PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “posture control model”

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.

At least 343 records · Page 19Linked to original sources
PubMedDate not supplied

[Motor cortex functions in the reorganization of postural coordinations].

A well-known function of the motor cortex (MCx) is control of the limb distal musculature, in particular, isolated finger movements during precise and fine hand movements. However, MCx has another function connected with the motor learning process, namely, a suppression of synergies and coordinations interfering with a movement being elaborated. This was shown for various limb movements. However, majority of movements is accompanied by postural adjustment as well. Two experimental models of rearrangement of an innate pattern of the postural adjustment were developed, and MCx was shown during such kind of learning to suppress the activity of structures providing the innate postural patterns. In contrast to the control of limb movements, the MCx influences were found to be bilateral for the postural pattern reorganization. It was revealed recently, however, that a possibility of recovery for the sequential MCx lesions depends on the sequence of the lesions, so, perhaps the role of MCx of different hemispheres in the compensation is different.

Animals↗
PubMed1990

Early behavioral development in capuchins (Cebus).

Capuchin infants (genus Cebus) are born in a behaviorally more altricial state than is known for infants of other primate taxa except apes. Development in the first 2 months after birth is characterized by the major reorganization of sleeping and waking, assumption of postural control and the appearance of prehension. Capuchins develop postural control, prehension and locomotion later than do squirrel monkeys, baboons or macaques, presenting a pattern of motor development intermediate between these relatively more precocial genera and apes. Capuchins provide a useful model primate system in which to study development and its links with behavioral variability and life history.

Animals↗
PubMed2004

Evaluation of head-to-trunk control in whiplash patients using digital CranioCorpoGraphy during a stepping test.

We used digital-CranioCorpoGraphy (dCCG) to document whiplash effects on head-on-trunk stabilization while subjects walked on the spot (Fukuda test). Twenty-five healthy subjects were compared with 33 whiplash patients. Whiplash patients were classified as chronic (more than 6 months after injury) and recent (less than 6 months after injury). Clear differences between healthy subjects and patients were seen and three different strategies were detected. Pattern A appeared similar to normals but quantitative analysis showed significant differences with paradoxical head over-stabilization (collar-effect); pattern B decreased head stability; pattern C decreased head stabilization with reduced displacements of the body. Due to the complexity of the data analyzed for each marker, a coefficient of performance (CP) was calculated to simplify the cut-off between normal and pathological tests. CP clearly identified an abnormal stepping pattern. Our findings indicate that firstly dCCG identified a specific vestibular task in whiplash patients, secondly whiplash did not always provoke vestibular involvement and thirdly dCCG could be a tool to discriminate patients with and without vestibular involvement after whiplash.

Acute Disease↗
PubMed2000

Effects of respiration and gravity on infradiaphragmatic venous flow in normal and Fontan patients.

BACKGROUND: In the Fontan circulation, pulmonary and systemic vascular resistances are in series. The implications of this unique arrangement on infradiaphragmatic venous physiology are poorly understood. METHODS AND RESULTS: We studied the effects of respiration and gravity on infradiaphragmatic venous flows in 20 normal healthy volunteers (control) and 48 Fontan patients (atriopulmonary connection [APC] n=15, total cavopulmonary connection [TCPC] n=30). Hepatic venous (HV), subhepatic inferior vena caval (IVC), and portal venous (PV) flow rates were measured with Doppler ultrasonography during inspiration and expiration in both the supine and upright positions. The inspiratory-to-expiratory flow rate ratio was calculated to reflect the effect of respiration, and the supine-to-upright flow rate ratio was calculated to assess the effect of gravity. HV flow depended heavily on inspiration in TCPC compared with both control and APC subjects (inspiratory-to-expiratory flow rate ratio 3.4, 1.7, and 1.6, respectively; P:<0.0001). Normal PV flow was higher in expiration, but this effect was lost in TCPC and APC patients (inspiratory-to-expiratory flow rate ratio 0.8, 1.0, and 1.1, respectively; P:=0.01). The respiratory influence on IVC flow was the same in all groups. Gravity decreased HV flow more in APC than in TCPC patients (supine-to-upright flow rate ratio 3.2 versus 2.1, respectively; P:<0.04) but reduced PV flow equally in all groups. CONCLUSIONS: Gravity and respiration have important influences on infradiaphragmatic venous return in Fontan patients. Although gravity exerts a significant detrimental effect on lower body venous return, which is more marked in APC than in TCPC patients, the beneficial effects of respiration in TCPC patients are mediated primarily by an increase in HV flow. These effects may have important short- and long-term implications for the hemodynamics of the Fontan circulation.

Adolescent↗
PubMed2006

A systematic review of the methodology of telemedicine evaluation in patients with postural and movement disorders.

We reviewed the methodology used in telemedicine research concerning patients with postural and movement disorders. Literature searches were performed using various computerized databases through to October 2005. Twenty-two studies met the criteria for review. Two broad models of telemedicine delivery were represented in the literature: (1) telemedicine between health-care professionals at each telemedicine site (n=16) and (2) telemedicine between health-care professionals and a patient at a remote site (n=6). Disparate research methodologies were used to investigate these two models. Most studies were limited to investigating the technical feasibility and acceptability of a telemedicine service rather than focusing on the overall effect of introducing the telemedicine service into routine health care. Nonetheless, it is possible to conclude that telemedicine is acceptable for both patients and professionals when used in rehabilitation. Since the two models of telemedicine evaluation tend to explore different outcomes (diagnostic accuracy versus health status), it is recommended that separate methodologies should be used. In contrast to evaluations of telemedicine model 2, randomized controlled trials appear to be less valuable for telemedicine model 1.

Delivery of Health Care↗
PubMed2006

Is equilibrium point control feasible for fast goal-directed single-joint movements?

Several types of equilibrium point (EP) controllers have been proposed for the control of posture and movement. EP controllers are appealing from a computational perspective because they do not require solving the "inverse dynamic problem" (i.e., computation of the torques required to move a system along a desired trajectory). It has been argued that EP controllers are not capable of controlling fast single-joint movements. To refute this statement, several extensions have been proposed, although these have been tested using models in which only the tendon compliance, force-length-velocity relation, and mechanical interaction between tendon and contractile element were not adequately represented. In the present study, fast elbow-joint movements were measured and an attempt was made to reproduce these using a realistic musculoskeletal model of the human arm. Three types of EP controllers were evaluated: an open-loop alpha-controller, a closed-loop lambda-controller, and a hybrid open- and closed-loop controller. For each controller we considered a continuous version and a version in which the control signals were sent out intermittently. Only the intermittent hybrid EP controller was capable of generating movements that were as fast as those of the subjects. As a result of the nonlinear muscle properties, the hybrid EP controller requires a more detailed representation of static muscle properties than generally assumed in the context of EP control. In sum, this study shows that fast single-joint movements can be realized without explicitly solving the inverse dynamics problem, but in a less straightforward manner than implied by proponents of conventional EP controllers.

Adult↗
PubMed2005

Association between lower extremity posture at contact and peak knee valgus moment during sidestepping: implications for ACL injury.

BACKGROUND: Knee valgus load during sports movement is viewed as an important predictor of non-contact anterior cruciate ligament injury risk, particularly in females. Formulating movement strategies that can reduce valgus loading during these movements therefore appears pertinent to reducing anterior cruciate ligament injury rates. With this in mind, the current study examined the relationship between peak valgus moment and lower extremity postures at impact during a sidestep cutting task. METHODS: Ten male and ten female NCAA athletes had initial contact three-dimensional hip, knee and ankle angles and subsequent knee valgus moment quantified during the execution of (n=10 trials) sidesteps. Peak valgus data were normalized to mass and height and tested for the main effect of gender (ANOVA, P<0.05). Intra-subject correlations between the eight initial joint angles and the normalized valgus moment were then conducted across the ten sidestepping trials. The ensuing slopes of regression were submitted to a two-sample t-test to determine whether mean slope values were significantly different from zero and for the main effect of gender (P<0.05). FINDINGS: Females had significantly larger normalized knee valgus moments than males. A greater peak valgus moment was associated with larger initial hip flexion and internal rotation, and with larger initial knee valgus angle. Peak knee valgus moment was more sensitive to initial hip internal rotation and knee valgus position in females. INTERPRETATION: Training of neuromuscular control at the hip joint may reduce the likelihood of anterior cruciate ligament injury via a valgus loading mechanism during sidestepping, especially in females.

Adult↗
PubMed2000

Central control components of a 'simple' stretch reflex.

The monosynaptic stretch reflex is a fundamental feature of sensory-motor organization in most animal groups. In isolation, it serves largely as a negative feedback devoted to postural controls; however, when it is involved in diverse movements, it can be modified by central command circuits. In order to understand the implications of such modifications, a model system has been chosen that has been studied at many different levels: the crayfish walking system. Recent studies have revealed several levels of control and modulation (for example, at the levels of the sensory afferent and the output synapse from the sensory afferent, and via changes in the membrane properties of the postsynaptic neuron) that operate complex and highly adaptive sensory-motor processing. During a given motor task, such mechanisms reshape the sensory message completely, such that the stretch reflex becomes a part of the central motor command.

Animals↗
PubMed1980

Optimal and adaptive control in canine postural regulation.

For analytic purposes, dogs trained to stand quietly on an oscillating platform can be likened to a fixed-length inverted pendulum with a point mass. Describing function analysis permitted derivation of torque and error values as functions of phase and gain relative to platform movement. A phase criterion was determined for minimization of either control torque at a given error amplitude or error at a given control torque amplitude. Describing functions for dogs with and without vision approached optimal phase. Stretch reflex control involving proportional-plus-rate feedback is not sufficient to account for the approach to optimal phase. Blindfolded labyrinthectomized dogs did not exhibit optimal behavior and the phase constraint for stretch reflex control was satisfied at most frequencies. The observed behavior is best accounted for by a model involving both otolith and visual feedforward (pursuit-precognitive) control processes. Reductions in phase lag by blindfolded dogs during the first few cycles of platform motion provide evidence of adaptive control.

Animals↗
PubMed1996

The influence of different sitting positions on cervical and lumbar posture.

STUDY DESIGN: This study used a repeated measures design to assess the effects of multiple sitting postures on various spinal angles. All subjects were tested in slouched, erect, forward inclined, and comfortable postures. OBJECTIVES: The purposes of this study were to evaluate the changes in head, cervical, lumbar, and pelvic postures in different sitting positions and also to determine if there is a relation between lumbar posture and cervical posture during sitting. SUMMARY OF BACKGROUND DATA: Clinicians commonly assert that head and neck position is strongly influenced by lumbar and pelvic position. A biomechanical model was developed that allowed detailed, quantitative description of head, neck, lumbar, and pelvic postures. This model enabled a distinction to be made between upper and lower cervical motions. METHODS: Various spinal angles were measured in 30 healthy subjects in four sitting positions using a three-dimensional digitizing system. Reliability of the measurement procedure was determined using an intraclass correlation coefficient and the values for most angles was above 0.8. RESULTS: With the exception of head orientation, analysis of variance revealed significant differences in spinal angles between different sitting positions. Head orientation appeared to be maintained by compensatory adjustments in both the upper and lower cervical spine and changes in lumbar posture were associated with compensatory changes in overall cervical position. As the lumbar spine moved toward extension, the cervical spine flexed and as the lumbar spine flexed the cervical spine extended. However, there was variation among subjects as to whether cervical spine adjustments occurred primarily in the upper or lower cervical region. CONCLUSIONS: Different sitting postures clearly resulted in changes in cervical spine position. Lumbar and pelvic position should be considered when control of cervical posture is desired.

Adult↗
PubMed2002

A method for assessing balance control in rodents.

Recent research has shown that after spinal cord injury, the nervous system reorganizes. Nevertheless, little is known of the effects of neural reorganization, or plasticity, on motor skills. In this work, we present a method that utilizes kinetic and kinematic analysis, for investigating balance control in a rodent model of incomplete spinal cord injury. In this setup, the animals sit unconstrained on their hindlimbs on a platform while they eat a Fruitloop. In this posture, the animal is supporting all the body weight on its hindquarters removing the need for the animal to support itself on its hindlimb or maintain appropriate forelimb-hindlimb coordination for functional gait. The platform is bolted to a force transducer to provide measurements of shear forces in orthogonal directions in the horizontal plane. Reflective markers on the hip and tail of the animal indicate sway of the animals body. Using this method the effect of extensive 12 week long treadmill locomotor training on balance control in rodents with incomplete thoracic spinal cord contusion injury (iSCI) was assessed. One iSCI rat did not undergo training, while a sham injured and 3 other iSCI rats underwent training. The shear forces and sway produced by the injured untrained rat were much larger than for the sham or the injured but trained rats. Stance width assessed from overground walking in a separate study was also larger in the injured untrained rat. These data suggest that balance control may be improved by a locomotor training paradigm. This simple method for assessing balance control could thus be utilized in longitudinal studies to evaluate the effectiveness of pharmacological and locomotor therapies for repair and recovery after spinal cord injury.

Animals↗
PubMed2000

Middle-ear influence on otoacoustic emissions. II: contributions of posture and intracranial pressure.

Although it seems likely that body tilt or surgically provoked variations in intracranial pressure (ICP) can result in variations of intralabyrinthine pressure, the channels for pressure transmission remain controversial and the reasons why evoked otoacoustic emissions (EOAEs) exhibit attendant modifications are unclear. The theoretical framework implemented in the companion paper [Avan et al. part I, 2000] provides sensitive and non-invasive means to identify the middle-ear mechanism(s) entailed in EOAE changes. It was thus applied to analyze the influence of posture on EOAE phases and magnitudes as a function of frequency, in a series of experiments involving body tilt from sitting to supine (0 degrees or -30 degrees ). Controlled ICP variations were surgically carried out in a series of hydrocephalic patients and the resulting EOAE changes were compared to posture data and model predictions. In all cases, the EOAE changes closely resembled those due to an increase in the stiffness of the stapes' annular ligament, in keeping with the assumption that ICP gets transmitted to intralabyrinthine spaces and modifies the hydrostatic load on the stapes, thereby influencing EOAE features. A small additional contribution of middle-ear pressure to EOAE changes was identified in addition to the main stapes component. Dynamical EOAE measurements showed that sudden ICP changes were transmitted to the inner ear within 8-30 s. The high sensitivity of EOAE phases below 2 kHz to ICP changes, together with the absence of any significant confounding middle-ear effect, favors EOAEs for a reliable non-invasive monitoring of ICP and intralabyrinthine pressures.

Acoustic Impedance Tests↗
PubMed2000

Adaptive plasticity in vestibular influences on cardiovascular control.

Data collected in both human subjects and animal models indicate that the vestibular system influences the control of blood pressure. In animals, peripheral vestibular lesions diminish the capacity to rapidly and accurately make cardiovascular adjustments to changes in posture. Thus, one role of vestibulo-cardiovascular influences is to elicit changes in blood distribution in the body so that stable blood pressure is maintained during movement. However, deficits in correcting blood pressure following vestibular lesions diminish over time, and are less severe when non-labyrinthine sensory cues regarding body position in space are provided. These observations show that pathways that mediate vestibulo-sympathetic reflexes can be subject to plastic changes. This review considers the adaptive plasticity in cardiovascular responses elicited by the central vestibular system. Recent data indicate that the posterior cerebellar vermis may play an important role in adaptation of these responses, such that ablation of the posterior vermis impairs recovery of orthostatic tolerance following subsequent vestibular lesions. Furthermore, recent experiments suggest that non-labyrinthine inputs to the central vestibular system may be important in controlling blood pressure during movement, particularly following vestibular dysfunction. A number of sensory inputs appear to be integrated to produce cardiovascular adjustments during changes in posture. Although loss of any one of these inputs does not induce lability in blood pressure, it is likely that maximal blood pressure stability is achieved by the integration of a variety of sensory cues signaling body position in space.

Afferent Pathways↗
PubMed2004

Dynamics, stability, and control of stepping.

The dynamics, stability, and control of stepping are considered. The role of internal models is elaborated. The main objective of the paper is to provide a better understanding of the machinery and processing in the central nervous system (CNS) that relates to stepping. The role of the vestibular system in balance and balance recovery is described. Balance and balance recovery are essential in stepping, and guarantee the stability of the system before, during, and after stepping. In sagittal standing, humans use two distinct sets of control strategies to maintain their postural stability in response to external disturbance. In one set of strategies, the configuration of the base of support, namely, the position of the feet, remains unchanged. The ankle and hip strategies are examples of postural adjustments where the feet do not move. When the disturbances are large, and move the center of mass or pressure outside the support boundaries, stepping strategies are required. A simple control strategy is proposed for illustrative purposes. Its effectiveness is verified by computer simulation of a seven-link two-dimensional sagittal biped. The applications of the model in assessing trauma and injury are discussed.

Computer Simulation↗
PubMed1986

A structural model of the thoracic cage in the cat.

A homogeneous shell model of the mechanical characteristics of the thoracic cage in the cat is presented. The global characterization proposed parallels the characterization--presented elsewhere--of the motor control of the intercostal musculature in terms of a conceptual spatially continuous control function, that underlies the discretely distributed muscular activity and reflects an inferred global dynamic control of the intercostal muscles during breathing. Proposing a static, homogeneous shell characterization of the thoracic cage, which is heterogeneous and composed of an assembly of mobile structures, implies assuming that other elements are indirectly giving this system features that make it resemble, from a structure analysis point of view, a homogeneous, static one. The pattern of the lines of stress along the shell structure proposed as a model compares favourably with the shape of the ribs. In agreement with previous findings, supporting the need for muscular activity to satisfy demands of purely structural character, it is suggested that this global shell-like functional character is achieved by neuromuscular global dynamic integration of the components of the rib cage by the nervous control of the intercostal muscles.

Animals↗
PubMed1998

Large scale stereopsis and optic flow: depth enhanced by speed and opponent-motion.

To understand better the range of conditions supporting stereoscopic vision, we explored the effects of speed, as well as specific optic flow patterns, on judgments of the depth, near or far of fixation, of large targets briefly presented in the upper periphery. They had large disparities (1-6 deg) and moved at high speeds (20-100 deg/sec). Motion was either vertical or horizontal, as well as either unidirectional or layered in bands of alternating directions (opponent-motion). High stimulus speeds can extend dmax. The effects are explained by models having linear filters that signal both faster speeds and larger disparities. Stereo depth localization can also be enhanced by opponent-motion even when kinetic depth itself is not apparent. Improvements are greatest with wide-field, horizontal opponent-motion. The results imply functions such as vection, posture-control, and vergence may benefit from disparity information enhanced by optic flow patterns that are commonly available to a moving, binocular observer.

Depth Perception↗
PubMedDate not supplied

ISMAR: an autotherapeutic device assisting patients from drooling to articulated speech.

This overview of three decades of clinical experience with oral therapies complemented by oral devices-vestibular screens (VS) and ISMARs (Innsbruck sensory motor activators and regulators)-tries to put these devices into an oral functional context including postural control of mobile structures both inside and outside the mouth-down to the feet. ISMARs have certain unique features which teach a person not only better postural control of the lower jaw and, hence, hyoid bone and tongue, but also to stimulate movements of lips and tongue to improve salivary control, functions of eating and drinking and the domain of communication, e.g. facial movements and articulation of speech. A review of the relevant postural background is provided and the mechanisms are explained and may serve as models for other oral therapies. The inter-relation and multi-functionality of muscular connections throughout the body explains the uniformity of facial, oral and pharyngeal dysfunctions in different conditions such as cerebral palsy, Moebius syndrome, chronic nasal congestion or developmental retardation and exposes patients with oral dysfunctions to the risks of vicious circles. However, at the same time the opportunity is given to trigger beneficious circles. Three principles of postural control in and for the neck region are postulated. Clinical observations and experiments with volunteers are described and some supporting information is given-hopefully enough to stimulate clinical work and give rise to further experimental work to illuminate this field which is extremely important for both human communication and inter-relation.

Activator Appliances↗