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Results for “Postural control”

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PubMed1999

Influence of visual feedback on successive control mechanisms in upright quiet stance in humans assessed by fractional Brownian motion modelling.

An up-to-date way to model the centre of pressure (CP) trajectories may consist in using fractional Brownian motion (fBm). By doing so, one may note that standing still is in fact controlled by two separate and successive mechanisms. The point raised in this study concerns the nature of these control mechanisms and their level of interaction. Following this idea, visual feedback (VFB), which is known to affect postural control by significantly decreasing sway magnitudes, was used. Twelve healthy adults, instructed to stand as still as possible, were tested under this VFB protocol (via a PC screen). In order to model the CP trajectories as fBm, variograms (mean square distances, MSD, expressed as a function of increasing time intervals deltat) were bi-logarithmically plotted. The main visual effect of VFB on these variograms concerns longest latency scaling regimes which reveal less stochastic and consequently more accurate control (P < 0.05 and P < 0.01 for X and Y components, respectively). An increase in the MSD of the transition point, which corresponds to the switch between the two control mechanisms, is also noted (P < 0.05). Overall, evidence is provided from this data that long latency scaling regimes do operate through a feedback process. Interestingly, this improved determinism in feedback control in turn induces a similar effect on the control operating over the shortest deltat. Thus, by privileging a control strategy based on feedback mechanisms, VFB in turn would make the subjects quicker in their initial displacement in order to reach a position capable of initiating a feedback mechanism.

Adult↗

PubMedDate not supplied

Anticipatory postural adjustments associated with arm movements during balancing on unstable support surface.

This study aims to investigate the pattern of anticipatory postural adjustments associated with arm movements during balancing on unstable support surface as a mechanism of coordination between movement and posture in this specific motor task. The experiments were arranged in two series: (1) the subjects stood on a force platform, and (2) on unstable platform (see-saw). They performed self-paced arm elevations as fast as possible for each support condition. EMG activity of deltoideus anterior (DA), soleus (SOL), tibialis anterior (TA), biceps femoris (BF) and erector spinae (ES) muscles were recorded. The mean EMG of SOL and TA muscles during balancing and during the last 100 ms prior to DA EMG onset were measured. For both series the anticipatory postural adjustment of BF preceded the ES activation. During balancing on see-saw the following differences from the stable condition were found: (1) co-contraction of SOL and TA muscles; (2) significantly earlier recruitment of BF; (3) delayed related activity of ES; (4) decrease of SOL and increase of TA mean EMG activities during balancing and just prior to the onset of DA EMG activity. These data showed that posture control during balancing on unstable support surface consists mainly in adapting the motor program according to the postural requirements rather than in changes of the postural strategy.

Adult↗

PubMed2006

Differences in multiple segment tremor dynamics between young and elderly persons.

BACKGROUND: Physiological tremor is an intrinsic and highly variable motor output that is sensitive to alteration in both neuromuscular function and/or changing task demands. Given that any tremor increase can severely influence fine motor performance, there is a requirement to clarify what factors lead to increased tremor. Identification of those factors that alter tremor may be particularly pertinent for elderly persons, who often exhibit a decline in postural control and amplified tremor. The aim of this study was to examine the effect of whole body posture (seated vs standing) on multiple segment tremor and forearm electromyogram (EMG) activity of younger and older individuals. METHODS: Fourteen older and 12 young participants performed a bilateral pointing task. Tremor data were collected using accelerometers attached to the forearm, hand, and finger segments of each arm. Surface EMG data were also collected from the extensor digitorum muscle of each arm. RESULTS: Although the pattern of tremor was similar between age groups, older participants exhibited increased hand and finger tremor amplitude and increased EMG activity across all postural conditions. For older individuals, tremor increases were greatest when the participant performed the task in a standing position. All age-related increases in hand and/or finger tremor were confined to increases in peak power between 8 Hz and 12 Hz. CONCLUSIONS: From a clinical perspective, these findings illustrate that using multiple segment tremor analyses can provide additional insight into potential age-related tremor differences. Additionally, the fact that postural position had a pronounced effect on tremor in older individuals suggests that body posture should be considered as a potential confounding factor when assessing tremor differences between population groups.

Adult↗

PubMed1993

Development of posture in the rat.

Postural development has not attracted much attention in investigations of neuro-ontogeny. In the rat, motor behaviours have been studied repeatedly but the development of postural control has been largely neglected. In the present study we have taken inventory of behavioural aspects of postural development. Postures and postural skills of 10 pups were 3-dimensionally recorded on video tape from the 2nd to the 20th day. The development of posture may be subdivided into three periods. During the first period, lasting until the 4th or 5th day, neonates were unable to lift their trunk from the floor, and the only indication for postural activity being head lifting. From then until the 12th-13th day, pups were able to walk, though staggering, and in addition they groomed and reared with forelimb support. From then, in a rapid development lasting until day 16, the adult type of fluent locomotion developed as well as grooming and rearing without support. In addition, complex motor acts developed. These results are discussed in the perspective of the structural and functional development of postural systems.

Animals↗

PubMed1993

Sensorimotor and perceptual function of muscle proprioception in microgravity.

Adaptive properties of the human proprioceptive systems were studied during the French-Soviet orbital flight (Aragatz mission, December 1988). The present space experiment investigated the hypothesis that the modifications of both biomechanical and physiological conditions occurring under microgravity involve considerable reorganization of body perception and postural control. The proprioceptive information originating in muscles is known to contribute, together with visual, vestibular, and sole cutaneous information to postural regulation. Moreover, by specifically activating the proprioceptive channel, muscle vibration is able to elicit both illusory movement sensations and postural responses. This experimental tool was used in microgravity in order to test various aspects of muscle sensory function. Ankle flexor and extensor vibration was applied under different experimental conditions. Quantitative analysis of motor responses was carried out on leg muscle EMG, goniometric, and kinesigraphic recordings. Joystick recordings and astronauts' comments were used to describe the kinaesthetic sensations. The main results were as follows: 1) Under microgravity, the sensitivity of muscle receptors remains unchanged. 2) During the flight, the tonic vibration reflexes (TVR) increased significantly in flexor muscles, which exhibited a sustained tonic activity. 3) The whole-body postural responses normally induced by ankle flexor muscle vibration were suppressed, whereas they remained unchanged or were only reduced when vibrations were applied to the ankle extensor muscles. In all cases, the postural response velocity decreased. 4) A disfacilitation of the vibration-induced postural illusions was observed to occur during long-term exposure to microgravity. These illusions became atypical however. For example: body lift illusion could be induced by tibialis anterior muscle vibration, whereas it was never induced in the controls. The characteristics of the illusory body movements described under normal gravity can be restored by artificially increasing the axial foot support forces during the flight. In conclusion, these data suggest that a functional reorganization of the proprioceptive information processing occurs in microgravity, affecting both perceptual and motor aspects of behavior. It is possible that these proprioceptive adaptations may be partly attributable to the new whole-body propulsive foot functions imposed by exposure to weightlessness and to the adaptation of motor behavior to the third dimension of space.

Adaptation, Physiological↗

PubMed2002

Risk of falling: predictors based on reduced strength in persons previously affected by polio.

OBJECTIVES: To examine the contributions of sensorimotor factors to postural control and falling in people with prior polio and to determine whether these contributions differ from those found in normal populations. DESIGN: Survey and case-control study. SETTING: A falls and balance laboratory in Australia. PARTICIPANTS: Forty persons with prior polio (age range, 28-71 y) and 38 age- and sex-matched control subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Lower-limb muscle strength, sway, vision, lower-limb sensation, reaction time, foot-tapping speed, and falls. RESULTS: Compared with the control subjects, the prior polio subjects performed similarly in sensory tests but worse in tests that involved a motor component. Within the prior polio group, lower-limb strength was strongly associated with postural sway on a compliant surface and explained more of the variance in sway than in control subjects. Prior polio subjects who fell multiple times had reduced lower-limb strength, slower reaction time, lower foot-tapping speed, and increased sway compared with those who fell less often. However, the rate of decline in lower-limb strength within the prior polio group did not exceed normal, age-related changes. CONCLUSIONS: This investigation of prior polio subjects provides an appropriate model for studying muscle weakness as a falls risk factor. Weakness was directly associated with falls, and had an indirect effect mediated through increased sway.

Accidental Falls↗

PubMed2006

Effects of postural anxiety on the soleus H-reflex.

Previous research has proposed that spinal reflex modulation may mediate anxiety-related changes in postural control. This study investigated how soleus H-reflex amplitude was influenced by standing at heights that induced different levels of anxiety. H-reflexes were elicited in 15 participants standing at the center and edge of a platform raised from a low to a high height (with and without vision). Increased skin conductance confirmed the anxiety effect of elevated surface heights. When standing at the edge of the platform with vision, H-reflex amplitude was attenuated in the high compared to low height condition. Changes in background muscle activity could not explain observed H-reflex changes, suggesting the potential involvement of pre-synaptic inhibition or fusimotor drive on anxiety-related changes in reflex modulation. This study reveals that healthy participants reduce spinal reflex excitability in the presence of increased postural anxiety and a postural threat imposed by standing at the edge of a raised platform. These findings have implications for understanding control of standing balance in individuals with postural instability and/or fear of falling, such as the elderly or stroke.

Adult↗

PubMed2003

Vertical posture and head stability in patients with chronic neck pain.

OBJECTIVE: To evaluate postural performance and head stabilization of patients with chronic neck pain. DESIGN: A single-blind comparative group study. SUBJECTS: Patients with work-related chronic neck pain (n = 9), with chronic whiplash associated disorders (n = 9) and healthy subjects (n = 16). METHODS: During quiet standing in different conditions (e.g. 1 and 2 feet standing, tandem standing, and open and closed eyes) the sway areas and the ability to maintain the postures were measured. The maximal peak-to-peak displacement of the centre of pressure and the head translation were analysed during predictable and unpredictable postural perturbations. RESULTS: Patients with chronic neck pain, in particular those with whiplash-associated disorders, showed larger sway areas and reduced ability to successfully execute more challenging balance tasks. They also displayed larger sway areas and reduced head stability during perturbations. CONCLUSION: The results show that disturbances of postural control in chronic neck pain are dependent on the aetiology, and that it is possible to quantify characteristic postural disturbances in different neck pain conditions. It is suggested that the dissimilarities in postural performance are a reflection of different degrees of disturbances of the proprioceptive input to the central nervous system and/or of the central processing of such input.

Adult↗

PubMed1980

Postural reactions of dogs to sinusoidal motion in the peripheral visual field.

Dogs were trained to stand quietly on a movable table that was surrounded by a movable roof. The position of the dogs was monitored while the table was stationary and the roof was moved to provide an optokinetic stimulus restricted to the lateral visual fields. Sinusoidal oscillation of the visual surround caused these quietly standing dogs to generate consistent changes in body position. At low frequencies (around 0.1 Hz) the body position changes tended to lead the position of the optokinetic stimulus. At higher frequencies of visual surround oscillation, the dogs' position changes lagged the optokinetic stimulus position by larger amounts as the frequency of motion got higher. These data showing a postural reaction due to motion of the optokinetic stimulus demonstrate a strong visual component of the postural control system.

Animals↗

PubMedDate not supplied

[Characteristics of the pressure center movement under upright posture regulation].

The hypothesis was put forward that, along with the regulation of mass center projection, the system of upright posture control stabilizes the deviation of pressure center from the position of the mass center projection. The regularities in the behavior of the trajectories of pressure center and mass center projection were analysed. Experimental evidence was obtained supporting the validity of the hypothesis. The structure of the control system that corresponds to the new understanding of the variables being regulated during the maintenance of vertical posture was considered.

Algorithms↗

PubMed1997

Comparison of upper-extremity balance tasks and force platform testing in persons with hemiparesis.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate the relationship between clinically accessible functional balance tools and sophisticated force platform measures in a standing position. SUBJECTS: Twenty persons who had hemiparesis secondary to a stroke and were ambulatory (mean age = 57.9 years, SD = 13.6, range = 35-79) were evaluated during a single testing session. METHODS: Performances on self-generated upper-extremity balance tasks using the nonparetic side (Functional Reach Test [FRT], arm raise and arm reach tasks) were compared with responses to external perturbations on the Balance System (postural sway, symmetry of weight distribution). RESULTS: No relationship was found between the upper-extremity balance tests and the force platform measures of postural sway. After suppressing the effect of age by means of partial correlation coefficients, the FRT was correlated with measures of postural symmetry in parallel stance on the Balance System (r = .66-.78). The FRT was only moderately correlated with the arm raise and arm reach tasks (r = .43 and .44). CONCLUSION AND DISCUSSION: Postural sway in response to force platform perturbations may have little relation to the postural control necessary for self-generated upper-extremity balance tasks. In contrast, the FRT and the force platform measures of postural symmetry appear to be evaluating comparable standing-balance abilities in persons with hemiparesis. The modest relationship between the FRT and the arm raise and arm reach tasks limits the finding's clinical relevance.

Adult↗

PubMed2000

Responses of reticulospinal neurons in intact lamprey to vestibular and visual inputs.

A lamprey maintains the dorsal-side-up orientation due to the activity of postural control system driven by vestibular input. Visual input can affect the body orientation: illumination of one eye evokes ipsilateral roll tilt. An important element of the postural network is the reticulospinal (RS) neurons transmitting commands from the brain stem to the spinal cord. Here we describe responses to vestibular and visual stimuli in RS neurons of the intact lamprey. We recorded activity from the axons of larger RS neurons with six extracellular electrodes chronically implanted on the surface of the spinal cord. From these multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal around its longitudinal axis in steps of 45 degrees through 360 degrees. Nonpatterned visual stimulation was performed by unilateral eye illumination. All RS neurons were classified into two groups depending on their pattern of response to vestibular and visual stimuli; the groups also differed in the axon position in the spinal cord and its conduction velocity. Each group consisted of two symmetrical, left and right, subgroups. In group 1 neurons, rotation of the animal evoked both dynamic and static responses; these responses were much larger when rotation was directed toward the contralateral labyrinth, and the dynamic responses to stepwise rotation occurred at any initial orientation of the animal, but they were more pronounced within the angular zone of 0-135 degrees. The zone of static responses approximately coincided with the zone of pronounced dynamic responses. The group 1 neurons received excitatory input from the ipsilateral eye and inhibitory input from the contralateral eye. When vestibular stimulation was combined with illumination of the ipsilateral eye, both dynamic and static vestibular responses were augmented. Contralateral eye illumination caused a decrease of both types of responses. Group 2 neurons responded dynamically to rotation in both directions throughout 360 degrees. They received excitatory inputs from both eyes. Axons of the group 2 neurons had higher conduction velocity and were located more medially in the spinal cord as compared with the group 1 neurons. We suggest that the reticulospinal neurons of group 1 constitute an essential part of the postural network in the lamprey. They transmit orientation-dependent command signals to the spinal cord causing postural corrections. The role of these neurons is discussed in relation to the model of the roll control system formulated in our previous studies.

Action Potentials↗

PubMed1999

Transneuronal tracing of neural pathways controlling an abdominal muscle, rectus abdominis, in the ferret.

Abdominal muscles participate in generating a large number of behaviors and reflex responses, including expiration, coughing, sneezing, vomiting, postural control, production of speech, straining, facilitation of venous return to the heart, and reaction to vestibular stimulation. However, the only premotor neurons that have been conclusively shown to influence abdominal motoneurons are located in nucleus retroambiguus, the expiratory region of the caudal ventral respiratory group. In the present study, the neural circuitry controlling the activity of one abdominal muscle, rectus abdominis, was mapped using the transneuronal tracer pseudorabies virus (PRV) in the ferret. Injections of PRV into rectus abdominis labeled large presumed motoneurons in the ventral horn of T12-L4, and smaller presumed interneurons that were scattered in laminae VII, VIII, IX, and X of T4-L4. In addition, neurons in several areas of the medulla and caudal pons, including the retroambigual nucleus, medial and ventromedial reticular formation, nucleus prepositus hypoglossi, vestibular nuclei, and raphe nuclei, were infected by transynaptic passage of PRV from rectus abdominis motoneurons. Thus, the multifunctional roles of abdominal muscles appear to be coordinated by premotor neurons located in both the spinal cord and several regions of the brainstem.

Animals↗

PubMed2001

A sequence of postural muscle excitations precedes and accompanies isometric ramp efforts performed while sitting in human subjects.

The purpose of this study was to explore how the muscles which control postural body segments are activated during bilateral isometric ramp pushes exerted with the upper limbs by seated subjects. The paradigm under study presents the advantage that the subject is in a quasi-static posture, and since upper limbs are stretched out, the dynamic phenomena, which might occur, can only originate from the rest of the body, which means from the postural chain. A dynamometer was used to measure the horizontal force, Fx, exerted on the bar, and a custom-designed force-plate was used to measure global reaction forces (Rx) and displacement of the centre of pressure (Xp) along the antero-posterior axis. Electromyograms (EMGs) were picked up by bipolar surface electrodes from 14 muscles crossing the lower limb, pelvis, trunk and upper limb joints. It was shown that transient push efforts require monotonous EMG increase in postural as well as in focal muscles. The EMG sequence starts with the postural muscles and ends with the focal ones. The postural EMG sequence is anticipatory. It is concluded that the EMG sequence is programmed according to the task parameters, and that its role is to counteract in advance the perturbing effect of the effort, in order to allow the effort to be performed efficiently. It is suggested that excitation between the postural muscles is distributed according to their biomechanical role in relation to the supports.

Biomechanical Phenomena↗

PubMed2003

Combined effect of vestibular and craniomandibular disorders on postural behaviour.

A correlation has been reported in the dental literature between temporomandibular disorders and musculoskeletal abnormalities, however, the question whether they modify body postural sway remains controversial. In the present investigation, the Craniomandibular Index was used to evaluate the clinical extension of temporomandibular joint dysfunction and related problems in 40 patients with normal vestibular function and in 42 patients with peripheral vestibular disorders. Balance function was assessed by static posturography and body sway area was measured in two conditions: i) eye open, and g) eye closed. Data were compared to those of 40 healthy subjects. Postural control showed a significantly different behaviour between groups with an increase in average body sway in patients with craniomandibular disorders as opposed to controls (p < 0.005). Although the involvement of the stomatognathic apparatus was not quantitatively different in the two groups of patients, those also presenting a peripheral vestibular disorder exhibited greater average body sway than patients with only craniomandibular disorders (p < 0.005). The latter showed a greater average body sway than controls only in the trial with eyes closed (p < 0.05). The results demonstrated that craniomandibular alterations could produce moderate postural instability in patients with a normal vestibular function. Conversely, their association with peripheral vestibular disorders becomes a real challenge to the upright quiet stance probably due to a negative effect of somatosensory origin on the vestibulo-spinal reflex impairment.

Adult↗

PubMed2005

Beneficial effects of postural intervention on prehensile action for an individual with ataxia resulting from brainstem stroke.

PRIMARY OBJECTIVE: This paper examined the effectiveness of postural training on upper extremity performance in an ataxic individual. The ataxia resulted from a brain stem stroke. RESEARCH DESIGN: Before-after, single-subject experimental design. EXPERIMENTAL INTERVENTION: Four-week course of postural training, comprised of three one-hour sessions/week. MAIN OUTCOMES AND RESULTS: The patient demonstrated an increase in function of the ataxic limb, as evidenced by appreciable increases in the Fugl-Meyer score and modest increases in the Postural Assessment Scale for Stroke Patients (PASS) score. CONCLUSIONS: Improvement in postural control influences upper extremity function affecting the speed and accuracy of the movement. We demonstrate the effectiveness of using postural training as an intervention towards reducing the effects of ataxia, a movement coordination impairment for which relatively few therapeutic techniques have been specifically developed or evaluated.

Aged↗

PubMed2003

Impairments of trunk movements following left or right hemisphere lesions: dissociation between apraxic errors and postural instability.

Stroke patients present with apraxic or postural deficits involving trunk movements. Praxis and posture control have been associated with the functions of the left and the right hemisphere, respectively. For the first time, in this study the occurrence of apraxic and postural components in trunk movement deficits following right and left hemisphere lesions were investigated in the same participants. Twenty-three patients with left (L/pt), 12 with right (R/pt) hemisphere lesion, and 30 healthy controls were evaluated with a 21-item test assessing the imitation of meaningless, symbolic and reaching movements presented twice on visual or proprioceptive modality. Erroneous, motor responses of the trunk were classified as postural (compensations to overcome stability or asymmetry deficits) or apraxic (execution errors not due to biomechanical constraints). Postural instability reactions were significantly more frequent among the R/pts, whilst apraxic responses were overwhelming within the L/pts. The findings are consistent with the view that the left hemisphere is dominant for praxis and suggest that this dominance be extended to trunk praxis. The results also support the hypothesis that trunk postures are coded in relation to the environment by a representational system. A widespread network, mainly sitting in the right hemisphere, subserves this postural system. The distinction between praxic and postural deficits in executing trunk movements should be kept in mind when evaluating trunk movement difficulties shown by stroke patients, in following up their recovery or when tailoring rehabilitation programmes.

Adult↗

PubMed2005

Standing balance in persistent whiplash: a comparison between subjects with and without dizziness.

OBJECTIVE: Dizziness and unsteadiness, associated with altered balance, are frequent complaints in subjects suffering persistent whiplash associated disorders. Research has been inconclusive with respect to possible aetiology. This study assessed balance responses in subjects with whiplash associated disorders, taking into account several possible causes. DESIGN: A prospective, 3 group, observational design. SUBJECTS: 100 subjects with persistent whiplash associated disorders, 50 complaining of dizziness, 50 not complaining of dizziness and 50 healthy controls. METHODS: The Clinical Test for Sensory Interaction in Balance was performed in both comfortable and tandem stance. The sway trace was analysed using wavelet analysis. CONCLUSION: The results indicated that the energy of the sway signal for comfortable stance tests was significantly greater in the group with dizziness compared with the group without dizziness. In the group without dizziness the energy was greater than controls for all tests, but significantly different on selected tests. In selected tandem stance tests, subjects with dizziness were significantly less able to complete the test than subjects without dizziness and controls. These deficits could not be attributed to medications, compensation, anxiety or age and are likely to be due to disturbances to the postural control system possibly originating from abnormal cervical afferent input.

Adult↗