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PubMed1986

Muscular synergies during different conditions of postural activity.

With the view to studying the muscular synergies in maintaining of upright posture EMG activity of soleus (SOL), tibialis anterior (TA), peroneus longus (PL), biceps femoris (BF), vastus lateralis (VL) and gluteus medius (GM) muscles during easy standing, voluntary leaning and induced body oscillations in frontal and sagital plane were recorded. The data showed that during easy standing and during small external disturbances the vertical posture was maintained mainly by the activity of SOL (triceps surae muscle) which was modulated by the modification of the external force field. TA remained silent. PL muscle was slightly active as a synergist of SOL. The pattern of muscular synergies during fast voluntary leaning and induced body oscillations differed as compared to the muscular synergies at easy standing. The activity of all muscles studied increased and became continuous with exception of that of the TA. The latter was silent but was involved earlier when gravity center passed behind its projection. VL being a synergist of TA during slow sway became continuously active as a synergist of SOL during the fast sway. Typical changes in muscular synergies appeared when induced body oscillations were imposed during horizontal and rotational movements of the platform. The various patterns of muscular synergies during pronation and supination of the foot depended on the knee joint angle. The amplitude of body leaning forward and backward and its variability as well as the plane of the lateral sway depended on the biomechanical variables and related motor programs for postural control.

Electromyography↗

PubMed2005

Postural responses triggered by multidirectional leg lifts and surface tilts.

The aim of the present study was to investigate the relationship between proactive and reactive components of postural control. We contrasted the kinematic and electromyographic (EMG) responses to multidirectional voluntary leg lifts with those elicited by unexpected surface tilts. In particular, we addressed the role of trunk stabilization following either a voluntary or forced weight shift from double to single limb support. Nine young female subjects stood with a standing posture of 45 degrees toe-out and their arms abducted to shoulder level. On the experimenter's signal, subjects either (1) lifted one leg as fast as possible in one of six directions (R/L side, R/L diagonal front, R/L diagonal back) to a height of 45 degrees or (2) maintained standing as the support surface tilted at a rate of 53 degrees /s to a height of 10 degrees in one of six directions (R/L-up, R/L diagonal toes-up, R/L diagonal toes-down). For both tasks, our results showed that the center of pressure (COP) displacement began before or in conjunction with displacement of the center of mass (COM), after which the COP oscillated about the horizontal projection of the COM. In addition, the muscles were recruited in a distal-to-proximal sequence, either in anticipation of the voluntary leg lift or in response to the sudden surface tilt. Thus, the COP was being used dynamically to control displacement of the COM. The axial postural strategy comprising head, trunk, and pelvis movements was quantified by means of principal component analysis. More than 95% of the variance in the data could be described by the first two eigenvectors, which revealed specific coordination patterns dominated by pelvis rotation in one direction and head/trunk rotation in the opposite direction. Unexpected surface tilting elicited an automatic response strategy that focused on controlling the orientation of the head and trunk with respect to the vertical gravity vector while trunk verticality was compromised for movement generation and the recovery of postural equilibrium during leg lifting. In conclusion, regardless of the type (voluntary versus involuntary) or direction of perturbation, the strategy employed by the central nervous system to control the body COM displacement concerns mainly trunk stabilization.

Adult↗

PubMed2006

Antidepressants and dizziness.

Despite several evidences supporting a close relationship between dizziness and anxiety symptoms, the role of antidepressants in the treatment of such conditions remains poorly explored. The high prevalence of dizziness during serotonin reuptake inhibitors discontinuation syndrome and the few reports suggesting efficacy of antidepressants in treating some vestibular disorders justify a careful investigation. Neurophysiologic studies suggest possible focus of investigation on mechanisms of drug action. Psychophysiologic studies also suggest a possible role of antidepressant drugs in improving balance control and cognitive functioning. Controlled studies involving antidepressants with selective action in different neurotransmitters systems are necessary to elucidate the complex pathophysiologic mechanisms involving emotional and balance control. For future researches, special attention must be paid to the methodology of balance evaluation and the interaction between posture control and cognitive functioning.

Antidepressive Agents↗

PubMed1994

Coordinate transformations in the control of cat posture.

1. Global geometric variables represent high-order parameters in the control of cat posture. In particular, limb length and orientation are accurately controlled in response to tilts of the support platform. There is now electrophysiological evidence, obtained in anesthetized cats, that spinal sensory neurons projecting to the cerebellum are broadly tuned to limb length and orientation. Limb length and orientation specify the position of the limb end-points in body-centered polar coordinates. They define an intended posture in a global manner, leaving the detailed geometric configuration of the limbs undetermined. The planar covariation of limb joint angles described in the accompanying paper suggests the existence of an intermediate processing stage that transforms endpoint coordinates into the angular coordinates of the joints (inverse mapping). In this paper we address the question of the nature of this coordinate transformation. Because the number of degrees of freedom of angular motion in each limb exceeds that of endpoint motion in world space, several different angular configurations are compatible with any given endpoint position in world space. Thus the problem of coordinate transformation is a priori indeterminate. We have tested a number of different hypotheses. 2. Coordinate transformation could be accomplished implicitly by means of discrete kinematic synergies. Any given geometric configuration of the limb would result from a weighed combination of only two distinct patterns of angular covariations, the first pattern affecting selectively limb length and the second pattern affecting limb orientation. This decomposition, however, was found in only a few sporadic cases. 3. We also tested the possibility that the coordinate transformation involves the Moore-Penrose generalized inverse. We found that this algorithm produces a planar covariation of the joint angles, but with an orientation orthogonal to the experimental plane. By contrast, a linear transformation with constant, position-independent terms can fit the experimental plane of angular covariations but predicts large errors in endpoint position. 4. The particular orientation in joint space of the experimental plane, coupled with the scatter of data points around the plane, bears a specific implication for the problem of inverse mapping. The experimental plane crosses the constant position lines (the loci of all possible changes of the joint angles that correspond with an invariant position of the endpoint) at an acute angle. Consequently the specification of limb orientation is little sensitive to joint configurations: relatively small changes in orientation can be produced by large changes in joint configurations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2006

Bipedal locomotion: toward unified concepts in robotics and neuroscience.

This review is the result of a joint reflection carried out by researchers in the fields of robotics and automatic control on the one hand and neuroscience on the other, both trying to answer the same question: what are the functional bases of bipedal locomotion and how can they be controlled? The originality of this work is to synthesize the two approaches in order to take advantage of the knowledge concerning the adaptability and reactivity performances of humans and of the rich tools and formal concepts available in biped robotics. Indeed, we claim that the theoretical framework of robotics can enhance our understanding of human postural control by formally expressing the experimental concepts used in neuroscience. Conversely, biological knowledge of human posture and gait can inspire biped robot design and control. Therefore, both neuroscientists and roboticists should find useful information in this paper.

Cybernetics↗

PubMed2003

Static balance and developmental coordination disorder.

The development of static balance is a basic characteristic of normal motor development. Most of the developmental motor tests include a measure of static balance. Children with a developmental coordination disorder (DCD) often fail this item. Twenty-four children at risk for DCD with balance problems (DCD-BP) and 24 matched control children in the age range of 6-12 years participated in a detailed study of balance control. Additional groups of children (6-7 years, N=25; 10-11 years, n=16; with M-ABC scores >15th percentile) were selected randomly to study developmental changes in balance control in the age range of interest. Three experiments were conducted to examine developmental and clinical differences in the control of static balance. In the first, we measured the excursion of the centre of pressure (force-plate) in conditions with and without vision while standing still on one or two legs for 20 s. In the second experiment, EMGs were measured while standing on one leg. In the third experiment, in which only a subgroup of the DCD-BP and matched control children participated, a short unexpected force in the back lightly perturbed normal standing and EMG and force-plate responses were measured during balance recovery. In conditions of one-leg stance, children were not always able to maintain balance. Only epochs of stable postural control (7.5-20 s) were analysed. The results showed improvement of static balance with age, but only subtle differences between the DCD and control groups. Centre of pressure measures differed in the more difficult conditions. DCD-BP children had more difficulty standing on one leg with eyes closed. While standing on the non-preferred leg the EMGs of the DCD-BP children showed slightly more co-activation of the muscles of lower and upper leg. Perturbation of standing resulted in longer duration of recovery in the first trial in this group. Apparently DCD children learn to compensate for the perturbation within a few trials as well as control children do. The clear improvement with age shows that our measures of balance control are sensitive to detect changes. The general conclusion that may be drawn from this study is that under normal conditions static balance control is not a problem for children with DCD. Only in difficult or novel situations they seem to suffer from increased postural sway as a result of non-optimal balance control.

Child↗

PubMed1999

Assessing muscle stiffness from quiet stance in Parkinson's disease.

In previous studies, we developed a postural stiffness measure that is extracted from foot center-of-pressure (COP) trajectories from quietly standing individuals and is based on an analytical mechanical model of posture control. Here we apply this measure to patients with Parkinson's disease (PD). We correlated the postural stiffness measure with different clinical rating scales, obtained from patients. Kendall's rank correlation was highly significant between the stiffness measure and rigidity, bradykinesia, posture impairment, gait, and leg agility, respectively, as rated by the Unified Parkinson's Disease Rating Scale. These results provide further evidence that a higher intrinsic muscle stiffness may contribute to the aforementioned clinically defined symptoms. From a clinical standpoint, this work indicates that the proposed postural stiffness measure may be useful as an assessment tool for the evaluation of PD patients subsequent to pharmacological and surgical treatment.

Disability Evaluation↗

PubMed1984

Parametric analysis of dynamic postural responses.

A detailed theoretical understanding of postural control mechanisms must be preceded by careful quantification of both the deterministic and stochastic aspects of postural behavior of normal and abnormal subjects under various dynamic conditions. Toward this end, concise parametric transfer function plus noise models were derived for both shoulder and waist position data obtained by applying a linear anterior-posterior bandlimited pseudorandom disturbance to the base of support of human subjects. Model orders as well as model parameters were determined empirically. One advantage of this modeling procedure is the conciseness of the postural models, permitting easy statistical analysis of the data obtained under different dynamic conditions from many subjects. Model features, including pole and zero locations, from 6 normal subjects each tested on 5 consecutive days under 3 input amplitudes and eyes open and closed conditions are presented. The resulting transfer function models consist of only 1 or 2 poles near the integration position on the Z plane unit circle and 0 to 2 zeros. Locations of the poles indicate that the eyes closed responses are more oscillatory, less damped, and with higher gains than the eyes open responses. These transfer functions are similar to nonparametric ones of other authors. The noise model orders are also small. Their spectra are those of low pass systems. Also, the quantity and frequency range of the postural noise is positively related to the amplitude of platform motion as well as related to the presence or absence of vision.

Adult↗

PubMed1998

Evaluating sensory conflict and postural instability. Theories of motion sickness.

Two experiments were carried out to evaluate the sensory conflict and the postural instability theories of motion sickness. The central hypothesis of sensory conflict theory is that motion sickness is caused by conflict between the current pattern of sensory inputs about self-movement and the pattern that is expected on the basis of previous experience. A subsidiary hypothesis is that the degree of motion sickness is proportional to the magnitude of sensory conflict. The central hypothesis of postural instability theory is that motion sickness is caused by loss of postural control. A subsidiary hypothesis is that the degree of motion sickness is proportional to amount of postural instability, which can be manipulated by physical restraint. In both experiments there were two levels of sensory conflict and two levels of postural restraint. Dependent variables were latency of onset and severity of motion sickness. The widespread occurrence of motion sickness in both experiments clearly confirmed the main hypothesis of sensory conflict theory. The results from Experiment 1, that there was significantly more motion sickness in the restrained condition, and from Experiment 2, that there was no significant difference in symptoms between the two restraint conditions, provide no support for the subsidiary hypothesis of postural instability theory. Evidence relating to the subsidiary proposition of sensory conflict theory was inconsistent.

Adolescent↗

PubMed1991

Prolonged peroneal reaction time in ankle instability.

The peroneal reflex time to sudden ankle inversion and the postural control of 15 athletes with functionally instable ankles were compared with 15 stable controls. A trapdoor produced sudden ankle inversion. Surface electrodes recorded electromyographic activity of the peroneal muscles. Postural sway was expressed by a transverse sway value obtained during single limb stance on a force plate. Increased postural sway was found in subjects with functional instability (p less than 0.01). This is in accordance with previous studies. Functionally instable subjects also displayed an increased peroneal reaction time (p less than 0.01) supporting the theory that functional instability is induced by a proprioceptive reflex defect. Nine of the 15 instable subjects were unilaterally instable and showed lower peroneal reaction time and postural sway values for the stable ankle, but the difference was not significant. There was a high degree of correlation between postural sway and peroneal reaction time (Spearman's rho = .92). In ten functionally instable athletes tested with and without ankle taping, it could not be verified that a reflex enhancing effect of taping occurs through stimulation of cutaneous afferents.

Adult↗

PubMed2002

[Stabilimetry and cranio-cervico-mandibular disorders].

BACKGROUND: Cranio-cervico-mandibular disorders can cause disturbances in posture. Stabilimetry measures spatio-temporal variations in the center of body pressure and evaluates the mechanisms of maintenance of balance. The study used a stabilimetric platform to evaluate posture changes in patients with cranio-cervico-mandibular disorders before and after treatment for malocclusion. METHODS: Between February 1998 and December 2000, 60 patients with cranio-cervico-mandibular disorders were recruited from the Dentistry Clinic of the University of Sassari. Each patient underwent two stabilimetric examinations (closed mouth with cotton wads inserted between the dental arches). The tests were conducted on a stabilimetric platform. Measurement of body posture load and sway were analyzed with a specific software program that correlated the vestibular, somatosensory and visual systems, and determined the role of each in postural control. RESULTS: The stabilimetric analysis showed that the adoption of the plaque allowed rebalance of the postural system, without affecting the visual system. After treatment, 64% of patients experienced remission of pain symptoms with orthotic therapy. CONCLUSIONS: The relationship between malocclusion and posture should be seen from a holistic standpoint in other to gain a global therapeutic outcome.

Adolescent↗

PubMed1995

Interaction between postural and respiratory control of human intercostal muscles.

To study the interaction between postural and respiratory control of intercostal muscles, we used electromyography of intercostal muscles of the lateral chest wall in conscious humans. Bipolar fine-wire electrodes were placed in external and internal intercostal muscles in the midaxillary line of four subjects who sat on a bench and breathed through a pneumotachograph. They were instructed to hold their breath at end expiration, rotate their thorax to the right or left, and then hold the rotation while resuming breathing. Holding a rotation induces steady tonic activity in either internal or external intercostal muscles, depending on the direction of the rotation. The degree of rotation was varied from one run to the next, resulting in varied levels of tonic postural activity. When breathing resumes, internal intercostal muscles have their activity almost completely suppressed with each inspiration independently of whether the tonic postural tone is small or large. External intercostal muscles show inspiratory increases in activity superimposed on the postural tone, which apparently amplifies the effect of respiratory input to their motoneurons.

Adult↗

PubMed1986

The basal ganglia and the locomotor regions.

This review cites evidence suggesting that the pedunculopontine nucleus (PPN), long known as a site of termination for basal ganglia outputs, is equivalent to the mesencephalic locomotor region (MLR), an area known to modulate spinal locomotion oscillators. The presence of cholinergic cells in this area also identifies it with the CH-5 cell group. In keeping with its cellular make-up, evidence is reviewed suggesting that the descending output of the PPN/MLR is cholinergic. This output may be under nigral GABAergic control which, in turn, may be under subthalamic influence. From various lines of evidence, it appears that the PPN/MLR receives elements of information from the motor cortex and basal ganglia centers involved in postural control. This area may be involved in the relay of information useful in the control of the center of gravity and other postural functions during locomotion. Pathological evidence is reviewed implicating basal ganglia afferents to the PPN/MLR (Parkinson's disease) and PPN/MLR efferents (Alzheimer's disease) in the deficits in locomotion observed in certain disorders.

Alzheimer Disease↗

PubMed1997

Dissociation between the perception of body verticality and the visual vertical in acute peripheral vestibular disorder in humans.

Estimates of the subjective visual and postural vertical were obtained from five patients with acute peripheral vestibular lesions and 20 normal subjects. The visual vertical was assessed by asking the subjects to align a target line to earth vertical by means of remote control. Postural vertical judgments were obtained by exposing them to rotational displacements in the roll plane while sitting on a motor-driven chair and requiring them to align their body to vertical using a joystick control. While the patients showed strong deviations of the visual vertical towards the lesion side, their postural vertical judgments remained veridical. We conclude that the above perceptions are not processed identically and that the participating sensory systems are differently weighted during these tasks.

Adult↗

PubMed1998

[Static balance is controlled by a non-linear dynamic system].

Different techniques of stabilometric signal analysis have been used in order to study the adaptation of the fine postural control system to the wearing of corrective glasses with or without prisms. The comparison between the results obtained with conventional techniques and those obtained with non-linear dynamic methods demonstrates the better efficiency of the latter. These results confirm that the postural system behaves as a non-linear dynamical system and may explain the outstanding sensitivity of the fine postural system to small perturbations.

Adult↗

PubMed1995

A dorsal light reflex in a squid.

A dorsal light reflex is described in the squid Lolliguncula brevis. When illuminated from the side in visually homogeneous surroundings, a free-swimming squid rolls the dorsal side of its head and trunk 10-20 degrees towards the light. With the trunk restricted in a holder, the squid rolls its head 4-5 degrees towards the light; this reaction increases by about 50% when the statocysts are bilaterally removed and increases further when the neck receptor organ is also destroyed. The results indicate a multi-modal interaction of visual, statocyst and proprioceptive inputs during postural control.

Animals↗

PubMed2001

Hemodynamics as a possible internal mechanical disturbance to balance.

The postural control system is assessed by observing body sway while the subject involved aims at maintaining a specified up-right posture. Internal masses generate internal reaction forces that constitute an internal mechanical stimulus that may contribute to cause segmental displacements, i.e. body sway. Thus, gaining knowledge about the amplitude and direction of these reaction forces would contribute to gain insights into the mechanisms that influence the maintenance of balance and into its control. The 3-D force vector that acts on the body centre of mass (COM) and is associated with the transient blood movement at each cardiac cycle was assessed in a population sample of 20 young adults during the maintenance of a quiet up-right posture. Typical patterns of the three components of this force vector were identified. Relevant parameters were selected and submitted to sample statistics. For a number of them, linear correlation with subject-specific parameters was found. The antero-posterior force component was characterised by a triphasic major wave, the peaks of which had values up to 0.40 N. The vertical component showed a repeatable triphasic wave with peak-to-peak values in the range 1.3-3.0 N. The medio-lateral component showed relatively low peak-to-peak values (in the range 0.05-0.10 N). The resultant vector had an amplitude that underwent several oscillations during the cardiac cycle and reached its maximal value in the range 0.6-1.7 N.

Adaptation, Physiological↗

PubMed2003

The effect of walking aids on balance and weight-bearing patterns of patients with hemiparesis in various stance positions.

BACKGROUND AND PURPOSE: Standard and quad canes are often prescribed to patients with hemiparesis, yet their effect on postural control remains unclear. Thus, the objective of this study was to examine the effects of standard and quad canes on postural sway and on weight-bearing patterns in patients with hemiparesis. SUBJECTS: Thirty subjects with a diagnosis of unilateral hemiparesis following a stroke (patient group; mean age=71.2 years, SD=7.0) and 20 age-matched, community-dwelling volunteers without hemiparesis (comparison group; mean age=72.1 years, SD=5.2) participated in the study. METHODS: Postural sway and percentage of body weight (%BW) borne by each extremity were measured in 3 positions: with the heels aligned with each other (aligned position) and in staggered foot positions with either the affected or unaffected extremity placed forward (affected FW and unaffected FW positions). All subjects were tested in each position with no cane, a standard cane, and a quad cane. The order of tests was randomized, and analysis of data included use of an analysis of variance and adjusted Tukey-Kramer tests. RESULTS: In both the aligned and unaffected FW positions, postural sway was reduced only with the quad cane. Both types of canes reduced postural sway in the affected FW position; however, the quad cane had a greater effect. An asymmetrical weight distribution between the lower extremities did not change in the patient group across positions, even with walking aids. DISCUSSION AND CONCLUSION: A quad cane appears to be more effective than a standard cane in decreasing postural sway in patients with moderate impairment secondary to hemiparesis during stance. The greatest effect on postural sway occurred when the assistive device was contralateral to the foot placed forward. The use of a cane does not appear to adversely affect the asymmetrical weight-bearing pattern during stance that is characteristic of patients with hemiparesis, even when balance is challenged by decreasing the base of support.

Aged↗