantly larger in DSF than in SSF or in STE; however, this was not observed for RA. Further, there were no differences in levels of muscle activity in RA between tasks. Our findings reveal that corticospinal excitability of the ES muscles appears greater during dynamic anticipatory posture-related adjustments than during static tasks requiring postural (SSF) and goal-directed voluntary (STE) activity. These results suggest that task-oriented rehabilitation of trunk muscles should be considered for optimal transfer of therapeutic effect to function.

Gain of postural responses increases in response to real and anticipated pain

This study tested two contrasting theories of adaptation of postural control to pain. One proposes alteration to the postural strategy including inhibition of muscles that produce painful movement; another proposes amplification of the postural adjustment to recruit strategies normally reserved for higher load. This study that aimed to determine which of these alternatives best explains pain-related adaptation of the hip muscle activity associated with stepping down from steps of increasing height adaptation of postural control to increasing load was evaluated from hip muscle electromyography (fine-wire and surface electrodes) as ten males stepped from steps of increasing height (i.e. increasing load). In one set of trials, participants stepped from a low step (5 cm) and pain was induced by noxious electrical stimulation over the sacrum triggered from foot contact with a force plate or was anticipated. Changes in EMG amplitude and onset timing were compared between conditions. Hip muscle activation was earlier and larger when stepping from higher steps. Although ground reaction forces (one of the determinants of joint load) were unchanged before, during and after pain, trials with real or anticipated noxious stimulation were accompanied by muscle activity indistinguishable from that normally reserved for higher steps (EMG amplitude increased from 9 to 17 % of peak). These data support the notion that muscle activation for postural control is augmented when challenged by real/anticipated noxious stimulation. Muscle activation was earlier and greater than that required for the task and is likely to create unnecessary joint loading. This could have long-term consequences if maintained.

Afferent inhibition and cortical silent periods in shoulder primary motor cortex and effect of a suprascapular nerve block in people experiencing chronic shoulder pain

OBJECTIVE

To characterise short afferent inhibition (SAI) and the cortical silent period (CSP) in the primary motor cortex representations of the infraspinatus muscle in healthy adults and people experiencing chronic shoulder pain, to determine the impact of a suprascapular nerve block (SSNB).

METHODS

Neurophysiological measures were obtained in 18 controls and 8 patients with chronic shoulder pain, pre and post SSNB and 1 week later. Pain intensity was assessed by a visual analogue scale.

RESULTS

SAI was apparent in controls (all P<0.03) and a CSP was observed which reduced in the presence of SAI (all P<0.0001). Compared to controls, shoulder pain patients demonstrated higher active motor threshold (P=0.046), less SAI (P=0.044), a longer CSP (P=0.048) and less modulation of the CSP by SAI (P=0.045). Higher motor thresholds were related to higher pain scores (P=0.009). The SSNB immediately restored SAI (P=0.013), with a positive relationship between increased SAI and reduced pain (P=0.031). The SSNB further reduced modulation of CSP by SAI at 1 week post injection (P=0.006).

CONCLUSIONS

SAI and the CSP were present and demonstrated robust interaction in controls, which was aberrant in patients. The SSNB transiently restored SAI but had no effect on the CSP; however CSP modulation by SAI was further attenuated 1 week post injection.

SIGNIFICANCE

The current findings improve understanding of the neurophysiology of the shoulder motor cortex and its modulation by chronic pain. The effect of SSNB in shoulder pain patients should be interpreted with caution until proven in a larger population. Interventions that target intracortical inhibition might increase efficacy in people with chronic shoulder pain.

How does anodal transcranial direct current stimulation of the pain neuromatrix affect brain excitability and pain perception? A randomised, double-blind, sham-control study

Background

Integration of information between multiple cortical regions of the pain neuromatrix is thought to underpin pain modulation. Although altered processing in the primary motor (M1) and sensory (S1) cortices is implicated in separate studies, the simultaneous changes in and the relationship between these regions are unknown yet. The primary aim was to assess the effects of anodal transcranial direct current stimulation (a-tDCS) over superficial regions of the pain neuromatrix on M1 and S1 excitability. The secondary aim was to investigate how M1 and S1 excitability changes affect sensory (STh) and pain thresholds (PTh).

Methods

Twelve healthy participants received 20 min a-tDCS under five different conditions including a-tDCS of M1, a-tDCS of S1, a-tDCS of DLPFC, sham a-tDCS, and no-tDCS. Excitability of dominant M1 and S1 were measured before, immediately, and 30 minutes after intervention respectively. Moreover, STh and PTh to peripheral electrical and mechanical stimulation were evaluated. All outcome measures were assessed at three time-points of measurement by a blind rater.

Results

A-tDCS of M1 and dorsolateral prefrontal cortex (DLPFC) significantly increased brain excitability in M1 (p < 0.05) for at least 30 min. Following application of a-tDCS over the S1, the amplitude of the N20-P25 component of SEPs increased immediately after the stimulation (p < 0.05), whilst M1 stimulation decreased it. Compared to baseline values, significant STh and PTh increase was observed after a-tDCS of all three stimulated areas. Except in M1 stimulation, there was significant PTh difference between a-tDCS and sham tDCS.

Conclusion

a-tDCS of M1 is the best spots to enhance brain excitability than a-tDCS of S1 and DLPFC. Surprisingly, a-tDCS of M1 and S1 has diverse effects on S1 and M1 excitability. A-tDCS of M1, S1, and DLPFC increased STh and PTh levels. Given the placebo effects of a-tDCS of M1 in pain perception, our results should be interpreted with caution, particularly with respect to the behavioural aspects of pain modulation.

Trial Registration

Australian New Zealand Clinical Trials, ACTRN12614000817640, http://www.anzctr.org.au/.