Comments on "The role of the human cerebellum in short- and long-term habituation of postural responses".
Explore the source record for details and available documents.
Cerebellar Diseases↗
SEARCH · PubMed Health
Results for “Postural Balance”
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The relationship of asymmetric weight-bearing with postural sway and visual reliance in stroke.
Due to motor and sensory deficits in individuals with stroke, we proposed that they must compensate for these impairments during standing with greater dependence on vision. In addition, we hypothesized that asymmetric weight-bearing, which occurs following stroke, is related to increased postural sway and those with greater asymmetry will have greater reliance on vision. Twenty-eight individuals with stroke and 28 healthy older adult controls stood quietly with eyes open (EO) or closed on a force platform while postural sway was quantified by centre of pressure measures and weight-bearing asymmetry was calculated from vertical ground reaction forces. To determine the influence of vision on postural sway, a visual ratio (eyes open/eyes closed (EC)) was calculated for the sway measures. The results demonstrated that individuals with stroke had greater visual dependence for the control of postural sway velocity in the medial-lateral (ML), but not anterior-posterior (AP) direction, compared to controls. Further, we found that greater asymmetry was moderately related to increased medial-lateral sway for the individuals with stroke. Contrary to predictions, those individuals with stroke with mild asymmetry had greater visual dependence than those with more severe asymmetry.
Case-Control Studies↗
The effect of anxiety on the regulation of upright standing among younger and older adults.
We tested the hypothesis that fall anxiety would differentially influence the regulation of upright standing among younger and among older adults. Fall anxiety was imposed by a manipulation of environmental context that increased the threat to postural control by introducing the potential for injurious consequences should a fall occur. Fifteen younger and 15 older adults participated in this study. Regardless of age, postural control was more conservative when fall anxiety increased, however, age did not affect how anxiety influenced the regulation of postural control. Our findings imply that the motor consequences of fall anxiety are no more pervasive for older adults than for younger adults, and that age does not alter the ability to accommodate to environmental demands that heighten fall anxiety.
Accidental Falls↗
Aging affects coordination of rapid head motions with trunk and pelvis movements during standing and walking.
The head, containing the gravity sensors (vestibular system) and the visual system, must be stabilized in space to provide a steady reference. During walking, the head also needs to be free to move to allow scanning of surrounding objects and steering of locomotion. With aging, deteriorations in motor and sensory systems and their integration are commonly observed. Nevertheless, the strategies used by elderly subjects to complete challenging tasks that require precise sensorimotor integration, such as turning the head rapidly during gait, is not known. The objective of this study was to determine the effects of aging on the movement coordination of the head, trunk and pelvis when executing a rapid head motion in response to a visual signal. Elderly and young subjects turned their head rapidly (up, down, left, right or none) in response to a visual signal, during standing and walking. The 3-D positions of head, trunk and pelvis were recorded and analyzed. All subjects, young and old, successfully performed the task during both standing and walking without any loss of balance. Postural stability was maintained as large head motions were accompanied by relatively small trunk and pelvis movements. Horizontal plane movements associated with right and left head turns were significantly larger than sagittal plane movements associated with head up and down motions. Head motions were significantly slower and smaller in elderly subjects, and resulted in disrupted horizontal plane trunk-pelvis coordination during walking. We conclude that head, trunk and pelvis movements are coordinated in a task-dependent manner such that their movement amplitudes induced by rapid voluntary head motions are larger in walking than in standing. This task-dependent movement coordination is affected by aging.
Adult↗
Insertion of the force applied to handles into centre of pressure calculation modifies the amplitude of centre of pressure shifts.
This study examined situations where handles were used as additional postural supports. It aimed at determining the amplitude of centre of pressure (COP) shifts when considering or not the vertical handles reaction force. Eight healthy male subjects (24+/-6 years, body mass 65+/-5kg and height 175+/-7cm) voluntarily took part in the experiment. Subjects had to voluntarily rock on their heels or rise on their toe-tips while using handles. The vertical component of the handles forces and ground reaction force was measured and the shifts of the COP were calculated while inserting or not the handles forces. Significant differences were observed when comparing the amplitude of COP shifts calculated with or without the insertion of the handles forces. This study shows that the measurement of the handles forces should not be omitted, for a rigorous analysis of postural tasks performed in conditions including additional postural supports like handles.
Adult↗
The influence of sensory information on two-component coordination during quiet stance.
When standing quietly, human upright stance is typically approximated as a single segment inverted pendulum. In contrast, investigations, which perturb upright stance with support, surface translations or visual driving stimuli have shown that the body behaves like a two-segment pendulum, displaying both in-phase and anti-phase patterns between the upper and lower body. We have recently shown that these patterns co-exist during quiet stance; in-phase and anti-phase for frequencies below and above 1 Hz, respectively. Here we investigated whether the characteristics of these basic patterns were influenced by the addition or removal of sensory information. Ten healthy young subjects stood upright on a rigid platform with different combinations of sensory information: eyes were open or closed with or without light touch contact (<1N) of the right index fingertip with a 5 cm diameter rigid force plate. The in-phase and anti-phase pattern co-exist in both the anterior-posterior (AP) and medial-lateral (ML) directions of sway. The real part of trunk-leg complex coherence decreased with the addition of vision and light touch, corresponding to a transition from the in-phase to anti-phase pattern at a lower frequency. In the AP direction, the decrease was only observed at frequencies below 1 Hz where the in-phase pattern predominates. Additional sensory information had no observable effect at sway frequencies above 1 Hz, where the anti-phase pattern predominates. Both patterns are clearly the result of a double-linked inverted pendulum dynamics, but the coherence of the in-phase pattern is more susceptible to modulation by sensory information than the anti-phase pattern.
Adult↗
Effects of explicit sway-minimization on postural--suprapostural dual-task performance.
Participants performed a visual search task under immersive visualization conditions while standing in open or closed stance. In the combined instruction condition, participants were asked to minimize their sway while they performed the search task, and in the search-only condition, they were advised that sway was not of interest, and they were asked to focus their efforts on performing the search task. Regardless of instructions, participants swayed more and made more errors as search load increased. Participants also succeeded in reducing their sway when asked to do so. While search in closed stance tended to be faster than in open stance under search-only instructions, this pattern reversed significantly under combined instructions. We suggest that neither the facilitatory control hypothesis nor any resource-competition model of postural--suprapostural dual-tasking can fully account for the observed interplay of task-facilitation and task-interference effects. We offer adaptive resource-sharing as an alternative to these theories.
Adolescent↗
Postural sway and joint kinematics during quiet standing are affected by lumbar extensor fatigue.
The purpose of this study was to investigate changes in postural sway and strategy elicited by lumbar extensor muscle fatigue. Specifically, changes in center of mass (COM), center of pressure (COP), and joint kinematics during quiet standing were determined, as well as selected cross correlations between these variables that are indicative of movement strategy. Twelve healthy male participants stood quietly both before and after exercises that fatigued the lumbar extensors. Whole-body movement and ground reaction force data were recorded and used to calculate mean body posture and variability of COM, COP, and joint kinematics during quiet standing. Three main findings emerged. First, participants adopted a slight forward lean post-fatigue as evidenced by an anterior shift of the COM and COP. Second, post-fatigue increases in joint angle variability were observed at multiple joints including joints distal to the fatigued musculature. Despite these increases, anterior-posterior (AP) ankle angle correlated well with AP COM position, suggesting the body still behaved similar to an inverted pendulum. Third, global measures of sway based on COM and COP were not necessarily indicative of changes in individual joint kinematics. Thus, in trying to advance our understanding of how localized fatigue affects movement patterns and the postural control system, it appears that joint kinematics and/or multivariate measures of postural sway are necessary.
Adult↗
Exploring the geometric and mechanical characteristics of the spine musculature to provide rotational stiffness to two spine joints in the neutral posture.
Joint stiffness is inherently linked to both performance and injury. Muscular activation is the predominant provider of stiffness to the lumbar spine, and is essential to ensure optimal spine performance. The purpose of the current paper was to examine the potential of the trunk muscles to provide rotational joint stiffness at two spine joints in the neutral posture, and to demonstrate the sensitivity of this stiffening potential to various muscle orientation and stiffness assumptions. Two separate anatomical models were utilized to analyze the muscular contributions to the 3-dimensional rotational stiffness about each of the L1-L2 and L4-L5 spine joints. Total muscular stiffening potentials, for both joints in each anatomical model, were found to be highest about the global lateral bend axis, and lowest about the global axial twist axis. The stiffening potential was found to depend highly on both the assumed muscle stiffness coefficient (q value) and the moment arm of the muscle about the joint in question. Analyses of spine stiffness were found to be greatly affected by both the anatomical representation of the surrounding musculature and the selection of the q value in the determination of muscular stiffness. Inappropriate choices of either of these factors could lead to errors in stiffness and subsequently stability estimates, and in the interpretation and possible clinical recommendations stemming from such estimates.
Biomechanical Phenomena↗
Effect of the posterior cruciate ligament on posterior stability of the knee in high flexion.
Most biomechanical studies of the knee have focused on knee flexion angles between 0 degrees and 120 degrees. The posterior cruciate ligament (PCL) has been shown to constrain posterior laxity of the knee in this range of flexion. However, little is known about PCL function in higher flexion angles (greater than 120 degrees ). This in vitro study examined knee kinematics before and after cutting the PCL at high flexion under a posterior tibial load and various muscle loads. The results demonstrated that although the PCL plays an important role in constraining posterior tibial translation at low flexion angles, the PCL had little effect in constraining tibial translation at 150 degrees of flexion under the applied loads.
Aged↗
An equation to calculate individual muscle contributions to joint stability.
The purpose of the current paper was to use the energy approach to develop a simplified equation for quantifying individual muscle contributions to mechanical stability about all three axes of a particular joint. Specific examples are provided for muscles acting about the lumbar spine's L4/L5 joint. The stability equation requires input of: (1) origin and insertion coordinates, relative to the joint of interest, (2) muscle force, and (3) muscle stiffness. The muscle force must be derived from a biomechanical analysis that first results in static equilibrium about all axes being studied. The equation can also accommodate muscles with nodes that change the line of action, with respect to a particular joint, as it passes from the origin to insertion. The results from this equation were compared to those from a Moment approach using more than two million simulated muscles with three-dimensional orientations. The differences between approaches were negligible in all cases. The primary advantage of the current method is that it is very easy to implement into any 2D or 3D biomechanical model of any joint, or system of joints. Furthermore, this approach will be useful in dissecting total joint stability into the individual contributions of each muscle for various systems, joints, postures and recruitment patterns.
Abdominal Muscles↗
Development and evaluation of an optimization-based model for power-grip posture prediction.
An optimization-based model for power-grip posture prediction was proposed. The model was based on the premise that the hand prehensile configuration in a power grip best conforms to the object shape. This premise was embodied by an optimization procedure that minimized the sum of distances from the finger joints to the object surface. The model was evaluated against data from an experiment that measured the grasp postures of 28 subjects having diverse anthropometry. The intra- and inter-person variabilities in grip postures were empirically assessed and used as benchmark values for model evaluation. The evaluation showed that the root-mean-square (RMS) values of angle differences between the predicted and measured postures had a 13.7 degrees grand mean (across all joints, subjects, and two cylindrical handles grasped), whereas the RMS values of the inter- and intra-person variabilities in measured postures had grand means of 13.0 degrees and 4.4 degrees , respectively. The model can be readily generalized to the prediction of postures in power-grasping objects of different shapes, and adapted for testing alternative prehensile strategies or performance criteria.
Adult↗
Intra-abdominal pressure increases stiffness of the lumbar spine.
Intra-abdominal pressure (IAP) increases during many tasks and has been argued to increase stability and stiffness of the spine. Although several studies have shown a relationship between the IAP increase and spinal stability, it has been impossible to determine whether this augmentation of mechanical support for the spine is due to the increase in IAP or the abdominal muscle activity which contributes to it. The present study determined whether spinal stiffness increased when IAP increased without concurrent activity of the abdominal and back extensor muscles. A sustained increase in IAP was evoked by tetanic stimulation of the phrenic nerves either unilaterally or bilaterally at 20 Hz (for 5 s) via percutaneous electrodes in three subjects. Spinal stiffness was measured as the force required to displace an indentor over the L4 or L2 spinous process with the subjects lying prone. Stiffness was measured as the slope of the regression line fitted to the linear region of the force-displacement curve. Tetanic stimulation of the diaphragm increased IAP by 27-61% of a maximal voluntary pressure increase and increased the stiffness of the spine by 8-31% of resting levels. The increase in spinal stiffness was positively correlated with the size of the IAP increase. IAP increased stiffness at L2 and L4 level. The results of this study provide evidence that the stiffness of the lumbar spine is increased when IAP is elevated.
Abdomen↗
Adaptive system identification applied to the biomechanical response of the human trunk during sudden loading.
Epidemiological evidence indicates that sudden loading of the torso is a risk factor for low back injury. Accurately quantifying the time-varying loading of the spine during sudden loading events and how these loading profiles are affected by workplace factors such as fatigue, expectation, and training can potentially lead to intervention strategies that can reduce these risks. Electromyographic and trunk motion data were collected from six male participants who performed a series of sudden loading trials with varying levels of expectation (no preview, 300-ms audible preview), fatigue (no fatiguing exertion preceding sudden load, short duration/high intensity fatiguing exertion preceding sudden load), and training (untrained, trained). These data were used as inputs to an adaptive system identification model wherein time-varying lower back stiffness, torque, work, and impulse magnitudes were calculated. Results indicated that expectation significantly increased peak and average stiffness by 70% and 113%, respectively, and significantly decreased peak torque, work, and impulse magnitudes by 36%, 50%, and 45%, respectively. Training significantly decreased peak torque and work by 25% and 34%, respectively. The results also showed a significant interaction between expectation and training wherein training had a positive effect during the trials with preview but no effect during the trials with no preview (increased peak stiffness by 17% and decreased impulse magnitude by 43%).
Abdomen↗
A model-based study of passive joint properties on muscle effort during static stance.
This study examined the impact of lower extremity joint stiffnesses and simulated joint contractures on the muscle effort required to maintain static standing postures after a spinal cord injury (SCI). Static inverse computer simulations were performed with a three-dimensional 15 degree of freedom musculoskeletal model placed in 1600 different standing postures. The required lower extremity muscle forces were calculated through an optimization routine that minimized the sum of the muscle stresses squared, which was used as an index of the muscle effort required for each standing posture. Joint stiffnesses were increased and decreased by 100 percent of their nominal values, and contractures were simulated to determine their effects on the muscle effort for each posture. Nominal muscle and passive properties for an individual with a SCI determined the baseline muscle effort for comparisons. Stiffness changes for the ankle plantar flexion/dorsiflexion, hip flexion/extension, and hip abduction/adduction directions had the largest effect on reducing muscle effort by more than 5 percent, while changes in ankle inversion/eversion and knee flexion/extension had the least effect. For erect standing, muscle effort was reduced by more than 5 percent when stiffness was decreased at the ankle plantar flexion/dorsiflexion joint or hip flexion/extension joint. With simulated joint contractures, the postural workspace area decreased and muscle effort was not reduced by more than 5 percent for any posture. Using this knowledge, methods can be developed through the use of orthoses, physical therapy, surgery or other means to appropriately augment or diminish these passive moments during standing with a neuroprosthesis.
Humans↗
Flexion-relaxation response to gravity.
The objective of this report was to study the influence of the orientation of gravitational loading on the behavior of anterior and posterior trunk muscles during anterior trunk flexion-extension. Participants (N=13) performed five (5) cycles of trunk flexion-extension while standing with gravity parallel to the body axis and five (5) cycles while in the supine condition (e.g. sit-ups) with gravity perpendicular to the body axis. Surface electromyographic (EMG) patterns from lumbar paraspinal, rectus abdominis, external oblique, rectus femoris, semimembranosis, and biceps femoris muscles were analyzed during each condition. EMG signals were synchronized with lumbar flexion and trunk inclination angles. Flexion-extension from the standing position resulted in a myoelectric silent period of the lumbar posterior muscles (e.g. flexion-relaxation phenomena (FRP)) as well as the hamstring muscles through deep angles during which activity was observed in abdominal muscles. Flexion-extension during sit-ups, however, resulted in a myoelectric silent period of the abdominal muscles and the quadriceps through deep angles during which the lumbar posterior muscles were active. In this condition, the FRP was not observed in posterior muscles. The new findings demonstrate the profound impact of the orientation of the gravity vector on the FRP, the abdominal muscles reaction to gravitational loads during sit-ups and its relationships with lumbar antagonists and thigh musculature. The new findings suggest that gravitational moments requirements dominate the FRP through the prevailing kinematics, load sharing and reflex activation-inhibition of muscles in various conditions. Lumbar kinematics or fixed sensory motor programs by themselves, however, are not the major contributor to the FRP. The new findings improve our insights into spinal biomechanics as well as understanding and evaluating low back disorders.
Adolescent↗
Role of reflex gain and reflex delay in spinal stability--a dynamic simulation.
The goal of this study was to investigate the role of reflex and reflex time delay in muscle recruitment and spinal stability. A dynamic biomechanical model of the musculoskeletal spine with reflex response was implemented to investigate the relationship between reflex gain, co-contraction, and stability in the spine. The first aim of the study was to investigate how reflex gain affected co-contraction predicted in the model. It was found that reflexes allowed the model to stabilize with less antagonistic co-contraction and hence lower metabolic power than when limited to intrinsic stiffness alone. In fact, without reflexes there was no feasible recruitment pattern that could maintain spinal stability when the torso was loaded with 200N external load. Reflex delay is manifest in the paraspinal muscles and represents the time from a perturbation to the onset of reflex activation. The second aim of the study was to investigate the relationship between reflex delay and the maximum tolerable reflex gain. The maximum acceptable upper bound on reflex gain decreased logarithmically with reflex delay. Thus, increased reflex delay and reduced reflex gain requires greater antagonistic co-contraction to maintain spinal stability. Results of this study may help understanding of how patients with retarded reflex delay utilize reflex for stability, and may explain why some patients preferentially recruit more intrinsic stiffness than healthy subjects.
Humans↗
Relative contribution of the pressure variations under the feet and body weight distribution over both legs in the control of upright stance.
The resultant centre of pressure (CP(Res)) trajectories are aimed at controlling body movements in upright stance. When standing on two legs, these trajectories are generated by exerting reaction forces under each foot and by loading-unloading mechanisms intervening at the hip level. To assess the respective contribution of each of these factors in stance maintenance, a group of healthy individuals were tested in several conditions including standing quietly and voluntarily producing under each foot larger CP displacements in phase and in opposite phase along medio-lateral (ML) and antero-posterior (AP) axes. The results, based on the computation of coefficients of correlation between CP(Res) trajectories and various time series including the relative body weight applied to one leg and plantar CP trajectories, highlight some differences according to the axes along which the displacements take place and the amplitudes of the movements. Furthermore, the comparison of the CP(Res) trajectories resulting from each one of these two factors reveals the predominant role played by the loading-unloading mechanisms intervening at the hip level for the movements along the ML axis and those of the plantar CP displacements along the AP axis. Increasing the plantar CP displacements in phase or in opposite phase substantially modifies these contributions although without inferring a shift to the benefit of the other mechanism. The specific morphology of the ankle and hip joints implicated in this postural task plainly explains this postural control organisation. In particular, the link between the segmental configuration of the lower limbs and these mechanisms are discussed.
Adult↗