Lombaire

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Many people with recurrent low back pain (LBP) have deficits in postural control of the trunk muscles and this may contribute to the recurrence of pain episodes. However, the neural changes that underlie these motor deficits remain unclear. As the motor cortex contributes to control of postural adjustments, the current study investigated the excitability and organization of the motor cortical inputs to the trunk muscles in 11 individuals with and without recurrent LBP. EMG activity of the deep abdominal muscle, transversus abdominis (TrA), was recorded bilaterally using intramuscular fine-wire electrodes. Postural control was assessed as onset of TrA EMG during single rapid arm flexion and extension tasks. Motor thresholds (MTs) for transcranial magnetic stimulation (TMS) were determined for responses contralateral and ipsilateral to the stimulated cortex. In addition, responses of TrA to TMS over the contralateral cortex were mapped during voluntary contractions at 10% of maximum. MTs and map parameters [centre of gravity (CoG) and volume] were compared between healthy and LBP groups. The CoG of the motor cortical map of TrA in the healthy group was approximately 2 cm anterior and lateral to the vertex, but was more posterior and lateral in the LBP group. The location of the CoG and the map volume were correlated with onset of TrA EMG during rapid arm movements. Furthermore, the MT needed to evoke ipsilateral responses was lower in the LBP group, but only on the less excitable hemisphere. These findings provide preliminary evidence of reorganization of trunk muscle representation at the motor cortex in individuals with recurrent LBP, and suggest this reorganization is associated with deficits in postural control.

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Toujours intéressant de voir où en est rendu l'équipe de Hodges dans le compréhension des lombalgies. Ainsi, avec ce dernier projet de recherche, ils ont pu mettre en évidence que la zone active du cortex moteur dans le contrôle postural est différent du lombalgique que du patient non symptômatique. Il semble ainsi évident que le type d'exercices à favoriser est des exercices de contrôle moteur exigant une certaine précision, et non pas du renforcement brut. Il a par ailleurs été démontré que le transverse de l'abdomen n'est pas nécessairement faible mais présente plutôt un délai de contraction. S'il faut repositionner la zone active du cortex afin de corriger le contrôle moteur déficient, on comprend que ce n'est pas une tâche facile et surtout pas rapide, quoique il est surprenant de voir à quel point le système nerveux central peut être plastique. Finalement, il a été démontré aussi avec une autre étude qu'il y a le même déplacement de la zone du cortex activée dans le cas du cortex sensorimoteur. Ce qui fait en sorte que c'est tout de même complexe ce qui se passe dans nos centres supérieurs, surtout qu'il y a possiblement d'autres zones supraspinales affectées dans ce remaniement, tel que par exemple les neurones des troncs vestibulospinaux. À suivre. Nous suivons de près tes études cher Dr Paul Hodges...

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Clinical texts have described methods for palpation of the iliolumbar ligament but have not clearly illustrated the position of the ligament in relation to the surrounding tissues. Examination of the clinical anatomy of the lumbar spine revealed that the iliolumbar ligament is embedded in layers of muscle and fascia and its iliac attachment lies on the deep inner surface of the ilium below the level of the iliac crest. These fi ndings highlight the need for consideration of the anatomy when evaluating the biological rationale underlying a clinical procedure.

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En résumé, le ligament est très profond et recouvert d'une multitude d'autres tissus. Ceci a pour effet de limiter l'accès à ce ligament et de nous faire questionner sur la nature des tissus que nous croyons palper, et donc traiter.

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STUDY DESIGN: This study examined the coactivation of trunk flexor and extensor muscles in healthy individuals. The experimental electromyographic data and the theoretical calculations were analyzed in the context of mechanical stability of the lumbar spine. OBJECTIVES: To test a set of hypotheses pertaining to healthy individuals: 1) that the trunk flexor-extensor muscle coactivation is present around a neutral spine posture, 2) that the coactivation is increased when the subject carries a load; and 3) that the coactivation provides the needed mechanical stability to the lumbar spine. SUMMARY OF BACKGROUND DATA: Theoretically, antagonistic trunk muscle coactivation is necessary to provide mechanical stability to the human lumbar spine around its neutral posture. No experimental evidence exists, however, to support this hypothesis. METHODS: Ten individuals executed slow trunk flexion-extension tasks, while six muscles on the right side were monitored with surface electromyography: external oblique, internal oblique, rectus abdominis, multifidus, lumbar erector spinae, and thoracic erector spinae. Simple, but realistic, calculations of spine stability also were performed and compared with experimental results. RESULTS: Average antagonistic flexor-extensor muscle coactivation levels around the neutral spine posture as detected with electromyography were 1.7 +/- 0.8% of maximum voluntary contraction for no external load trials and 2.9 +/- 1.4% of maximum voluntary contraction for the trials with added 32-kg mass to the torso. The inverted pendulum model based on static moment equilibrium criteria predicted no antagonistic coactivation. The same model based on the mechanical stability criteria predicted 1.0% of maximum voluntary contraction coactivation of flexors and extensors with zero load and 3.1% of maximum voluntary contraction with a 32-kg mass. The stability model also was run with zero passive spine stiffness to simulate an injury. Under such conditions, the model predicted 3.4% and 5.5% of maximum voluntary contraction of antagonistic muscle coactivation for no extra load and the added 32 kg, respectively. CONCLUSIONS: This study demonstrated that antagonistic trunk flexor-extensor muscle coactivation was present around the neutral spine posture in healthy individuals. This coactivation increased with added mass to the torso. Using a biomechanical model, the coactivation was explained entirely on the basis of the need for the neuromuscular system to provide the mechanical stability to the lumbar spine.

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The EMG signal levels recorded from the trunk muscles in a neutral posture were very low and presented some technical difficulties. The heart beat contamination of the raw signal was evident, but it was eliminated with an adaptive filtering algorithm. Additionally, the electrode background noise, the amplifier noise, and any resting muscle activity were obtained for each subject lying down in a relaxed supine position. These baseline EMG values then were subtracted from all of the trial data. Therefore, the 1% to 3% MVC EMG levels observed in the present study represent the actual noise-free muscle activity above their resting states. The low level of muscle coactivation documented in the present study is also consistent from the point of view of muscle fatigue. Jonsson 13 has published data on acceptable levels of muscle contractions sustained over a long period of time that serve as ergonomics guidelines. He showed that the prolonged 5% MVC muscle contraction correlated with muscular pain. It seems reasonable to expect that the requirement of spine stability in a neutral posture should not demand more than 5% MVC of muscle coactivation, because that could lead to muscle fatigue during the course of the entire day.

The authors of the present study analyzed the coactivation of combined trunk flexor and extensor muscles. A variety of muscle coactivation strategies existed, however, when the six monitored muscles were looked at individually. Most of the individuals maintained a constant level of internal oblique muscle activity regardless of the trunk angle. Some individuals activated the multifidus in a similar manner. Others exhibited an overlap of activity between all of the trunk flexors and extensors. Such individual differences were not surprising, given the vast redundancy present in the human neuromuscular system. Similar individual differences were observed in the muscle recruitment strategies during the execution of the trunk isometric moments.3 The redundancy in the neuromuscular system makes it very flexible and adaptable to the changes in the everyday environment; however, it also makes motor control more complex and vulnerable to errors. The hypotheses of such errors as the etiology of some low back disorders can be studied in the future with spine stability models that contain adequate anatomic detail.

Ceci pointe le modèle de force/stabilité actuel de plus en plus vers un modèle de contrôle moteur.

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OBJECTIVE: To determine whether the abdominal hollowing technique is more effective for lumbar spine stabilization than a full abdominal muscle cocontraction. DESIGN: Within-subject, repeated-measures analysis of variance was used to examine the effect of combining each of 4 loading conditions with either the hollow or brace condition on the dependent variables of stability and compression. A simulation was also conducted to assess the outcome of a person activating just the transversus abdominis during the hollow. SETTING: Laboratory. PARTICIPANTS: Eight healthy men (age range, 20-33y). INTERVENTIONS: Electromyography and spine kinematics were recorded during an abdominal brace and a hollow while supporting either a bilateral or asymmetric weight in the hands. MAIN OUTCOME MEASURES: Spine stability index and lumbar compression were calculated. RESULTS: In the simulation "ideal case," the brace technique improved stability by 32%, with a 15% increase in lumbar compression. The transversus abdominis contributed .14% of stability to the brace pattern with a less than 0.1% decrease in compression. CONCLUSIONS: Whatever the benefit underlying low-load transversus abdominis activation training, it is unlikely to be mechanical. There seems to be no mechanical rationale for using an abdominal hollow, or the transversus abdominis, to enhance stability. Bracing creates patterns that better enhance stability.

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BACKGROUND AND PURPOSE: The purpose of this randomized controlled trial was to examine the usefulness of the addition of specific stabilization exercises to a general back and abdominal muscle exercise approach for patients with subacute or chronic nonspecific back pain by comparing a specific muscle stabilization-enhanced general exercise approach with a general exercise-only approach. SUBJECTS: Fifty-five patients with recurrent, nonspecific back pain (stabilization-enhanced exercise group: n=29, general exercise-only group: n=26) and no clinical signs suggesting spinal instability were recruited. METHODS: Both groups received an 8-week exercise intervention and written advice (The Back Book). Outcome was based on self-reported pain (Short-Form McGill Pain Questionnaire), disability (Roland-Morris Disability Questionnaire), and cognitive status (Pain Self-Efficacy Questionnaire, Tampa Scale of Kinesiophobia, Pain Locus of Control Scale) measured immediately before and after intervention and 3 months after the end of the intervention period. RESULTS: Outcome measures for both groups improved. Furthermore, self-reported disability improved more in the general exercise-only group immediately after intervention but not at the 3-month follow-up. There were generally no differences between the 2 exercise approaches for any of the other outcomes. DISCUSSION AND CONCLUSION: A general exercise program reduced disability in the short term to a greater extent than a stabilization-enhanced exercise approach in patients with recurrent nonspecific low back pain. Stabilization exercises do not appear to provide additional benefit to patients with subacute or chronic low back pain who have no clinical signs suggesting the presence of spinal instability.

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Selon cette étude, il n'y a donc pas de gains supplémentaires à faire des exercices de stabilisation chez des individus avec des douleurs lombaires chroniques, sans signe d'instabilité.