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PubMed1998

Postural motor programming in paraplegic patients during rehabilitation.

One of the basic aims in the rehabilitation of thoracic spinal cord injured (SCI) patients concerns the regaining of sitting posture control. This implies the development of new postural strategies requiring the adjustment of motor programming processes. The aim of this study was to investigate the time course of postural reorganization during active, clinical rehabilitation of thoracic SCI patients with different SCI levels. Thus changes in motor programming in sitting balance control were investigated in two groups of complete low or high thoracic SCI patients. At several stages during the rehabilitation process an experiment was held in which sitting posture was perturbed systematically using submaximal reaching movements over four reaching distances. This bimanual reaching task was presented as a visual precue choice reaction time (RT) task in which reaching distance (i.e. grade of postural perturbation) was precued. Results indicated that in both high and low thoracic SCI patients RTs in movements involving postural perturbation became shorter during the course of the rehabilitation period. However, low thoracic SCI patients were generally slower in the programming of balance perturbing movements than high thoracic SCI patients, a phenomenon that did not change over time. Furthermore, initial differences in RTs as a function of grade of postural perturbation disappeared in both groups in the course of the rehabilitation phase. Precue benefit, equally large for both groups, did not change as a function of rehabilitation time. It is concluded that the observed phenomena signify the gradual development of new central postural control processes in both SCI groups during rehabilitation. Low thoracic SCI patients, having more residual sensorimotor functions, seem to adopt more complex strategies in maintaining and restoring sitting balance that take longer to specify and to programme. High thoracic SCI patients seem to rely on simpler strategies using more passive postural support.

Adolescent↗
PubMed2004

Development of a virtual reality environment for somatosensory and perceptual stimulation in the balance assessment of children.

In this study, we developed a balance assessment system in which the visual stimulus was generated by a virtual reality (VR) technique and somatosensation was obtained from a movable platform. By standing on the movable platform, the center of pressure (COP) was measured to express the subject's postural control in response to varied visual stimuli. From the COP data, a singular value decomposition technique was used to derive the sway area and direction, represented in a polar form. Our system demonstrated the feasibility of using a VR environment in postural control trials and provided more realistic somatosensory and visual inputs.

Adolescent↗
PubMed2001

Human multisensory fusion of vision and touch: detecting non-linearity with small changes in the sensory environment.

Previous investigations using relatively large amplitude sensory stimuli or complete removal of sensory input have demonstrated non-linear processing of sensory information for postural control. In the present study, we asked whether a linear range of sensory fusion exists when smaller amplitude stimuli are used. The amplitudes of visual and somatosensory input were simultaneously co-varied within a trial. The postural responses were characterized by analyzing how the Fourier transform of postural sway at the driving frequency varied with sensory movement amplitudes. If the postural control system is linear with constant weighting of sensory inputs, then the pattern of Fourier transforms should be a linear function of movement amplitude. However, in 28 of 58 trials we observed non-linearity in this function. The results clearly show that even at very small amplitudes of sensory change, the nervous system processes multisensory information in a non-linear fashion.

Fourier Analysis↗
PubMed1989

Evaluation of a generalized model of human postural dynamics and control in the sagittal plane.

A two-step identification method is used to evaluate a generalized model of human postural control in the sagittal plane. Postural dynamics are represented as a planar open-chain linkage system supported by a triangular foot. The control mechanism is modeled as a state feedback element in which the torque acting at a given link is an arbitrary function of the state variables--angles and angular velocities. To validate the approach, six normal subjects underwent two series of experiments. The first series were used to determine an appropriate model of the system dynamics. The second series were used to estimate the parameters of the feedback model. A computer simulation of the complete system shows that the model predictions closely match the observed responses. These results suggest that the proposed model provides a useful framework for analysis of postural control mechanisms.

Computer Simulation↗
PubMed2003

Postural sway in normal subjects aged 20-70 years.

So far, no population-based reference material of postural sway has been presented in the literature. This study evaluated postural control by measuring posturographic parameters, with the aim of establishing useful standards with regard to gender, age, body weight, cigarette smoking, alcohol consumption and articular hypermobility. This was performed in an age-stratified random sample of 195 subjects from the Copenhagen City Heart Study, of whom, 133 agreed to participate. Measurement of postural sway was performed the Balance Master Pro(R). Outcome parameters were average angular velocity, target sway area, per cent maximum stability and per cent ankle strategy. Using SAS Proc Mixed, backward stepwise elimination was performed and 95% prediction intervals were obtained. Sway increased with increasing difficulty of the test (P<0.001) and with increasing age (P<0.001). No differences were found between the sexes. Ankle-strategy did not change with age, but decreased with increasing body weight, and increased in subjects reporting a consumption of modest amounts of alcohol (P<0.001), or with the finding of increased hypermobility (P = 0.006). The present material may be used as a reference in further studies of postural control.

Adult↗
PubMed1980

Anticipatory control of postural and task muscles during rapid arm flexion.

A multicomponent pattern of premovement (anticipatory) activity in both task and postural muscles was examined for a unilateral rapid arm flexion movement (Belen'kii, Gurflnkel, & Pal'tsev, 1967) performed under simple visual reaction-time conditions. Subjects performed 30 right- and 30 left-side responses on each of four consecutive days. The anticipatory postural muscle activity may be considered a valid component of voluntary unilateral arm flexion. Invariances and variability in the spatial and temporal characteristics of the neuromuscular pattern are described in relationship to behavioral and motor control models of response organization. It is suggested that some temporal patterning among response components may not be preprogrammed centrally.

Journal Article↗
PubMed1970

Behavioral engineering: control of posture by informational feedback.

The effects of informational feedback on a socially undesirable behavior were studied. The feedback was a mild vibrotactile stimulus and the response was slouching. When subjects slouched, a behavioral engineering apparatus provided vibrotactile stimulation to the shoulder. All subjects slouched less when stimulation was provided. A procedural control revealed that slouching will decrease because of the informational aspect of the stimulus consequence and not because of its aversive properties. When the subjects were instructed to slouch, the effects of feedback were reversed: feedback increased, rather than decreased, slouching. These results indicate that the effect of feedback for a response depends on the subject's motivation to perform that response. It is suggested that informational feedback could be used more widely as a therapeutic procedure to modify human behaviors, but only those behaviors that a patient is strongly motivated to change.

Journal Article↗
PubMed1997

Bronchopulmonary dysplasia: a comparative study of motor development to two years of age.

This study investigated the influence of bronchopulmonary dysplasia (BPD) on the motor development of children in the first two years of life. Sixty-four children with BPD and 53 control infants were assessed at eight months and two years corrected for prematurity using the neuro-sensory and motor development assessment (NSMDA). Results indicated a significant delay in gross motor performance of the study children at eight months. By two years, considerable catch-up had occurred, but a significant difference in postural control and balance between the study and control groups was identified. When corrected for periventricular haemorrhage and ventricular dilatation, although substantial, the difference was not statistically significant. When growth <10th centile was considered in the study infants, postural control, overall motor performance and neurological status were significantly less than in those whose growth was within normal limits.

Journal Article↗
PubMed2004

Exercise programs for older men: mode and intensity to induce the highest possible health-related benefits.

BACKGROUND: Although health-related benefits of fitness training in older men are well established, it is not clear yet which mode and intensity of a exercise program is most effective. This study addresses whether the combination of endurance (ED) and resistance training in older men have supplementary health-related benefits in addition to profits attained through endurance training alone. Additionally, effects of moderate- and low-intensity resistance training are compared. METHODS: Men, 55-75 years of age, were randomly assigned to a control group (N = 13) or one of three exercise groups (20 weeks, two to three times per week): endurance plus moderate resistance (MR) training (N = 22), endurance plus low resistance (LR) training (N = 22) and endurance training only (N = 22). Cardiovascular (CV) risk factors, muscular fitness and postural control were assessed before and after training. RESULTS: All exercise groups revealed significant (P < 0.05) improvements in resting heart rate, work capacity and recovery, waist girth, insulin response and knee-extensor strength with no differences among groups. Body composition, resting metabolic rate (RMR), VO2peak and postural control did not change in exercise groups. CONCLUSION: In older men, a fitness program consisting of 20 weeks endurance training combined with resistance training is equally effective as endurance training alone. Moderate vs. low resistance training added to endurance training yields similar health-related benefits.

Aged↗
PubMed2003

Recovery of standing balance and functional mobility after stroke.

OBJECTIVE: To examine the extent to which recovery of functional balance and mobility is accompanied by change in a few specific physiologic measures of postural control. DESIGN: Longitudinal prospective study. SETTING: Laboratory setting in Ontario. PARTICIPANTS: Twenty-seven volunteers (age, 64.2+/-13.7y) undergoing 4 weeks of rehabilitation after stroke participated. At initial testing, patients were 32.7+/-18.4 days poststroke and exhibited a moderate level of motor recovery (lower-extremity and postural control, stages 3-4 on the Chedoke-McMaster Stroke Assessment Impairment Inventory). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Three functional measures (Berg Balance Scale, Clinical Outcome Variables Scale, gait speed) were assessed. Three physiologic measures (electromyographic data of hamstrings and soleus muscles bilaterally, postural sway, arm acceleration) were taken while subjects stood quietly on a force platform and while they performed a rapid shoulder flexion movement of the nonparetic upper extremity. RESULTS: After 1 month of rehabilitation, there was an overall significant improvement in all outcome measures (functional, physiologic). However, 10 patients failed to show any improvement in the electromyographic activation of hamstrings muscle on the paretic side in response to the rapid arm movement. These patients compensated by increasing the anticipatory activation of the nonparetic hamstrings. CONCLUSION: After stroke, patients showed improvement in both physiologic and functional measures of balance and mobility over a 1-month period. We have identified some patients who may be using compensatory strategies to increase function. The factors that may predict those patients who are likely to use compensatory strategies awaits further study.

Aged↗
PubMed1995

Postural responses to platform perturbation: kinematics and electromyography.

Dynamic postural control may be studied using feedback paradigms which disturb standing balance. In this study the kinematics and electromyography of the reaction to an unexpected slip were examined simultaneously in 16 young, healthy volunteers to characterize the response to postural perturbation in the context of the perturbation characteristics. Kinematically, results showed ankle plantarflexion, knee flexion, hip extension, and shoulder flexion. Electromyographically, sequences of activation of the postural muscles of the leg were primarily anterior distal. Data is presented that supports a new model of the reaction to perturbation which incorporates the timing and type of muscular activity, the type of motion (active or passive), and the perturbation characteristics. RELEVANCE--:Understanding the interplay of the neurophysiological and biomechanical aspects of dynamic postural control gives insight into balance reactions. Simultaneous consideration of the kinematics, muscle activation, and perturbation characteristics allows a more comprehensive view of recovery of balance.

Journal Article↗
PubMed2003

Studies on vestibular organs in the fry of mutant Medaka.

We provide an overview of the features of vestibular organs, especially of otolith organs in mutant Medaka ha. The ha fish have a dysfunction in sensing gravity due to the absence of utricular otoliths either unilaterally or bilaterally. Especially in their early developmental stages, the posture control is predominantly depend on light rather than on gravity seen in the wild-type. The ha juveniles that were kept and tolerated in an environment with altered light directions indicated a strong light dependency on the posture maintenance, while the fish under an ordinary light environment gradually changed their posture control by sensing light to gravity around 30 days after hatching and beyond. Their behavior under microgravity agreed with such phenomena observed in ground laboratory.

Animals↗
PubMed1997

Influence of visual control, conduction, and central integration on static and dynamic balance in healthy older adults.

Aging is associated with decreased balance abilities, resulting in an increased risk of fall. In order to appreciate the visual, somatosensory, and central signals involved in balance control, sophisticated methods of posturography assessment have been developed, using static and dynamic tests, eventually associated with electromyographic measurements. We applied such methods to a population of healthy older adults in order to appreciate the respective importance of each of these sensorial inputs in aging individuals. Posture control parameters were recorded on a force-measuring platform in 41 healthy young (age 28.5 +/- 5.9 years) and 50 older (age 69.8 +/- 5.9 years) adults, using a static test and two dynamic tests performed by all individuals first with eyes open, then with eyes closed. The distance covered by the center of foot pressure, sway area, and anteroposterior oscillations were significantly higher, with eyes open or closed, in older people than in young subjects. Significant differences were noted in dynamic tests with longer latency responses in the group of old people. Dynamic recordings in a sinusoidal test had a more regular pattern when performed eyes open in both groups and evidenced significantly greater instability in old people. These data suggest that vision remains important in maintaining postural control while conduction and central integration become less efficient with age.

Adult↗
PubMed1997

Altered astronaut lower limb and mass center kinematics in downward jumping following space flight.

Astronauts exposed to the microgravity conditions encountered during space flight exhibit postural and gait instabilities upon return to earth that could impair critical postflight performance. The aim of the present study was to determine the effects of microgravity exposure on astronauts' performance of two-footed jump landings. Nine astronauts from several Space Shuttle missions were tested both preflight and postflight with a series of voluntary, two-footed downward hops from a 30-cm-high step. A video-based, three-dimensional motion-analysis system permitted calculation of body segment positions and joint angular displacements. Phase-plane plots of knee, hip, and ankle angular velocities compared with the corresponding joint angles were used to describe the lower limb kinematics during jump landings. The position of the whole-body center of mass (COM) was also estimated in the sagittal plane using an eight-segment body model. Four of nine subjects exhibited expanded phase-plane portraits postflight, with significant increases in peak joint flexion angles and flexion rates following space flight. In contrast, two subjects showed significant contractions of their phase-plane portraits postflight and three subjects showed insignificant overall changes after space flight. Analysis of the vertical COM motion generally supported the joint angle results. Subjects with expanded joint angle phase-plane portraits postflight exhibited larger downward deviations of the COM and longer times from impact to peak deflection, as well as lower upward recovery velocities. Subjects with postflight joint angle phase-plane contraction demonstrated opposite effects in the COM motion. The joint kinematics results indicated the existence of two contrasting response modes due to microgravity exposure. Most subjects exhibited "compliant" impact absorption postflight, consistent with decreased limb stiffness and damping, and a reduction in the bandwidth of the postural control system. Fewer subjects showed "stiff" behavior after space flight, where contractions in the phase-plane portraits pointed to an increase in control bandwidth. The changes appeared to result from adaptive modifications in the control of lower limb impedance. A simple 2nd-order model of the vertical COM motion indicated that changes in the effective vertical stiffness of the legs can predict key features of the postflight performance. Compliant responses may reflect inflight adaptation due to altered demands on the postural control system in microgravity, while stiff behavior may result from overcompensation postflight for the presumed reduction in limb stiffness inflight.

Acceleration↗
PubMed2005

Differential anaesthetic effects following microinjection of thiopentone and propofol into the pons of adult rats: a pilot study.

Identifying the central nervous system sites of action of anaesthetics is important for understanding the link between their molecular actions and clinical effects. The aim of the present pilot study was to compare the anaesthetic effect of bilateral microinjections of propofol and thiopentone (both 200 microg/microl, in Intralipid and 0.9% saline respectively) into a recently discovered anaesthetic-sensitive region in the rat brainstem, the "mesopontine tegmental anaesthetic area" (MPTA). Microinjections (1 microl per side) were made into the MPTA of fifteen male Sprague-Dawley rats. The effect of each agent on spontaneous behaviour, postural control and nociceptive responsiveness was subjectively assessed according to established criteria. The main finding was that thiopentone induced an "anaesthesia-like" state, including complete atonia and loss of righting ability, in 20% of the subjects. Overall, thiopentone significantly reduced postural control and had a moderate antinociceptive effect compared to saline microinjections (P < 0.01 and 0.05, respectively, Wilcoxon test). In contrast, propofol did not induce "anaesthesia" in any animal tested, although a similar antinociceptive effect to that of thiopentone was observed (P < 0.05, Wilcoxon test). In summary, propofol and thiopentone have different effects when microinjected into the MPTA. While both agents reduced reflex withdrawal to a nociceptive stimulus, only thiopentone induced an "anaesthesia-like" state.

Anesthesia↗
PubMedDate not supplied

Dizziness of suspected cervical origin distinguished by posturographic assessment of human postural dynamics.

Useful clinical tests are lacking for the controversial entity "cervical vertigo". In earlier studies patients assumed to suffer from cervical vertigo or dizziness manifested disturbed postural control as compared to healthy subjects, but were hard to distinguish from patients with other balance disorders. Using posturography in which stance was perturbed by a vibratory stimulus applied towards the calf muscles, we studied 16 consecutive patients with recent onset of neck pain and concomitant complaints of vertigo or dizziness, but normal findings at otoneurological examination and electronystagmography; 18 patients with recent vestibular neuritis; and 17 healthy subjects. We performed system identification of a model of the control of upright human stance, using the vibratory stimulus as input and the recorded body sway as output. According to values for the three normalized parameters of the transfer function of the model (i.e., swiftness, stiffness, and damping), cervical vertigo patients were distinguished both from healthy subjects (P < 0.001), and from vestibular neuritis patients (P < 0.001). It was also possible to distinguish the vestibular neuritis group from the group of healthy subjects (P < 0.01). The results show disturbed postural control in patients with cervical vertigo to differ from that in patients with recent vestibular neuritis, and indicate posturographic assessment of human posture dynamics to be a possible future tool for use in diagnosing cervical vertigo.

Adult↗
PubMedDate not supplied

The contribution of vision in dynamic spontaneous sways of male classical dancers according to student or professional level.

We investigated the involvement of vision in the regulation of dynamic equilibrium in male children and young adults performing a physical activity requiring a high level of spatial skill: self-induced body sways of ballet dancers on a free unstable platform, 45 professional male dancers (Paris Opera) participated in the study. They included two student groups (beginners and confirmed) and two performer groups (adolescent and adult). They maintained their equilibrium on the platform under different visual and position conditions. The displacement of the seesaw platform were calculated from accelerometer measures. Fast Fourier transform processing of stabilograms allowed spectral frequency analysis. The total spectrum energy and the energies of the three frequency bands (0-0.5 Hz, 0.5-2 Hz, 2-20 Hz) were determined. For all groups, ANOVA indicated that values were higher for eyes-closed than for eyes-open conditions. The visual dependence differed according to age: for 14-year-old students the postural control for dynamic equilibrium was less visually dependent than for 11-year-old students. The 18-year-old dancers, although professional, were more dependent on vision than 14-year-old student dancers. These 18-year-old dancers were still adolescent because they had recently undergone growth acceleration which could disturb their proprioceptive references and internal body representations. Thus, visual input may dominate over the other sensory inputs in the regulation of postural control.

Adolescent↗