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PubMed2001

Postural control and torque of the knee joint after healed tibial shaft fracture.

Muscular atrophy occurs as a consequence of trauma and immobilisation. This cohort comparison study was conducted to evaluate the limb function after healed tibial shaft fractures, which were treated by casting versus nailing. Balance (as centre of pressure) and muscle strength (as torque of the knee joint during knee extension) have been measured in 27 patients with tibial shaft fractures with a mean age of 39 (19-73) years, 1 year after fracture healing. Fourteen patients were treated by intramedullary nailing 'nailed group' and 13 by plaster cast with or without minimal internal fixation 'casted group'. Centre of pressure was measured on a force platform. Knee extension torque was measured during isometric and concentric muscle actions by an isokinetic dynamometer. Centre of pressure tended to be more towards the uninjured leg in patients who had been treated by plaster cast (P<0.05). Side-to-side differences for isometric torque were significantly higher within the casted group (P<0.05). Patients with tibial shaft fractures treated by intramedullary nailing showed better postural control, one-leg standing test, and side-to-side differences for isometric muscle strength compared with patients treated by cast. Therefore, we recommend intramedullary nailing as a better method of treatment for tibial shaft fractures, with regard to recovery of muscle function.

Adult↗
PubMed2000

The effect of shoe lifts on static and dynamic postural control in individuals with hemiparesis.

OBJECTIVE: To determine the effect of lifts to the shoe of the nonaffected leg on weight symmetry and dynamic posturography in individuals with hemiparesis. DESIGN: Quantitative posturography was performed to determine subjects' response to sudden perturbations. Subjects received graded forward and backward perturbations while standing on a movable force platform. Compelled shift of the body weight was induced with sized lifts to the shoe of the nonaffected leg. Balance responses were analyzed in terms of latency and strength of neuromuscular response. Symmetry scores were used to characterize the symmetry of stance. SETTING: Free-standing acute inpatient rehabilitation hospital. PARTICIPANTS: Ten individuals with hemiparesis as a result of unilateral stroke. MAIN OUTCOME MEASURES: Weight symmetry scores, latencies of each leg's active response to the support surface translations, and response strength scores of each leg to the platform translations. RESULTS: When no lift was used, weight symmetry was characterized by underloading of the affected limb, as well as by longer onset latencies for the affected limb compared with the stronger one (158.5 +/- 3.9 vs 151.1 +/- 3.5 ms; p < .01 for large backward translations; 165.7 +/- 7.2 vs 158.0 +/- 5.1 ms; p < .01 for large forward translations). Response strength of the nonparetic limb was 2 times greater than the response strength of the weaker extremity (p < .05). Compelled weight shift induced by lifts applied to the shoe of the nonparetic limb promoted improved weight symmetry, shortened latencies, and increased magnitudes of the response strength. CONCLUSION: Lifts applied to the shoe of the stronger limb induced a body weight shift toward the paretic limb and resulted in improved symmetry of stance and postural control of individuals with hemiparesis. We suggest that compelled weight distribution induced by lifts to the shoe of the stronger limb could help treat ambulatory individuals with asymmetric stance and hemiparesis caused by unilateral stroke.

Adult↗
PubMed1999

An investigation of postural control in postoperative anterior cruciate ligament reconstruction patients.

OBJECTIVE: To investigate quadriceps strength and static and dynamic balance in the anterior cruciate ligament (ACL)-reconstructed patient and to compare these findings with an age-matched, injury-free control group. DESIGN AND SETTING: A 2 x 2 mixed-design analysis of variance (group x leg) was applied to the static posture, dynamic balance, and strength data. In addition, Pearson product-moment correlations were calculated to determine the strength of the relationships among the dependent measures. All data were collected in the Motor Control Laboratory at Indiana University. SUBJECTS: The experimental group was composed of 20 individuals who had undergone ACL reconstruction with a patellar tendon autograft. The control group comprised 20 participants with no history of significant orthopaedic injuries to the lower extremities. MEASUREMENTS: The dependent variables were sway path linear mean for the static condition, dynamic-phase recovery time after perturbation for the dynamic measure, and quadriceps peak torque for strength. RESULTS: We found significant differences between the ACL and control groups on the measures of dynamic-phase duration and peak torque. The static sway variable did not show a significant difference. CONCLUSIONS: Evaluation of the postural control system under 2 conditions, static and dynamic, showed differences between the ACL and control groups for the dynamic condition only. These results suggest the presence of independent control mechanisms for the control of static and more dynamic postures. In addition, because there were no differences between the injured and noninjured legs of the ACL group, the theory of a central postural control scheme is supported.

Journal Article↗
PubMed2005

The effects of an attentional demand tasks on standing posture control.

The present study sought to determine if the postural sway of a subject required to grasp a tray (motor task) holding a cup filled with water and prevent spilling (mental task), would be reduced by consciously redirecting attention to maintain the tray in a horizontal position. We hypothesized the mental task would increase the stabilization of standing postural balance. Postural sway was measured in 17 normal subjects under the following conditions: 1) holding a 100 g weight in each hand (total 200 g; no mental task), 2) holding with both hands a tray on which 200 g was placed (tray-holding task), and 3) holding with both hands a tray on which a cup filled with water weighing 200 g was placed in the center (mental task). Postural sway was significantly reduced during the mental task versus other tasks. Standing posture balance was stabilized when a mental task was added. Thus, we concluded that higher brain functions such as attention and consciousness exerted a significant influence over the control of standing posture.

Adult↗
PubMed2005

Repeated visually-guided saccades improves postural control in patients with vestibular disorders.

One of the most recent and promising theoretical hypotheses for compensation of persistent asymmetry of dynamic vestibulo-ocular gain is sensory substitution. As a switch between oculomotor and vestibulo-ocular systems, saccadic eye movements are engaged in humans to compensate the angular displacement of the head towards the labyrinthine defective side thus preserving the foveal fixation of the target. This study focused on the possibility that saccadic eye movements might also compensate for the impaired vestibulo-spinal reflexes and force the postural system to a more effective control on upright stance and verified whether this sway-stabilizing effect could be applied to patients with vestibular disorders and balance dysfunction. In the first experiment, 27 patients with unilateral labyrinthine hypofunction, 24 patients with central vestibular disorders and 24 healthy volunteers were evaluated by static posturography in 3 different visual conditions: (a) eye open with fixation of a steady target, (b) eye closed, and (c) while performing horizontal visually-guided saccades. The percentage of individuals with a decreased body sway area during the oculomotor task was found to be higher in labyrinthine-defective patients as compared to those with central vestibular disorders and controls. In the second experiment, 46 patients with vestibular disorders both of central and peripheral origin, whose postural control improved by eye-tracking, as assessed by posturography, were later submitted to 12 consecutive training sessions based on repeated visually-guided saccades. Both the saccadic performances and postural control improved in all patients but a more pronounced effect was observed in those with peripheral vestibular disorders. Outcome of this rehabilitation technique was also corroborated by a general reduction of the perceived overall impairment from balance disorders as tested by a specific questionnaire.

Adult↗
PubMed2004

Seated postural control in adolescents with idiopathic scoliosis.

STUDY DESIGN: The center of pressure (COP) path in 14 adolescents with idiopathic scoliosis and 12 age-matched able-bodied adolescents was compared using traditional measures and a two-level decomposition. OBJECTIVES: To investigate whether asymmetries in the spines of children with idiopathic scoliosis are reflected in altered sway patterns in quiet sitting. SUMMARY OF BACKGROUND DATA: Previous studies have studied the sway of children with scoliosis while standing. However, the standing posture is typically controlled at the ankle joint. To date, there are no studies with this population of sitting sway, where the movement is controlled by the trunk muscles. METHODS: Traditional measures of the COP of the trunk were analyzed. The COP was also decomposed into an approximation of the center of mass path and deviations around this path. RESULTS: COP movement in sitting, reflecting the postural control of the spine, was decreased in adolescents with idiopathic scoliosis. Children with scoliosis had symmetric sitting COP trajectories and most measures were similar between the two groups. CONCLUSIONS: The results suggest a control strategy for maintaining a sitting posture that does not change with the development of scoliosis but does adapt by decreasing movement to maintain the trunk in a region where the it can remain "passively" stable.

Adolescent↗
PubMed1993

Postural control and age.

We quantified the effect of vision, pressoreceptor function and proprioception on the postural stability at different ages. Altogether 212 healthy volunteers (ages from 6 to 90 years) were examined by using a computerised force platform. The sway velocity (SV) was measured with eyes open and eyes closed during quiet stance on a bare platform and a foam plastic covered surface. In addition, to study the proprioceptive system, pseudorandom vibration perturbation was applied on the calf muscles. The SV showed a U-shaped curve: the children and the oldest swayed most. Equilibrium was most stable around 50 years. The visual system was of most importance for balance control in the old. The children were sensitive of pressoreceptor and proprioceptive perturbation, indicating the importance of these systems for their postural control.

Adult↗
PubMed1998

Gabapentin and carbamazepine affect eye movements and posture control differently: a placebo-controlled investigation of acute CNS side effects in healthy volunteers.

This prospective study examined the effects of the new antiepileptic drug (AED) gabapentin (GBP) compared to the standard AED carbamazepine (CBZ) and placebo (PLA) on eye movements, posture and finger force control in 12 healthy volunteers who received single doses of 600 mg GBP and 400 mg CBZ in a placebo-controlled, double-blind, cross-over, randomized trial. CBZ and GBP reduced almost equally (8% vs. 10%) the mean peak saccade velocity as compared to PLA (P < 0.05). CBZ, but not GBP, significantly prolonged the duration of saccades as compared to placebo (14-24%) (P < 0.05). GBP produced a greater maximal increase of body sway than CBZ with eyes open (P < 0.01) and eyes closed (P < 0.001). CBZ and GBP did not significantly influence control of grip force. CBZ effects were better correlated with plasma levels. Subjective side effects were more pronounced with CBZ than GBP. Although CBZ and GBP cause similar CNS side effects, the effects on eye movements and body sway were different. CBZ predominantly affects saccadic eye movements, whereas GBP had more impact on posture control. Thus, electro-oculography seems to be more appropriate in the detection of CBZ-induced side effects and posturography appears to be more sensitive in the detection of side effects associated with GBP.

Acetates↗
PubMed2000

Neuronal mechanisms for the control of body orientation in clione II. Modifications in the activity of postural control system.

The marine mollusk Clione limacina, when swimming, can stabilize different body orientations in the gravitational field. The stabilization is based on the reflexes initiated by activation of the statocyst receptor cells and mediated by the cerebro-pedal interneurons that produce excitation of the motoneurons of the effector organs; tail and wings. Here we describe changes in the reflex pathways underlying different modes of postural activity; the maintenance of the head-up orientation at low temperature, the maintenance of the head-down orientation at higher temperature, and a complete inactivation of the postural mechanisms during defense reaction. Experiments were performed on the CNS-statocyst preparation. Spike discharges in the axons of different types of neurons were recorded extracellularly while the preparation was rotated in space through 360 degrees in different planes. We characterized the spatial zones of activity of the tail and wing motoneurons and the CPB3 interneurons mediating the effects of statocyst receptor cells on the tail motoneurons. This was done at different temperatures (10 and 20 degrees C). The "fictive" defense reaction was evoked by electrical stimulation of the head nerve. At 10 degrees C, a tilt of the preparation evoked activation in the tail motoneurons and wing retractor motoneurons contralateral to the tilt and in the wing locomotor motoneurons ipsilateral to the tilt. At 20 degrees C, the responses in the tail motoneurons and in the wing retractor motoneurons occurred reversed; these neurons were now activated with the ipsilateral tilt. In the wing locomotor motoneurons the responses at 20 degrees C were suppressed. During the defense reaction, gravitational responses in all neuron types were suppressed. Changes in the chains of tail reflexes most likely occurred at the level of connections from the statocyst receptor cells to the CPB3 interneurons. The changes in gravitational reflexes revealed in the present study are sufficient to explain the corresponding modifications of the postural behavior in Clione.

Animals↗
PubMed2001

Static and dynamic postural control in long-term microgravity: evidence of a dual adaptation.

The adaptation of dynamic movement-posture coordination during forward trunk bending was investigated in long-term weightlessness. Three-dimensional movement analysis was carried out in two astronauts during a 4-mo microgravity exposure. The principal component analysis was applied to joint-angle kinematics for the assessment of angular synergies. The anteroposterior center of mass (CM) displacement accompanying trunk flexion was also quantified. The results reveal that subjects kept typically terrestrial strategies of movement-posture coordination. The temporary disruption of joint-angular synergies observed at subjects' first in-flight session was promptly recovered when repetitive sessions in flight were analyzed. The CM anteroposterior shift was consistently <3-4 cm, suggesting that subjects could dynamically control the CM position throughout the whole flight. This is in contrast to the observed profound microgravity-induced disruption of the quasi-static body orientation and initial CM positioning. Although this study was based on only two subjects, evidence is provided that static and dynamic postural control might be under two separate mechanisms, adapting with their specific time course to the constraints of microgravity.

Adaptation, Physiological↗
PubMed2006

Effects of preparatory period on anticipatory postural control and contingent negative variation associated with rapid arm movement in standing posture.

We investigated CNS motor preparation state and anticipatory postural muscle activation while subjects performed bilateral rapid arm movement at various intervals between warning and response stimulus (preparatory period) during standing. Motor preparation state was evaluated by integrated values of the late components of the contingent negative variation (late CNV), obtained by averaging electroencephalograms during the last 100ms of the preparatory period. For quantifying anticipatory postural muscle activation, we measured the onset of burst activity in postural muscles (lumbar paraspinal, biceps femoris, and gastrocnemius) with respect to anterior deltoid activity and integrated values of preceding activation. Subjects performed the arm movement with minimal delay in the warning stimulus-response stimulus-motor response paradigm under preparatory periods of 2.0, 3.0 and 3.5s. Late CNV did not differ between the 2.0-s and 3.0-s period, but was significantly smaller in the 3.5-s period than in the 2.0-s period, suggesting difficulty in predicting response timing in the 3.5-s period. No change was found on integrated values of preceding activations of postural muscles. Burst onset of all postural muscles significantly preceded anterior deltoid activation in all periods. Burst activity for gastrocnemius only occurred earlier in the 3.5-s period than in the 2.0-s and 3.0-s periods. Weak correlations were observed between late CNV and onset time of gastrocnemius activity. It is suggested that earlier activation of gastrocnemius is a strategy adopted when response stimulus timing is relatively difficult to predict.

Adult↗
PubMed2006

Asymmetries in postural control and locomotion in chimpanzees (Pan troglodytes).

Posture and locomotion are two of the most primitive and basic motor manifestations of an organism's behavior. Although the restrictions they impose on other motor functions are evident, few studies have considered the possibility of asymmetries in these behaviors in human and nonhuman primates, and how they might impact other asymmetries at higher functional levels. The aim of the current study was to explore in a group of 10 chimpanzees at the Madrid Zoo-Aquarium the degree of asymmetry in four behaviors related to locomotion (walking, ascending, descending, and brachiating) and four behaviors associated with posture (sitting, lying, hanging, and changing postures). Few subjects showed individual preferences, but significant trends in the group for some of the behaviors were found, including right-hand use when initiating quadruped walking, and left-hand use when descending and hanging. Some significant correlations also emerged: a negative one between walking and descending, and a positive one between walking and brachiating and between sitting and changing postures. No correlations were found between locomotor and postural modes. Although we cannot make generalizations on the population level at this time, these findings highlight the importance of considering postural and locomotion factors when studying motor asymmetries in primates.

Animals↗
PubMed1997

The effects of hyperventilation on postural control mechanisms.

The effect of hyperventilation on postural balance was investigated. Voluntary hyperventilation increased body sway in normal subjects, particularly in the sagittal plane. The possibility that this hyperventilation-induced unsteadiness is due to interference with lower limb somatosensory input, vestibular reflexes or cerebellar function was assessed. (i) The effect of hyperventilation on peripheral compound sensory action potentials (SAPs) and somatosensory evoked potentials (SEPs) (recorded centrally, from the scalp) elicited by electrical stimulation of the sural nerve was measured in six normal adults. A reduction in the scalp SEP amplitude and an increase in the peripheral SAP amplitude were observed during hyperventilation, which reversed during the recovery period. These changes indicate increased peripheral neural excitability which could lead to a higher level of ectopic activity; the latter would interfere with central reception of peripheral input. (ii) The click-evoked vestibulo-collic reflex was recorded to study the effect of hyperventilation on vestibulo-spinal activity. EMG recordings from both sternocleidomastoid muscles of six healthy subjects were made in response to loud clicks presented to either ear. Neither the amplitude nor the latency of the response were altered significantly by hyperventilation. (iii) Eye-movement recordings were obtained in the six normal subjects to assess the effect of hyperventilation on the vestibulo-ocular reflex and its visual suppression, the latter being a function largely mediated by the cerebellum; no changes were detected. (iv) Three-dimensional eye-movement recordings and body-sway measurements were obtained in six patients with longstanding unilateral vestibular loss in order to evaluate if hyperventilation disrupts vestibular compensation. In all patients, a horizontal nystagmus either appeared or was significantly enhanced for > or = 60 s after voluntary hyperventilation. Sway was also enhanced by hyperventilation in these patients, particularly in the frontal plane. This study suggests that hyperventilation disrupts mechanisms mediating vestibular compensation. The increase in sway may be, at least partly, mediated by deranged peripheral and central somatosensory signals from the lower limbs. Hyperventilation seems to spare vestibular reflex activity and cerebellar-mediated eye movements.

Acoustic Stimulation↗
PubMed2000

Goal directed reaching and postural control in supine position in healthy infants.

The present study focussed on the development and interaction of reaching and posture in supine position in young infants. The kinematics of goal directed reaches and the concurrent ground reaction forces of the total body centre of pressure (COP) in cranial-caudal and medial-lateral direction were recorded in twelve healthy fullterm infants at 4 and 6 months of age. From eight infants, data were available at both ages. The results indicated that between 4 and 6 months, postural stability during reaching in supine position increased, as the oscillatory COP displacement in the medial-lateral direction decreased significantly with increasing age. Concurrently, reaching performance improved, which was reflected by a decrease in the number of movement units (MU), the length of the displacement-path of the hand and an increase of the length and duration of the first MU. The kinematic data of the reaching movements and the COP data were correlated at both ages, but the nature of the relation changed. At 4 months of age, the number of MU was related to the number of COP oscillations in the cranial-caudal direction, whereas at 6 months the maximum velocity of the hand movement was related to the maximum velocity of COP displacement in cranial-caudal and medial-lateral direction. This change might point to the development of a more subtle control of postural adjustments during reaching movements in supine position.

Aging↗
PubMed1999

Long-term adaptation of postural control in microgravity.

Orbital microgravity represents a unique environment, which allows the isolation of variables assumed to be involved in the mechanism of body positioning in space. In this context, the alignment of the trunk axis along allocentric references and the positioning of the body center of mass inside the supporting base compete for the role of the primary-controlled variable when assuming erect posture. This paper reports the quantitative evaluation of the postural strategies exhibited by two subjects with feet fixed to the floor of the space module along a 4-month period of exposure to microgravity. With respect to previous findings in parabolic flights and short term space missions, the analysis focused on long-term process of sensorimotor adaptation to weightlessness. Results show that while trunk-axis orientation is preserved and used as a stable postural frame of reference, the positioning of the body center of mass appears to be significantly biased backward and turns out to be involved in a long-term process of adaptation throughout the entire flight towards the re-emergence of a typically terrestrial postural regulation compatible with equilibrium.

Adult↗
PubMed1988

Response preparation and posture control. Neuromuscular changes in the older adult.

Experiments comparing the characteristics of neuromuscular responses underlying balance control in young and old adults have shown a number of differences between the two populations. Postural muscle response latencies of the ankle musculature activated by external threats to balance are slightly, but significantly, longer in the latter population. In addition, some aging subjects show a temporal reversal of proximal and distal muscle response onset in some trials. There is also a breakdown of the correlation of the amplitude of the muscle responses within a synergy in some of the older subjects tested. Older adults also exhibited cocontraction of agonist and antagonist muscles within a response synergy to a greater extent than young adults. This stiffening of the joints by antagonist cocontraction could be a compensation for the lack of the ability to fine-tune the postural responses to the same degree as the young adults. Analysis of sensory integration abilities showed an impairment in balance control under conditions of reduced or conflicting sensory information. When they were given inappropriate visual and somatosensory inputs, half of the older adults lost balance on the first trial. In most instances, however, the older adults were able to maintain balance during a second trial consisting of the same sensory stimuli. When visual cues were reduced by restricting the visual field to either central or peripheral visual cues, we found no difference in postural muscle response latencies. However, the aging adult group showed more losses of balance than the younger group with peripheral vision removed or with eyes closed. In addition, there was a strong correlation between the subjects that showed stronger deficits on an initial neurological exam and the number of times that balance was lost. Studies on changes in the linkage between postural and voluntary muscle interactions during voluntary arm movements in older adults indicate an increase in the latency of feed-forward activation of postural muscles. However, voluntary muscle response onset latencies show greater increases in the old compared to the young. This suggests that deterioration of the speed of activation of the postural control system is not the only factor that limits the speed of voluntary movement onset. Measurements have not yet been made on the amplitude regulation of feed-forward responses of postural muscles during a voluntary task. It may be that the regulation of the speed of activation of the two systems is less important than the fine tuning of the correlation of appropriate response amplitudes between the two systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed2005

Development of postural control in healthy children: a functional approach.

From a set of experimental studies showing how intersegmental coordination develops during childhood in various posturokinetic tasks, we have established a repertoire of equilibrium strategies in the course of ontogenesis. The experimental data demonstrate that the first reference frame used for the organization of balance control during locomotion is the pelvis, especially in young children. Head stabilization during posturokinetic activities, particularly locomotion, constitutes a complex motor skill requiring a long time to develop during childhood. When studying the emergence of postural strategies, it is essential to distinguish between results that can be explained by biomechanical reasons strictly and those reflecting the maturation of the central nervous system (CNS). To address this problem, we have studied our young subjects in situations requiring various types of adaptation. The studies dealing with adaptation of postural strategies aimed at testing short and long-term adaptation capacity of the CNS during imposed transient external biomechanical constraints in healthy children, and during chronic internal constraints in children with skeletal pathologies. In addition to maintenance of balance, another function of posture is to ensure the orientation of a body segment. It appears that the control of orientation and the control of balance both require the trunk as an initial reference frame involving a development from egocentric to exocentric postural control. It is concluded that the first step for children consists in building a repertoire of postural strategies, and the second step consists in learning to select the most appropriate postural strategy, depending on the ability to anticipate the consequence of the movement in order to maintain balance control and the efficiency of the task.

Adaptation, Physiological↗