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PubMed1986

Postural changes in cardiac volumes in men in relation to adult age.

Cardiac volumes by equilibrium gated cardiac blood pool scans and heart rate were measured in the supine and sitting positions in 64 male volunteer subjects (age 25-80 yrs) who had been rigorously screened to exclude cardiovascular disease. After the upright position was assumed, the average cardiac output of all subjects was unchanged but heart rate increased and stroke volume decreased due to a decrease in end diastolic volume. Neither the supine or sitting cardiac output nor the average postural change in cardiac output, cardiac volumes or heart rate was age-related. While the average cardiac output among the subjects was unaltered with a change in posture, in some individuals it increased slightly while in others it decreased. The postural change in cardiac output among the individuals correlated by linear regression analysis with a change in heart rate only in younger subjects and with a change in stroke volume in all age groups, but the slope of this relationship was greater in older than in younger subjects. The postural change in stroke volume was strongly correlated with a change in end diastolic volume and this relationship did not vary with age. Thus, although the average postural change in cardiac output among healthy subjects is not age-related, a given change in cardiac output with posture in an older individual depends more on a change in stroke volume and less on a heart rate change than in a younger one. This result, like the response to vigorous upright exercise previously demonstrated to occur with aging, indicates a greater reliance in the elderly on the Frank-Starling mechanism than on heart rate for a given change in cardiac output in response to perturbations from the basal supine state.

Adult↗
PubMed1989

The influence of cephalostatic ear rods on the positions of the head and neck during postural recordings.

This study examined the effect of cephalostatic ear rods on the positions of the head and neck. The method error was assessed for postural recordings of the head and neck position made with and without ear rods. A photographic angle was correlated with the postural angles on x-ray film. The material compared 33 dental students who were recorded with ear rods in and with ear rods out. Subjects were chosen randomly to repeat the postural recordings. The differences between the mean for each postural variable were subjected to comparative analysis, using Student's t test for paired samples. A significant difference (p less than or equal to 0.05) was found between the means of the inclination of the cervical spine to the true horizontal and the means of the photographic angle. The mean values for the remaining postural variables showed an insignificant but consistent pattern of axial extension of the cervical spine. Cephalostatic ear rods may alter head and neck position during postural recordings. The method error made for recording total head and neck position with ear rods was higher than without ear rods. The difference in the photographic angle was found to have a moderate positive correlation with the difference in the cervical inclination and the total head and neck position. These data suggest that lateral cephalostatics without ear rods may be used to record total head and neck position and the photographic technique may be used as a quick, inexpensive method for the clinician to determine head and neck positional changes before and after treatment.

Adult↗
PubMed1995

Feedforward postural adjustments in a simple two-joint synergy in patients with Parkinson's disease.

Patients with Parkinson's disease, age-matched controls and young control subjects performed discrete elbow or wrist movements in a sagittal plane under the instruction to move one of the joints "as fast as possible." Relative stability of the other, postural joint was comparable in all 3 groups, while movement time was the highest in the patients and the lowest in young controls. Typically, EMG patterns in both muscle pairs acting at the joints demonstrated a commonly observed "tri-phasic" pattern. A cross-correlation analysis of the EMGs confirmed virtually simultaneous bursts in the wrist and elbow flexors and in the wrist and elbow extensors. In all 3 groups, there were no signs of anticipatory activation of postural muscles in about 90% of movements. We consider postural anticipation not a separate process, but a separate peripheral pattern of a single control process that may involve a number of joints and muscles. We conclude that the postural deficits in Parkinson's disease are not related to a basic deficit in the ability to generate feedforward postural adjustments but to other factors that may include the specificity of maintaining the vertical posture in the field of gravity.

Aged↗
PubMed1994

Postural control system.

The postural control system has two main functions: first, to build up posture against gravity and ensure that balance is maintained; and second, to fix the orientation and position of the segments that serve as a reference frame for perception and action with respect to the external world. This dual function of postural control is based on four components: reference values, such as orientation of body segments and position of the center of gravity (an internal representation of the body or postural body scheme); multisensory inputs regulating orientation and stabilization of body segments; and flexible postural reactions or anticipations for balance recovery after disturbance, or postural stabilization during voluntary movement. The recent data related to the organization of this system will be discussed in normal subjects (during ontogenesis), the elderly and in patients with relevant deficits.

Age Factors↗
PubMed2005

Further evidence of a quantitative trait locus on chromosome 18 influencing postural change in systolic blood pressure: the Hypertension Genetic Epidemiology Network (HyperGEN) Study.

BACKGROUND: Postural change in systolic blood pressure (SBP) is prospectively associated with several disease outcomes including hypertension, stroke, and coronary heart disease. The objective of this study was to characterize further a possible quantitative trait locus on chromosome 18q21 influencing SBP response to a postural challenge. METHODS: A prior genome scan of postural SBP response in 636 subjects of white ethnicity from 285 hypertensive sibships in the Hypertension Genetic Epidemiology Network (HyperGEN) indicated suggestive evidence for linkage on chromosome 18q21. This study included a de novo set of 452 African American pedigrees from the HyperGEN study and an expanded set of 372 white pedigrees. Variance components linkage analysis of postural SBP change was conducted using microsatellite markers on chromosome 18, and association studies were performed with a common single nucleotide polymorphism (variant 13) in the gene encoding NEDD4L, a key regulator of fine sodium reabsorption in the distal nephron. RESULTS: Combined analysis of all white and African American pedigrees yielded a LOD score of 4.25 at 80 cM on chromosome 18q21, with at least nominal evidence of linkage at this position in both white (LOD: 3.43) and African American (LOD: 1.14) subjects. Postural SBP response was associated with variant 13 of the NEDD4L in a subset of white subjects taking medications effective in treating sodium volume-dependent hypertension (alpha1-blockers, calcium channel blockers, and/or diuretics). CONCLUSION: These data provide further evidence for a quantitative trait locus on chromosome 18q21 influencing postural change in SBP.

Adult↗
PubMed2005

Are the postures adopted according to requested linguistic categories similar to those classified by the recording protocols?

Knowledge on how workers perceive and associate their postures for trunk flexion with respect to linguistic categories, could allow for the development of simple and valid instruments for self-assessment and for more effective postural training. Considerable time and expense could be saved if reliable self-assessments were available. This study describes the anterior flexion angles of the trunk adopted by individuals according to linguistic categories (mild, moderate and severe) and registered by photograph. The postures were compared with postural recording protocols. Twenty sedentary individuals (10 male and 10 female) and 12 industrial female workers (6 healthy and 6 low back sufferers) participated. Subjects were capable of discriminating linguistic postural categories, since they adopted different trunk postures when distinct categories were requested (p< 0.0001). However, the individual variability was high for each category estimated. This could explain, at least in part, the low level of agreement between self-assessment and observational studies.

Adolescent↗
PubMed2005

Postural versus chair design impacts upon interface pressure.

An investigation of postural and chair design impacts upon seat pan interface pressure has been performed in an effort to identify whether differences in posture or chair design result in greater pressure differences. Investigation of postural variables focused on trunk-thigh angle and use of armrests. Twelve ergonomic office chairs were used to assess chair design differences. Both male and female subjects were included. Gender effects were controlled through use of a repeated Latin square design, with squares defined by gender. Significant gender-based interaction was observed amongst postural treatments and chair effects. Postural treatments, chairs designs, and participant effects all resulted in significant interface pressure differences, though gender-based interaction yielded some non-additivity of results between males and females. The final conclusion drawn from the results is that chair design differences had the greatest effect on seat pan interface pressure, followed by participant effects, and lastly postural treatments.

Adaptation, Physiological↗
PubMed2006

Posture recognition in Alzheimer's disease.

BACKGROUND: Apraxia is neurologically induced deficit in the ability perform purposeful skilled movements. One of the most common forms is ideomotor apraxia (IMA) where spatial and temporal production errors are most prevalent. IMA can be associated Alzheimer's disease (AD), even early in its course, but is often not identified possibly because the evaluation of IMA by inexperienced judges using performance tests is unreliable. The purpose of this study, therefore, is to learn if the Postural Knowledge Test (PKT), a praxis discrimination test that assesses knowledge of transitive (PKT-T subtest) and intransitive (PKT-I subtest) postures and does not require extensive training, is as sensitive and specific as the praxis performance tests. METHODS: We studied 15 subjects with probable AD as well as 18 age-matched controls by having them perform transitive and intransitive gestures to command and imitation, as well as having them discriminate between correct and incorrect transitive and intransitive postures. RESULTS: Overall on all tests, the control subjects performed better than those with AD. In addition all subjects had more trouble with transitive than intransitive gestures. Using a stepwise discriminative analysis, 81.8% of the subjects could be classified according to Group (94.4% of Controls, 66.7% of AD subjects). In this analysis, the PKT-T (transitive posture subtest) was the only measure that contributed to the discrimination of subjects. CONCLUSION: We found that having subjects select the correct transitive hand postures in this "booklet test" was more sensitive than grading their praxis performances even when using judges with extensive training. This suggests that this discrimination test might be an excellent means for diagnosing and screening patients for AD. The reason why recognition of transitive postures is relatively more difficult for our AD subjects is not known. Two possibilities are that the representations for intransitive movements are stronger than those for transitive movements, and hence, more resistant to degradation, or that intransitive acts are stored in parts of the brain not affected by AD.

Aged↗
PubMed2006

Neural substrates of knowledge of hand postures for object grasping and functional object use: evidence from fMRI.

A number of lines of evidence suggest that computation of hand posture differs for object grasping as compared to functional object use. Hand shaping for grasping appears to rely strongly upon calculations of current object location and volume, whereas hand shaping for object use additionally requires access to stored knowledge about the skilled manipulation specific to a given object. In addition, the particular hand postures employed for functional object use may be either prehensile (clenching, pinching) or non-prehensile (e.g., palming, poking), in contrast to the prehensile postures that are obligatory for grasping. In this fMRI study, we assessed the hypothesis that a left-hemisphere-lateralized system including the inferior parietal lobe is specifically recruited for the computation and recognition of hand postures for functional object use. Fifteen subjects viewed pictures of manipulable objects and determined whether they would be grasped with a pinch or clench (Grasp condition), functionally used with a pinch or clench (Prehensile Use condition), or functionally used with a palm or poke hand posture (Non-prehensile Use condition). Despite the fact that the conditions were equated for behavioral difficulty, significantly greater activations were observed in the left inferior frontal gyrus (IFG), posterior superior temporal gyrus (STG), and inferior parietal lobule (IPL) in Non-prehensile Use trials as compared to Grasp trials. Comparison of Non-prehensile Use and Prehensile Use activations revealed significant differences only in the left IPL. These data confirm the importance of the left IPL in storing knowledge of hand postures for functional object use, and have implications for understanding the interaction of dorsal and ventral visual processing systems.

Adolescent↗
PubMed2003

Inverse relation between postural variability and difficulty of a concurrent short-term memory task.

We measured postural stability while participants simply stood or stood while performing a digit rehearsal task of varying levels of difficulty in order to examine the effects on postural control of concurrent short-term memory demands. The rehearsal task manipulation avoided factors that contaminate postural sway measurements, such as vocal articulation or visual fixation during posture data collection. When participants performed the more difficult digit tasks (longer digit strings), postural sway was reduced relative to when performing an easy version of the task (few digits). The results identified a complex relation between postural control and cognitive or attentional demands.

Analysis of Variance↗
PubMed2005

Effects of foreperiod duration on anticipatory postural adjustments: determination of an optimal preparation in standing and sitting for a raising arm movement.

The purpose of the present experiment was to examine the motor and postural preparation processes evolving during the foreperiod (known to be optimal at 500 ms in sitting) in a voluntary upper limb movement executed while standing. The foreperiod duration (300, 500, 700 and 900 ms) and the postural conditions (sitting versus standing) were manipulated using a priming procedure. Two types of prime were provided: (1) a prime giving valid information on the side of the raising arm movement to execute, and (2) a prime giving non-valid information (prime opposite to the required side). In a sitting and standing condition, eight normal subjects performed a raising arm movement with a 1 kg load at the level of the wrist. Premotor time and acceleration of arm movement were recorded in the two postural conditions. In the standing condition, anticipatory postural adjustments (APAs) were also quantified using the relative latency of electromyographic (EMG) data and the centre of foot pressure (CoP) displacements. Results (1) showed that the optimal foreperiod duration (i.e., leading to the shortest premotor time) increased as a function of postural conditions (500 versus 700 ms in the sitting and standing conditions, respectively), and (2) emphasized the existence of a temporal modulation in the central organization of the postural and focal commands according to the foreperiod duration.

Adaptation, Physiological↗
PubMed2004

Modulation of ankle muscle postural reflexes in stroke: influence of weight-bearing load.

OBJECTIVE: Given the known sensorimotor deficits and asymmetric weight-bearing posture in stroke, the aim of this study was to determine whether stroke affects the modulation of standing postural reflexes with varying weight-bearing load. METHODS: Ten individuals with chronic stroke and 10 healthy older adult controls were exposed to unexpected forward and backward platform translations while standing. Three different stance conditions were imposed: increased weight-bearing load, decreased weight-bearing load, and self-selected stance. Surface electromyography from bilateral ankle dorsiflexors (tibialis anterior) and extensors (gastrocnemius) were recorded and the magnitude of background muscle activity (prior to the platform translation) and postural reflex onset latency and magnitude (75 ms following reflex onset) were determined. RESULTS: Load modulation of ankle extensors was found in controls and individuals with stroke. Although controls demonstrated modulation of ankle dorsiflexors to different loads, individuals with stroke did not show this modulation. Further, load did not change the onset latency of postural reflexes of the individuals with stroke. CONCLUSIONS: The delayed paretic muscle onset latencies in conjunction with impaired modulation of ankle dorsiflexor postural reflexes may contribute to the instability and frequent falls observed among individuals with stroke. SIGNIFICANCE: The results provide some insight into standing postural reflexes following stroke.

Aged↗
PubMed2005

Measurement of the visual contribution to postural steadiness from the COP movement: methodology and reliability.

We studied the reliability of different measures of the visual contribution to postural steadiness by recording the postural sway during standing with eyes open (EO) or eyes closed (EC). The COP trajectory was recorded in 21 subjects aged 42-61 standing on a firm or foam support. The improvement of postural steadiness due to vision was measured with a higher reliability (i.e. lower intra- and inter-subject variabilities) with the sway velocity V, than with the position RMS. Due to the increase of the variability of V and RMS with their own mean values, we quantified the visual contribution to posture by the stabilization ratio (SR), based on a logarithm transform of V or RMS. As compared to the Romberg quotient (EC/EO), SR improved the reliability of the measurement of the visual contribution to posture within individuals, across subjects, and even across different studies in the literature. Our method led to decrease the inter-subject coefficient of variation of this measurement to about 25%, using a foam support. It leads to a similar accuracy in binocular and monocular vision, and it also applies to the quantification of other non-visual sensory contributions to posture.

Adult↗
PubMed2005

Postural strategy changes with fatigue of the lumbar extensor muscles.

The purpose of this study was to investigate the effect of lumbar extensor fatigue on postural strategy in response to a balance perturbation. Anteriorly-directed force perturbations were applied to the upper back with a padded pendulum and attempted to challenge the postural control system without eliciting a stepping response. In three separate sessions, subjects were perturbed both before and after a fatiguing protocol that induced lumbar extensor fatigue to one of three different fatigue levels. Postural strategy was quantified using center of pressure position along with joint angles and joint torques for the ankle, knee, hip, and "low back" joints. Results showed both proactive and reactive changes in postural strategy. Proactive changes involved a slight anterior lean prior to the perturbation, and reactive changes were consistent with a shift toward more of a hip strategy with fatigue. In addition, results suggested that subjects classified as moving mostly at the hip prior to fatigue were more affected by fatigue compared to subjects classified as moving roughly equal amounts at the ankle and hip prior to fatigue. Increasing fatigue level exaggerated some, but not all, of the changes in postural strategy with fatigue. These findings illustrate that neuromuscular fatigue can influence postural strategy in response to a balance perturbation.

Adult↗
PubMed2006

Effects of abdominal muscle fatigue on anticipatory postural adjustments associated with arm raising.

Anticipatory postural adjustments (APAs) are postulated to ameliorate the effects of the disturbance to posture caused by voluntary movement. The primary hypothesis tested in our study was that the magnitude of anticipatory trunk muscle activity is altered by abdominal muscle fatigue. A subsidiary aim of the present study was to examine the directional nature of APAs and use this information to elucidate the central or peripheral nature of changes in postural muscle activity associated with abdominal muscle fatigue. The present study was a within subject design, where abdominal muscle fatigue was induced by a static abdominal curl. Surface EMG was used to assess postural muscle activity in the following trunk muscles; rectus abdominis, erector spinae and internal oblique. Following abdominal muscle fatigue, the magnitude of muscle activity during APAs was significantly reduced by 20% in both the rectus abdominis (fatigued muscle) and the erector spinae (not fatigued) indicating a central rather than peripheral fatigue effect on muscle activity. Abdominal muscle fatigue also induced a 30% increase in the baseline muscle activity of the internal oblique. The changes in magnitude of APA muscle activity may reflect a change in system gain or a change in postural control perhaps related to a change in perceived postural stability. An increase in baseline muscle activity in the internal oblique may compensate partially for the reduction in APAs.

Abdominal Muscles↗
PubMed2004

The scaling of postural adjustments during bimanual load-lifting in traumatic brain-injured adults.

Previous postural studies of traumatic brain injury (TBI) patients have been limited to identifying deficits in static and quasi-dynamic postural control tasks such as weight shifting. In this study, we examined whether or not patients with TBI are able to scale adequately their postural adjustments during the performance of the dynamic task of bimanual load-lifting. An age matched group of healthy adults served as controls. We used the Tetrax posturography system that calculates a stability score (ST) based on fluctuations in vertical ground reaction forces, normalized for body weight. During quiet standing, the ST scores of the TBI group were significantly higher than the control group. Forward weight shift and percentage change in the vertical ground reaction forces (lift postural adjustment (LPA) and post-lift postural adjustment (PLPA) scores) linearly increased with increasing load weight in both healthy and TBI subjects. Group differences were found in the magnitude of forward weight shift but not in the relative increase of the LPA and PLPA scores during the lifting and post-lifting phases respectively. The forward weight shift of the TBI group was lower-than-normal and asymmetrical--there was significantly less forward weight shift on the more affected than on the less affected limb. In addition, a significant amplitude coupling was found between the scaling of the weight shift of the heel and forefoot of each limb. However, no coupling was found between the weight shift amplitudes of homologous parts of both limbs in the TBI group. The results showed that scaling based on prior experience was preserved in the TBI group, though some TBI subjects demonstrated absent scaling in either the more affected or less affected heel or forefoot. The differences between the normal and TBI groups in postural adjustments are not necessarily a sign of pathology; rather they may represent a deliberate choice of the central nervous system to counteract predictable disturbances.

Adult↗
PubMed2006

Postural fluctuations during pointing from a unilateral or bilateral stance.

An experiment was conducted to compare the effects of bilateral and unilateral stance on postural fluctuations and intralimb coordination during active balance control. Fifteen participants stood bilaterally and unilaterally while conducting a pointing task with an outstretched arm. Excursion of center of foot pressure (CoP) and limb movements were recorded with a force plate and eight dual-axis accelerometers, respectively. Compared to bilateral stance, unilateral stance resulted in wider CoP trajectories and greater postural fluctuations, especially in the lower limbs. The limb-dependent postural fluctuations during unilateral stance were associated with an increased coupling between the upper limb segments and a decreased coupling between the segments of the stance leg. Unilateral stance further resulted in greater regularity and spectral changes in postural fluctuations of the trunk and lower limb due to increased central oscillations (8-15 Hz). The observed structural differences in postural fluctuations between unilateral and bilateral stance strongly suggested that the postural control system modulates joint stiffness in a stance-dependent manner. Probably, in unilateral stance, attentive control was shifted to the stance leg at the expense of increasing arm stiffness to reduce movement redundancy.

Adult↗
PubMed2005

The functional role of central and peripheral vision in the control of posture.

Three experiments were conducted to investigate the role of central and peripheral vision (CV and PV) in postural control. In Experiment 1, either the central or peripheral visual field were selectively stimulated using a circular random dot pattern that was either static or alternated at 5 Hz. Center of foot pressure (CoP) was used to examine postural sway during quiet standing under both CV and PV conditions. The results showed that, when the visual stimulus was presented in the periphery, the CoP area decreased and more so in the anterior-posterior (AP) than in the medio-lateral (ML) direction, indicating a characteristic directional specificity. There was no significant difference between the static and dynamic (alternating) conditions. Experiment 2 investigated the directional specificity of body sway found in Experiment 1 by having the trunk either be faced toward the stimulus display or perpendicularly to it, with the head always facing the display. The results showed that the stabilizing effect of peripheral vision was present in the direction of stimulus observation (i.e., the head/gaze direction), irrespective of trunk orientation. This suggested that head/gaze direction toward the stimulus presentation, rather than a biomechanical factor like greater mobility of the ankle joint in AP direction than in ML direction, was essential to postural stability. Experiment 3 further examined whether the stabilizing effect of peripheral vision found in Experiments 1 and 2 was caused because more dots (500) were presented as visual cues to the peripheral visual field than to the central visual field (20 dots) by presenting the same number of dots (20) in both conditions. It was found that, in spite of the equal number of dots, the postural sway amplitudes were larger for the central vision conditions than for the peripheral vision conditions. In conclusion, the present study showed that peripheral rather than central vision contributes to maintaining a stable standing posture, with postural sway being influenced more in the direction of stimulus observation, or head/gaze direction, than in the direction of trunk orientation, which suggests that peripheral vision operates primarily in a viewer-centered frame of reference characterized by the head/gaze direction rather than in a body-centered frame of reference characterized by the anatomical planes of the body.

Body Height↗