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At least 361 records · Page 20Linked to original sources

PubMed2005

Effects of changes in skiing posture on the kinetics of the knee joint.

This study was performed to investigate the effects of changes in the skiing posture on mechanical stress across the knee joint. The aim of the present study was to establish a safer form of skiing for the prevention of injury to the anterior cruciate ligament of the knee (ACL). Ten healthy volunteers were placed on a force plate on an artificial slope, and assumed forward and backward bending postures with a single leg by changing their centre of gravity. The knee flexion angles were limited to approximately 30 degrees by orthotics in each posture. Joint moments of the lower extremity were analyzed using a motion analysis system, and the muscle activities of the lower extremity were recorded by EMG and digitised to integrated EMG in each posture. In addition, extrusion of the lower leg by the boot was measured using a force sensor sheet inserted behind the calf. We found that the extension moment of the hip and ankle joints, and muscular activity of the hamstrings were increased in forward bending, whereas the extension moment of the knee and muscular activity of the quadriceps were decreased. Conversely, the muscular activity of the quadriceps, the flexion moment of the hip, extension moment of the knee joint, and pressure of the boot were increased in backward bending, whereas muscular activity of the hamstrings was decreased. The dependency on the hamstrings increased in forward bending in a skiing posture on a slope with slight knee flexion. Therefore, forward bending seemed to be an advantageous posture for the prevention of ACL injury. Conversely, in a backward bending skiing posture, the extension moment of the knee joint produced by muscle contraction of the quadriceps also increased imbalance in the hamstrings. The results of this study suggest that the internal force exerted by the quadriceps, in addition to the passive factor of extrusion of the lower leg by the boot, may contribute to non-contact ACL injury in a backward bending posture while skiing.

Adult↗

PubMed2004

A quantitative measure of postural sway deficits in schizophrenia.

Clinicians rely on observational methods to assess obvious signs of postural abnormalities in schizophrenia, yet subtle signs of postural deficits may go unnoticed. Posture is controlled, in large part, by the cerebellum, which has been implicated in numerous reports of structural and functional deficits in schizophrenia. Given the possibility of an underlying disruption of cerebellar function in schizophrenia, this study used an objective, quantitative measure to assess the magnitude of postural stability in this disorder. A total of 36 schizophrenia patients and 36 non-psychiatric age-matched controls stood on a pressure-sensitive platform that recorded shifts in weight (body sway) through pressure points in the feet. Patients demonstrated more postural sway than did healthy controls (p<0.01). When patients with noticeable signs of tardive dyskinesia were removed from analyses, group differences remained (p<0.01). There was no significant correlation between neuroleptic medication level and degree of postural sway (r=0.16, p=0.37). These results indicate that patients with schizophrenia have subtle, yet quantifiable, disturbances in the control of posture and balance. Quantitative measures of postural sway may provide a more sensitive means of detecting disturbances of movement than do standard clinical observations alone.

Adult↗

PubMedDate not supplied

Comparison of thoracic kyphosis and postural stiffness in younger and older women.

BACKGROUND CONTEXT: An increase in thoracic kyphosis and postural stiffness is commonly associated with aging and many pathological conditions. Simple clinical measurements are needed to estimate the relative degree of postural stiffness to determine whether clinical interventions, such as exercise, are beneficial. PURPOSE: To compare the amount of kyphosis and postural stiffness in the thoracic spine of younger and older women. STUDY DESIGN/SETTING: Experimental design conducted at a large health science center in southeastern Texas. PATIENT SAMPLE: Fifty-one healthy adult women, 25 between the ages of 21 and 51 years and 26 aged 66 to 88 years. OUTCOME MEASURES: Index of kyphosis (IK) measured with a surveyor's flexicurve. Differences, percent change and ratios between IK measures taken in the relaxed and maximally erect positions were used to estimate postural stiffness. METHODS: Subjects were measured while standing in their usual relaxed posture and again in their maximally erect posture by three different raters. IK measures were calculated by each rater and averaged for further data analysis. Independent t tests were used to compare the two age groups at the .05 alpha level. RESULTS: Significant differences were found in both the relaxed (p= .018) and erect (p< .001) IK measures of younger and older women. The differences, percent change and ratio between the two IK measures were also significantly different in that the younger women demonstrated a greater degree of active reduction of their kyphosis (in the erect posture) than older women. CONCLUSIONS: Age-related differences in thoracic kyphosis and postural stiffness were documented between younger and older women by means of repeated flexicurve measurements performed in both a relaxed and a maximally erect position.

Adult↗

PubMed2005

A new translational platform for evaluating aging or pathology-related postural disorders.

CONCLUSIONS: Dynamic posturography using a translational platform and new parameters for quantifying postural reactions to linear displacements were suitable for differentiating between aging and pathological effects in upright postural control. These tools should be used on a wider scale in the near future for both routine tests and rehabilitation purposes, including the prevention of falls in elderly people. OBJECTIVE: To demonstrate that dynamic posturography using a translational platform and new parameters for quantifying postural reactions to linear displacements constitute a more suitable way of discriminating age and/or pathology-induced postural effects. MATERIAL AND METHODS: Three groups of young healthy, elderly healthy and elderly unstable patients were tested on a translational platform using ramp (0.03, 0.07 and 0.1 m/s) and sinusoidal (0.25 and 0.5 Hz) stimulations. Their dynamic performances were compared to their postural evaluation on a static platform using classical stabilometric parameters (surface, length, etc.) and stabilogram-diffusion analysis (critical point coordinates and short-term diffusion coefficient). RESULTS: The translational platform, the new parameters elaborated for quantifying postural reactions (energy and time for postural stabilization, phase and gain of the postural response) and the visual condition under which the subjects were tested (eyes open versus eyes closed) discriminated all groups better than the classical methods.

Adult↗

PubMed2003

Effect of chronic bilateral subthalamic nucleus (STN) stimulation on postural control in Parkinson's disease.

Postural instability is one of the most incapacitating factors in Parkinson's disease (PD). The underlying deficits and the effects of treatment are still not well understood. The aims of the present study were: (i) to identify abnormalities of postural control in PD patients during unperturbed stance and externally perturbed stance (anterior-posterior tilts of the support surface and of the visual scene); (ii) to assess the effects of L-dopa medication and subthalamic nucleus (STN) stimulation on posture control; and (iii) to characterize potential differential or additive effects of both treatments. Eight PD patients under chronic STN stimulation were investigated and compared with 10 normal controls. The assessment was performed in a crossover design (+/- STN stimulation, +/- L-dopa). During unperturbed stance, we recorded measures of spontaneous sway in terms of displacement, velocity and frequency of the centre of pressure (COP), lower body (LB) and upper body (UB) excursions. In addition, inter-segmental UB-LB coupling was investigated as a measure of axial stiffness. All these measures were abnormally large in patients OFF treatment. Under L-dopa treatment, the velocity, frequency and coupling measures were reduced, whereas sway amplitude increased. Very similar effects were obtained under STN stimulation, and these effects became more pronounced in the combined treatment condition. In these data, reduction of inter-segmental coupling correlated with increase in sway amplitude. The finding suggests that axial stiffness reduction under treatment revealed a treatment- resistant deficit in the sensorimotor postural control loop. However, these two effects did not correlate with the motor subscores of the unified Parkinson's disease rating scale (UPDRS), which indicates that they are of minor functional relevance for posture control. A frequency peak in the COP excursions at 0.7-1.1 Hz, which we take to indicate a resonance behaviour of the postural control loop, became reduced under therapy. The reduction of this peak did correlate with most improvements in the UPDRS under therapy. Support surface tilt revealed that an UB righting on the LB segment, which is present in normal controls, is missing in the patients. The postural responses to visual tilt were abnormally large in patients, independent of whether the support was stable or slightly moving, while the control subjects clearly profited from a stable support. This finding suggests that PD patients lack the ability of normal subjects to use sensory or cognitive information when suppressing the destabilizing effect of visual tilt. These abnormal tilt reactions of the patients were resistant to treatment with L-dopa, STN stimulation and a combination of the two. Overall, the effects of STN stimulation on posture control essentially paralleled those of L-dopa during both unperturbed and externally perturbed stance.

Activities of Daily Living↗

PubMed1999

Phase-dependent modulation of proximal and distal postural responses to slips in young and older adults.

BACKGROUND: Phase-dependent modulation of postural responses plays an important functional role in integrating reflexes into ongoing locomotion behaviors. This study tested the hypotheses that proximal and distal postural responses are modulated differently according to the phases of the gait cycle in young adults and that there is a decline in this modulatory ability with normal aging. METHODS: Thirty-three healthy young adults (age = 25 +/- 4 years) and 32 healthy older adults (mean age 74 +/- 14 years) participated. Subjects walked across a movable force plate with its movement timed to heel strike or midstance to simulate a forward slip occurring at different times during the gait cycle. Surface electromyography was recorded from bilateral leg, thigh, hip, and trunk muscles. Kinematic data were collected from the right (perturbed) side of the body. RESULTS: Postural responses to the heel strike slips occurred more frequently, and were of shorter latency, longer burst duration, and greater burst magnitude, than those in response to the midstance slips. Whereas the early and predominant postural responses came from bilateral tibialis anterior, rectus femoris, and biceps femoris muscles in heel strike slips, early postural responses were observed in bilateral erector spinae muscles in midstance slips. The late postural responses in midstance slips (from bilateral biceps femoris muscles and medial gastrocnemius and tibialis anterior of the nonperturbed leg) assisted in foot liftoff of the perturbed leg and earlier and safe landing with the nonperturbed leg. In response to the heel strike versus midstance slips, older adults preserved the phase-dependent modulatory abilities of the occurrence, onset latency, and burst duration of their postural responses, but not the ability to modulate burst magnitude, as compared to young adults. CONCLUSION: Postural responses from the proximal and distal muscles in reaction to different temporal phasing of slips during the step cycle showed differential modulation to meet the different task requirements. Older adults preserve this modulatory ability but with limited capacity. Physiological or psychological factors may influence older adults' phase-dependent modulatory capacity.

Accidental Falls↗

PubMed2000

Attentional demands and postural control: the effect of sensory context.

BACKGROUND: This study used a dual task design to examine the effect of sensory context on postural stability during the concurrent performance of an attentionally demanding cognitive task in young and older adults with and without a history of imbalance and falls. METHODS: A choice reaction time auditory task was used to produce changes in attention during quiet stance in six different sensory conditions that changed the availability of accurate visual and somatosensory cues for postural control. Postural stability was quantified by using forceplate measures of center of pressure in 18 young adults, 18 healthy older adults, and 18 older adults with balance impairments and a history of recent falls. Reaction time and accuracy of verbal response to the auditory task were quantified by using a repeated measures analysis of variance. RESULTS: In young adults the auditory task did not affect postural stability in any of the sensory conditions. However, in the older adults the effect of the auditory task depended on sensory context. For healthy older adults, the addition of an auditory tone task significantly affected sway only when both visual and somatosensory cues for postural control were removed. In the balance-impaired older adults, the addition of the auditory task significantly affected postural stability in all sensory conditions. In addition, as sensory conditions became more difficult, older adults who had been able to maintain stability in a single task context lost balance when performing a secondary task. CONCLUSION: Results suggest that with aging, attentional demands for postural control increase as sensory information decreases. In addition, the inability to allocate sufficient attention to postural control under multitask conditions may be a contributing factor to imbalance and falls in some older adults.

Accidental Falls↗

PubMed2000

Centrally initiated postural adjustments in parkinsonian patients on and off levodopa.

This study investigates the effects of parkinsonism and dopamine replacement therapy (levodopa) on centrally initiated postural activity preceding rising onto the toes. The electromyographic (EMG) and force magnitude, scaling, sequencing, and postural stabilization were compared when rising-to-toes under two conditions, slow/low versus fast/high, for parkinsonian patients and elderly control subjects. Parkinsonian subjects were tested after withholding their levodopa medication for 12-16 h and again 1 h after taking their medication when parkinsonian signs were diminished. Parkinsonian subjects showed reduced magnitudes and delayed timing of the postural and voluntary components of the rise-to-toes task, as if they had difficulty turning off the postural, tibialis anterior (TIB) component and initiating the voluntary, gastrocnemius (GAS) component. Dopamine improved the relative timing, as well as the magnitude of both postural and voluntary components of rise-to-toes. Although the magnitude of dorsiflexion torque was smaller for parkinsonian subjects ON and OFF than for healthy elderly controls, the parkinsonian subjects showed intact scaling of the magnitude of postural activity. Parkinsonian subjects do not perform the rise-to-toes task like normal subjects who are instructed to rise slowly; the relative timing of TIB and GAS activation was different even at comparable speeds of performance. Parkinsonian subjects, both ON and OFF, exhibited greater risk of falling than elderly control subjects when rising to toes. This increased risk of falling was reflected in a smaller safety margin between the peak center of mass (CoM) and peak center of pressure (CoP) during the task. The magnitude of mean postural dorsiflexion torque in the rise-to-toes task was highly correlated with a clinical rating scale of gait and balance, suggesting that force control is a critical factor influencing postural control in patients with Parkinson's disease.

Accidental Falls↗

PubMedDate not supplied

Influence of the visual environment on the postural stability in healthy older women.

BACKGROUND: A poor postural stability in older people is associated with an increased risk of falling. It is recognized that visual environment factors (such as poor lighting and repeating patterns on escalators) may contribute to falls, but little is known about the effects of the visual environment on postural stability in the elderly. OBJECTIVE: To determine whether the postural stability of older women (using body sway as a measure) differed under five different visual environment conditions. METHODS: Subjects were 33 healthy women aged 65-76 years. Body sway was measured using an electronic force platform which identified the location of their centre of gravity every 0.05 s. Maximal lateral sway and anteroposterior sway were determined and the sway velocity calculated over 1-min trial periods. Body sway was measured under each of the following conditions: (1) normal laboratory lighting (186 lx); (2) moderate lighting (10 lx); (3) dim lighting (1 lx); (4) eyes closed, and (5) repeating pattern projected onto a wall. RESULTS: Each measure of the postural stability was significantly poorer in condition 4 (eyes closed) than in all other conditions. Anteroposterior sway was greater in condition 3 than in conditions 1 and 2, whilst the sway velocity was greater in condition 3 than in condition 2. Lateral sway did not differ significantly between different lighting levels (conditions 1-3). A projected repeating pattern (condition 5) did not significantly influence the postural stability relative to condition 1. CONCLUSIONS: The substantially greater body sway with eyes closed than with eyes open confirms the importance of vision in maintaining the postural stability. At the lowest light level, the body sway was significantly increased as compared with the other light levels, but was still substantially smaller than on closing the eyes. A projected repeating pattern did not influence the postural stability. Dim lighting levels and removing visual input appear to be associated with a poorer postural stability in older people and hence might be associated with an increased risk of falls.

Accidental Falls↗

PubMed1994

Sensory stimulation promotes normalization of postural control after stroke.

BACKGROUND AND PURPOSE: In a randomized study of hemiparetic stroke patients with a median age of 75 years, functional recovery was significantly better in those who received additional sensory stimulation (n = 38), including electrostimulation, than in control patients (n = 40) given the same physiotherapy and occupational therapy; group differences for balance, mobility, and activities of daily living were significant. The present study was designed to investigate postural control in patients who survived more than 2 years after stroke onset. METHODS: The 48 survivors (mean, 2.7 years; range, 2.0 to 3.8 years), 22 from the treatment group and 26 from the control group, were compared with 23 age-matched healthy subjects. Subjects were perturbed by vibrators applied to calf muscles or with galvanic vestibular stimulation. We evaluated postural control in terms of sway variances or sway velocities and the dynamics of postural control as a feedback system using system identification with a model previously validated for human postural control. RESULTS: Significantly more patients of the treatment group than of the control group maintained stance during perturbations (P < .01). Among patients capable of maintaining stance during perturbation, the control patients were characterized by significant divergence from normal values in two of the three characteristic parameters of dynamic postural control (ie, swiftness and stiffness; P < .05) compared with the treatment subgroup or age-matched subjects. CONCLUSIONS: The course of sensory stimulation enhanced recovery of postural function, an enhancement still significant 2 years after the lesion and treatment. The differences and near normalization of characteristic parameters of dynamic postural control among treated patients suggest that improved recovery after sensory stimulation may be achieved by patients regaining normal or near normal dynamics of human postural control.

Activities of Daily Living↗

PubMed1999

Disruption of postural readaptation by inertial stimuli following space flight.

Postural instability (relative to pre-flight) has been observed in all shuttle astronauts studied upon return from orbital missions. Postural stability was more closely examined in four shuttle astronaut subjects before and after an 8 day orbital mission. Results of the pre- and post-flight postural stability studies were compared with a larger (n = 34) study of astronauts returning from shuttle missions of similar duration. Results from both studies indicated that inadequate vestibular feedback was the most significant sensory deficit contributing to the postural instability observed post flight. For two of the four IML-1 astronauts, post-flight postural instability and rate of recovery toward their earth-normal performance matched the performance of the larger sample. However, post-flight postural control in one returning astronaut was substantially below mean performance. This individual, who was within normal limits with respect to postural control before the mission, indicated that recovery to pre-flight postural stability was also interrupted by a post-flight pitch plane rotation test. A similar, though less extreme departure from the mean recovery trajectory was present in another astronaut following the same post-flight rotation test. The pitch plane rotation stimuli included otolith stimuli in the form of both transient tangential and constant centripetal linear acceleration components. We inferred from these findings that adaptation on orbit and re-adaptation on earth involved a change in sensorimotor integration of vestibular signals most likely from the otolith organs.

Adaptation, Physiological↗

PubMed2005

Improvement in automatic postural coordination following alexander technique lessons in a person with low back pain.

BACKGROUND AND PURPOSE: The relationship between abnormal postural coordination and back pain is unclear. The Alexander Technique (AT) aims to improve postural coordination by using conscious processes to alter automatic postural coordination and ongoing muscular activity, and it has been reported to reduce low back pain. This case report describes the use of the AT with a client with low back pain and the observed changes in automatic postural responses and back pain. CASE DESCRIPTION: The client was a 49-year-old woman with a 25-year history of left-sided, idiopathic, lumbrosacral back pain. Automatic postural coordination was measured using a force plate during horizontal platform translations and one-legged standing. OUTCOMES: The client was tested monthly for 4 months before AT lessons and for 3 months after lessons. Before lessons, she consistently had laterally asymmetric automatic postural responses to translations. After AT lessons, the magnitude and asymmetry of her responses and balance improved and her low back pain decreased. DISCUSSION: Further research is warranted to study whether AT lessons improve low back pain-associated abnormalities in automatic postural coordination and whether improving automatic postural coordination helps to reduce low back pain.

Biofeedback, Psychology↗

PubMed1990

Posture in otoneurology. Volume I.

In this study, posture is studied in the context of neuro-otological problems. In the several chapters, postural elements, postural influence upon balance aspects as well as postural components of the balance function in normal and pathological conditions are emphasized. Two main applications are put forward: rehabilitation by postural treatment techniques (REHAB) and examination techniques for the vestibulospinal aspects (posturography--PG). I. Balance function Balance is provided by automatic reflexes for stabilization of the visual field (vestibulo-ocular reflex--VOR) and for a correct posture, erect standing (vestibulo-spinal reflex--VSR) and head position (vestibulo-collic reflex--VCR). The fundamental characteristics of these reflexes are described, especially of those related to posture. The reflexes are elaborated on the basis of sensory inputs that inform about changed relations to space and environment, provided by visual, vestibular and proprioceptive systems. The sensory signals are further processed by the centers to adequate reflexes and to some extent to a conscious awareness. II. Dysfunction and adaptation Dysfunction in the balance mechanisms leads to erroneous reflexes, but most importantly to frightening sensations of vertigo. The peripheral disturbances produce a sensory mismatch which is the primum movens of vertigo. Built-in adaptive mechanisms cope with this disturbance and restore global balance function. The mechanisms involved have been studied as vestibular compensation and habituation, VOR-reflex plasticity and sensory "substitutive" compensation. The mechanisms are set into action by the dysfunctional situation and constitute an error-controlled process. Emphasis is laid upon the items related to rehabilitation treatment and posturography. A survey of clinical entities of vestibular peripheral dysfunction is included. III. Examination techniques The logical approach to the patient with vertigo consists in an analysis of the complaints pattern, correlation of it with the dysfunctional state revealed by clinical observation, and functional tests of balance. Correct interpretation of the test results is a pre-requisite. Postural aspects of these examination techniques, especially posturography, are put into evidence in this review. The strategy used in the department is sketched. IV. Contribution of the examination techniques: functional evaluation results The several data obtained by each examination technique are discussed within the scope of the experiences in the department. Data from the literature and from personal experience, especially interpreted in the context of rehabilitation and posturography, are analysed. V. Reh

Adaptation, Physiological↗

PubMed2005

Hands and knees posture in late pregnancy or labour for fetal malposition (lateral or posterior).

BACKGROUND: Lateral and posterior position of the baby's head (the back of the baby's head facing to the side or the mother's back) may be associated with more painful, prolonged or obstructed labour and difficult delivery. It is possible that certain positions adopted by the mother may influence the baby's position. OBJECTIVES: The objective of this review is to assess the effects of adopting a hands and knees maternal posture in late pregnancy or during labour when the presenting part of the fetus is in a lateral or posterior position, compared with no intervention. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group Trials Register (November 2004) and the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 4, 2004). SELECTION CRITERIA: Randomised trials of hands and knees maternal posture compared to other postures or controls. DATA COLLECTION AND ANALYSIS: Both review authors assessed trial eligibility and quality. MAIN RESULTS: Two trials of hands and knees posture during pregnancy were included. In one trial involving 100 women, four different postures (four groups of 20 women) were combined for the comparison with the control group of 20 women. Lateral or posterior position of the presenting part of the fetus was less likely to persist following 10 minutes in the hands and knees position compared to a sitting position (one trial, 100 women, relative risk (RR) 0.25, 95% confidence interval (CI) 0.17 to 0.37). In a second trial including 2547 women, advice to assume the hands and knees posture for 10 minutes twice daily in the last weeks of pregnancy had no effect on the baby's position at delivery or any of the other pregnancy outcomes measured. No trials of hands and knees posture during labour were included. AUTHORS' CONCLUSIONS: Use of hands and knees position for 10 minutes twice daily to correct occipitoposterior position of the fetus in late pregnancy cannot be recommended as an intervention. This is not to suggest that women should not adopt this position if they find it comfortable. The use of this position during labour has not been addressed in this review. In view of the promising short-term effects of the technique and its simplicity, further trials are justified to determine whether encouraging the use of hands and knees posture during rather than before labour, has any effect on substantive outcomes.

Delivery, Obstetric↗

PubMed2006

Arboreal bipedalism in wild chimpanzees: implications for the evolution of hominid posture and locomotion.

Field observations of bipedal posture and locomotion in wild chimpanzees (Pan troglodytes) can serve as key evidence for reconstructing the likely origins of bipedalism in the last prehominid human ancestor. This paper reports on a sample of bipedal bouts, recorded ad libitum, in wild chimpanzees in Bwindi Impenetrable National Park in southwestern Uganda. The Ruhija community of chimpanzees in Bwindi displays a high rate of bipedal posture. In 246.7 hr of observation from 2001-2003, 179 instances of bipedal posture lasting 5 sec or longer were recorded, for a rate of 0.73 bouts per observation hour. Bipedalism was observed only on arboreal substrates, and was almost all postural, and not locomotor. Bipedalism was part of a complex series of positional behaviors related to feeding, which included two-legged standing, one-legged standing with arm support, and other intermediate postures. Ninety-six percent of bipedal bouts occurred in a foraging context, always as a chimpanzee reached to pluck fruit from tree limbs. Bipedalism was seen in both male and female adults, less frequently among juveniles, and rarely in infants. Both the frequency and duration of bipedal bouts showed a significant positive correlation with estimated substrate diameter. Neither fruit size nor nearest-neighbor association patterns were significantly correlated with the occurrence of bipedalism. Bipedalism is seen frequently in the Bwindi chimpanzee community, in part because of the unusual observer conditions at Bwindi. Most observations of bipedalism were made when the animals were in treetops and the observer at eye-level across narrow ravines. This suggests that wild chimpanzees may engage in bipedal behavior more often than is generally appreciated. Models of the likely evolutionary origins of bipedalism are considered in the light of Bwindi bipedalism data. Bipedalism among Bwindi chimpanzees suggests the origin of bipedal posture in hominids to be related to foraging advantages in fruit trees. It suggests important arboreal advantages in upright posture. The origin of postural bipedalism may have preceded and been causally disconnected from locomotor bipedalism.

Age Factors↗

PubMed1993

Posture affects motion coupling patterns of the upper cervical spine.

Measurements of motions of the cervical spine are used to help diagnose the problems of clinical instability due to degenerative changes and trauma. For a better interpretation of the three-dimensional motions of the upper cervical spine, knowledge of the effects of posture on these motions is necessary. Seven fresh human cadaveric C0-C3 spinal specimens were utilized. Each specimen was put in three distinct sagittal plane postures: full flexion, neutral, and full extension. At each posture, two load types were applied: left and right axial torques, and left and right lateral bending moments up to 1.5 Nm. The resulting three-dimensional relative motions of C0-C1 and C1-C2 were measured, with use of nonconstraining stereophotogrammetry, in the form of load-displacement curves. We found that the curves were nonlinear. The most dramatic change due to modification in posture was found in coupled sagittal plane rotation, which changed from extension at extended posture to flexion at flexed posture at both levels and in response to both load types. For the axial torque, the main axial rotation and coupled lateral bending changed little with posture. For the lateral bending moment, the main lateral bending rotation and coupled axial rotation decreased; the latter changed direction at C1-C2 as the spine was put into flexed posture. The motions for the right and left load applications generally were mirror images, except for the coupled sagittal plane rotations, which did not change with the direction of the load.

Adult↗

PubMed1990

Postural maintenance during movement: simulations of a two joint model.

Voluntary movements of the upper body are accompanied by anticipatory postural adjustments to the lower body in a standing subject. The long-standing hypothesis is that these anticipatory adjustments serve to counteract the perturbation to the body's center of gravity caused by the voluntary arm movement. This paper presents model simulations investigating the possible roles of anticipatory postural activity that accompanies a rapid, upward arm swing. The model incorporates two (idealized) antagonistic muscle pairs controlling the movements of a double-joint system, with a "shoulder joint" between the arm and stiff body links, and an "ankle joint" between the stiff body-leg segment and the ground. Each muscle is represented by a nonlinear viscoelastic element and also includes proprioceptive feedback. Four inputs to the model define the motor control signals for muscle force generation in both the arm and the postural muscle pairs. The neurological component of the model describes consequences of alternate strategies for cocontractions, stretch reflex activity, and anticipatory and synchronous postural activities (or combinations thereof). Simulations with this model show that: (1) none of the postural maintenance schemes considered in these simulations (including varying anticipation) could suppress the initial backward thrust on the body link; (2) the more important destabilizing perturbation is a subsequent forward sway that, left uncountered by postural activity, would eventually leave the body to fall flat on its face; and (3) anticipatory silencing of the postural extensor followed by a brief period of extensor activation (descending control) and synchronous reflex activity (feedback control) appears to be the most likely postural stabilizing strategy that inhibits the continuous forward sway and is consistent with the experimental evidence.

Arm↗

PubMed1995

Task dependence of primate arm postures.

We studied the relations between arm posture and hand location as monkeys performed tasks involving three-dimensional arm movements. Two specific questions were addressed: how reliable are these relations from trial to trial and from day to day, and are the arm postures dictated only by the location of the hand or are the postures also dependent on the task being performed? Based on the variable errors in linear regressions, we found that monkeys performed the tasks in a very stereotypic fashion from trial-to-trial: for a given monkey and task, knowing the position of the hand was sufficient to determine the posture of the arm. These relations did not change from day to day; the relation between hand location and posture was stable over the course of the experiments. In some of the tasks, the postures employed by the monkeys were strikingly similar to those observed in human psychophysical studies. The relations between hand location and arm posture exhibited a large degree of task dependence. Changing the required orientation of the hand resulted in changes in the arm posture.

Animals↗