Changes in motor planning of feedforward postural responses of the trunk muscles in low back pain

Changes in trunk muscle recruitment have been identified in people with low-back pain (LBP). These differences may be due to changes in the planning of the motor response or due to delayed transmission of the descending motor command in the nervous system. These two possibilities were investigated by comparison of the effect of task complexity on the feedforward postural response of the trunk muscles associated with rapid arm movement in people with and without LBP. Task complexity was increased by variation of the expectation for a command to either abduct or flex the upper limb. The onsets of electromyographic activity (EMG) of the abdominal and deltoid muscles were measured. In control subjects, while the reaction time of deltoid and the superficial abdominal muscles increased with task complexity, the reaction time of transversus abdominis (TrA) was constant. However, in subjects with LBP, the reaction time of TrA increased along with the other muscles as task complexity was increased. While inhibition of the descending motor command cannot be excluded, it is more likely that the change in recruitment M of TrA represents a more complex change in organisation of the postural response.

Experimental muscle pain changes feedforward postural responses of the trunk muscles

Many studies have identified changes in trunk muscle recruitment in clinical low back pain (LBP). However, due to the heterogeneity of the LBP population these changes have been variable and it has been impossible to identify a cause-effect relationship. Several studies have identified a consistent change in the feed-forward postural response of transversus abdominis (TrA), the deepest abdominal muscle, in association with arm movements in chronic LBP. This study aimed to determine whether the feedforward recruitment of the trunk muscles in a postural task could be altered by acute experimentally induced LBP. Electromyographic (EMG) recordings of the abdominal and paraspinal muscles were made during arm movements in a control trial, following the injection of isotonic (non-painful) and hypertonic (painful) saline into the longissimus muscle at L4, and during a 1-h follow-up. Movements included rapid arm flexion in response to a light and repetitive arm flexion-extension. Temporal and spatial EMG parameters were measured. The onset and amplitude of EMG of most muscles was changed in a variable manner during the period of experimentally induced pain. However, across movement trials and subjects the activation of TrA was consistently reduced in amplitude or delayed. Analyses in the time and frequency domain were used to confirm these findings. The results suggest that acute experimentally induced pain may affect feedforward postural activity of the trunk muscles. Although the response was variable, pain produced differential changes in the motor control of the trunk muscles, with consistent impairment of TrA activity.

Perturbed upper limb movements cause short-latency postural responses in trunk muscles

Addition of a load to a moving upper limb produces a perturbation of the trunk due to transmission of mechanical forces. This experiment investigated the postural response of the trunk muscles in relation to unexpected limb loading. Subjects performed rapid, bilateral shoulder flexion in response to a stimulus. In one third of trials, an unexpected load was added bilaterally to the upper limbs in the first third of the movement. Trunk muscle electromyography, intra-abdominal pressure and upper limb and trunk motion were measured. A short-latency response of the erector spinae and transversus abdominis muscles occurred similar to 50 ms after the onset of the limb perturbation that resulted from addition of the load early in the movement and was coincident with the onset of the observed perturbation at the trunk. The results provide evidence of initiation of a complex postural response of the trunk muscles that is consistent with mediation by afferent input from a site distant to the lumbar spine, which may include afferents of the upper limb.

Influence of Imposed Optic Flow Characteristics and Intention on Postural Responses

This study examined the influence of both optic flow characteristics and intention on postural control responses. Two groups of 10 adults each were exposed to the room's movement either at 0.6 cm/s (low velocity group) or 1.0 cm/s (high velocity group). All the participants stood in the upright stance inside of a moving room and were informed about the room movement only after the fourth trial as they were asked to resist to its influence. Results revealed that participants from both groups were influenced by the imposed visual stimulus in the first trials, but the coupling strength was weaker for the high velocity group. The request to resist the visual influences decreased visual influences oil body sway, but only for the low velocity group. These results indicate that intention might play a role in stimulus influences on body sway but it is stimulus dependent.

Deceleration affects anticipatory and reactive components of triggered postural responses

Understanding the physiological and psychological factors that contribute to healthy and pathological balance control in man has been made difficult by the confounding effects of the perturbations used to test balance reactions. The present study examined how postural responses were influenced by the acceleration-deceleration interval of an unexpected horizontal translation. Twelve adult males maintained balance during unexpected forward and backward surface translations with two different acceleration-deceleration intervals and presentation orders (serial or random). SHORT perturbations consisted of an initial acceleration (peak acceleration 1.3 m s(-2); duration 300 ms) followed 100 ms later by a deceleration. LONG perturbations had the same acceleration as SHORT perturbations, followed by a 2-s interval of constant velocity before deceleration. Surface and intra-muscular electromyography (EMG) from the leg, trunk, and shoulder muscles were recorded along with motion and force plate data. LONG perturbations induced larger trunk displacements compared to SHORT perturbations when presented randomly and larger EMG responses in proximal and distal muscles during later (500-800 ms) response intervals. During SHORT perturbations, activity in some antagonist muscles was found to be associated with deceleration and not the initial acceleration of the support surface. When predictable, SHORT perturbations facilitated the use of anticipatory mechanisms to attenuate early (100-400 ms) EMG response amplitudes, ankle torque change and trunk displacement. In contrast, LONG perturbations, without an early deceleration effect, did not facilitate anticipatory changes when presented in a predictable order. Therefore, perturbations with a short acceleration-deceleration interval can influence triggered postural responses through reactive effects and, when predictable with repeated exposure, through anticipatory mechanisms.

Preparatory trunk motion accompanies rapid upper limb movement

Evaluation of trunk movements, trunk muscle activation, intra-abdominal pressure and displacement of centres of pressure and mass was undertaken to determine whether trunk orientation is a controlled variable prior to and during rapid bilateral movement of the upper limbs. Standing subjects performed rapid bilateral symmetrical upper limb movements in three directions (flexion, abduction and extension). The results indicated a small (0.4-3.3 degrees) but consistent initial angular displacement between the segments of the trunk in a direction opposite to that produced by the reactive moments resulting from limb movement. Phasic activation of superficial trunk muscles was consistent with this pattern of preparatory motion and with the direction of motion of the centre of mass. In contrast, activation of the deep abdominal muscles was independent of the direction of limb motion, suggesting a non-direction specific contribution to spinal stability. The results support the opinion that feedforward postural responses result in trunk movements, and that orientation of the trunk and centre of mass are both controlled variables in relation to rapid limb movements.

Motor unit synchronization is reduced in anterior knee pain

Anterior knee pain (AKP) is common and has been argued to be related to poor patellofemoral joint control due to impaired coordination of the vasti muscles. However, there are conflicting data. Changes in motor unit firing may provide more definitive evidence. Synchronization of motor unit action potentials (MUAPs) in vastus medialis obliquus (VMO) and vastus lateralis (VL) may contribute to coordination in patellofemoral joint control. We hypothesized that synchronization may be reduced in AKP. Recordings of single MUAPs were made from VMO and multiunit electromyograph (EMG) recordings were made from VL. Averages of VL EMG recordings were triggered from the single MUAPs in VMO. Motor units in VL firing in association with the VMO motor units would appear as a peak in the VL EMG average. Data were compared to previous normative data. The proportion of trials in which a peak was identified in the triggered averages of VL EMG was reduced in people with AKP (38%) compared to controls (90%). Notably, although 80% of subjects had values less than controls, 20% were within normal limits. These results provide new evidence that motor unit synchronization is modified in the presence of pain and provide evidence for motor control dysfunction in AKP. Perspective: This study shows that coordination of motor units between the medial and lateral vasti muscles in people with anterior knee pain is reduced compared to people without knee pain. It confirms that motor control dysfunction is a factor in this condition and has implications for selection of rehabilitation strategies. (c) 2005 by the American Pain Society.

Effects of tensioning the lumbar fasciae on segmental stiffness during flexion and extension - Young investigator award winner

Study Design. Biomechanical study of unembalmed human lumbar segments. Objective. To investigate the effects of tensioning the lumbar fasciae ( transversus abdominis [TrA]) aponeurosis) on segment stiffness during flexion and extension. Summary of Background Data. Animal and human studies suggest that TrA may influence intersegmental movement via tension in the middle and posterior layers of lumbar fasciae ( MLF, PLF). Methods. Compressive flexion and extension moments were applied to 17 lumbar segments from 9 unembalmed cadavers with 20 N lateral tension of the TrA aponeurosis during: 1) static tests: load was compared when fascial tension was applied during static compressive loads into flexion-extension; 2) cyclic loading tests: load, axial displacement, and stiffness were compared during repeated compressive loading cycles into flexion-extension. After testing, the PLF was incised to determine the tension transmitted by each layer. Results. At all segments and loads (< 200 N), fascial tension increased resistance to flexion loads by similar to 9.5 N. In 15 of 17, fascial tension decreased resistance to extension by similar to 6.6 N. Fascial tension during cyclic flexion loading decreased axial displacement by 26% at the onset of loading (0 - 2 N) and 2% at 450 N ( 13 of 17). During extension loading, fascial tension increased displacement at the onset of loading ( 10 of 17) by similar to 23% and slightly (1%) decreased displacement at 450 N. Segment stiffness was increased by 6 N/mm in flexion (44% at 25 N) and decreased by 2 N/mm (8% at 25 N) in extension. More than 85% of tension was transmitted through the MLF. Conclusions. Tension on the lumbar fasciae simulating moderate contraction of TrA affects segmental stiffness, particularly toward the neutral zone.

On the functional integration between postural and supra-postural tasks on the basis of contextual cues and task constraint

In order to evaluate the effects of uncertainty about direction of mechanical perturbation and supra-postural task constraint on postural control young adults had their upright stance perturbed while holding a tray in a horizontal position Stance was perturbed by moving forward or backward a supporting platform contrasting situations of certainty versus uncertainty of direction of displacement Increased constraint on postural stability was Imposed by a supra-postural task of equilibrating a cylinder on the tray Performance was assessed through EMG of anterior leg muscles angular displacement of the main Joints involved in the postural reactions and displacement of the tray Results showed that both certainty on the direction of perturbation and Increased supra-postural task constraint led to decreased angular displacement of the knee and the hip Furthermore combination of certainty and high supra-postural task constraint produced shorter latency of muscular activation Such postural responses were paralleled by decreased displacement of the tray Thesi results suggest a functional integration between the tasks with central set priming reactive postural responses from contextual cues and Increased stability demand (C) 2010 Elsevier B V All rights reserved

Dynamics of inter-modality re-weighting during human postural control

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Efeitos da manipulação do estímulo visual e da intenção na oscilação postural de idosas

Este estudo investigou a influência de características do estímulo visual e o efeito da intenção nas respostas do controle postural frente à manipulação visual de adultas idosas. As 20 participantes permaneceram em pé em uma sala móvel durante sete tentativas com duração de 1 minuto cada, olhando para um alvo fixo, medindo-se sua oscilação corporal. Na primeira tentativa não houve qualquer movimento da sala, porém a partir da segunda a sala foi movimentada no sentido ântero-posterior. Para dez participantes, a velocidade de pico da movimentação foi de 0,6 cm/s e, para as demais, de 1,0 cm/s. A partir da quinta tentativa, as participantes foram informadas do movimento da sala e orientadas a resistir à movimentação. Os resultados indicam que a oscilação corporal das idosas é induzida pelo movimento da sala móvel. Intenção e alteração da característica do estímulo visual reduzem a influência da informação visual na oscilação corporal, mas a manipulação de propriedade do estímulo (neste caso, velocidade), é menos efetiva que a intenção. Essa maior dependência da intenção para alterar a influência de um estímulo sensorial no controle postural indica que o funcionamento do sistema de controle postural em idosos não possibilita ajustes automáticos de respostas posturais frente a pequenas variações das condições ambientais. Iinformações sobre tais variações podem ser direcionadas de forma a compensar essa diferença.

Processos adaptativos no sistema de controle postural de bebês, crianças e adultos: Paula Fávaro Polastri Zago. -

Pós-graduação em Ciências da Motricidade - IBRC

Age-related differences in postural control: effects of the complexity of visual manipulation and sensorimotor contribution to postural performance

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)