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At least 1,189 records · Page 66Linked to original sources
PubMed2004

Chronic ultra-mild stress improves locomotor performance of B6D2F1 mice in a motor risk situation.

Chronic low grade stress predispose to psychopathological disorders. We consistently showed that chronic ultra-mild stress (CUMS) applied to B6D2F1 female mice induced behavioral disinhibition in several conflict exploration models. Insufficient reactivity to conflicts may be maladaptive and lead to inappropriate appreciation of potential risks and impaired ability to cope with those. Therefore, the purpose of the study was to assess the effect of a CUMS procedure on the behavior of mice in a motor risk situation based on multisensory conflict. Following three weeks exposure to various mild stressors, stressed and control B6D2F1 mice were tested on the rotating beam to determine how CUMS exposure affected balance control, posture stability and locomotor performance in response to a sensory-motor challenge. Detailed behavioral analysis included several parameters, both postural (height of the trunk, tail angle, number of imbalances, falls and head movements) and kinetic (mean velocity on the beam, distance covered with large and small movements, plus time spent in no-motion episodes). Comparisons between control and stressed mice showed that CUMS exposure increased mean velocity and improved locomotor performance in the learning task. In addition, sensitivity to sensory conflict seemed to be reduced in stressed mice, which displayed fewer behavioral adjustments to the increasing difficulty of the test compared to control mice. The results are discussed in terms of the possible influence of disturbances in behavioral and attentional inhibitory processes following CUMS exposure. Whether longer periods of CUMS exposure would shift the performance on the RTB from improvement to deterioration remain to be established.

Adaptation, Psychological↗
PubMed1999

Sensation and action during active and passive movement.

In order to determine the cause of active or passive sensation and action, we studied the effect of perception on gaze and posture control. Normal adults and a patient with bilateral labyrinthine loss underwent whole body rotation seated in a chair (120 degrees/s) or standing on a platform (60 degrees/s), while tilting their head with their vision normal or covered. Eye movements were recorded by a CCD video camera and body sways by a force platform. In normal subjects, gaze and posture became ataxic when head tilting with their vision covered, but they remained skilled under conditions of normal vision. The patient with bilateral labyrinthine loss did not undergo the effect of head tilting with no vision. It seems likely that sensation and action, whether they are skilled or ataxic, are controlled by the perception of an outer world which is integrated from visual and vestibular inputs and functions as a vector in the head.

Adult↗
PubMedDate not supplied

Galvanically induced body sway in the anterior-posterior plane.

Anterior-posterior body sway was evoked with monopolar bi-aural galvanic stimulus of the vestibular nerves in normal subjects and recorded with a force platform, two experiments being conducted. In an experiment of paired design, 9 normal subjects showed an increase in anterior-posterior sway as compared with lateral sway when exposed to the stimulus. In a second experiment another group of 10 normal subjects were exposed to a galvanic stimulus between a neck electrode and two electrodes placed on the arms, but there was no change in the relationship between anterior-posterior and lateral body sway. It is concluded that monopolar galvanic stimulus of the vestibular nerves can induce anterior-posterior body sway, a phenomenon which can be utilised to investigate the vestibulo-spinal contribution in postural control in the anterior-posterior plane.

Adult↗
PubMed2005

Effects of visual and auditory short-term memory tasks on the spatiotemporal dynamics and variability of postural sway.

The authors measured postural sway while participants (N = 20 in each experiment) stood on a rigid or a compliant surface, with their eyes open or closed, and while they did or did not perform a short-term memory (STM) task. In Experiment 1, the STM stimuli were presented visually; in Experiment 2, the stimuli were presented auditorily. In both experiments, fine-scaled, mediolateral postural-sway variability decreased as the cognitive load imposed by the STM task increased. That effect was independent of support surface and vision manipulations. The spatiotemporal profile of postural sway was affected by both visual and auditory STM tasks, but to a greater degree by the auditory task. The authors discuss implications of the results for theories and models of postural control.

Adolescent↗
PubMed2006

The effects of therapeutic taping on gross motor function in children with cerebral palsy.

PURPOSE: Therapeutic taping to address dysfunctional sitting control in children with cerebral palsy (CP) was investigated in this study. METHODS: Eighteen children with quadriplegic CP, Gross Motor Function Classification System for Cerebral Palsy levels IV (n = 9) and V (n = 9) participated in the 12-week program. Subjects were assigned randomly to one of two groups: therapeutic taping + physical therapy or physical therapy only. Therapeutic taping was applied for periods of up to 72 hours over the paraspinal region. The effects were assessed with the Gross Motor Function Measure (GMFM-88) at baseline, six weeks, and 12 weeks. A factorial analysis of variance was used to examine group differences over time. RESULTS: No significant differences were found for the GMFM-88 scores between groups over time. CONCLUSION: Therapeutic taping does not evoke a positive functional change in the seated postural control of children with quadriplegic cerebral palsy. Subjective observation, however, suggested that one child with athetosis benefited from therapeutic taping over the paraspinal region.

Back↗
PubMed2005

A 'cheap' optimal control approach to estimate muscle forces in musculoskeletal systems.

This paper shows a new method to estimate the muscle forces in musculoskeletal systems based on the inverse dynamics of a multi-body system associated optimal control. The redundant actuator problem is solved by minimizing a time-integral cost function, augmented with a torque-tracking error function, and muscle dynamics is considered through differential constraints. The method is compared to a previously implemented human posture control problem, solved using a Forward Dynamics Optimal Control approach and to classical static optimization, with two different objective functions. The new method provides very similar muscle force patterns when compared to the forward dynamics solution, but the computational cost is much smaller and the numerical robustness is increased. The results achieved suggest that this method is more accurate for the muscle force predictions when compared to static optimization, and can be used as a numerically 'cheap' alternative to the forward dynamics and optimal control in some applications.

Humans↗
PubMed1998

Effects of a multidisciplinary rehabilitation programme on health-related quality of life in patients with prolonged musculoskeletal disorders: a 6-month follow-up of a prospective controlled study.

PURPOSE: The aim of this prospective, controlled, follow-up study (6 months) was to examine the effects of a multidisciplinary rehabilitation programme on perceived health-related quality of life (HRQL) in patients with prolonged musculoskeletal disorders (PMSD). The programme focused on body awareness therapy and cognitive and relaxation treatment. METHOD: The rehabilitation group comprised 122 patients, and there were 114 patients in the matched control group (CG). Both groups of patients had access to primary health care. Baseline data were compared with 6-month follow-up data within and between the groups. The following measurements were employed: HRQL (Nottingham Health Profile), body awareness, postural control, pain (VAS), pain-related medicine consumption, isometric arm muscle endurance, aerobic capacity, psychosomatic symptoms, physical and psychosocial working environment and sick leave. RESULTS: Variables that improved significantly as compared with the CG were: HRQL, anxiety, pain related to movements, psychosomatic symptoms and need for pain-related medicines. CONCLUSIONS: The multidisciplinary rehabilitation programme used here improved HRQL in patients with PMSD to a greater extent than the standard treatment provided within primary heath care (p = 0.01) at least in the short term.

Adult↗
PubMed2006

The early motor milestones in infancy and later motor skills in toddlers: a structural equation model of motor development.

The relationship between the achievement of early motor milestones in infancy and later motor development was studied in 130 children with (N = 66, 35 male/31 female) and without (N = 64, 31 male/35 female) familial risk for dyslexia. A structured parental questionnaire was used to assess motor development in infancy, and the Movement Assessment Battery for Children was used to assess motor skills at age 3.5 years. No differences were found at the group level and therefore the structural equation model was constructed by entering both groups simultaneously. An Early Body Control factor, computed from the infant data, explained 38% of the variance of the Gross Motor Skills factor at the age of 3.5 years. The results suggest a relationship between gross motor milestones in infancy and gross motor skills in toddler age. Unexpectedly, the early appearance of Early Hand Control skills in infancy had a negative association with the development of the gross motor domain at 3.5 years (explanation ratio was 9%). No significant connections between early and later fine motor skills were found. The mediating role played by postural control is discussed.

Chi-Square Distribution↗
PubMed2002

Perceptual-motor contributions to static and dynamic balance control in children.

The authors addressed balance control in children from the perspective of skill development and examined the relationship between specific perceptual and motor skills and static and dynamic balance performance. Fifty 11- to 13-year-old children performed a series of 1-legged balance tasks while standing on a force platform. Postural control was reflected in the maximum displacement of the center of mass in anterior-posterior and mediolateral directions. Simple visual, discrimination, and choice reaction times; sustained attention; visuomotor coordination; kinesthesis; and depth perception were also assessed in a series of perceptual and motor tests. The correlation analysis revealed that balancing under static conditions was strongly associated with the ability to perceive and process visual information, which is important for feedback-based control of balance. On the other hand, when greater task demands were imposed on the system under dynamic balancing conditions, the ability to respond to the destabilizing hip abductions-adductions in order to maintain equilibrium was associated with motor response speed, suggesting the use of a descending, feedforward control strategy. Therefore, like adults, 11- to 13-year-old children have the ability to select varying balance strategies (feedback, feedforward, or both), depending on the constraints of a particular task.

Child↗
PubMed2000

Validity of weight distribution and sway measurements of the Balance Performance Monitor.

BACKGROUND AND PURPOSE: The Balance Performance Monitor (BPM) is a device which provides auditory and visual feedback on weight distribution and the magnitude of lateral and anterior-posterior sway during quiet standing. This study investigated the validity of the measurements provided by the BPM using a Kistler force plate (KFP) as the gold standard. METHOD: Percentage weight distribution between the BPM foot plates was validated using both a series of calibration weights and the vertical component of ground reaction force, measured by the KFP, during normal standing in 18 young normal subjects. The lateral and anterior-posterior sway indices from the BPM were validated against the standard deviation of the position of the centre of pressure, again obtained using the KFP, during normal standing with eyes open and eyes closed and standing with feet together with eyes open. Concurrent validity of the percentage weight distribution measurements was assessed by calculating the 'limits of agreement' between the corresponding measurements from the BPM and KFP and the 95% confidence intervals for these 'limits'. Differences in the units of measurement obtained from the BPM and KFP resulted in the concurrent validity of the sway indices being assessed using correlation and regression. RESULTS: Excellent agreement was found between the percentage weight distribution values provided by the BPM and the KFP, which showed that the BPM may read only 3% of body weight above or below that given by the KFP. High correlations (r = 0.61-0.99) were found between both the lateral and anterior-posterior sway indices from the BPM and the motion of the centre of pressure from the KFP in the respective direction. Despite this, further analysis of regression equations and the 95% prediction intervals showed poor concurrent validity of the BPM sway indices in relation to KFP measurements. This was thought to be due to the different methods by which the sway indices and the motion of the centre of pressure were calculated. CONCLUSIONS: The BPM may be used to provide a valid measure of the symmetry aspect, but not necessarily the steadiness aspect of postural control.

Adult↗
PubMed1990

Head stabilization during various locomotor tasks in humans. I. Normal subjects.

Head kinematics were studied in ten normal subjects while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of motion of joint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. This was done by recording the displacement of a line approximating the plane of horizontal semi-circular canals (the Frankfort plane: F-P). Four conditions were studied: free walking (W) walking in place (WIP) running in place (R) and hopping (H). In the 4 experimental conditions, amplitude and velocity of head translation along the vertical axis ranged from 1 cm to 25 cm and 0.15 m/s to 1.8 m/s. In spite of the disparities in the tasks regarding the magnitude of dynamic components, we found a significant stabilization of the F-P around the earth horizontal. Maximum amplitude of F-P rotation did not exceed 20 degrees in the 4 situations. Vertical angular velocities increased from locomotion tasks to the dynamic equilibrium task although the maximum values remained less than 140 degrees/s. Predominant frequencies of translations and rotations in all the tasks were within the range 0.4-3.5 Hz and harmonics were present up to 6-8 Hz. During walking in darkness, mean head position is tilted downward, with the F-P always below the earth horizontal. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, WIP and R, but during H the amplitude decreased by 37%. Residual head angular displacement is found to compensate for head translation during the 4 conditions. Our study emphasizes the importance of head stabilization as part of the postural control system and described as a basis for inertial guidance.

Adult↗
PubMed2005

Joint coordination during quiet stance: effects of vision.

Stabilization of the center of mass (CM) is an important goal of the postural control system. Coordination of several joints along the human "pendulum" is required to achieve this goal. We studied the coordination among body segments with respect to horizontal CM stabilization during a quiet stance task and the effects of vision on CM stability. Subjects were asked to stand quietly on a narrow wooden block supporting only the mid-foot, with either open (EO) or closed (EC) eyes on separate trials. Instant equilibrium points (IEPs) in the center of pressure (CP) trajectory were determined when the horizontal component of the ground reaction force was zero and the CP data were decomposed into their rambling and trembling components. The joint angle, CM and CP data were divided into short cycles (time-normalized to 100 data points) or longer segments (time-normalized to 1000 data points) of equal length beginning and ending in an IEP. Motor abundance with respect to patterns of joint coordination was evaluated using the uncontrolled manifold (UCM) approach. Here, a UCM is a subspace spanning all joint combinations resulting in a given CM position. All combinations of joint angles that lie within this subspace are equivalent with respect to that CM position while joint angle combinations lying in a subspace orthogonal to the UCM lead to deviation from that CM position. UCM analysis was performed on data organized either across time within longer segments or at each point in time across multiple segments or across multiple cycles. Regardless of method of analysis, most of the variance in joint space was constrained to be within the UCM, preserving the mean CM position in both the EO and EC conditions. Joint configuration variance was significantly higher in the EC than in the EO condition although this increase occurred primarily within the UCM rather than in the orthogonal subspace that would have led to variation of the CM position. These results demonstrate the ability of the control system to selectively "channel" motor variability into directions in joint space that stabilize the CM position. This effect was enhanced when the task was made more challenging in the absence of vision. There was also a significant relationship between joint variance that led to a change in the CM position and, in particular, the rambling component of the CP path, lending some support to the idea that the CNS prescribes a certain stable trajectory of the CP during quiet stance that leads to a small controlled movement of the CM.

Adult↗
PubMed2006

Effects of distance and gaze position on postural stability in young and old subjects.

Visual stabilization of posture is known to improve when the distance to target fixation decreases; this is attributed to increased angular size of retinal slip induced by body sway. At near distance, however, the eyes converge and efferent or afferent oculomotor signals could also be involved in posture stabilization. The goal of this study is to test whether the distance effect exists for both young and elderly and to test the role of vergence itself and of gaze position. Eighteen young (25.3 years) and 17 elderly (61.6 years) subjects were asked to fixate a target in quiet stance presented either at close (40 cm) or at far distance (200 cm); the vergence angle was 9 degrees and 2 degrees , respectively. For each distance, three gaze positions were studied straight-ahead (0 degrees ), 15 degrees up or down. We found a decrease in the surface of center of pressure (CoP), of standard deviation of antero-posterior and lateral body sway and of speed variance at near distance that occurs for both young and elderly. At far distance, the surface of CoP is smaller for 15 degrees up or down gaze in comparison with straight-ahead position, but at near distance there is no such gaze position effect. In an additional experiment, subjects fixated a target at far distance (200 cm) but prisms were used to cause the eyes to converge by an amount similar to that required for 40 cm viewing distance. The use of prisms decreased surface of CoP to values similar to those for natural near viewing distance. The effect of gaze position and of convergence (experiment with prisms) leads us to suggest that in addition to retinal slip, the ocular motor signals and perhaps related neck muscle activity are involved in postural stabilization. Finally, the elderly presented higher speed variance of CoP than the young subjects even though the surface itself was similar to adult values. We suggest that increment of speed variance is the first sign of senescence in postural control.

Adaptation, Physiological↗
PubMed1996

Influence of the initial projection of the centre of gravity on posturo-kinetic coordination in humans. Application from a horizontal quadrupedal stance during voluntary limb raising.

The purpose of the study is to investigate the influence of initial projection of the centre of gravity (CG) on the spatial and temporal organization of the dynamic phenomena accompanying a voluntary movement in humans. From a horizontal quadrupedal stance, ten normal subjects were instructed to raise the right forelimb towards a support target in self paced velocity conditions. Three experimental conditions were tested for which the initial CG projection was either within (C1), at the limits of (C2) or outside the supporting triangle (C3). The results showed that vertical force variations on the four supports always preceded the first vertical displacement of the right wrist (onset of the movement). From C1 to C3, the duration of these anticipatory dynamic phenomena increased enabling an adjustment of the CG position such that equilibrium constraints were fulfilled. For all conditions, the acceleration peak of the CG occurred prior to the onset of movement and from C1 to C3, its magnitude increased in a single direction of the horizontal plane. For each condition, the load transfer was directed to the left forelimb and the right hindlimb (diagonal strategy) and reached a maximal value at the time of lift-off. With respect to this moment, the onset of the movement occurred increasingly early from C1 to C3. These results suggest that contribution of peripheral cues to postural control is more important, when the requirements of horizontal CG displacement increase.

Adult↗
PubMed1994

Cross-correlation analysis of the lateral hip strategy in unperturbed stance.

Subjects standing heel-to-toe on either hard ground or soft support were instructed to stand upright keeping optimal balance. Lateral accelerometric measurements at head, hip and ankle levels were subjected to conjugate cross-correlations analysis in order to determine the co-ordinated movements or strategies. The results strongly suggest that there exists a hip lateral strategy which is very similar to the hip strategy previously described in fore-aft body oscillations. This lateral hip strategy was only observed when the greatest body oscillations were observed, namely on the soft supporting surface, and its descending sequence of co-ordinated movements is consistent with the idea of a top-down organization of postural control during movement or difficult stance conditions.

Acceleration↗
PubMed2006

Influence of differences of visual acuity in various visual field conditions on spectral characteristics of the center of pressure sway.

This study examined the influence of visual acuity and visual field on the spectral characteristics of the center of pressure during standing. 17 men and 20 women participated in High and Low visual acuity groups. Both groups underwent center of pressure measurements under three visual field conditions: No vision: subjects were given no visual information, Central vision: they were given only central visual field information, and Full vision: they were given full visual information. To assess the spectral characteristics of center of pressure, mean power frequency and frequency of maximal power were calculated from medial-lateral and anterior-posterior center of pressure directions. The Friedman test and Scheffé pairwise comparison tests showed that frequency of maximal power was higher in the No vision than in the Central and Full vision conditions in the High visual acuity group. In conclusion, people with high visual acuity are more susceptible to visual field conditions than those with low visual acuity. It is suggested that postural control characteristics differ with visual acuity or resolution in the central visual field.

Adult↗
PubMed2005

Decreased trunk angular displacement during sitting down: an early feature of aging.

BACKGROUND AND PURPOSE: Trunk motion plays an important role in achieving both sit-to-stand and stand-to-sit transfers. However, these 2 body transfers depend on different postural and mechanical constraints. Although the effects of aging on sit-to-stand transfers have been widely studied, there is a lack of information concerning stand-to-sit transfers. The aim of this study was to determine how angular displacements of the trunk and shank are affected by aging during sit-to-stand and stand-to-sit transfers. SUBJECTS: Ten community-dwelling older adults (mean age=75.9 years, SD=3.2) and 9 young adults (mean age=26.8 years, SD=4.7) volunteered to participate. METHODS: Maximal angular displacements of the trunk and shank with respect to the vertical (ie, orientation angles) were measured, during standing up and sitting down, using an optoelectronic movement analyzer. RESULTS: For standing up, there was no difference between the young and older adults with regard to both maximal orientation angles. During sitting down, the maximal shank orientation angle was not affected by age, whereas the older adults had a smaller trunk motion compared with the young adults (approximately 10 degrees less). DISCUSSION AND CONCLUSION: The results showed that older adults tended to minimize the forward body displacement during sitting down. This strategy could be seen as an adaptive mechanism to decrease the risk of anterior disequilibrium. The authors suggest that this feature could be used as an early marker of aging on postural control.

Adult↗