Louis-David Beaulieu

Task-specificity of bilateral anticipatory activation of the deep abdominal muscles in healthy and chronic low back pain populations

STUDY DESIGN Cross-sectional study of lumbopelvic muscle activation during rapid limb movements in chronic low back pain (CLBP) patients and healthy controls. INTRODUCTION Controversy exists over whether bilateral anticipatory activation of the deep abdominal muscles represents a normal motor control strategy prior to all rapid limb movements, or if this is simply a task-specific strategy appropriate for only certain movement conditions. OBJECTIVE To assess the onset timing of the transversus abdominis/internal oblique muscles (TrA/IO) during two rapid limb movement tasks with different postural demands - bilateral shoulder flexion in standing, unilateral hip extension in prone lying - as well as differences between CLBP and controls. METHODS Twelve CLBP and 13 controls performed the two tasks in response to an auditory cue. Surface EMG was acquired bilaterally from five muscles, including TrA/IO. RESULTS In both groups, 50% of bilateral shoulder flexion trials showed bilateral anticipatory TrA/IO activation. This was rare, however, in unilateral hip extension for which only the TrA/IO contralateral to the moving leg showed anticipatory activation. The only significant difference in lumbo-pelvic muscle onset timing between CLBP and controls was a delay in semitendinosus activation during bilateral shoulder flexion in standing. CONCLUSION Our data suggest that bilateral anticipatory TrA/IO activation is a task-specific motor control strategy, appropriate for only certain rapid limb movement conditions. Furthermore, the presence of altered semitendinosus onset timing in the CLBP group during bilateral shoulder flexion may be reflective of other possible lumbo-pelvic motor control alterations among this population.

Corticomotor control of lumbar multifidus muscles is impaired in chronic low back pain: concurrent evidence from ultrasound imaging and double-pulse transcranial magnetic stimulation

Chronic low back pain (CLBP) is often associated with impaired control of deep trunk muscles and reorganization of the primary motor areas (M1). Precisely, functional changes of the lumbar multifidus muscles (MF) involved in spine stability may be of special interest in rehabilitation. Therefore, we tested MF corticomotor control using double transcranial magnetic stimulation (TMS) paradigms for the first time in this muscle and examined its link with MF volitional activation. Eleven individuals with lateralized CLBP and 13 pain-free participants were recruited. Ultrasound imaging enabled measurement of MF volitional isometric contraction in prone lying. TMS of MF M1 area was used to test hemispheric excitability and mechanisms in relation to motor programming, i.e., active motor threshold (AMT), amplitude of motor-evoked potentials and short-interval intracortical inhibition (SICI) and facilitation (SICF). In CLBP, SICI level was lower in the left hemisphere and MF volitional contraction was not related to AMT (M1 excitability), conversely to what was observed in the pain-free group. No other between-group difference was detected. These original findings support a plasticity of cortical maps controlling paravertebral muscles and likely including a different motor strategy for the control of MF. Changes of M1 function may thus underlie impaired motor control of lumbopelvic spine and pain persistence in CLBP.

Reliability and minimal detectable change of transcranial magnetic stimulation outcomes in healthy adults: A systematic review

BACKGROUND Transcranial magnetic stimulation (TMS) is used worldwide for noninvasively testing human motor systems but its psychometric properties remain unclear. OBJECTIVE/HYPOTHESIS This work systematically reviewed studies on the reliability of TMS outcome measures of primary motor cortex (M1) excitability in healthy humans, with an emphasis on retrieving minimal detectable changes (MDC). METHODS The literature search was performed in three databases (Pubmed, CINAHL, Embase) up to June 2016 and additional studies were identified through hand-searching. French and English-written studies had to report the reliability of at least one TMS outcome of M1 in healthy humans. Two independent raters assessed the eligibility of potential studies, and eligible articles were reviewed using a structured data extraction form and two critical appraisal scales. RESULTS A total of 34 articles met the selection criteria, which tested the intra- and inter-rater reliability (relative and absolute subtypes) of several TMS outcomes. However, our critical appraisal of studies raised concerns on the applicability and generalization of results because of methodological and statistical pitfalls. Importantly, MDC were generally large and likely affected by various factors, especially time elapsed between sessions and number of stimuli delivered. CONCLUSIONS This systematic review underlined that the evidence about the reliability of TMS outcomes is scarce and affected by several methodological and statistical problems. Data and knowledge of the review provided however relevant insights on the ability of TMS outcomes to track plastic changes within an individual or within a group, and recommendations were made to level up the quality of future work in the field.

Effects of repetitive peripheral magnetic stimulation on normal or impaired motor control. A review.

INTRODUCTION Repetitive magnetic stimulation at the periphery (rPMS), i.e. over spinal roots, nerves or muscles, represents a new painless and noninvasive approach that can contribute to motor recovery. This method is based on the assumption that, under rPMS, neural networks involved in motor control would be regulated by the large recruitment of proprioceptive afferents, with little activation of cutaneous receptors. STUDY AIM This literature review dealing with rPMS after-effects on motor control aimed at better understanding the outcome measures and further discussing some possible involved mechanisms. RESULTS Our literature search resulted in 13 studies that used different types of outcomes (neurophysiological, biomechanical, clinical) to test the influence of rPMS over spinal roots or muscles in healthy individuals and in persons with stroke or spinal disorders. Dynamic changes were reported post-rPMS, such as spasticity reduction and improvements of movement dynamics. Studies also brought about some interesting insights on the cortical plasticity associated with rPMS effects, such as the activation of fronto-parietal loops that may explain the post-rPMS improvement of motor planning. CONCLUSIONS Due to the heterogeneous and scant literature on the topic, no conclusion can be drawn to date. However, the results encourage the concurrent testing of clinical, neurophysiological and biomechanical outcomes to investigate more precisely the relevance of rPMS in neurological rehabilitation.

Repetitive peripheral magnetic stimulation to reduce pain or improve sensorimotor impairments: A literature review on parameters of application and afferents recruitment.

INTRODUCTION Repetitive peripheral magnetic stimulation (rPMS over spinal root, nerve or muscle belly) is a promising technology in physiopathology research. As compared to electrical stimulation, rPMS is deemed to activate deep conductive structures and produce strong muscle contractions and massive proprioceptive afferents with minimal cutaneous recruitment. RPMS may thus act differently on neural plasticity involved in pain reduction and motor recovery in musculoskeletal or neurological conditions. However, literature is very scant and still controversial concerning afferents recruited by rPMS, thus no consensus is reached yet for its clinical use. STUDY AIM This review dealt with stimulation parameters reported in any scientific research that applied rPMS as an intervention to improve somatosensory or motor disorders with a view of proposing recommendations for future applications. Also, controversy on afferents recruitment was discussed. RESULTS The literature search resulted in 24 studies. Literature is scant on the topic but our review presents the rationale and the experimental data that may underlie the selection of parameters in future studies using rPMS as an intervention. Although controversy remains, the review presents that the specific recruitment of sensory afferents by magnetic stimulation may offer advantages and disadvantages depending on the pathology. CONCLUSIONS The review proposed recommendations to improve rPMS application in clinical research. However, the development of guidelines still requires methodological and clinical studies enrolling larger samples and with randomized sham-controlled designs.

Brain control of volitional ankle tasks in people with chronic stroke and in healthy individuals

This study explored the relationships between motor cortical control of ankle dorsiflexors and clinical impairments of volitional ankle dorsiflexion in people with chronic stroke. Eighteen persons with stroke and 14 controls were evaluated. Clinical tools were used to assess ankle dorsiflexion amplitude and isometric strength. Transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) tested the functional integrity of cortical circuits controlling the tibialis anterior (TA). All clinical scores and most TMS outcomes were impaired in people with chronic stroke. The lower clinical scores were related to the reduction of the strength of corticospinal projections onto spinal motoneurons. Concurrent TMS and clinical testing in chronic stroke provided original data demonstrating relationships between the integrity of cortical and corticospinal components of TA motor control and volitional ankle tasks. Our study proposes that volitional ankle mobilization in chronic stroke may be explained by the residual abnormal M1 circuits which may be responsive for rehabilitation intervention. This should be confirmed in longitudinal studies with larger samples to determine whether TMS outcomes associated with lower limb muscles are predictive of clinical changes or vice versa.

Influence of chronic low back pain and fear of movement on the activation of the transversely oriented abdominal muscles during forward bending

INTRODUCTION Chronic low back pain (CLBP) and fear of movement (kinesiophobia) are associated with an overactivation of paravertebral muscles during forward bending. This impairs spine motor control and contributes to pain perpetuation. However, the abdominal muscles activation is engaged too in spine stabilization but its modulation with kinesiophobia remains unknown. Our study tested whether CLBP and kinesiophobia affected the activation pattern of abdominal muscles during trunk flexion/extension. METHODS Surface electromyographical recordings of the internal oblique/transversus abdominis (IO/TrA) and external oblique (EO) muscles were analyzed in 12 people with CLBP and 13 pain-free subjects during low-velocity forward bending back and forth from erected posture. Tampa Scale of Kinesiophobia was also administrated. RESULTS IO/TrA activation, but not EO, was modulated across the phases of movement in both groups, i.e. maximal at onset of flexion and end of extension, and minimal at full flexion. In CLBP group only, IO/TrA activation was increased near to full trunk flexion and in correlation with kinesiophobia. CONCLUSIONS The phase-dependence of IO/TrA activation during trunk flexion/extension in standing may have a role in spine motor control. The influence of kinesiophobia in CLBP should be further investigated as an important target in CLBP management.

Peripheral Magnetic Stimulation to Decrease Spasticity in Cerebral Palsy

Muscle spasticity in pediatric cerebral palsy limits movement and disrupts motor performance, thus its reduction is important in rehabilitation to optimize functional motor development. Our pilot study used repetitive peripheral magnetic stimulation, because this emerging technology influences spinal and cerebral synaptic transmission, and its antispastic effects were reported in adult neurologic populations. We tested whether five sessions of tibial and common peroneal nerve stimulation exerted acute and long-term effects on spasticity of the ankle plantar flexor muscles in five spastic diparetic children (mean age, 8 years and 3 months; standard deviation, 1 year and 10 months). Muscle resistance to fast stretching was measured with a manual dynamometer as a spasticity indicator. A progressive decrease was observed for the more impaired leg, reaching significance at the third session. This sustained reduction of spasticity may reflect that the peripheral stimulation improved the controls over the spinal circuitry. It thus suggests that a massive stimulation-induced recruitment of sensory afferents may be able to influence central nervous system plasticity in pediatric cerebral palsy.

The side of chronic low back pain matters: evidence from the primary motor cortex excitability and the postural adjustments of multifidi muscles

Hemispheric lateralization of pain processing was reported with overactivation of the right frontal lobe. Specifically in chronic low back pain (CLBP), functional changes in the left primary motor cortex (M1) with impaired anticipatory postural activation (APA) of trunk muscles have been observed. Given the connections between frontal and M1 areas for motor planning, it is hypothesized that the pain side could differently influence M1 function and APA of paravertebral multifidus (MF) muscles. This study aimed at testing whether people with right- versus left-sided CLBP showed different M1 excitability and APA. Thirty-five individuals with lateralized CLBP (19 right-sided and 16 left-sided) and 13 pain-free subjects (normative values) were tested for the excitability of MF M1 area (active motor threshold—AMT) with transcranial magnetic stimulation and for the latency of MF APA during bilateral shoulder flexion and during unilateral hip extension in prone lying. In the right-sided CLBP group, the AMT of both M1 areas was lower than in the left-sided group and the pain-free subjects; the latency of MF APA was shorter in bilateral shoulder flexion and in the left hip extension tasks as compared to the left-sided group. In CLBP, an earlier MF APA was correlated with lower AMT in both tasks. People with right-sided CLBP presented with increased M1 excitability in both hemispheres and earlier MF APA. These results likely rely on cortical motor adaptation related to the tasks and axial muscles tested. Future studies should investigate whether CLBP side-related differences have a clinical impact, e.g. in diagnosis and intervention.

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

Abstract 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 aftereffects on Ml 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 Ml 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 Ml 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.