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PubMed2006

A cognitive intersensory interaction mechanism in human postural control.

Human control of upright body posture involves inputs from several senses (visual, vestibular, proprioceptive, somatosensory) and their central interactions. We recently studied visual effects on posture control and their intersensory interactions and found evidence for the existence of an indirect and presumably cognitive mode of interaction, in addition to a direct interaction (we found, e.g., that a 'virtual reality' visual stimulus has a weaker postural effect than a 'real world' scene, because of its illusory character). Here we focus on the presumed cognitive interaction mechanism. We report experiments in healthy subjects and vestibular loss patients. We investigated to what extent a postural response to lateral platform tilt is modulated by tilt of a visual scene in an orthogonal rotational plane (anterior-posterior, a-p, direction). The a-p visual stimulus did not evoke a lateral postural response on its own. But it enhanced the response to the lateral platform tilt (i.e., it increased the evoked body excursion). The effect was related to the velocity of the visual stimulus, showed a threshold at 0.31 degrees /s, and increased monotonically with increasing velocity. These characteristics were similar in normals and patients, but body excursions were larger in patients. In conclusion, the orthogonal stimulus arrangement in our experiments allowed us to selectively assess a cognitive intersensory interaction that upon co-planar stimulation tends to be merged with direct interaction. The observed threshold corresponds to the conscious perceptual detection threshold of the visual motion, which is clearly higher than the visual postural response threshold. This finding is in line with our notion of a cognitive phenomenon. We postulate that the cognitive mechanism in normals interferes with a central visual-vestibular interaction mechanism. This appears to be similar in vestibular loss patients, but patients use less effective somatosensory instead of vestibular anti-gravity mechanisms.

Adult↗

PubMed1990

Changes in posture control across the life span--a systems approach.

In this article, a systems approach to the development of posture control across the life span and its integration with voluntary tasks such as walking is described. Research shows a clear cephalocaudal gradient in the development of postural responses. Postural muscle synergies develop appropriate temporal organization through experience in each new level of postural skill development. Sensory inputs contributing to posture control influence postural responses very early in development, with responses being elicited by vision alone, or by somatosensory and vestibular cues in isolation. Studies of older adults indicate small, but significant, increases in onset latencies and disruptions in the temporal organization of postural muscle responses when subjects are given external threats to balance. In addition, older adults, like young children, use antagonist muscles more often in coactivation with agonist muscles. Older adults also have more difficulty balancing when sensory inputs are reduced experimentally or pathologically. Ankle dorsiflexor muscle weakness is also a factor in balance dysfunction in the older adult.

Aging↗

PubMed1991

Posture control and the risk of industrial accident: a stabilographic investigation in a naval shipyard.

In a previous case-control study on the effect of impaired perceptual acuity on the risk of industrial injuries at a naval shipyard, three factors which might influence the perception and processing of sensory impressions--alcohol consumption, hearing loss exceeding 20 decibels (dB) and exposure to noise exceeding 82 dB(A)--were found to contribute to the risk of injury. According to recent reports, these factors can all lead to impaired posture control. Because in general about 40% of all accidents are associated with falling, tripping, slipping and the like, a supplementary study has been carried out to unravel possible confounding effects of posture control on these three risk factors. Cases (who had suffered two or more accidents during the preceding 4 years) and controls (who had been accident-free in the same period) were compared as regards posture control measured during silence or noise. No significant difference in posture control was found between cases and controls, either in silence or during exposure to heavy noise.

Accidents, Occupational↗

PubMed2001

Effect of long-duration spaceflight on postural control during self-generated perturbations.

This report is the first systematic evaluation of the effects of prolonged weightlessness on the bipedal postural control processes during self-generated perturbations produced by voluntary upper limb movements. Spaceflight impacts humans in a variety of ways, one of which is compromised postflight postural control. We examined the neuromuscular activation characteristics and center of pressure (COP) motion associated with arm movement of eight subjects who experienced long-duration spaceflight (3--6 mo) aboard the Mir space station. Surface electromyography, arm acceleration, and COP motion were collected while astronauts performed rapid unilateral shoulder flexions before and after spaceflight. Subjects generally displayed compromised postural control after flight, as evidenced by modified COP peak-to-peak anterior-posterior and mediolateral excursion, and pathlength relative to preflight values. These changes were associated with disrupted neuromuscular activation characteristics, particularly after the completion of arm acceleration (i.e., when subjects were attempting to maintain upright posture in response to self-generated perturbations). These findings suggest that, although the subjects were able to assemble coordination modes that enabled them to generate rapid arm movements, the subtle control necessary to maintain bipedal equilibrium evident in their preflight performance is compromised after long-duration spaceflight.

Adult↗

PubMed1996

Postural control under clinorotation in upside-down catfish, Synodontis nigriventris.

The upside-down catfish Synodontis nigriventris has a unique habit of swimming and resting upside-down in free water. This behavior leads to the assumption that the catfish has a specific gravity information processing system. We examined the postural control behaviors in the catfish under clinorotation which is usually used for producing pseudo-microgravity. Synodontis nigriventris kept its body posture at a stable area of the rotated flask in which the catfish was kept, when it was clinorotated at the rate of 60 rpm. In contrast to Synodontis nigriventris, a related species, Corydoras paleatus, did not show such steady postural control. When the flask was rotated at a lower rate of 30 rpm or a higher rate of 100 rpm, Synodontis nigriventris as well as Corydoras paleatus showed a considerable disturbed control of body posture. In this condition, they were frequently rotated with the flask. These findings suggest that Synodontis nigriventris has a high ability to keep upside-down posture and the gravity sensation in this catfish is likely to contribute to its different postural control from that of many other fishes.

Animals↗

PubMed1985

Recovery of postural control following chronic bilateral hemisections at different spinal cord levels in adult cats.

Chronic cats with double hemisections of the spinal cord, first at a lower thoracic level followed by a contralateral midthoracic cord at intervals of 0 to 126 days (T-T preparations) or first at an upper cervical followed by a midthoracic at intervals of 15 to 74 days (C-T preparations), eventually recovered quadrupedal standing 7 to 53 days after the second hemisection. For about 7 days following the first hemisection at a lower thoracic level, floor reaction force (FRF) of the hind limb of the hemisected side decreased to 25 to 30% of the normal value, then recovered to the control value. A group of cats whose second hemisection was done within 7 days after the first hemisection needed 24 to 53 (mean 43) days to recover quadrupedal standing, whereas cats whose second hemisection occurred after 10 to 126 days needed 7 to 22 (mean 15) days. During the recovery period many unusual reflexes were elicited which eventually disappeared as the cats resumed standing and walking. Lateral stability of the double-hemisected cats deteriorated significantly, whereas segmental reflexes were augmented. These results indicate the importance of descending impulses over the segmental motoneuron pools to control standing posture and locomotion. It was assumed that the descending impulses were conveyed by polysynaptic pathways which had minimal functions before the hemisections.

Animals↗

PubMed1995

Age-related changes in open-loop and closed-loop postural control mechanisms.

In an earlier posturographic investigation (Collins and De Luca 1993) it was proposed that open-loop and closed-loop control mechanisms are involved in the regulation of undisturbed, upright stance. In this study, stabilogram-diffusion analysis was used to examine how the natural aging process affects the operational characteristics of these control mechanisms. Stabilogram-diffusion analysis leads to the extraction of repeatable center-of-pressure (COP) parameters that can be directly related to the steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect posture. Twenty-five healthy young males (aged 19-30 years) and twenty-five elderly males (aged 71-80 years) who were free of major gait and postural disorders were included in the study. An instrumented force platform was used to measure the time-varying displacements of the COP under each subject's feet during quiet standing. The COP trajectories were analyzed as one-dimensional and two-dimensional random walks, according to stabilogram-diffusion analysis. Using this technique, it was demonstrated cross-sectionally that healthy aging is associated with significant changes in the 'quasi-static' dynamics of the postural control system. (It was also shown that more traditional posturographic analyses, i.e., summary statistics, were not sensitive enough to detect these age-related differences.) It was found that the steady-state behavior of the open-loop postural control mechanisms in the elderly is more positively correlated and therefore perhaps more unstable, i.e., the output of the overall system has a greater tendency to move or drift away from a relative equilibrium point over the short term. In contrast with this result, it was also found that the steady-state behavior of the closed-loop postural control mechanisms in the elderly is more negatively correlated and therefore perhaps more stable, i.e., over the longer term, there is an increased probability that movements away from a relative equilibrium point will be offset by corrective adjustments back towards the equilibrium position. In addition, it was demonstrated that the elderly utilize open-loop control schemes for longer time intervals and correspondingly larger COP displacements during periods of undisturbed stance. This result suggests that in the elderly there is a greater delay, on average, before closed-loop feedback mechanisms are called into play. Finally, it was shown that there is an increased heterogeneity of postural control abilities in healthy older adults.

Adult↗

PubMed2006

Parkinsonian deficits in sensory integration for postural control: temporal response to changes in visual input.

This study investigated the effect of Parkinson's disease (PD) on the time course for postural control following the removal and reinsertion of visual information. Twelve medicated PD patients (PD) and 12 age matched control (CTRL) subjects performed two 45-s quiet standing trials, during which visual feedback was available (0-15s), deprived (15-30s), and then restored (30-45s). The 45s test trial was divided into 5s time bins to compare the time-based effect of sensory reorganization during deprivation and reintegration. Results revealed an increase in Elliptical Sway Area (ESA) following visual deprivation for both groups; this increased ESA remained significantly higher than the baseline level for the duration of the deprivation period among PD patients and returned to baseline the level among CTRL. Despite elevated ESA at the end of visual deprivation among PD patients, neither group showed a change in ESA after visual information was restored. These results indicate a PD-associated deficit with the reorganization of sensory priorities for postural control, and may implicate the basal ganglia as being critical for integration of sensory information for postural control.

Aged↗

PubMed1992

Postural control, muscle function and psychological factors in rheumatoid arthritis. Are there any relations?

The aim of the present study was to relate postural control, as measured on a quantitative test battery as standing balance on an AMTI force platform, to results of muscle function of the lower extremities, aerobic capacity, disease characteristics, attitudes revealing anxiety, and demographic variables in patients with rheumatoid arthritis (RA). A group of 61 patients with RA was investigated. Multiple regression analyses, using both the stepwise and the backward elimination method, were employed for length of sway path in two-leg standing looking straight ahead and blindfolded as dependent variables. The results revealed postural control in two-leg standing looking straight ahead to be highly related to age and sex but also to isokinetic endurance and to anxiety. In the model, 55% of the variance was explained by these variables at a significance level of p = 0.05. Characteristics of the RA disease, such as c-reactive protein and joint-mobility did not play any major role in explaining postural control.

Adult↗

PubMed2005

Is postural control affected by expertise in alpine skiing?

OBJECTIVES: This study examined the postural performance of two groups of male skiers competing at different levels and the consequences on postural control of the suppression of visual afferences by eye closure. METHODS: Seven national level (NAT) skiers and 7 regional level (REG) skiers were asked to stand as still as possible on a force platform with eyes opened and closed and while wearing or not wearing their ski boots in a stable posture and in two unstable postures (in the sagittal or frontal plane). Postural performance was assessed with centre of foot pressure measurements. RESULTS: REG and NAT skiers were similarly influenced by the absence of visual information and presented similar postural performance when tests were performed with ski boots. However, without ski boots, REG skiers displayed better postural performance than NAT skiers. CONCLUSIONS: The inferior postural performance of NAT skiers without ski boots could be a long term effect of repetitive wearing of ski boots, which impairs postural performance by restricting the range of motion of the ankle-foot complex. Since individuals with decreased postural performance are believed to be more susceptible to ankle injury than those with finer postural control, NAT skiers should benefit from specific training aimed at improving postural ability and preventing ankle injury.

Adolescent↗

PubMed2001

Optimal posture control of a musculo-skeletal arm model.

In this paper maximal performance posture control of the human arm is investigated by means of model simulations. Recent experiments (F.C.T. van der Helm, submitted, 2000) have shown that the reflexive feedback during postural control varies with the bandwidth of the applied force disturbances. This paper focusses on the influence of the frequency content of force disturbances on the reflexive feedback gains by means of optimization. The arm is modelled by a nonlinear musculo-skeletal model with two degrees of freedom and six muscles. To facilitate the optimization of the model parameters, the arm model is linearized. A performance criterion is minimized for stochastic force disturbances in a two-step procedure: (1) optimization of static muscle activations using an additional energy criterion to obtain a unique and energy-efficient solution; antid (2) optimization of reflex gains using an additional control effort criterion to obtain a unique solution. The optimization reveals that for the given task and posture, the shoulder muscles have the largest contribution, whereas the bi-articular muscles have a relatively small contribution to the behaviour. The dynamics at the endpoint level are estimated so that a comparison can be made with the experiments. Compared to the experiments, the intrinsic damping of the model is relatively large (about 150%), whereas the intrinsic stiffness is relatively small (about 60%). These differences can be attributed to unmodelled mechanical effects of crossbridges in Hill-type muscle models. The optimized reflex gains show remarkable similarities with the values found in the experiments, implying that humans can adjust their reflexive feedback gains in an optimal way, weighting the performance and energy. The approach in this paper could be useful in the study of various posture tasks, for example in the prediction of the relation between the control parameters of various musculo-skeletal models and different experimental variables.

Arm↗

PubMed1996

Psychomotor speed and postural control in chronic low back pain patients A controlled follow-up study.

STUDY DESIGN: Psychomotor speed (reaction time) and postural control (center point of force velocity) among healthy control volunteers and patients with chronic low back pain (LBP) were studied at the beginning of an active, functional, restoration back rehabilitation program and 5 months after the program. OBJECTIVES: To study cross-sectionally reaction times and center points of force velocity among control volunteers and patients with low back pain, and to evaluate the effects of the restoration on these measures of motor function in a follow-up examination. SUMMARY OF BACKGROUND DATA: Deficits of motor skills and of coordination have been reported in association with musculoskeletal disorders, but one can only speculate about an association between proprioceptive dysfunction and low back disorders on the basis of the currently available data. METHODS: Sixty-one healthy control volunteers and 99 patients with low back pain-68 of these patients experienced moderate pain; 31 experienced severe pain-participated in the study. Reaction times for upper and lower limbs were tested with a system based on a microcomputer. Postural stability was measured with a vertical force platform. RESULTS: A consistent trend was found in which patients with low back pain had reaction times slower than these of control volunteers. Man with severe low back pain had significantly longer hand reaction times than men in the control group (P = 0.03). Women with severe low back pain also had poorer postural control than women with moderate low back pain (P = 0.02) and women in the control group (P = 0.04). Functional restoration seemed to have an effect on reaction times. The restoration was considered successful if the condition of a patient with a disability that had resulted from low back pain improved during the follow-up examination and unsuccessful if the disability worsened. Patients who experienced these results were identified in groups called "good" and "poor," respectively. Among men, the reaction times improved in the control group and "good" groups, but they became slower in the "poor" group. The difference between "good" and "poor" groups was significant (P = 0.008). Women in the "good" group achieved the most improved reaction times, and the difference between these women and the control women almost reached significance (P = 0.076). CONCLUSION: The results indicate that patients with chronic low back pain have impaired psychomotor speed and, among women, impaired postural control. Psychomotor speed improved during an active, functional, restoration back rehabilitation program.

Adult↗

PubMed2001

Knee bracing for medial compartment osteoarthritis: effects on proprioception and postural control.

OBJECTIVE: To evaluate the effects of a functional knee brace specifically designed for patients with varus gonarthrosis on measures of proprioception and postural control. SUBJECTS: Fourteen men and six women (aged 59+/-9 yr) with measurable varus alignment and osteoarthritis of the knee medial compartment. METHODS: Proprioception was assessed in the sitting position using an isokinetic dynamometer and was quantified as the ability to replicate target knee-joint angles. Postural control was assessed with a force platform using tests of single-limb standing balance performed, while the patient was standing on a stable surface and standing on foam, and was quantified as the total length of the path of the centre of pressure. All tests were performed with and without the patient's own custom-fit valgus brace. RESULTS: Proprioception was significantly improved following application of the brace [mean difference=0.7 degrees, 95% confidence interval (CI)=0.2 to 1.1 degrees ). Postural control was not significantly affected by the use of the brace during the stable surface test (mean difference=2.6 cm, 95% CI=-4.3 to 9.5 cm) or the foam surface test (mean difference=0.9 cm, 95% CI=-7.5 to 9.4 cm). CONCLUSION: Although enhanced proprioception may be partially responsible for reported improvements with the use of a brace, the present findings call into question the functional importance of the small changes observed.

Braces↗

PubMed2004

Cognitive influences in postural control of patients with unilateral vestibular loss.

The aim of this study was to investigate the interference between postural control and cognitive processing in patients with surgically confirmed unilateral vestibular lesions. These patients were well-compensated for vestibular lesions with no symptoms of dizziness or definable postural deficit. We hypothesized that attentional processes would play a greater role in postural control of these patients compared to healthy age-matched controls suggesting that successful compensation for a vestibular impairment involves ongoing increased attentional resources, and is not an automatic process. To explore this hypothesis, we used a dual-task paradigm that combined postural challenges with concurrently performed cognitive tasks. The postural conditions were seated, standing on a fixed floor, standing on a sway-referenced floor, and standing on a translating floor. Cognitive tasks were simple, inhibitory, and forced choice reaction time (RT) tasks. Patients had slower RTs compared to the controls under all conditions, including the seated condition. This effect was particularly large for the choice and inhibitory tasks. Both groups had increased RTs as the postural task became more challenging. Postural sway increased similarly in the patients and controls when performing the RT tasks for all postural conditions. These results suggest that patients with vestibular lesions that are well-compensated require increased attention compared to healthy controls; however, this increased demand on attention extends beyond postural control. The site of action may be at the sensory integration level resolving multiple sensory signals for spatial orientation.

Adult↗

PubMed2005

The influence of dynamic visual cues for postural control in children aged 7-12 years.

Young children rely heavily on vision for postural control during the transition to walking. Although by 10 years of age, children have automatic postural responses similar to adults, it is not clear when the integration of sensory inputs becomes fully developed. The purpose of this study was to examine this transition in the sensory integration process in children aged 7-12 years. Healthy children and adults stood on a fixed or sway-referenced support surface while viewing full-field optic flow scenes that moved sinusoidally (0.1 and 0.25 Hz) in an anterior-posterior direction. Center of pressure was recorded, and measures of sway amplitude and phase were calculated at each stimulus frequency. Children and adults had significant postural responses during approximately two-thirds of the trials. In adults, there was a 90% decrease in sway on the fixed surface compared with the sway-referenced surface, but only a 50% decrease in children. The phase between the optic flow stimulus and postural response in children led that of adults by 52 degrees at 0.1 Hz and by 15 degrees at 0.25 Hz. Adults and children aged 7-12 years have similar ability to use dynamic visual cues for postural control. However, 7-12-year-old children do not utilize somatosensory cues to stabilize posture to the same extent as adults when visual and somatosensory cues are conflicting.

Adult↗

PubMed2005

Efficacy and effectiveness of physical therapy in enhancing postural control in children with cerebral palsy.

The purpose of this article was to conduct a systematic review of studies that examined the efficacy and effectiveness of postural control intervention strategies for children with CP. Only physical therapy interventions were included, e.g. adaptive seating devices, ankle foot orthoses, neurodevelopmental treatment. A multifaceted search strategy was employed to identify all potential studies published between 1990 and 2004. The search strategy included electronic databases, reference list scanning, author and citation tracking of relevant studies, and hand searching of pediatric physical therapy journals and conference proceedings. Twelve studies (1991-2004), comprising ten group design studies and two single subject studies, met our inclusion criteria. A variety of age ranges and severity of children with cerebral palsy (n=132) participated in the studies. The study quality scores ranged from 2 to 7 (total possible range of 0 to 7) with a median score of 5.5 and a mode of 6. As was true in an earlier systematic review on adaptive seating, most of the 12 'experimental' studies published since 1990 that were aimed at evaluating the effectiveness of postural control strategies provided lower levels of evidence, i.e. Sackett Levels III to V. Additional studies with stronger designs are needed to establish that postural control interventions for children with CP are effective.

Adult↗

PubMed1992

Postural control in young and elderly adults when stance is perturbed: kinematics.

Increased postural sway and falling are associated with aging and are likely related to problems with postural control in the elderly. We investigated the motions of individual body segments in 24 healthy young adults and 15 healthy elderly adults (mean ages 26 and 72) in response to four tasks: (a) standing with feet flat on an anteriorly accelerating platform (Flat Translation); standing on a narrow beam support that was (b) stationary (Beam Standing) and (c) accelerating anteriorly (Beam Translation); and (d) standing on a rotatable but otherwise stationary springboard (Springboard Standing). An optoelectronic camera system was used to measure rotations of body segments, particularly regarding their maximum excursions, time to first rotation response, direction of initial rotation, and time to first rotation reversal. In general, larger rotation excursions were noted in the elderly compared to the young group, particularly in the Beam Standing and Beam Translation tasks, but the magnitude of rotation difference was small. All rotation magnitudes were well within the available ranges of motion of the body joints. In both excursion magnitudes and directions of initial rotation, the elderly showed greater variability than the young. In the Beam Translation task, the elderly group, compared to the young, tended to rotate their upper body segments more than in the Flat Translation task. These data suggest that healthy elderly adults with no apparent musculoskeletal or neurological impairments have small but consistent differences in postural control kinematics, particularly when more challenging conditions are presented. Moreover, these data provide the basis for biomechanical analyses of joint torques and other dynamic requirements of these responses.

Adult↗

PubMed2005

Added cognitive load through rotary auditory stimulation can improve the quality of postural control in the elderly.

This study examined the effect of rotary auditory stimulation on postural control in the elderly. Thirty-two subjects aged over sixty were submitted to two rotary auditory stimulations, with a meaningful and a non-meaningful message, during a postural task. Although the non-meaningful task did not lead to postural control modification, the meaningful task allowed a reduction in the postural parameter values and therefore, a better stabilisation of posture. The attention, paid to the geography of the sound in understanding the story being told, forced the subject into taking into consideration the regularity and rotation of the stimulation, which meant relying on an auditory anchorage and so facilitated posture regulation.

Acoustic Stimulation↗