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PubMed1999

Age-related changes in rate and magnitude of ankle torque development: implications for balance control.

BACKGROUND: One of the key components of postural control is the motor system's ability to produce appropriate torques to counteract perturbations that may lead to a loss of balance. Evidence exists to show that there is an age-related decline in absolute strength and in the ability to rapidly produce torque. The relationship between age-related decreases in these voluntary torque production capabilities and the ability to rapidly produce torques in a reactive balance task has not been studied. Thus, the purpose of this study was to examine the magnitude and rate of torque production in younger and older adults under reactive balance conditions. METHODS: Older (OA) and younger (YA) adults received forward and backward support surface translations of varying amplitudes and velocities. Maximum ankle muscle torque (maxMa) and rate of change of ankle muscle torque (Ma) following a perturbation were calculated. RESULTS: Two balance responses emerged: a no-step and a step response. With increasing perturbation difficulty, YA and OA used different responses. The no-step and step responses were examined for age-group differences in the force characteristics. No significant age-group differences were found for maxMa or rate of change of Ma within either no-step or step responses. CONCLUSION: The results of this study suggest that neither the magnitude nor rate of ankle muscle torque production, as produced during the initial balance response in this set of reactive balance control tasks, determines the different balance responses seen in younger versus older adults.

Adult↗

PubMed1997

Comparison of soleus H-reflex gain from prone to standing in dancers and controls.

To examine the differences in soleus H-reflex gain between trained dancers and control subjects, the soleus H-reflex amplitude and background muscle activity of 9 trained dancers (means of 20.3 +/- 2.1 years of age, and 14.3 +/- 3.8 years of training) and 9 control subjects (mean 23.3 +/- 3.2 years of age) were compared at rest and at 10, 20, and 30% of a maximal voluntary soleus contraction during two conditions: prone and standing. The ratio of the maximal H-reflex (H-max) to the maximal motor response (M-max) was also measured during both conditions. Correlation was performed between background EMG and the resultant H-reflex to determine reflex gain. The results demonstrated that the control subjects and the dancers displayed a similar reflex gain during the prone condition (slope = 3.30 vs. 3.64, respectively). However, during the standing condition, dancers demonstrated a significantly lower reflex gain (slope = 1.78) than did control subjects (slop = 3.68). Furthermore, although both groups significantly decreased the H-max/M-max ratio from prone to standing, no differences were found between groups at either condition. This suggests that the differences in standing reflex gain between the dancers and control subjects were a product of differential control of reflex modulation involved in postural control. An initial hypothesis explaining the differences between the standing reflex gain of the groups relates to plasticity of central inhibitory control mechanisms, primarily presynaptic and/or reciprocal inhibition.

Adult↗

PubMed1995

Modulation of vestibulospinal reflexes through microinjection of GABAergic agents in the dorsal pontine tegmentum of decerebrate cats.

1. The locus coeruleus (LC) neurons control posture as well as the gain of the vestibulospinal (VS) reflexes either through direct coeruleospinal (CS) projections or by inhibiting the dorsal pontine reticular formation (pRF) and the related medullary inhibitory reticulospinal (RS) systems. After the demonstration that the LC neurons are under the inhibitory control of GABAergic afferents, experiments were performed to investigate whether the same system could also suppress the activity of the dorsal pRF, thus intervening in the control of posture and VS reflexes. 2. In precollicular decerebrate cats, unilateral microinjection into the dorsal pRF of the GABA-A antagonist bicuculline or the GABA-B antagonist faclofen (0.13-0.25 microliter at 2.5 micrograms/microliter saline) decreased the tonic contraction of the ipsilateral triceps brachii, but greatly increased the amplitude of the EMG responses of the same muscle to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees). This increase in gain of the VS reflexes was not associated with great changes in phase angle of the responses, which were always characterized by an increased EMG activity during ipsilateral tilt and a decreased activity during contralateral tilt. The same injection also produced in some instances a slight decrease of the extensor tonus of the contralateral forelimb, associated with a moderate increase in the amplitude of modulation and thus in the response gain of contralateral triceps brachii to labyrinth stimulation. However, when the ipsilateral effects were prominent, the response gain of the contralateral triceps muscle was slightly depressed, while the pattern of response reversed. 3. The changes in posture and reflexes described above appeared 5-10 min after unilateral injection of the GABA antagonists in the pRF, reached the highest values in about 30 min and fully recovered to the control levels within 2 h after the injection. These effects were not due to irritative phenomena following injection of the fluid, since neither changes in posture nor in the response gain of the triceps brachii to labyrinth stimulation were observed after injection of an equal volume of vehicle in the pRF of that side. On the other hand, an increase in postural activity associated with a decrease in the response gain of the ipsilateral and contralateral triceps brachii to animal tilt was observed after unilateral microinjection into the dorsal pRF of GABA agonists. 4. Histological controls indicated that the structure responsible for the postural and reflex changes was located in the dorsal pontine reticular formation, ventral to the LC.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Nonspiking local interneurons in insect leg motor control. I. Common layout and species-specific response properties of femur-tibia joint control pathways in stick insect and locust.

1. Locusts (Locusta migratoria) and stick insects (Carausius morosus) exhibit different strategies for predator avoidance. Locusts rely primarily on walking and jumping to evade predators, whereas stick insects become cataleptic, catalepsy forming a major component of the twig mimesis exhibited by this species. The neuronal networks that control postural leg movements in locusts and stick insects are tuned differently to their specific behavioral tasks. An important prerequisite for the production of catalepsy in the stick insect is the marked velocity dependency of the control network, which appears to be generated at the level of nonspiking local interneurons. We examined interneuronal pathways in the network controlling the femur-tibia joint of the locust middle leg and compared its properties with those described for the stick insect middle leg. It was our aim to identify possible neural correlates of the species-specific behavior with regard to postural leg motor control. 2. We obtained evidence that the neuronal networks that control the femur-tibia joints in the two species consist of morphologically and physiologically similar--and thus probably homologous--interneurons. Qualitatively, these interneurons receive the same input from the femoral chordotonal organ receptors and they drive the same pools of leg motoneurons in both species. 3. Pathways that contribute to the control of the femur-tibia joint include interneurons that support both "resisting" and "assisting" responses with respect to the motoneuron activity that is actually elicited during reflex movements. Signal processing via parallel, antagonistic pathways therefore appears to be a common principle in insect leg motor control. 4. Differences between the two insect species were found with regard to the processing of velocity information provided by the femoral chordotonal organ. Interneuronal pathways are sensitive to stimulus velocity in both species. However, in the locust there is no marked velocity dependency of the interneuronal responses, whereas in the same interneurons of the stick insect it is pronounced. This characteristic was maintained at the level of the motoneurons controlling the femur-tibia joint. Pathways for postural leg motor control in the locust thus lack an important prerequisite for the generation of catalepsy, that is, a marked velocity dependency.

Animals↗

PubMed2003

The integration of multiple proprioceptive information: effect of ankle tendon vibration on postural responses to platform tilt.

Previous studies have looked at co-processing of multiple proprioceptive inputs but few have investigated the effect of separate dynamic and tonic predominantly proprioceptive disruptions applied concurrently at the same segment. The purpose of the present study was to investigate how simultaneous ankle tendon vibration, a tonic stimulus, with a dynamic toes-up (TU) or toes-down (TD) platform perturbation (1) affects postural stability and (2) influences the adaptation process. Sixteen normal subjects (ten male, six female, mean age 26 +/- 4.8 years) stood blindfolded on a moving platform with vibrators attached bilaterally over the Achilles tendons. Participants were tested in quiet stance (QS), and with five successive TU and TD tilts. All tests were conducted both with (QS+V, TU+V, TD+V) and without vibration. Centre of pressure (CoP) displacements and pitch angular trunk velocity were recorded. Results for QS+V showed a significant 1.02-cm backward CoP displacement (P<0.01) and a significant increase in trunk velocity (peak-to-peak amplitude, P<0.05; SD of trunk velocity, P<0.05). TU+V resulted in a non-significant increase of maximum backwards CoP displacement when compared to TU alone. In addition, no notable effect of vibration on other measures of CoP (pre-tilt position, SD and area of sway) and trunk velocity (peak-to-peak, SD and area of sway) indicates that TU+V does not introduce significantly greater instability compared to tilt alone. In the TD condition, vibration was found to be a stabilising influence, causing a significant shift of the mean pre-tilt position 0.85 cm backwards (P<0.01) and a substantial decrease in the area of forward CoP displacement (P<0.01). However, maximum forwards CoP displacement and trunk velocity measures were not significantly altered during TD+V. Furthermore, in neither TU nor TD was the time-course or pattern of adaptation disrupted by the additional application of vibration. In conclusion, although vibration significantly affects postural measures when applied in isolation, this finding does not hold when it is applied in combination with a more dynamic stimulus. Instead it seems that once postural stability has been disrupted the central nervous system can rapidly assess information from a weaker tonic input and utilise or suppress it appropriately, depending on its effect towards overall postural control. It can be concluded that postural responses to the concurrent application of different predominantly proprioceptive stimuli are dependent upon the type of stimulus and the ability of the central nervous system to rapidly assess and re-weigh available sensory inputs.

Adaptation, Physiological↗

PubMed2001

The effect of expertise in gymnastics on proprioceptive sensory integration in human subjects.

The ability of experts in motor skills requiring a fine postural control to keep a stable upright posture while facing the task of reinserting proprioceptive information was investigated. Seven expert gymnasts and seven experts in other non-gymnastics sports were asked to stand as immobile as possible in two conditions of vision and no-vision. Within a trial, ankle proprioceptive input was modified by means of tendon vibration of both antagonistic ankle muscles. Center of foot pressure (COP) displacements were recorded using a force platform. Contrasting with the non-gymnasts, the gymnasts were able to rapidly take advantage of the reinsertion of proprioceptive information to decrease their COP displacements. These results suggest that the efficiency of the integration process leading to the reweighting of sensory information can be significantly improved through a specific training.

Adult↗

PubMed2003

Adaptations of writing posture in response to task demands for left- and right-handers.

Handedness and writing posture are visible manifestations of differences between left- and right-handers. Although an inverted posture is witnessed in both groups, there is a much higher proportion of left-handers who invert. This study is framed within the adaptation hypothesis of writing posture, which states that invertedness in left-handers develops in response to the demands of cursive writing. Participants (N = 57) comprising left-handed inverters, left-handed standard writers, and right-handed standard writers engaged in tasks that required them to form letters and pen strokes at extreme angles. In addition participants were questioned about attempts to change writing posture. We hypothesised that letter angle controls posture in both left- and right-handers and that inverted posture would be a target of intervention. The results of the study showed some support for these hypotheses in that left- and right-handers adapted their posture in response to the constraints placed upon them and inverters reported more intervention.

Journal Article↗

PubMed2004

Influence of postural anxiety on postural reactions to multi-directional surface rotations.

Previous studies have shown significant effects of increased postural anxiety in healthy young individuals when standing quietly or performing voluntary postural tasks. However, little is known about the influence of anxiety on reactive postural control. The present study examined how increased postural anxiety influenced postural reactions to unexpected surface rotations in multiple directions. Ten healthy young adults (mean age: 25.5 yr, range: 22-27 yr) were required to recover from unexpected rotations of the support surface (7.5 degrees amplitude, 50 degrees/s velocity) delivered in six different directions while standing in a low postural threat (surface height: 60 cm above ground) or high postural threat (surface height: 160 cm above ground) condition. Electromyographic data from 12 different postural leg, hip, and trunk muscles was collected simultaneously. Full body kinematic data were also used to determine total body center of mass (COM) and segment displacements. Four distinct changes were observed with increased postural anxiety: increased amplitude in balance-correcting responses (120-220 ms) in all leg, trunk, and arm muscles; decreased onset latency of deltoid responses; reduced magnitude of COM displacement; and reduced angular displacement of leg, pelvis, and trunk. These observations suggest that changes in dynamic postural responses with increased anxiety are mediated by alterations in neuro-muscular control mechanisms and thus may contribute significantly to the pathophysiology of balance deficits associated with aging or neurological disease.

Adult↗

PubMed1985

Posture-correlated responses to vestibular polarization in vermal versus intermediate posterior cerebellar cortex.

Cerebellar lesion experiments have led to the concept that the medial longitudinal zone controls postural tone while the intermediate zone controls discrete movement. This study is a test of the hypothesis that, of the two zones, the medial zone is more closely linked to the resting discharge of vestibular afferent fibers, a prime source of neural tonus underlying the tonus of posture. Unilateral polarizations of the vestibular apparatus via the round window in awake, unrestrained guinea pigs caused step changes of postural attitude, the direction of which was polarity dependent. In anesthetized animals, these currents caused nonadapting step changes, or posture-correlated responses in the level of resting discharge in vestibular primary afferent fibers. In the medial and the intermediate cerebellar cortices of the posterior lobe, the proportion of step-like responses was similar, in contradiction to the hypothesis. This suggests that the cerebellar computations for controlling both postural tonus and discrete movements require information about vestibular tonus in terms of simple spike activity.

Action Potentials↗

PubMed2004

Postural response in older adults with different levels of functional balance capacity.

BACKGROUND AND AIMS: Aging is frequently accompanied by a deterioration in postural control, but it is not clear whether the primary contributor is increasing age or a progressive loss of functional balance capacity. The purpose of this study was to test the hypothesis that functional balance capacity contributes more than age to changes in postural response in the elderly. METHODS: The study considered 3 groups of healthy young, and functionally-stable and functionally-unstable older adults (N = 16 each group). Postural responses, including behavioral response patterns, joint angular displacement, displacement of the center of mass and center of pressure, and ground reaction forces, were induced and examined by submitting standing subjects to unexpected backward displacements in the surface supporting them. RESULTS: Functionally-stable older adults showed similar postural response patterns to those of young adults, whereas functionally-unstable older adults differed from young adults in the control of hip, trunk, shear force, and center of pressure trajectory during balance recovery. CONCLUSIONS: These findings support the hypothesis that changes in postural control in the elderly correlate with their functional balance capacity and are not just a matter of age.

Accidental Falls↗

PubMed2005

Undisturbed upright stance control in the elderly: Part 1. Age-related changes in undisturbed upright stance control.

The authors investigated age-related changes in postural control in 33 healthy young adults (18-31 years), 29 seniors (62-75 years), and 22 elderly people (75-96 years). A force platform recorded the results. The horizontal motions of the center of gravity (CGh) and their difference in the plane of support CP - CGv were deduced from the complex center of pressure (CP) trajectories. With fractional Brownian modeling, one can establish that the aging process seems to induce a transition phase in which seniors take more time to initiate the corrective process in the mediolateral (ML) axis than do younger people. The elderly develop a new strategy characterized by the mobilization of higher neuromuscular energy to maintain equilibrium. In the ML axis, the larger displacements could be caused mainly by a hip strategy that could facilitate step initiation. In the anteroposterior (AP) axis, seniors and elderly individuals maintain a relative ability to stabilize their CG into the base of support compared with younger people.

Adolescent↗

PubMed2004

Tai Chi and vestibular rehabilitation effects on gaze and whole-body stability.

Tai Chi (TC) is a comparatively new intervention for peripheral vestibular hypofunction, which is often treated with vestibular rehabilitation (VR). We compared gaze stability (GZS), whole-body stability (WBS) and footfall stability (FFS) during locomotion among 26 people with vestibulopathy (VSP), randomized into two treatment arms (13 TC and 13 VR). Each intervention program was offered for 10 weeks. GZS improved more for VR than for TC, but WBS (and FFS) improved more for TC than for VR. There was a significant relationship between changes in GZS and WBS for the VR subjects (r=0.60, p=0.01), but not for TC subjects. There was a significant relationship between changes in WBS and FFS for both VR (r=0.65, p <0.01) and TC (r=0.58, p=0.02) groups; the relationship disappeared in the VR but not the TC group when controlling for GZS. These findings suggest that VR and TC both benefit patients with VSP but via differing mechanisms. Moreover, these data are the first to test the assumption that improving gaze control among patients with VSP perforce improves postural stability: it does not. We conclude that GZS is most improved in those who receive VR, but that TC improves WBS and FFS without improving GZS, suggesting patients with VSP can rely on non-gaze related mechanisms to improve postural control.

Female↗

PubMed1998

Control of spatial orientation in a mollusc.

The main function of postural nervous mechanisms in different species, from mollusc to man, is to counteract the force of gravity and stabilize body orientation in space. Here we investigate the basic principles of postural control in a simple animal model, the marine mollusc Clione limacina. When swimming, C. limacina maintains its vertical orientation because of the activity of the postural neuronal network. Driven by gravity-sensing organs (statocysts), the network causes postural corrections by producing tail flexions. To understand how this function occurs, we studied network activity by using a new method. We used an in vitro preparation that consisted of the central nervous system isolated with the statocysts. Output signals from the network (electrical activity of tail motor neurons) controlled an electrical motor which rotated the preparation in space. We analysed the activity of individual neurons involved in postural stabilization under opened or closed feedback loop. When we closed this artificial feedback loop, the network stabilized the vertical orientation of the preparation. This stabilization is based on the tendency of the network to minimize the difference between the activities of the two antagonistic groups of neurons, which are driven by orientation-dependent sensory inputs.

Animals↗

PubMedDate not supplied

[Maintenance of logopedic orientation in a patient with oropharyngeal dysphagia of neurogenic origin].

INTRODUCTION: Speech therapy treatment on patients who have a neurogenically induced dysphagia begins at hospital, in the intensive rehabilitation units. This study shows some of the difficulties found dealing with and orienting the family and the patient from a therapy point of view, mainly during his return to home surroundings. DEVELOPMENT: To better understand the dysphagic situation, normal swallowing steps (oral, pharyngeal and esophageal) steps have been described. These were then related to the dysphagic problems, with their evaluation, classification and characteristics. Under dysphagia rehabilitation the therapeutic guidance should be lead by the appropriate nutritional demands, and prevent aspirations. Some of the therapeutic procedures for treating and controlling neurogenic dysphagia have been described (head posture control, tactile and thermal stimuli, etc.). The author questions the difficulties found controlling orientation and maintaining conduct outside the hospital environment, principally with patients at risk from aspirations.

Deglutition Disorders↗

PubMed2002

Adaptation of vibration-induced postural sway in individuals with Parkinson's disease.

Postural control requires accurate integration of visual, vestibular, cutaneous, and proprioceptive sensory information. Previous research suggests that patients with Parkinson's disease (PD) may have difficulty with this integration process, particularly involving incongruent visual information. The purpose of this study was to determine whether PD patients also show difficulty in adaptation to erroneous proprioceptive information. Postural reactions to soleus muscle vibration were explored in 8 PD patients, 8 healthy elderly, and 8 young adults. Postural sway was recorded using an electromagnetic motion analysis system in four conditions (2 vision x 2 vibration) with four trials in each condition to test subjects' adaptation to the vibrator stimulus. The results showed that PD patients did adapt to the vibration across trials, similar to those of both control groups. It was concluded that PD patients in the early stages of the disease could override inaccurate proprioceptive inputs, relying more on true vestibular and/or visual information. These results suggest that the basal ganglia are not critical for this adaptation process in postural control.

Adaptation, Physiological↗

PubMed2001

Passive tactile sensory input improves stability during standing.

The effects of passive tactile cues about body sway on stability during standing were evaluated in subjects with a wide range of sensorimotor and balance performance. Healthy young adults, diabetic subjects with varying degrees of peripheral sensory neuropathy and older subjects aged 70-80 years were studied. Body sway was measured when subjects stood on the floor and on a foam rubber mat, with or without an applied stimulus that rubbed on the skin at the leg or shoulder as the body swayed. The results show that this stimulus reduced body sway (mean reduction 24.8%+/-1.5) and thus had a stabilizing effect as big as vision or sensory information from the feet. The reduction in sway was not based on active touch. The stimulus was not restricted to a particular region of the body, but was more effective on the shoulder than the leg, and was more effective when standing with eyes shut or when standing on the foam mat. It was also most effective in those subjects who had the greatest sway during normal standing. Thus, the response appears to be graded with the amplitude of the stimulus. We concluded that, if passive sensory input about posture is available, the postural control process adapts to this input, modulating postural stabilizing reactions.

Adult↗

PubMed2001

Development of postural adaptation to arm raising.

We studied the development of the coordination between posture and movement by analyzing the shifts of the center of pressure (CoP) associated with arm raising. Three groups of children aged 3-5 years, 6-8 years, and 9-10 years and an adult group were tested. The subjects were required to raise their arms to the horizontal position while standing still, with their hands free or loaded (5% of the body weight). The arm movements were recorded by a TV-image processor, and the changes in position of the CoP were measured by a force platform and analyzed before, during, and after the arm movement. The data show that the CoP moved forward during arm raising, that additional load induced a greater shift in all age groups, and that the relative amplitude of the shift decreased with age. The greatest changes occurred between ages 3-5 years and 6-8 years. The pre- and postmovement CoP shift suggests qualitative changes in the postural adaptation to movement between these two age groups: the anticipatory postural adjustments moved from a supporting function to a compensatory function, yielding an increasing functional convergence between the feedforward and the feedback modes of postural control, and an increasing rapidness in recovering postural stability after arm movement. The postural behavior shown by the 9- to 10-year-old children and by the adults in the arms-free condition suggests an increased tolerance to unbalance when postural oscillations do not jeopardize static equilibrium.

Adaptation, Physiological↗

PubMed2005

Identification of distinct characteristics of postural sway in Parkinson's disease: a feature selection procedure based on principal component analysis.

We selected descriptive measures of the centre of pressure (CoP) displacement in quiet standing, by means of a procedure based on principal component analysis, in two groups particularly different in terms of postural behaviours, such as subjects with Parkinson's disease (PD) in the levodopa off and on states. We computed 14 measures of the CoP: 5 measures of CoP trajectory over the support surface, 3 measures that estimated the area covered by the CoP, 1 measure that estimated the principal CoP sway direction, 1 measure that quantified the CoP total power, 1 measure that estimated the variability of CoP frequency content and 3 measures of characteristic CoP frequencies [L. Rocchi, L. Chiari, A. Cappello, Feature selection of stabilometric parameters based on principal component analysis, Med. Biol. Eng. Comput. 42 (2004) 71-79; L. Rocchi, L. Chiari, F.B. Horak, Effects of deep brain stimulation and levodopa on postural sway in Parkinson's disease, J. Neurol. Neurosurg. Psychiatry, 73 (2002) 267-274]. The feature selection, independently applied to the measures obtained in the two groups, resulted in different principal component (PC) subspaces of the 14-dimension original data set (4 PCs in the off and 3 PCs in the on state to account for over 90% of the original variance), but in the same 5 CoP measures (selected features) needed to describe the different postural behaviours: root mean square distance; mean velocity; principal sway direction; centroidal frequency of the power spectrum; frequency dispersion. The five selected features were found to provide insight into the postural control mechanisms and to describe changes in postural strategies in the two groups of PD subjects, off and on levodopa. Thus, the five selected features may be recommended for use in clinical practice and in research, in the direction toward the definition of a standard protocol in quantitative posturography.

Aged↗