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At least 613 records · Page 34Linked to original sources

PubMed1998

Computerized dynamic posturography: What have we learned from space?

Computerized dynamic posturography (CDP) has been under development since 1970. Several reviews summarize key basic and clinical research studies and outline important clinical uses of CDP along with research applications. This report summarizes new information about the otolith control of posture obtained from the study of astronauts. The dynamics of recovery of postural control upon return from orbital flight provide insight to the peripheral vestibular and central nervous system components of vestibular compensation. The dynamics of postural compensation should aid the clinician in the diagnosis and management of imbalance of vestibular origin.

Adaptation, Physiological↗

PubMed1980

Designing a better postural measurement system.

For more than a century the phenomenon of postural sway has attracted the attention of neurologists, control engineers, and otoneurologists, because body sway provides a global assessment of the sensorimotor systems involved in postural control. This article presents an overview of the history of body sway studies, highlighting some of the shortcomings of past techniques. Spurred on by these shortcomings, we specified design criteria for a better postural measurement system. The system has been implemented, and some of the preliminary applications are detailed that demonstrate the utility of our approach.

Aged↗

PubMedDate not supplied

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↗

PubMed2001

Heel to toe motion characteristics in Parkinson patients during free walking.

OBJECTIVE: Plantar pressures of Parkinson patients in a mild or moderate stage of the disease were analyzed in order to determine characteristics of the heel to toe motion of the foot in Parkinson patients during free walking. DESIGN: Pressure sensitive insoles were used to quantify the in-shoe pressure distribution for 24 patients with Parkinson's disease and for 24 age-matched healthy adults. Peak plantar pressures, relative loads and the variability of relative loads were analyzed for 10 different anatomical foot areas. Inferential statistics and regression analyses were performed to compare subject groups and to relate pressure data to a clinical score (Webster). BACKGROUND: It is well-known that Parkinson patients experience disorders of balance, posture and gait. Recent studies revealed that Parkinson patients show abnormalities in foot strike during walking. However, only little is known about the heel to toe motion of the foot in Parkinson patients in compensating for instability during walking. RESULTS: Parkinson patients show significant changes in foot loading behavior. Parkinson patients have a reduced impact at heel strike. This mechanism was found to be related to the severity of the disease. Furthermore, Parkinson patients show a trend towards higher relative loads in the forefoot regions combined with a load shift towards medial foot areas. These mechanisms are highly stereotypical. CONCLUSION: Parkinson patients, even in a mild or moderate stage of the disease, show significant changes in heel to toe motion of the foot during free walking. The characteristics of Parkinsonian gait are probably caused by adaptive mechanisms of the patients to avoid unsteadiness during walking. RELEVANCE: The results of this study revealed that Parkinson patients have characteristic heel to toe motion pattern. The determination of the foot-loading pattern using plantar pressure measurement may be used as a valuable tool for diagnostic, treatment and rehabilitation purposes. Furthermore, the strategy of the forefoot control in gait of Parkinson patients should be considered in Parkinsonian research.

Analysis of Variance↗

PubMed2001

Mechanisms of failed recovery following postural perturbations on a motorized treadmill mimic those associated with an actual forward trip.

OBJECTIVE: To examine the recovery strategies employed during a treadmill acceleration task, to determine if mechanisms that contributed to failed recoveries on a motorized treadmill are the same general biomechanical mechanisms that contributed to falls from a trip, and to determine if failed recovery responses could be modified to allow for successful recoveries on subsequent trials. DESIGN: A motorized treadmill was used to induce postural perturbations in healthy older adults. BACKGROUND: Previously, we induced trips in older adults to identify the mechanisms of failed recovery. However, inducing trips is not a clinically practical test for identifying older adults who are predisposed to falling. METHODS: Safety-harnessed older adults stood on a treadmill that was accelerated from 0 to 0.89 m/s to impose a postural perturbation. Recoveries were classified as successful (n=42) or failed (n=23). Selected biomechanical variables were calculated using motion analysis methods. RESULTS: Initial failed recoveries had slower reaction times, shorter step lengths, and greater trunk flexion angles and velocities. Subjects who failed on the initial attempt modified their recovery strategy to successfully recover. The biomechanics of these recoveries resembled those used by subjects who successfully recovered on their initial attempt. CONCLUSIONS: The biomechanical mechanisms involved with a failed treadmill recovery mimic those responsible for failed recoveries from an induced trip. Subjects who failed on their initial recovery response made modifications allowing successful recoveries on subsequent attempts. RELEVANCE: This protocol may be useful as a testing and rehabilitation tool for fall recovery.

Accidental Falls↗

PubMed2002

Force measurements of postural sway and rapid arm lift in seated children with and without MMC.

OBJECTIVE: The aim was to investigate the horizontal ground reaction forces of seated postural sway and rapid arm lift in children with and without myelomeningocele. BACKGROUND; It is unclear whether children with myelomeningocele have limited control of body posture entirely caused by the impairment in the legs or also by other dysfunction. METHODS: 11 children with myelomeningocele, 10-13 years, and 20 children without physical impairment were investigated. Data were collected by force plate measurements during quiet sitting and during rapid arm lift. The forces were expressed as the corresponding acceleration of the centre of mass. The amplitude and the frequency of the centre of mass acceleration quantified the sway. Movement time, onset and anteroposterior peak acceleration were analysed during arm lift. RESULTS: The children with myelomeningocele had a low sway frequency under both conditions: eyes open and eyes closed. The movement time was longer for these children compared to the controls. The onset of initial anteroposterior centre of mass acceleration preceded the arm lift and was directed forward in both groups. The peak centre of mass acceleration was usually directed backward. CONCLUSIONS: The control of postural sway was different in children with myelomeningocele compared to children without disabilities and this could not be explained by the cele level. The children with myelomeningocele had a slow motor performance of the seated sway and during arm lift. RELEVANCE: Slow motor performance involves functional limitations in the individual child and is important for the therapy program.

Adolescent↗

PubMedDate not supplied

Stabilometric parameters are affected by anthropometry and foot placement.

OBJECTIVE: To recognize and quantify the influence of biomechanical factors, namely anthropometry and foot placement, on the more common measures of stabilometric performance, including new-generation stochastic parameters. DESIGN: Fifty normal-bodied young adults were selected in order to cover a sufficiently wide range of anthropometric properties. They were allowed to choose their preferred side-by-side foot position and their quiet stance was recorded with eyes open and closed by a force platform. BACKGROUND: biomechanical factors are known to influence postural stability but their impact on stabilometric parameters has not been extensively explored yet. METHODS: Principal component analysis was used for feature selection among several biomechanical factors. A collection of 55 stabilometric parameters from the literature was estimated from the center-of-pressure time series. Linear relations between stabilometric parameters and selected biomechanical factors were investigated by robust regression techniques. RESULTS: The feature selection process returned height, weight, maximum foot width, base-of-support area, and foot opening angle as the relevant biomechanical variables. Only eleven out of the 55 stabilometric parameters were completely immune from a linear dependence on these variables. The remaining parameters showed a moderate to high dependence that was strengthened upon eye closure. For these parameters, a normalization procedure was proposed, to remove what can well be considered, in clinical investigations, a spurious source of between-subject variability. CONCLUSION: Care should be taken when quantifying postural sway through stabilometric parameters. It is suggested as a good practice to include some anthropometric measurements in the experimental protocol, and to standardize or trace foot position. RELEVANCE: Although the role of anthropometry and foot placement has been investigated in specific studies, there are no studies in the literature that systematically explore the relationship between such BF and stabilometric parameters. This knowledge may contribute to better defining the experimental protocol and improving the functional evaluation of postural sway for clinical purposes, e.g. by removing through normalization the spurious effects of body properties and foot position on postural performance.

Adult↗

PubMed2003

Gait perturbation response in chronic anterior cruciate ligament deficiency and repair.

OBJECTIVE: To determine how chronic anterior cruciate ligament deficient and surgically repaired subjects react to unexpected forward perturbations during gait as compared to healthy controls. DESIGN: Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and three months following reconstructive surgery, and 10 uninjured controls. BACKGROUND: The ability of an anterior cruciate ligament injured individual to react and maintain equilibrium during gait perturbations is critical for the prevention of reinjury. No studies have investigated how these individuals respond to unexpected perturbations during normal gait. METHODS: An unexpected forward perturbation was induced upon heel strike using a force plate capable of translational movement. RESULTS: Prior to surgery, the anterior cruciate ligament subjects exhibited a greater knee extensor moment in response to the perturbation compared to healthy controls. Following surgery, the anterior cruciate ligament injured subjects exhibited a static knee position and a sustained knee extensor moment throughout stance in response to the perturbation as compared to controls. CONCLUSIONS: These data suggest that chronic anterior cruciate ligament deficient subjects rely heavily on knee extensor musculature to prevent collapse in response to an unexpected perturbation. This same reactive response was more pronounced 3 months following surgery. RELEVANCE: The results suggest that, prior to and following surgery, chronic anterior cruciate ligament injured subjects respond differently than healthy controls to an unexpected perturbation during gait. Anterior cruciate ligament injured or repaired subjects do not reduce or avoid vigorous contraction of the quadriceps muscles when responding to gait perturbations.

Adult↗

PubMed2003

Visual feedback induces opposite effects on elementary centre of gravity and centre of pressure minus centre of gravity motions in undisturbed upright stance.

OBJECTIVE: To evaluate the instantaneous effects of visual feedback on undisturbed stance control mechanisms. DESIGN: The controlling variable, the centre of pressure trajectories, recorded using a force platform, were decomposed into two elementary motions: (1) the horizontal displacements of the centre of gravity and (2) the vertical projection of the difference between centre of pressure and the centre of gravity. These motions were processed through frequential analysis and modelled as fractional Brownian motion. BACKGROUND: Even though visual feedback protocols are advantageously used for rehabilitation purposes, their immediate effects from biomechanical and motor control points of view need to be assessed. METHODS: Twelve healthy adult subjects were tested through eyes open and visual feedback conditions. RESULTS: A significant amplitude increase in the difference between the centre of pressure and the centre of gravity motions and a decrease in the centre of gravity motions are observed during visual feedback. The fractional Brownian motion modelling analysis reveals an enhanced control of these elementary motions. The point at which the corrective process is initiated is increased with visual feedback whereas the time delay remains the same. CONCLUSIONS: The decrease of the centre of pressure displacements classically observed through visual feedback protocol initially results in a reduction of the centre of gravity motions and an augmentation of the difference between centre of pressure and centre of gravity motions, hence suggesting increased muscular activity. RELEVANCE: Precise knowledge of the effects generated by such feedback protocol should allow to optimise it as a rehabilitation tool.

Adult↗

PubMed2003

Development of kinematics tests for the evaluation of lumbar proprioception and equilibration.

OBJECTIVE: This study aimed at developing lumbar repositioning and seated equilibration tests. DESIGN: 3D-electrogoniometric study of trunk repositioning and equilibration in seated position. BACKGROUND: Postural equilibrium and lumbar proprioception alterations have been shown in patients with low-back pain. METHODS: In 21 healthy volunteers, pure flexion and flexion+rotation repositioning error was measured using 3D-electrogoniometry. Lumbar kinematics was analysed (time and frequency domain) during antero-posterior and lateral equilibration tests in seated position. Reproducibility and stability of the protocol were evaluated. RESULTS: Reproducibility and stability were good. Pure flexion repositioning error was similar to previous reports. For flexion+rotation tests, repositioning error was 3 degrees for flexion and 1 degrees for rotation. Amplitude, imbalance time and power spectrum were significantly larger in lateral than in antero-posterior equilibration tests. CONCLUSIONS: The feasibility of kinematic analysis of lumbar repositioning and equilibration was shown. Repositioning error values were in agreement with previous studies. New tests and parameters were proposed. Lateral equilibration tests appeared more demanding than antero-posterior tests. RELEVANCE: In patients with low-back pain, lumbar repositioning and equilibration tests may be of use to define rehabilitation strategies and to evaluate treatment outcome.

Adult↗

PubMed2003

Evaluation of shoulder proprioception following muscle fatigue.

OBJECTIVE: To investigate the effect of shoulder muscle fatigue on glenohumeral proprioception. DESIGN: A repeated proprioception test was performed. BACKGROUND: The role of conditioning and fatigue in sport injuries remains controversial. It has been hypothesized that proprioceptive information plays an important role in joint stabilization and that muscle fatigue may alter proprioceptive ability. However, the effect of shoulder muscle fatigue on glenohumeral proprioception is still controversial. METHODS: Eleven normal subjects (mean age 27.3 years) participated in this study. Proprioception tests (on the dominant shoulder) were performed in which proprioception of the active reproduced and passive reproduced shoulder position was measured using an isokinetic dynamometer and a proprioception testing apparatus, respectively. The speed of active repositioning was at 2 deg/s and passive repositioning was at 0.5 deg/s. The mean value of maximum voluntary contraction and the number of repetitions for muscle fatigue were recorded. Post-fatigue proprioception test was started within 3 min after muscle fatigue. RESULTS: There was no significant difference of shoulder proprioception between pre- and post-fatigue determinations of passive repositioning in shoulder internal rotation, passive repositioning in external rotation and active repositioning in internal rotation. There was a significant difference between pre- and post-fatigue determination of active repositioning in external shoulder rotation (mean degrees: 2.57 (SD 1.02) vs. 4.96 (SD 1.73), P<0.05). CONCLUSION: Shoulder proprioception in active repositioning in external rotation was major affected by muscle mechanoreceptors in the presence of muscle fatigue. RELEVANCE: This study revealed that the shoulder proprioception after muscle fatigue in active repositioning in shoulder external rotation was affected more sensitively by the muscle mechanoreceptors than the joint mechanoreceptors. Increasing resistance of muscle fatigue would increase the shoulder proprioceptive ability.

Adaptation, Psychological↗

PubMed2003

Repeated spinal flexion modulates the flexion-relaxation phenomenon.

OBJECTIVES: To determine if repeated spinal flexion and loading modulate the deactivation of lumbar muscles near full flexion (flexion-relaxation). DESIGN: Repeated measures experimental study of the effect of repetitive trunk flexion and added mass on the flexion-relaxation phenomenon. BACKGROUND: Repeated flexion causes muscular fatigue, creep of passive tissues and diminished protective reflexes. However, flexion-relaxation has not been studied in repeated trunk flexion, and could be related to the increased risk of low-back disorders. METHODS: Thirty healthy young subjects performed 100 trunk flexion movements between standing and full flexion. Erector spinae electromyography and lumbar spine flexion were measured during cycles 1-10 (no load), 11-20 (performed holding a mass in the hands), 81-90 (mass in the hands) and 91-100 (no load). The spinal flexion angle at myoelectric silence and full flexion were extracted from each movement cycle. RESULTS: Twenty-three of the 30 subjects showed flexion-relaxation throughout the repeated trunk flexion. The flexion-relaxation and maximum flexion angles increased at the end of the experiment; the flexion-relaxation angle relative to the maximum flexion angle also increased. This effect depended on the load condition; the flexion-relaxation and maximum flexion angles showed a greater increase in the unloaded than loaded condition. CONCLUSIONS: The flexion-relaxation phenomenon was changed due to repeated trunk flexion. The increases in flexion-relaxation angle likely involve changes to the neuromuscular control system. RELEVANCE: The deactivation of the erector muscles near full flexion occurs at a greater spinal flexion angle and a greater proportion of maximum spinal flexion following repeated spinal flexion. This may be related to the increased risk of injury associated with repeated flexion.

Adaptation, Physiological↗

PubMed1999

Lumbosacral repositioning accuracy in standing posture: a combined electrogoniometric and videographic evaluation.

OBJECTIVE: To provide a new method of measuring repositioning accuracy in the lumbosacral spine in a standing position. DESIGN: A test-retest and parallel-forms reliability testing was performed. BACKGROUND: The contribution of proprioception to lumbar muscle function and to the stability of the lumbar spine is relatively unknown. METHOD: A piezoresistive electrogoniometer attached to the skin over the sacrum and a three-dimensional video analysis system with reflective markers on anatomical landmarks were both employed to measure the repositioning accuracy of pelvic tilting in standing. Eleven subjects without low back pain participated in this study. RESULTS: The overall mean repositioning accuracy was 1.87 degrees. Probability values from repeated measures ANOVA revealed no significant mean absolute error (AE) differences between sessions. Correlation coefficients between electrogoniometer and 3-D video analysis measurements of position sense ranged from 0.84 to 0.97. CONCLUSIONS: The proposed instruments and method are adequate for measuring lumbosacral repositioning accuracy. Healthy subjects are capable of repositioning their pelvis and back precisely. RELEVANCE: A reliable method assessing the lumbosacral repositioning accuracy can add insight into neuromuscular dysfunction as a cause of mechanical low back pain.

Biomechanical Phenomena↗

PubMed2000

Biomechanical analysis of sit-to-stand transfer in healthy and paraplegic subjects.

OBJECTIVE: An experimental study of the sit-to-stand transfer in healthy adults with/without arm-support and in paraplegic patients with/without electrical stimulation of the quadriceps muscles was performed. The study was aimed to compare the joint torques, momentum transfer hypothesis, and stability of the sit-to-stand transfer in the healthy and paraplegic subjects. METHODS: A planar 3-linkage rigid body model was used to compute the body-segmental linear momentum and the reaction forces and torques at the joints from measured data. RESULTS: In healthy subjects the arm-support enlarged the support base of the body and thus, increased the postural stability. Strong arm-assistance reduced the maximum hip and knee joint torques by more than 50%. It was observed that the healthy participants rising with arm-support used momentum transfer to facilitate the transition from sitting to standing. The paraplegic participants did not apply the momentum transfer strategy and the sit-to-stand transfer was accomplished in a quasi-static manner. Stimulating the quadriceps, the legs could participate partly in the movement dynamics. CONCLUSION: Our results indicate that some significant differences exist between the maneuver applied by the paraplegic patients to stand up and the strategies used by the healthy adults rising with arm-support. RELEVANCE: Analysis of the biomechanical factors underlying the sit-to-stand activity is essential in the design of competent closed-loop neuroprosthesis controllers which assist paraplegic patients during rising.

Adult↗

PubMed2000

Vestibular, visual, and somatosensory contributions to human control of upright stance.

We investigated the changes of human posture control of upright stance which occur when vestibular cues (VEST) are absent and visual and somatosensory orientation cues (VIS, SOM) are removed. Postural responses to sinusoidal tilts of a motion platform in the sagittal plane (+/-2 degrees, f=0.05, 0.1, 0.2 and 0.4 Hz) were studied in normal subjects (Ns) and patients with bilateral vestibular loss (Ps). We found that absence of VEST (Ps, visual reference) and removal of VIS (Ns, no visual reference) had little effect on stabilization of upright body posture in space. In the absence of both VEST and VIS (Ps, no visual reference) somatosensory graviception still provided some information on body orientation in space at 0.05 and 0.1 Hz. However, at the higher frequencies Ps qualitatively changed their behavior; they then tended to actively align their bodies with respect to the motion platform. The findings confirm predictions of a novel postural control model.

Cues↗

PubMed2000

The direction of postural instability affects postural reactions to ankle muscle vibration in humans.

Postural instability changes the weighting of different types of sensory information and the state of the equilibrium maintenance system. We have recently found that the effect of Achilles tendon vibration (so-called 'vibration-induced falling') strongly diminishes during unstable posture. However, it is unclear whether the state of postural instability has directionally specific or non-specific effects on the attenuation of proprioceptive influences from ankle muscles. To check this hypothesis, we varied the direction of support mobility and applied shank muscle vibration to subjects standing on a rocking platform movable in the sagittal, frontal or both directions. Postural reactions were present only on those supports that were stable in the sagittal direction. We suggest that the direction of postural instability affects information processing from ankle muscle receptors.

Adult↗

PubMed2001

Menstrual cycle effects on postural stability but not optokinetic function.

We investigated the effects of the menstrual cycle on visual-vestibular interaction by measuring optokinetic function and postural stability at different phases of the cycle. Menstrual cycle phase had no significant effect on gaze-holding, optokinetic nystagmus slow phase velocity, amplitude or frequency, circularvection latency or optokinetic afternystagmus frequency, amplitude or duration. While menstrual cycle phase had no significant effect on anterior-posterior sway, it did significantly affect lateral sway (P<0.001), with sway on day 5 significantly greater than on days 12 and 21 (P<0.05 and 0.01, respectively), and sway on day 25 significantly greater than that on day 21 (P<0.05).

Adolescent↗

PubMed2002

Initiation of a vertical jump: the human body's upward propulsion depends on control of forward equilibrium.

The aim of the study was to understand: (i), how far anticipatory postural adjustments (APA) participate in the sequences of a complex task; (ii), how, in the sagittal plane, horizontal and vertical progressions of the center of gravity (CG) are managed to achieve the prescribed goal. A posturo-kinetics sequence is identified during which forward CG progression is controlled in terms of a center of pressure (CP)-CG interaction. CP shifts and horizontal CG accelerations are correlated in timing and amplitude. There exists a control of whole body progression during the impulse, implying a braking of forwards movement. Vertical and horizontal CG accelerations are inter-dependent, and backward CP shift duration is related to its forward displacement. During the vertical jump initiation, whole body vertical propulsion and forward fall are linked. To increase impulse amplitude, initial whole body disequilibrium is lengthened and forward CG acceleration is greater. APA programming is probably elaborated on the basis of cognitive evaluation of the antero-posterior disturbance.

Acceleration↗