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Reliability of the soleus H-reflex from supine to standing in young and elderly.

OBJECTIVE: Many recent studies have used the soleus H-reflex methodology to examine age-related changes in neuromuscular function. However, reliability of the method has only been tested in young adults. The purpose of this study was to evaluate the inter-trial reliability of the soleus H-reflex in both young and elderly subjects during supine and standing conditions. METHODS: The experiment was carried out on 10 young and 10 elderly subjects. For each subject, 10 standardized soleus H-reflex trials were collected during each of the postural conditions. Intraclass correlations were calculated for the first 4, 6, 8, and 10 trials for each group at each body position. RESULTS: The largest decreases in reliability in this study were observed with a decrease in the number of trials used to estimate the elderly soleus H-reflex during the standing condition. The change from using ten trials to using four trials led to an 8% decrease in reliability. CONCLUSIONS: Due to the decreased postural control ability in the elderly population, at least ten trials should be used to estimate soleus H-reflex characteristics during standing or other functional weight-bearing conditions. SIGNIFICANCE: Using fewer than 10 trials could lead to an increase in statistical errors and misinterpretation of results.

Adult↗

The venoarteriolar response in diabetics.

Resting skin blood flow and the venoarteriolar response (VAR) were studied in 40 patients with diabetic microangiopathy and neuropathy, in 40 diabetics with microangiopathy, and in 30 normal subjects by means of laser-Doppler flowmetry. In patients with microangiopathy and neuropathy, resting flow (RF) was increased and the VAR was impaired to a greater extent than in patients without neuropathy. There was also a significant delay in the VAR in diabetics, particularly in patients with neuropathy. The microangiopathy index (VAR/RF) was on the average 71.3 in normal subjects, significantly lower (p less than 0.05) in diabetics without neuropathy (34.8), and even lower in those with neuropathy (13.6). The VAR was evaluated with different postural changes; The authors observed that in the passage from supine to standing the VAR is more evident. In conclusion these results confirm that the postural control of blood flow in the skin of the foot is impaired in diabetic microangiopathy, particularly in patients with neuropathy. The increased skin blood flow and the impaired VAR are causes of edema and may contribute to the thickening of capillary basement membranes observed in diabetes.

Blood Flow Velocity↗

Head stability during whole body movements in spastic diplegia.

Head angular stability is essential for postural control in whole body movement. Using the opto-electronic ELITE system, we have studied head orientation during the movements of squatting from the standing position and straightening-up from the squatting position in 12 children with spastic diplegia and 12 age-matched controls. Although no instruction was given regarding the head, diplegic children consistently performed excessive neck flexion in the squatting movement and excessive hyperextension in the straightening-up movement, whereas normal children maintained the initial orientation throughout both movements. We discuss pathophysiological implications.

Cerebral Palsy↗

Relative contribution of the pressure variations under the feet and body weight distribution over both legs in the control of upright stance.

The resultant centre of pressure (CP(Res)) trajectories are aimed at controlling body movements in upright stance. When standing on two legs, these trajectories are generated by exerting reaction forces under each foot and by loading-unloading mechanisms intervening at the hip level. To assess the respective contribution of each of these factors in stance maintenance, a group of healthy individuals were tested in several conditions including standing quietly and voluntarily producing under each foot larger CP displacements in phase and in opposite phase along medio-lateral (ML) and antero-posterior (AP) axes. The results, based on the computation of coefficients of correlation between CP(Res) trajectories and various time series including the relative body weight applied to one leg and plantar CP trajectories, highlight some differences according to the axes along which the displacements take place and the amplitudes of the movements. Furthermore, the comparison of the CP(Res) trajectories resulting from each one of these two factors reveals the predominant role played by the loading-unloading mechanisms intervening at the hip level for the movements along the ML axis and those of the plantar CP displacements along the AP axis. Increasing the plantar CP displacements in phase or in opposite phase substantially modifies these contributions although without inferring a shift to the benefit of the other mechanism. The specific morphology of the ankle and hip joints implicated in this postural task plainly explains this postural control organisation. In particular, the link between the segmental configuration of the lower limbs and these mechanisms are discussed.

Adult↗

Normal subject postural sway during the Romberg test.

Analysis of fixed force platform recordings of Romberg tests performed by 132 normal subjects demonstrated no statistically significant sex or age effect for adults aged 20 through 49 years. There was a strong stabilizing influence of vision upon postural control in most, but not all, normal subjects. Comparison trials showed no statistically significant differences between trials for the standard Romberg eyes-open maneuver. However, a significant improvement was demonstrated for the second trial for all other Romberg maneuvers. Tests repeated over a period of five consecutive days yielded results with large variances within normal limits and no systematic individual or group trends. Normal percentiles and confidence intervals for the 95th percentile were calculated for use as a normal data base. These percentile distributions derived from a relatively large population of normal subjects provide a normal statistical base for comparison with postural sway from abnormal subjects.

Adult↗

A pilot study of sensory retraining for the hemiparetic foot post-stroke.

Sensory training post-stroke has been favourably reported in the literature for the hemiparetic upper limb. Little is known, however, of the usefulness of such techniques in the lower limb. This is despite the knowledge that accurate sensory feedback is vital for adaptability in motor control, particularly during balance and weight shift during standing. This pilot study used a single-case, repeated-measures design, with three subjects with hemisensory loss in their lower limb. Pre-intervention and post-intervention measures included light touch and proprioception, duration of single-limb stance, sway path length and duration of transition from double-to single-limb stance. The intervention involved 2 weeks of intensive sensory appreciation training, involving a hierarchy of sensory education, experiences and interpretation. Testing post-intervention demonstrated statistically significant changes in light touch appreciation for two subjects and in some postural control parameters in the third subject. Clinically favourable trends were shown in other measures. This initial study shows promising results for the incorporation of sensory training in the lower limb post-stroke, particularly if consideration is given to motivation, attention and functional application.

Aged↗

The clinical use of dynamic posturography in the elderly.

We provide an overview of the clinical uses of dynamic posturography. Although the equipment described to perform this testing is expensive, the concepts, especially those for sensory organization, can be applied for +20.00. To apply the six sensory organization conditions, one merely needs some way to disrupt proprioceptive information by maintaining ankle angle and providing for visual conflict stimuli. We found that proprioceptive information can be disrupted easily by asking the patient to stand on a thick (4-inch) dense piece of foam rubber like that used in cushions for furniture. Visual stabilization conflict can be provided by having the patient wear a 19- to 20-inch Japanese lantern with a head-mounting system in the center so that the patient's movements do not reflect themselves in relative movements to the visual environment. With use of these two simple tools, the six sensory organization tests can be approximated in a clinical situation in a short time and can provide some relative information about a patient's postural control capabilities. With minor additional work, a quantitative measure of output that gives indications of the amount of anterior-posterior sway also can be provided. For elderly patients with a variety of problems ranging from general unsteadiness to frank vertigo, the risk of falling can be devastating, and it is important to provide a thorough investigation of the total balance system. The systematic investigation, qualitatively or quantitatively, of integration of sensory input and motor outputs provides a dimension that typically has been lacking in the routine "dizzy patient workup" for all ages but especially for elderly patients. Therefore, the application of the postural maintenance theory with the above-described procedures or variations in these procedures appears to have a great deal of clinical relevance in the evaluation of patients with gait and balance disorders. These types of evaluations represent an adjunct or addition to the evaluation of the vestibular system and the vestibulo-ocular reflexes and by no means should be considered a substitute for that traditional evaluation. It is the combination of information that can provide the clinician with a more global picture of the entire balance system and its functional capabilities.

Adult↗

Dynamical origins of stereotypy: relation of postural movements during sitting to stereotyped movements during body-rocking.

The relation between the movement dynamic properties of sitting still and of seated body-rocking in adults with stereotyped movement disorder and mental retardation and a contrast group of typically developing age-matched adults was examined. Continuous measurement of sequential displacements in center-of-pressure was made using a force platform while subjects were engaged in seated body-rocking and quiet sitting. Properties of movement were compared across conditions (rocking, sitting) and groups (stereotyped movement disorder, contrast). The contrast group had the same modal frequency for both movement properties. The intrinsic dynamics of the stereotyped movement disorder group were similar to those of the contrast group for body-rocking but very different for quiet sitting. Findings support the suggestion that body-rocking in stereotyped movement disorder originates partly as an adaptation to an inability to control posture in a seated position.

Adult↗

Does calf-muscle fatigue affect standing balance?

The purpose of this study was to find out whether fatiguing calf-muscle exercise affects postural sway during standing. Thirteen healthy subjects with a mean age of 25 years participated. Body sway in one leg stance was measured on a force plate before and after fatiguing exercises of the calf muscles of the subject's right leg. Repeated measurements for up to 10 min after exercises showed no increase of body sway. The results indicate that postural control in quiet standing can be maintained by compensatory mechanisms activated during muscle fatigue. A significant decrease of body sway over time on the non-fatigued leg, indicated a learning effect. A similar decrease was not observed on the fatigued leg, indicating interference of compensatory mechanisms on learning.

Adolescent↗

Effects of varying acceleration of platform translation and toes-up rotations on the pattern and magnitude of balance reactions in humans.

Different movement synergies used to restore balance in response to sudden support surface displacements have been described, which include the ankle movement synergy and a number of multisegmental movement synergies. The purpose of this study was to extend the analysis of the effects of stimulus magnitude on the pattern and scaling of balance reactions to larger magnitudes of balance disturbances, and to other types of balance disturbances, in particular, forward translations (FT), backward translations (BT), and toes-up rotations (RT). In addition, we examined whether the timing and magnitude of center of body mass (CM) displacement is an invariant feature of corrective responses to varying magnitudes of balance disturbances. Thirteen healthy adults were subjected to FT, BT, and RT of varying acceleration/velocity. The balance disturbance induced by FT and BT was fundamentally different from that induced by RT. The balance requirement during FT and BT was to rapidly translate the CM forward/backward to the new position within the displaced base of support. For RT, the requirement was to minimize the backward displacement of the CM. As evidenced from the initial phase of ankle, knee, and hip angular displacements and anterior-posterior (A-P) center of foot pressure displacement, the magnitude of the balance disturbance increased with increasing platform acceleration/velocity. For FT and BT, the present findings are consistent with the view that trajectory of CM is a control variable, as the timing, peak magnitude, and time to peak CM displacement did not vary as a function of platform acceleration/velocity. However, for RT, the peak magnitude and time to peak CM displacement did increase with increasing platform acceleration/velocity. The results demonstrate that in response to FT, BT, and RT, stability was restored by distinct multisegmental movement synergies. The corrective response to FT consisted of early knee flexion then ankle dorsiflexion and hip extension. The corrective response to BT consisted of hip flexion and ankle plantar flexion. For RT early hip flexion and knee flexion was observed. All muscles recorded (tibialis anterior, soleus, gastrocnemius, hamstrings, and quadriceps) were activated within a range of 60 to 170 ms from onset of platform displacement. For FT, BT, and RT, the pattern and timing of angular displacements and muscle responses did not vary as a function of platform acceleration/velocity, while there was a significant effect of platform acceleration/velocity on the magnitude of the corrective response, that is, peak magnitude of corrective hip, knee, and ankle angular displacements and magnitude of muscle responses. The present findings indicate that multiple sources of spatial information are necessary for the selection and initiation of the appropriate corrective response to meet the requirements of the different balance tasks. The present results strongly endorse the concept of a postural control network for recovery of standing balance, as opposed to positive feedback through local segmental or long loop reflex circuits.

Acceleration↗

Synchronization and coordination of sequences in two neural ensembles.

There are many types of neural networks involved in the sequential motor behavior of animals. For high species, the control and coordination of the network dynamics is a function of the higher levels of the central nervous system, in particular the cerebellum. However, in many cases, especially for invertebrates, such coordination is the result of direct synaptic connections between small circuits. We show here that even the chaotic sequential activity of small model networks can be coordinated by electrotonic synapses connecting one or several pairs of neurons that belong to two different networks. As an example, we analyzed the coordination and synchronization of the sequential activity of two statocyst model networks of the marine mollusk Clione. The statocysts are gravity sensory organs that play a key role in postural control of the animal and the generation of a complex hunting motor program. Each statocyst network was modeled by a small ensemble of neurons with Lotka-Volterra type dynamics and nonsymmetric inhibitory interactions. We studied how two such networks were synchronized by electrical coupling in the presence of an external signal which lead to winnerless competition among the neurons. We found that as a function of the number and the strength of connections between the two networks, it is possible to coordinate and synchronize the sequences that each network generates with its own chaotic dynamics. In spite of the chaoticity, the coordination of the signals is established through an activation sequence lock for those neurons that are active at a particular instant of time.

Action Potentials↗

Issues in the selection and use of mechanical transducers to directly measure motor activity in clinical settings.

The application of instrumentation in the social sciences to measure human behavior lags far behind medical practice and the physical sciences. According to Rugh and Schwitzgebel (1977), this primitive state of development and lack of technological sophistication is related to the prevailing belief that many variables of interest to psychologists are not subject to direct measurement. We identified five varieties of maladaptive behaviors commonly displayed by mentally retarded persons which can be measured directly by means of mechanical transducers: hyperactivity, hypoactivity, inadequate postural control, disorders of the sleep/wake cycle, and stereotyped movements. The operating characteristics of several types of motion sensors were described and issues related to the selection and use of these mechanical transducers in clinical settings were considered. Finally, various meanings of the terms reliability and validity were discussed as they pertain to the clinical application of these mechanical measurements of motor activity.

Behavior↗

Muscle responses to seated perturbations for typically developing infants and those at risk for motor delays.

This study examined spatial and temporal organization of muscle activity in response to seated forward platform perturbations in typically developing (TD) infants and in infants at risk for ongoing neuromotor delays. Twelve high-risk (HR) infants (six males, six females) and 12 TD infants (nine males, three females) aged 8 to 10 months (corrected for prematurity), who were all independent sitters, participated in this study. Surface electromyograms recorded muscle responses to forward perturbation in the neck, trunk, and leg (6cm amplitude, 12cm/s). Center of pressure measures were also recorded. The TD infants demonstrated significantly more phasic responses than the HR infants, who had more trials with tonic activity and more trials with no burst of muscle activity (Mann-Whitney U test, two-tailed, p=0.006). The TD infants demonstrated caudalcephalo, directionally appropriate recruitment patterns more often than the HR infants. There were some similarities between the two groups, with no significant difference between any of the center of pressure measures or onset latencies. Results suggest that postural development in HR infants with motor delays is complex. Some elements of seated postural control appear to be developmentally appropriate, e.g. presence of phasic activity in directionally appropriate muscles sequenced in a caudalcephalo pattern. However, frequency of these age appropriate responses was significantly lower in HR infants, who demonstrated many normal, albeit immature, responses, such as cephalocaudally sequenced muscle activity.

Child Development↗

Growth of pea epicotyl in low magnetic field: implication for space research.

A magnetic field is an inescapable environmental factor for plants on the earth. However, its impact on plant growth is not well understood. In order to survey how magnetic fields affect plant, Alaska pea seedlings were incubated under low magnetic field (LMF) and also in the normal geo-magnetic environment. Two-day-old etiolated seedlings were incubated in a magnetic shield box and in a control box. Sedimentation of amyloplasts was examined in the epicotyls of seedlings grown under these two conditions. The elongation of epicotyls was promoted by LMF. Elongation was most prominent in the middle part of the epicotyls. Cell elongation and increased osmotic pressure of cell sap were found in the epidermal cells exposed to LMF. When the gravitational environment was 1G, the epicotyls incubated under both LMF and normal geomagnetic field grew straight upward and amyloplasts sedimented similarly. However, under simulated microgravity (clinostat), epicotyl and cell elongation was promoted. Furthermore, the epicotyls bent and amyloplasts were dispersed in the cells in simulated microgravity. The dispersion of amyloplasts may relate to the posture control in epicotyl growth under simulated microgravity generated by 3D clinorotation, since it was not observed under LMF in 1G. Since enhanced elongation of cells was commonly seen both at LMF and in simulated microgravity, all elongation on the 3D-clinostat could result from pseudo-low magnetic field, as a by-product of clinorotation. (i.e., clinostat results could be based on randomization of magnetic field together with randomization of gravity vector.) Our results point to the possible use of space for studies in magnetic biology. With space experiments, the effects of dominant environmental factors, such as gravity on plants, could be neutralized or controlled for to reveal magnetic effects more clearly.

Cell Wall↗

Dynamic ankle-foot orthoses as a part of treatment in children with spastic diplegia--parents' perceptions.

BACKGROUND AND PURPOSE: Dynamic ankle-foot orthoses (DAFOs) are often recommended for children with spastic diplegia in order to facilitate better function. The aim of the present study was to explore how the parents of children with diplegic cerebral palsy experience the use of DAFOs. METHOD: A qualitative interview study with a broad research question: 'How do you perceive that DAFOs influence your child?' The parents of 15 children, aged 4-18 years, who all had spastic diplegia and wore DAFOs were interviewed. RESULTS: Content analysis resulted in the following categories: 'Physical effects'; 'New functions and activities'; 'The orthosis as a part of the treatment'; 'Opportunity for independence and play'; and 'Problems with DAFOs'. According to the parents, DAFOs appeared to contribute to the (mechanical) changes in posture affecting the muscular system. They meant that when wearing DAFOs the foot and ankle are more stable. This in turn enables postural control and alignment, contributing to functional activities under more favourable physiological conditions. The psychosocial effects were regarded by parents as being just as important as the physical effects. CONCLUSION: In clinical practice, DAFOs may (according to parents) be regarded as a suitable complement to other treatments in children with diplegic cerebral palsy.

Adolescent↗

Striatal dopamine denervation and sensory integration for balance in middle-aged and older adults.

UNLABELLED: The dopaminergic system of the basal ganglia has been implicated in the integration of sensory information important for balance based on studies in patients with Parkinson's disease. Striatal dopaminergic activity decreases with normal aging. OBJECTIVE: To investigate the relationship between regional striatal dopaminergic denervation and sensory information integration important for balance in middle-aged and older adults. METHODS: Community-dwelling subjects (N=35; age 41-83) with no clinical diagnoses of conditions affecting balance underwent dynamic posturography testing (Sensory Organization Test/SOT) and C-11-beta-CFT dopamine transporter positron emission tomography. RESULTS: Reduced ventral striatal dopamine was significantly correlated with increased anterior-posterior sway in three SOT conditions. Specifically, during quiet standing (SOT Conditions #1, 2) and when repeatedly to sway-referenced visual environments (SOT Condition #3, Trial #3), pre-synaptic dopaminergic denervation in the anteroventral striatum explained over 20-25% of the variability in sway magnitude above and beyond that explained by age (p<or=0.01). Striatal dopaminergic denervation did not impact balance in sway-referenced floor conditions. CONCLUSIONS: The SOT Condition #3 findings suggest that, in normal aging, the central ability to inhibit balance destabilizing vision-related postural control processes depends at least partially on striatal dopaminergic pathways. In contrast, striatal dopaminergic denervation does not appear to impair the ability to disengage destabilizing proprioceptive inputs and to trigger the vestibular control system during challenging sensory perturbations (SOT Conditions #4-6). Finally, quiet standing results (SOT Conditions #1, 2) justify the need to further investigate the impact of striatal dopaminergic denervation on the ability to tune muscle tone in healthy adults.

Accidental Falls↗

Effects of Pronated and Supinated Foot Postures on Static and Dynamic Postural Stability.

Context: The foot is the most distal segment in the lower extremity chain and represents a relatively small base of support on which the body maintains balance (particularly in single-leg stance). Although it seems reasonable that even minor biomechanical alterations in the support surface may influence postural-control strategies, the implications of a hypermobile or hypomobile foot on balance have received little attention to date.Objective: To determine if supinated and pronated foot types influence measures of static and dynamic balance.Design: Participants were assigned to 1 of 3 groups depending on foot type, as defined by navicular-drop measures: pronated (>/=10 mm), neutral (5-9 mm), or supinated (</=4 mm). Measures of static and dynamic balance were obtained for each participant and compared across groups.Setting: Sports medicine and athletic training research laboratory.Patients or Other Participants: Sixteen individuals with pronated (navicular drop = 13.0 +/- 3.7 mm), neutral (navicular drop = 6.2 +/- 1.1 mm), or supinated (navicular drop = 2.2 +/- 1.7 mm) foot postures volunteered to participate in the study.Main Outcome Measure(s): We used the Chattecx Balance System to measure center of balance, stability index, and postural sway during static single-limb stance under eyes-open and eyes-closed conditions. Center of balance was defined as the point on the foot at which the body weight was equally distributed between the medial-lateral and anterior-posterior quadrants and was recorded in centimeters. Stability index was defined as the mean deviation in sway around the center of balance. Postural sway was expressed as the maximum sway distance recorded (cm) in the medial-lateral and anterior-posterior directions. The Star Excursion Balance Test was used to measure dynamic balance, which was reported as the reach distance (cm) in each of the 8 directions tested. The average of 3 trials of each measure was calculated and normalized to the subject's height.Results: We found no difference in center of balance or postural sway as a function of foot type. The stability index was greater in pronators than in supinators, but neither group was different from those with neutral foot types. Dynamic reach differed among groups but only in some directions. Generally, pronators reached farther in the anterior and anterior medial directions and supinators reached farther in the posterior and posterio-lateral directions. In the lateral direction, supinators reached farther than pronators but not farther than neutrals.Conclusions: Our results suggest that postural stability is affected by foot type under both static and dynamic conditions. These differences appear to be related to structural differences as opposed to differences in peripheral input. These effects should be considered when clinicians use such balance measures to assess injury deficits and recovery.

Journal Article↗

Asymmetric vestibular function in the elderly might be a significant contributor to hip fractures.

The aim of this study was to assess postural control, vestibular symmetry and health status in otherwise healthy hip fracture subjects and compare these factors with controls. The fracture subjects were recruited from 113 consecutive patients operated 12-33 months earlier. Nineteen of those were otherwise healthy and fulfilled the inclusion criteria. They were assessed and compared with 28 age- and sex-matched controls. Nystagmus after head shake was checked for by video-nystagmoscopy (charged couple device cameras). Vibration sensation was tested with a tuning fork, medical history and posturography of vibration-induced sway were studied. The subjects had a significantly higher frequency of head shake nystagmus (p = 0.03), indicating a vestibular asymmetry and a history of previous fractures (p = 0.002). Nine out of 12 subjects had fallen and sustained the hip fracture towards the slow phase of the nystagmus, which is expected in a vestibular related fall. Losing balance during testing was more frequent among the subjects than among the controls (p = 0.002). The subjects with head shake nystagmus swayed more than those without, especially in the sagittal plane during neck vibration with eyes closed (p < 0.001). Vibration perception was significantly poorer in the operated legs than in the healthy legs (p = 0.021) and in the legs of the controls (p = 0.001). The findings suggest that vestibular asymmetries may contribute to falls and fractures in elderly people. As such asymmetries can be compensated to a certain degree by specific training programs, these might be advisable for elderly people, especially those with a history of falls or fractures or where a vestibular asymmetry is suspected.

Aged↗