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At least 991 records · Page 55Linked to original sources

PubMed2003

Aging, muscle activity, and balance control: physiologic changes associated with balance impairment.

Older adults demonstrate increased amounts of postural sway, which may ultimately lead to falls. The mechanisms contributing to age-related increases in postural sway and falls in the elderly remain unclear. In an effort to understand age-related changes in posture control, we assessed foot center-of-pressure (COP) displacements and electromyographic data from the tibialis anterior, soleus, vastus lateralis, and biceps femoris collected simultaneously during quiet-standing trials from elderly fallers, elderly non-fallers, and healthy young subjects. Both traditional measures of COP displacements and stabilogram-diffusion analysis were used to characterize the postural sway of each group. Regression analyses were used to assess the relationship between the COP measures and muscle activity. Elderly fallers demonstrated significantly greater amounts of sway in the anteroposterior (AP) direction and greater muscle activity during quiet standing compared with the young subjects, while elderly non-fallers demonstrated significantly greater muscle activation and co-activation compared with the young subjects. No significant differences were found between elderly fallers and elderly non-fallers in measures of postural sway or muscle activity. However, greater postural sway in both the AP and mediolateral (ML) directions and trends of greater muscle activity were found in those older adults who demonstrated lower scores on clinical measures of balance. In addition, short-term postural sway was found to be significantly correlated with muscle activity in each of these groups. This work suggests that high levels of muscle activity are a characteristic of age-related declines in postural stability and that such activity is correlated with short-term postural sway. It is unclear whether increases in muscle activity preclude greater postural instability or if increased muscle activity is a compensatory response to increases in postural sway.

Accidental Falls↗

PubMed2001

Simulating mechanical consequences of voluntary movement upon whole-body equilibrium: the arm-raising paradigm revisited.

Voluntary arm-raising movement performed during the upright human stance position imposes a perturbation to an already unstable bipedal posture characterised by a high body centre of mass (CoM). Inertial forces due to arm acceleration and displacement of the CoM of the arm which alters the CoM position of the whole body represent the two sources of disequilibrium. A current model of postural control explains equilibrium maintenance through the action of anticipatory postural adjustments (APAs) that would offset any destabilising effect of the voluntary movement. The purpose of this paper was to quantify, using computer simulation, the postural perturbation due to arm raising movement. The model incorporated four links, with shoulder, hip, knee and ankle joints constrained by linear viscoelastic elements. The input of the model was a torque applied at the shoulder joint. The simulation described mechanical consequences of the arm-raising movement for different initial conditions. The variables tested were arm inertia, the presence or not of gravity field, the initial standing position and arm movement direction. Simulations showed that the mechanical effect of arm-raising movement was mainly local, that is to say at the level of trunk and lower limbs and produced a slight forward displacement of the CoM (1.5 mm). Backward arm-raising movement had the same effect on the CoM displacement as the forward arm-raising movement. When the mass of the arm was increased, trunk rotation increased producing a CoM displacement in the opposite direction when compared to arm movement performed without load. Postural disturbance was minimised for an initial standing posture with the CoM vertical projection corresponding to the ankle joint axis of rotation. When the model was reduced to two degrees of freedom (ankle and shoulder joints only) the postural perturbation due to arm-raising movement increased compared to the four-joints model. On the basis of these results the classical assumption that APAs stabilise the CoM is challenged.

Arm↗

PubMed2004

Attentional demand for regulating postural sway: the effect of expertise in gymnastics.

A dual-task paradigm was used to investigate whether the expertise in motor skills requiring a fine postural control can modify the attentional demand necessary for regulating postural sway. Seven expert gymnasts and seven experts in other non-gymnastic sports were asked to respond as rapidly as possible to an unpredictable auditory stimulus while maintaining stable seated and in three upright postures of increasing difficulty: bipedal, unipedal, and unipedal on an unstable support (i.e. a 7 cm thick foam surface). RT values were used as an index of the attentional demand necessary for performing the postural tasks. Results showed that the attentional demand necessary for regulating postural sway increased as the postural task increased in difficulty. Interestingly, this effect was smaller for the gymnasts during unipedal stance. These findings suggest a decreased dependency on attentional processes for regulating postural sway during unipedal stance in gymnasts with respect to non-gymnasts.

Adolescent↗

PubMed2005

The influence of concurrent cognitive tasks on postural sway in children.

PURPOSE: The purpose of this study was to examine the influence of concurrent tasks on postural sway in children. METHODS: Nineteen fourth-grade students, while standing on a balance platform, were asked to stand still, count backward, and read second-grade level sentences. The AMTI Accusway System was used to calculate the length of center of pressure path (LCOP), sway range (SR), and variability (SV) in mediolateral (ML) and anteroposterior (AP) directions of sway. RESULTS: Analysis of variance revealed a main effect of cognitive task condition for SR-AP, SR-ML, SV-AP, and SV-ML. Post hoc comparisons revealed lower values of those four dependent measures for the counting backward task than for the standing still task and lower SV-AP for the counting backward task than for the reading task. In addition, there was a trend toward greater LCOP when performing a concurrent cognitive task. CONCLUSIONS: The demands of concurrent cognitive tasks while standing affect postural sway in children. The findings of this study contribute to our understanding of postural control in children and may explain why improvements in postural skills attained in clinical settings may not transfer to improved performance in other settings.

Analysis of Variance↗

PubMed1981

[Interaction of general body posture, oral and facial region. I. Literature and clinical findings (author's transl)].

Postural control of head and trunk is basic for adequate posture and movement of eyes, facial, oropharyngeal and limb muscles. On the other hand there are also influences of ocular and oro-pharyngeal movements on posture and movements of neck, trunk and limbs. After a review of experimental and clinical observations several pertinent own observations are presented. The advantage of the systematic use of these phenomena for habilitation and rehabilitation of patients with motor handicaps is stressed.

Adolescent↗

PubMed2003

Contribution of genetic and environmental effects to postural balance in older female twins.

The aim of the present study was to determine the relative roles of genetic and environmental influences on postural balance in older women. The participants were 97 monozygotic (MZ) and 102 dizygotic (DZ) female twins, aged 64-76 yr. Postural sway was measured during side-by-side stance with eyes open and eyes closed, and during semitandem stance with eyes open on a force platform. Sway data were condensed into four first-order and one second-order latent factors. The second-order factor, named balance, incorporates sway data from multiple tests and thus best describes the phenotype of postural balance. The contribution of genetic and environmental influences on the variability of the latent factors was assessed by using structural equation modeling. Additive genetic influences accounted for 35% and shared environmental influences accounted for 24% of the total variance in the balance factor. In the present study, postural balance in older women had a moderate genetic component. Genetic influences on postural balance may be mediated through gene variation in the systems that control posture. The finding that individual environmental influences accounted for almost one-half of the variance in postural balance points to the potential of targeted interventions to maintain and improve balance control in older persons.

Aged↗

PubMed2000

Is lower leg proprioception essential for triggering human automatic postural responses?

It is unknown to what extent automatic postural responses are triggered by lower leg proprioception. This issue was addressed by studying postural control in five carefully selected patients with subtle diabetic polyneuropathy (restricted to the lower legs) and 15 healthy subjects. All patients had bilaterally absent Achilles tendon reflexes and weak or absent patella tendon reflexes, but muscle strength was fully preserved. Subjects were tested while standing on a supporting, movable force-plate. The contribution of lower leg proprioception to automatic postural responses was investigated by randomly exposing the subjects to either a 4 degrees 'toe-up' rotational perturbation ('normal ankle input'), a simultaneous 4-cm rearward translation and 4 degrees toe-up rotation ('enhanced ankle input'), or a simultaneous 4-cm rearward translation and 4 degrees 'toe-down' rotation ('nulled ankle input'). We recorded surface EMG (stretch reflexes and balance-correcting responses) from leg and trunk muscles, ankle torque and angular velocities of the upper and lower legs and trunk. We argued that automatic postural responses that have abnormally small amplitudes in patients and are modulated in controls with the velocity of different types of ankle rotations must receive a major input from lower leg proprioception. Conversely, automatic postural responses that are weakly modified in amplitude or onset by different ankle perturbations and are present despite nulled ankle inputs and, finally, are unaffected in patients with distal polyneuropathy must be triggered or modulated by inputs other than from lower leg proprioception. Normal postural synergies and strategies were maintained in patients, although within a given synergy the timing and amplitude of some automatic postural responses were abnormal. A few automatic postural responses appeared to be triggered or modulated by lower leg proprioception. Thus, early stretch reflexes in soleus and medial gastrocnemius were severely diminished in patients, while in controls these stretch reflexes were modulated by different ankle perturbations. Furthermore, balance-correcting responses in tibialis anterior were diminished and delayed in patients, while in controls these balance-correcting responses were modulated by different ankle perturbations. Other automatic postural responses were apparently not triggered or modulated by lower leg proprioception, but likely received a major input from more proximal sensory systems. Thus, in both groups prominent balance-correcting responses were present in several muscles (soleus, gastrocnemius, quadriceps, paraspinals and trapezius) during the 'nulled ankle input' condition, where ankle position was stabilised over the first 250 ms. During the 'enhanced ankle input' condition, where prominent ankle dorsiflexion occurred during the first 200 ms, amplitudes of balance-correcting responses were only marginally weaker in patients than in controls. We analysed body segment displacements to unveil the potential nature of proximal triggers for automatic postural responses. As opposed to the 'inverted pendulum' concept of postural control, early movement occurred in the knees, hips and trunk well before the onset of automatic postural responses. For example, during the 'nulled ankle input' condition, the lower leg moved forward with early knee flexion, followed by knee extension. The trunk extended backwards at 80 ms, which was followed by forward flexion. The absent stretch reflex and weaker balance-correcting responses in patients produced changed trunk velocity profiles (mainly a reduced initial backward motion of the trunk), but lower-body segment movements showed no consistent differences between the two groups. Considering these body segment displacements, any automatic postural response with an onset within the first 200 ms could well be triggered by receptors located at the knee, hip or trunk. (ABSTRACT TRUNCATED)

Achilles Tendon↗

PubMed1995

The effects of proprioceptive ankle disk training on healthy subjects.

According to research, proprioceptive training enables injured subjects to reduce proprioceptive deficits and increase postural control. However, the effects of proprioceptive training have not been researched in healthy subjects. This study investigated the effects of Biomechanical Ankle Platform System (BAPS) training on postural sway of healthy subjects (N = 28). Subjects were pretested and posttested using the Kistler force platform while performing a single limb stance. The subjects stood on their dominant leg with the opposite hip and knee held in a self-selected position. Subjects trained the dominant leg three times per week for 10 weeks on the BAPS. Experimental subjects showed significant improvements in both the medial-lateral and anterior-posterior parameters of postural sway when compared with a control group. In conclusion, 10 weeks of proprioceptive ankle disk training significantly decreased postural sway in both the medial-lateral and anterior-posterior directions.

Adolescent↗

PubMed2006

Impaired scaling of responses to vestibular stimulation in incomplete SCI.

Patients with incomplete spinal cord injury (iSCI) have impaired postural control leading to a high danger of falling. Clinically, it is impossible to assess the extent to which postural instability due to sensorimotor deficit is influenced by a disturbance in the vestibulospinal pathways. Galvanic vestibular stimulation (GVS) was applied to investigate changes in the vestibular spinal responses and their potential influence on postural stability in iSCI patients. Six chronic iSCI patients and age-matched controls were stimulated with a bipolar binaural stimulus. The centre of pressure (CoP) and soleus EMG responses during free standing with closed eyes on firm and compliant ground were measured. The impairment in postural stability was assessed by the mean amplitude of CoP deflections during two minutes undisturbed standing. Although iSCI patients were significantly less stable than controls, direct GVS responses of the soleus EMG and postural sways tended to be increased on firm ground. The GVS responses increased when changing from firm to compliant ground, showing a close correlation between the extent of postural instability and the response amplitudes. Therefore, challenging proprioceptive feedback induced a significant up-modulation of the GVS responses. However, when we took the postural instability in iSCI patients into account, the EMG and CoP responses to GVS were reduced compared to controls. The combined assessment of EMG and CoP responses to GVS complements the clinical examination and permits evaluation of the preservation and modulation of vestibulospinal responses in iSCI.

Aged↗

PubMed1993

Impaired scaling of long latency postural reflexes in patients with Parkinson's disease.

Young normal subjects adapt the size of posturally stabilizing reflexes in the lower extremity to predictable and unpredictable perturbations through shifts in cognitive set. It is unknown whether limitations in this ability to shift cognitive set may contribute to impaired scaling of postural reflexes in patients with Parkinson's disease. In this study, we have addressed this issue in 12 posturally unstable Parkinson patients and 13 age- and sex-matched controls. Postural stability was disturbed by sudden toe-up rotations of a supporting platform upon which subjects were standing. Subjects' cognitive set was altered by varying the perturbation amplitude either predictably (serial 4 degrees versus serial 10 degrees) or unpredictably (random mixture of 4 degrees and 10 degrees). Posturally stabilizing long latency (LL) reflexes were recorded from the shortened tibialis anterior muscle of both legs. We found that Parkinson patients, unlike some control subjects, were unable to scale the size of their LL reflex in response to variations in perturbation amplitude during predictable conditions. In addition, we observed that Parkinson patients could not modify the amplitude of the LL reflex through alterations in cognitive set during random conditions. We conclude that Parkinson patients have a fundamental difficulty in modifying the size of posturally stabilizing LL reflexes, as reflected by both problems with amplitude scaling and difficulties with changes in cognitive set. It is possible that this inability to modify LL reflexes may be a factor contributing to postural instability in Parkinson's disease.

Adult↗

PubMed2001

Muscular contractions and their effect on the vertical ground reaction force during quiet stance--Part I: Hypothesis and experimental investigation.

There is no consensus as to the origins of the oscillations of the vertical ground reaction force during quiet stance. The concept of a cardiovascular origin is supported by many ballistocardiographic studies, but its exclusivity has never been proven. A new hypothesis was formulated to explain their genesis: there is a neuromuscular postural control system, possibly different from the well-investigated mechanisms controlling the macroscopic sway, responsible for compensating the small endogenous forces perturbing the posture by causing some muscles to contract proportionately to the magnitude of perturbation. These contractions contribute to the ground reaction force oscillations. To verify this hypothesis, a series of experiments simultaneously recording the electrocardiogram, the electromyogram of several muscles, and the ground reaction forces were conducted on ten informed and consenting human subjects. The experimental results confirmed that the hypothesized muscular activity in response to the perturbation induced by the cardiac contraction and subsequent blood movement does in fact exist. The signal detected by electromyography is not a cardioelectric artifact, but an actual myoelectrical activity. Several interesting patterns of muscular activity emerged in this investigation. These results provide the needed background and justification for investigating the use of the vertical ground reaction force, not only in the study of posture, but also in the study of clinical conditions affecting the neuromuscular control and the musculature of the trunk.

Adult↗

PubMed1998

Eye, head and trunk control: the foundation for manual development.

Mastery of reaching and manipulation relies on adequate postural control. The trunk must be balanced relative to a base of support to allow free movements of the arms and hands. Moreover, the head must be supported flexibly by the trunk so that gaze can be directed toward the target to provide a spatial frame of reference for reaching. For fine manipulation it is also crucial to avoid retinal slips which would introduce blur. Stabilizing gaze is generally accomplished through adjustments of both eye and head position. Until gaze is stabilized, it is difficult to establish a frame of reference between the target and the self. Thus, a nested hierarchy of support involving the eyes, head, and trunk forms an important foundation for manual activity.

Child↗

PubMed2004

An emerging postural response: is control of the hip possible in the newly walking child?

Previous researchers have proposed that because of their slow muscle-response latencies, 1- to 2-year-old children are unable to control hip-dominant postural responses when responding to balance threats (G. McCollum & T. Leen, 1989). To test that proposition, the authors exposed 41 children to backward support-surface translations and recorded muscle activations and movement kinematics. Children between 10 months and 10 years of age stood on a platform that was unexpectedly moved. Passive hip-dominant responses were observed among the least experienced walkers. In contrast, older children produced an active response, signified by higher levels of abdominal and quadriceps muscle activity and accompanied by larger hip flexor torques. Greater success in withstanding large magnitudes of perturbations were associated with actively generated hip responses.

Anthropometry↗

PubMed1986

Balance reactions and eye-hand coordination in idiopathic scoliosis.

We undertook this study to determine if subclinical postural control mechanisms were abnormal in idiopathic scoliosis. Ninety-one female patients and fifty-seven age-matched female controls were examined. We used a force plate ataxiometer to quantitate postural sway in the standing position and recorded the displacement and acceleration of the center of pressure during static stance and under perturbation with eyes opened and closed. A joystick-controlled video system was used to measure reaction time and eye-hand motor coordination. The scoliosis group demonstrated significantly less sway during two of the eight standing balance conditions and on the remaining balance tests there was a similar trend, albeit nonsignificant. The reaction time for the scoliosis group was also significantly slower, but the accuracy was not significantly worse. We noted no statistical differences between progressive and nonprogressive or between braced and unbraced patients. The subgroup of patients whose curves progressed despite bracing had a tendency to demonstrate greater stability on all standing tests. They also exhibited faster reaction times and less error in eye-hand coordination than other patient groups. No correlation existed between severity of curve and test performance. We found no indication of deficient balance in idiopathic scoliosis, and the tests could not predict curve progression.

Adolescent↗

PubMed2006

Early development of postural adjustments in standing with and without support.

This study investigates the early development of postural adjustments during external perturbations in two different standing positions: standing with support and standing without support. The aim of the study was to assess a group of 13 infants four times during the period in life when independent standing is achieved; at 8, 10, 12 and 14 months. However, longitudinal data could be achieved only in four infants. Muscle activations of the neck, hip and ankle were recorded using surface electromyography. Based on earlier studies and controversies, three main issues were addressed: (1) Is direction specificity present before independent standing is established? (2) How do postural adjustments change with increasing age (8-14 months)? (3) Are postural adjustments task-specific in the young child? The results showed that our small sample of infants aged 8 and 10 months, who were not yet able to stand independently, exhibited direction-specific postural adjustments both during standing with and without support, though not consistently during all trials and at all body levels. Therefore, we argue that direction specificity might constitute a prerequisite for the development of independent standing. We also found that the development of postural adjustments in standing with support resembles that of sitting, i.e. great variation in the postural adjustments at early age, and fine-tuning to the situation with increasing age and experience. This, we find that this is in agreement with the proposal that postural control develops through a selection process of the most suitable postural adjustments for the situation from a repertoire of direction-specific postural adjustments. The development of postural adjustments during standing without support is discussed. Additionally, differences in response rates were noted between the two standing positions, indicating that even before independent standing is established, sophisticated sensorimotor integration enables task-specific postural adjustments.

Age Factors↗

PubMed1998

Motor development after vestibular deprivation in rats.

This review summarizes the postural development in the rat and the influences of vestibular deprivation from the 5th postnatal day on this development. Vestibular deprivation leads to a delay in motor development. Most probably this delay is caused by a delay in the development of postural control, which is characterized by a retarded EMG development in postural muscles. Our results indicate that the developing nervous system cannot compensate for a vestibular deficit during the early phase of ontogeny.

Animals↗

PubMed2006

Loss of motor control and/or loss of consciousness during breath-hold competitions.

Since the first official world championships in breath-hold diving (1996), a sport has developed where the athletes compete in various disciplines of breath-hold diving. One of the rules is that the diver should surface from a dive without showing any signs of hypoxia. Depending on the severity of hypoxia, a diver may suffer disqualifying signs such as loss of consciousness (LOC) or loss of motor control (LMC), the latter including signs such as confusion, affected postural control, spasms or speech problems. Data was collected from the results of the major international competitions following AIDA guidelines (Association International pour le Dévelopment de l'Apnée) in 1998, 2001-2004. The data was analyzed for frequency of LOC and LMC during constant weight diving and during static apnea. In constant weight diving, the diver swims down (and up) as deeply as possible along a vertically suspended rope (current record 105 m). In static apnea, the diver strives for maximum duration, floating motionless face down in a pool (current record 8.58 min). A total of 601 static apnea (SA) performances and 596 constant weight dives were judged in the six competitions. On average, 10 % of SA, and 11 % of CW performances were disqualified due to signs of hypoxia. For the competitions in 2002-2004, a distinction was made in the rules between LOC and LMC; of a total number of 355 SA performances, 1.1 % resulted in LOC, while 9.6 % resulted in LMC. For CW, the number was 344 with 6.1 % LOC and 6.1 % LMC. Despite the relatively high incidence of dramatic signs, it is noteworthy that there have been no reports of fatal accidents or permanent injuries from any of the above-mentioned competitions. This descriptive paper shows a relatively high incidence of disqualifications due to signs of hypoxia in breath-hold competitions 1998-2004.

Competitive Behavior↗

PubMedDate not supplied

[Rehabilitation in multiple sclerosis: clinico-instrumental correlations].

The Authors report their experience in a patient with Multiple Sclerosis. The planning and the follow up of rehabilitative treatment were based on clinical, functional, electrophysiological and posturographic evaluation. The impairment degree was evaluated by Kurtzke's Expanded Disability Status Scale. The electrophysiological evaluation showed an abnormal recruitment flexor pattern at exteroceptive stimulus and posturography confirmed postural control disorder. The treatment was based on PNF techniques and postural feedback on standing balance platform. After rehabilitative treatment the clinical and functional improvement has been confirmed by normal exteroceptive flexion reflex and better stabilometric parameters.

Electromyography↗