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At least 1,243 records · Page 69Linked to original sources
PubMed2004

Activity of pyramidal tract neurons in the cat during postural corrections.

The dorsal side-up body orientation in quadrupeds is maintained by a postural control system. We investigated participation of the motor cortex in this system by recording activity of pyramidal tract neurons (PTNs) from limb representations of the motor cortex during postural corrections. The cat was standing on the platform periodically tilting in the frontal plane, and maintained equilibrium at different body configurations: with the head directed forward (symmetrically alternating loading of the left and right fore limbs), or with the head voluntary turned to the right or to the left (asymmetrical loading). We found that postural corrective responses to tilts included an increase of the contact forces and activity of limb extensors on the side moving down, and their decrease on the opposite side. The activity of PTNs was strongly modulated in relation to the tilt cycle. Phases of activity of individual PTNs were distributed over the cycle. Thus the cortical output mediated by PTNs appeared closely related to a highly automatic motor activity, the maintenance of the body posture. An asymmetrical loading of limbs, caused by head turns, resulted in the corresponding changes of motor responses to tilts. These voluntary postural modifications were also well reflected in the PTNs' activity. The activity of a part of PTNs correlated well with contact forces, in some others with the limb muscle activity; in still others no correlation with these variables was observed. This heterogeneity of the PTNs population suggests a different functional role of individual PTNs.

Animals↗
PubMed2004

Ratio of shear to load ground-reaction force may underlie the directional tuning of the automatic postural response to rotation and translation.

This study sought to identify the sensory signals that encode perturbation direction rapidly enough to shape the directional tuning of the automatic postural response. We compared reactions to 16 directions of pitch and roll rotation and 16 directions of linear translation in the horizontal plane in freely standing cats. Rotations and translations that displaced the center of mass in the same direction relative to the feet evoked similar patterns of muscle activity and active ground-reaction force, suggesting the presence of a single, robust postural strategy for stabilizing the center of mass in both rotation and translation. Therefore we postulated there should be a common sensory input that encodes the direction of the perturbation and leads to the directional tuning of the early electromyographic burst in the postural response. We compared the mechanical changes induced by rotations and translations prior to the active, postural response. The only consistent feature common to the full range of rotation and translation directions was the initial change in ground-reaction force angle. Other variables including joint angles, ground-reaction force magnitudes, center of pressure, and center of mass in space showed opposite or nonsignificant changes for rotation and translation. Change in force angle at the paw reflects the ratio of loading force to slip force, analogous to slips during finger grip tasks. We propose that cutaneous sensors in the foot soles detect change in ground-reaction force angle and provide the critical input underlying the directional tuning of the automatic postural response for balance.

Animals↗
PubMed2004

Independent and convergent signals from the pontomedullary reticular formation contribute to the control of posture and movement during reaching in the cat.

We have addressed the nature of the postural control signals contained within the discharge activity of neurons in the pontomedullary reticular formation, including reticulospinal neurons, during a reaching task in the cat. We recorded the activity of 142 neurons during ipsilateral reaching movements that required anticipatory postural adjustments (APAs) in the supporting limbs to maintain equilibrium. Discharge activity in 82/142 (58%) neurons was significantly increased before the onset of the reach. Most of these neurons discharged either in a phasic (22/82), tonic (10/82), or phasic/tonic (41/82) pattern. In each of these 3 groups, the onset of the discharge activity in some neurons was temporally related either to the go signal or to the onset of the movement. In many neurons, one component of the discharge sequence was better related to the go signal and another to the onset of the movement. Based on our previous behavioral study during the same task, we suggest that reticular neurons in which the discharge activity is better related to the go signal contribute to the initiation of the APAs that precede the movement. Neurons in which the discharge activity is better related to the movement signal might contribute to the initiation of the movement and to the production of the postural responses that accompany that movement. Together our results suggest the existence of neurons that signal posture and movement independently and others that encode a convergent signal that contributes to the control of both posture and movement.

Animals↗
PubMed1998

Vibration-induced postural posteffects.

It generally is known that vibration of various muscles in free-standing subjects evokes a spatially oriented postural response. Furthermore, it recently has been shown that when a vibratory stimulus is terminated, a powerful involuntary contraction of the previously vibrated muscle often occurs that, under the isotonic condition, is accompanied by movement of a limb. The aim of this study was to explore effects of a low-amplitude mechanical vibration, applied in a seated position, on the standing posture. The 30-s vibration was applied bilaterally at the ankle level to anterior or posterior tendons and at the cervical level in front or back of the neck, at one site only at a time. Center of pressure trajectories were monitored during quiet stance for </=19 min after the offset of vibration, and these measurements were compared with a previbration control trial. The results clearly indicate that vibration produced in all subjects strong, long-lasting dynamical modification of posture mainly in the anterior-posterior direction. Spatial orientation of the induced postvibratory shift in posture was dependent on the vibration side. We conclude that sustained Ia sensory inflow, evoked by vibration, has a powerful after-effect on the motor system at the postural level.

Adult↗
PubMed2001

Neck muscles in the rhesus monkey. II. Electromyographic patterns of activation underlying postures and movements.

Electromyographic (EMG) activity was recorded in < or = 12 neck muscles in four alert monkeys whose heads were unrestrained to describe the spatial and temporal patterns of neck muscle activation accompanying a large range of head postures and movements. Some head postures and movements were elicited by training animals to generate gaze shifts to visual targets. Other spontaneous head movements were made during orienting, tracking, feeding, expressive, and head-shaking behaviors. These latter movements exhibited a wider range of kinematic patterns. Stable postures and small head movements of only a few degrees were associated with activation of a small number of muscles in a reproducible synergy. Additional muscles were recruited for more eccentric postures and larger movements. For head movements during trained gaze shifts, movement amplitude, velocity, and acceleration were correlated linearly and agonist muscles were recruited without antagonist muscles. Complex sequences of reciprocal bursts in agonist and antagonist muscles were observed during very brisk movements. Turning movements of similar amplitudes that began from different initial head positions were associated with systematic variations in the activities of different muscles and in the relative timings of these activities. Unique recruitment synergies were observed during feeding and head-shaking behaviors. Our results emphasize that the recruitment of a given muscle was generally ordered and consistent but that strategies for coordination among various neck muscles were often complex and appeared to depend on the specifics of musculoskeletal architecture, posture, and movement kinematics that differ substantially among species.

Animals↗
PubMed2002

Adaptation to a visuomotor shift depends on the starting posture.

Previous studies have shown that human subjects can adapt to a new visuomotor relationship that depends on the trajectory of the arm. However, these studies have not distinguished between hand- and joint-based learning models. We have examined whether different endpoint kinematics are necessary to obtain a differential visuomotor shift. The joint trajectory was varied by changing the initial posture, while maintaining a similar finger trajectory. After learning, maximum after-effects were found when movement began with the posture used during exposure to the visuomotor shift and decreased with the difference between initial and trained posture. This was shown to be independent of the final posture attained. Our results show that adaptation to a visual remapping cannot be due to the recoding of a desired final posture and depends on the arm trajectory in joint space.

Adult↗
PubMed1989

Effect of exercise on postural sway in the elderly.

Fifty female subjects, aged 72-92 (mean 82) years, were enrolled in a 12-week (36 classes) exercise program aimed at increasing postural stability. Subjects were residents of sheltered apartments, rest homes or nursing homes, well enough and mobile enough to participate in the classes. The subjects were randomized into an exercise or a control group. Their postural sway, standing at rest on a force platform, was measured with eyes open and eyes closed. The groups were well matched in all respects. The results showed no improvement in the postural sway as a result of the exercise program. We hypothesize that increasing postural sway in the elderly represents a deterioration in, for the most part, the nervous system and may at this extreme of life indicate an irreversible loss of function. For this reason no improvement in postural sway may be possible.

Accidental Falls↗
PubMed1990

Postural stability in shooters.

Ten competition shooters were tested during simulated race using the force platform technique to investigate the effect of training on postural stability. The shooters were tested at 30-min intervals during a race simulating actual race conditions. Sway velocity was calculated during 27-second periods. The postural stability was evaluated with and without competition clothing. The shooters had significantly better stability than untrained control subjects, when tested without supportive clothing. The competition clothing reduced the sway velocity further both in visual and nonvisual conditions. The Romberg quotient was higher in shooters than in normal controls, indicating that the shooters used to an increased amount proprioceptive and vestibular cues to stabilize their posture. The good postural stability of the shooters apparently results from assiduous training aimed to improve postural stability.

Adolescent↗
PubMed2004

Evidence for a gene on chromosome 13 influencing postural systolic blood pressure change and body mass index.

Previous analysis in the Hypertension Genetic Epidemiology Network (HyperGEN) of the National Heart Lung and Blood Institute (NHLBI) Family Blood Pressure Program, a multicenter study of genetic and environmental factors related to hypertension, indicated regions of linkage for blood pressure traits together with several coincident regions for phenotypically correlated traits, including systolic blood pressure (SBP) response to a postural challenge and body mass index (BMI). Motivated by these findings and by our desire to better understand the physiology of these traits, we conducted bivariate linkage analysis of postural SBP change and BMI. Sibships in HyperGEN were recruited from 5 field centers in Massachusetts, North Carolina, Minnesota, Utah, and Alabama. All available affected siblings, their parents, and selected nonmedicated offspring were recruited. Among 1636 whites and 1747 blacks, we performed a maximum likelihood bivariate genome scan for quantitative trait loci influencing postural SBP change and BMI, similarly adjusted for race, study center, sex, age, and age-by-sex interactions. Genome scans were performed using SOLAR (version 2.0) and race-specific marker allele frequencies derived from founders. The maximum genome-wide logarithm of odds (LOD) score of 3.2 was detected on chromosome 13 at 24 cM. This marker (D13S493) lies within 20 cM of a marker previously linked to BMI in the Family Heart Study and is substantially higher than the univariate linkage for each trait (LOD scores for BMI and postural SBP change were 2.4 and 0.9, respectively). These findings suggest that a gene(s) on chromosome 13q jointly regulates the SBP response to postural change and BMI.

Adult↗
PubMed1995

Normal thoracoabdominal motions. Influence of sex, age, posture, and breath size.

The purpose of this study was to assess normal values of thoracoabdominal motions (TAM) during spontaneous breathing and vital capacity (VC) maneuvers in relation to sex, age, and body position. For this, 120 healthy subjects from 10 to > 60 yr old were studied using the respiratory inductive plethysmograph (Respitrace). The volume-motion coefficients obtained during quiet breathing for the rib cage (RC) were almost twice those for the abdomen (ABD) and were not influenced by sex or age and also not by posture, except for the increased ABD coefficients in the supine posture (p < 0.05). Under most conditions RC motion predominated over ABD motion, except quiet breathing in the supine position. Sex-related differences in TAM were not found during quiet breathing, yet during VC maneuvers the women were slightly more RC breathing (p < 0.01). Age-related differences were also only significant during VC maneuvers: men of more than 50 yr old especially became less RC breathing. Posture had a very significant effect (p < 0.001) during quiet breathing as well as during VC maneuvers: the RC predominance was greatest in the standing posture and least in the supine posture. During VC maneuvers the subjects became more RC breathers than during quiet breathing (p < 0.001). The X-Y coordinates of RC motion (on the Y axis) versus ABD motion (on the X axis) showed under all conditions a counterclockwise looping during the breathing cycle: the looping was elliptic during quiet breathing but was more irregular and variable during VC maneuvers, and this also depended on body position.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1987

Changes in pharyngeal cross-sectional area with posture and application of continuous positive airway pressure in patients with obstructive sleep apnea.

In an attempt to elucidate whether changes in posture (from sitting to supine) result in reduction in pharyngeal area, thus promoting pharyngeal occlusion during sleep in so predisposed persons, we studied 12 snoring apneic patients and 6 snoring nonapneic control subjects. in all subjects, we employed acoustic reflection technique to measure pharyngeal area at FRC sitting and supine. We also examined changes in pharyngeal area resulting from the application of positive intrapharyngeal pressure in sitting and supine posture. We found that (1) pharyngeal cross-sectional area at FRC was similar in both groups, (2) decrease in pharyngeal area with assumption of supine posture was also similar in both groups (21 +/- 11% in patients with OSA versus 15 +/- 13% in nonapneic control subjects), and (3) pharyngeal distensibility was significantly higher in apneic snorers than in nonapneic control subjects (0.090 +/- 0.039 cm H2O-1 in apneic snorers versus 0.032 +/- 0.027 cm H2O-1 in nonapneic control subjects; p less than 0.005). We conclude that changes in posture alone are not sufficient to convert a snorer into a patient with OSA; however, when physiologic abnormalities ("floppy" pharynx) are superimposed on postural reduction in pharyngeal area, airway occlusion results.

Humans↗
PubMed1971

The effects of posture and isoproterenol on the velocity of left ventricular contraction in man. The reciprocal relationship between left ventricular volume and myocardial wall force during ejection on mean rate of circumferential shortening.

A study was performed in five normal men in whom left ventricular volume was measured by thermodilution in the supine and 60 degrees head-up postures, in the control state, and then during steady-state response to isoproterenol. The mean rate of circumferential shortening of the left ventricle was calculated for each of the postures in both inotropic states and was found to remain constant in the control state at 12.5 +/-0.6 cm/sec in the supine posture and 13.3 +/-0.5 cm/sec in the tilted posture. Similarly, mean rate of circumferential shortening remained constant in response to the positive inotropic effect of isoproterenol at 20.9 +/-0.5 cm/sec in the supine position and 20.7 +/-0.5 cm/sec in the tilted posture. It is concluded that the constancy of mean rate of circumferential shortening over the relatively broad physiologic range of left ventricular end-diastolic volume and mean force of ejection during a given state of myocardial contractility represents the coupled reciprocal influences of ventricular wall tension and myocardial fiber length on the velocity of ventricular wall shortening. Unlike stroke work, stroke power, and mean rate of left ventricular ejection, which are volume-dependent parameters of myocardial performance, the mean rate of circumferential shortening appears to be a reasonable index of left ventricular contractility, which in steady-state conditions is independent of left ventricular end-diastolic volume and mean ventricular wall force of ejection. In this study, changes in mean rate of circumferential shortening associated with changes of heart rate were small and variable.

Adult↗
PubMed1989

Hip joint mobility and spinal angles in standing and in different sitting postures.

The spinal angles of 25 female subjects were measured in standing and in four different sitting postures with various trunk-thigh angles. Additionally, measurements of hip and lumbar mobility were made in an attempt to relate mobility to spinal curvature in the different sitting postures. Lumbar curvature was observed to decrease as the trunk-thigh angle decreased across the different sitting postures, and reduction in curvature was associated with hip mobility. An exploratory analysis of interrelationships among hip mobility, spinal mobility, and spinal curvature was also carried out. A significant correlation between lumbar and thoracic angular deviations in standing and hip flexion/extension range was obtained. The findings are discussed with reference to theories of sitting posture and the influence of hip joint mobility on postural adaptations to furniture. Further investigations, including studies of male subjects, are indicated.

Adult↗
PubMed1989

Arm posture and human movement capability.

Many workers perform manual assembly tasks or use hand tools while the hands are postured above the shoulders or to the side of the body. Experiments were conducted to study the sensitivity of speed-accuracy movement performance to a wide range of hand locations around the shoulder under various levels of hand loads, ratios of work to rest, and task durations. Subjects performed a spatially constrained stylus-to-hole Fitts reciprocal movement task designed to simulate high-incentive manual assembly operations while providing basic information regarding changes in human move and positioning capabilities. Significant decrements in movement performance occurred when hands were postured above shoulder level. Move and positioning times increased 15.3% and 26.5%, respectively, with elevation of the hand from -15 to 60 deg respective to shoulder level. Posturally based decrements in movement capability were unrelated to differences in subject strength capability found among test postures. The consequences of elevated arm postures on human move and positioning capability are presented along with workplace design and methods recommendations for job designers facing work-height decisions in manual assembly environments.

Arm↗
PubMed1994

Effects of postural change on aspiration in head and neck surgical patients.

This study was designed to define the effects of postural change on liquid aspiration during videofluorographic examination of oropharyngeal swallow in head and neck surgical patients. Thirty-two patients were given two swallows of five different amounts of liquid barium as tolerated. When aspiration occurred, the patient's head and/or body position was changed, new posture being determined by the swallowing disorder identified as the cause of the aspiration. Postural techniques were successful in eliminating aspiration on at least one volume of liquid in 81% of these patients. Patients in all surgical groups were able to use postures with equal success. A variety of positions were used in each type of surgical patient, indicating that these patients exhibited a variety of swallowing problems. Results emphasize the importance of introducing postural techniques during the radiographic study of oropharyngeal swallow to facilitate safe oral intake of liquids.

Adult↗
PubMed2005

Evaluation of body posture in individuals with internal temporomandibular joint derangement.

Temporomandibular dysfunctions (TMD) comprise a great number of disruptions that may affect the temporomandibular joint (TMJ), the masticatory muscles, or both. TMJ internal derangement is a specific type of TMD, of which the etiology and physiopathology are broadly unknown, but have been suggested to be linked to head, neck, and body posture factors. This study aimed at verifying possible relationships between body posture and TMJ internal derangements (TMJ-id), by comparing 30 subjects presenting typical TMJ-id signs to 20 healthy subjects. Subjects' clinical evaluations included anamnesis, stomatognatic system evaluation, and plotting analysis on body posture photographs. No statistically significant differences were found between the groups. Results do not support the assertion that body posture plays a role in causing or enhancing TMD; however, these results should be cautiously considered because of the small number of subjects evaluated and the many posture variables submitted to statistical procedures that lead to high standard deviations.

Adolescent↗
PubMedDate not supplied

Maximum handgrip force in relation to upper limb posture--a meta-analysis.

It is essential to establish normative values of handgrip force in relation to factors influencing the force. This study developed a predictive equation that expresses the maximum force of the handgrip in relation to upper limb posture and gender. To create the equation, data from published studies on experimental results of maximum handgrip force in different upper limb postures were used. Selected were only those studies that describe upper limb posture during experiments clearly enough so that it could be transferred according to the Seven Degrees of Freedom Model, which unambiguously defines upper limb posture with values of seven angles. A predictive equation for male maximum handgrip force in relation to angles of wrist flexion/extension, wrist adduction/abduction, forearm pronation/supination, elbow flexion, shoulder flexion/extension, shoulder horizontal adduction/abduction, and arm medial/lateral rotation along the long axis was developed. Also developed was a mathematical formula that expresses maximum handgrip force for men in relation to maximum handgrip force for women. The equation is general and can be used for calculating norm values. It can also be applied to a specific population by performing an experimental study for one upper limb posture and assessing maximum force on the basis of the predictive equation for others.

Adult↗
PubMed1980

Body posture and breathing frequency in newborn mammals.

The effects of changing body posture on breathing frequency (f) of anesthetized newborn rats, rabbits, and dogs have been studied. No significant changes were observed between horizontal postures (supine, prone, left, and right lateral). In the vertical head-down position, most of the animals did not show any significant variation of f. Breathing rate dropped significantly in the head-up position, and in all the animals, it was still below the horizontal value 1 min after the vertical head-up tilting. After bilateral vagotomy, no significant change with body posture occurred. In unanesthetized newborns, the +45 degree head-up tilting only occasionally caused a drop of f and to a lesser extent than after anesthesia. By comparing these results with those reported in adults, it is concluded that the postural effects of f are less evident in the newborn than in the adult. Even if a quantitative difference in the mechanical events after the change in body posture is the most likely explanation of the lower sensitivity of the newborn, other nonmechanical factors could also be involved.

Age Factors↗