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At least 541 records · Page 30Linked to original sources

PubMed2003

Comparison of the postural and movement components during learning by dogs of an operant defensive reflex.

Chronic experiments on six dogs using a model of an operant defensive reflex associated with maintenance of flexion of the hindlimb of specified amplitude were performed to compare the characteristics of the postural and movement components during the learning process. Dogs were placed standing on four tension platforms. Signals were activated and data were recorded and stored using original PC programs. Original programs running on another PC were used to analyze the data. All dogs showed a series of characteristics for the appearance of a diagonal pattern of conditioned reflex posture rearrangement. During the period of complete formation of the "coordinated" program of the operant reflex (indicated by high performance criteria for execution of the operant task), the diagonal pattern of posture rearrangement was seen extremely rarely, in only occasional performances in calm dogs. It was only during the period of complete automatization of the movement habit that the diagonal pattern of postural rearrangement was seen consistently in all performances. By this time, there was a sharp increase in the tensogram amplitudes for all four limbs, which sharp increases in the correlation coefficients between individual tensogram performances. These results suggest that in the experimental conditions used here, the diagonal pattern of postural rearrangement appeared significantly later than the movement pattern needed for resolving the operant task. These data also lead to the conclusion that dogs can complete operant defensive limb movements associated with maintaining a specified flexor posture in the absence of preliminary rearrangement of the posture having the diagonal pattern.

Animals↗

PubMed1975

Postural changes of plasma renin activity after renal transplantation.

1. Postural changes of plasma renin activity (PRA) before and after the administration of a beta-blocking agent (oxprenolol) were studied in nine patients with renal homotransplantation and in ten normal subjects. 2. In normal subjects PRA always increased during upright posture without any correlation with postural changes in mean arterial pressure. Oxprenolol reduced the postural increase of PRA. 3. A postural increase of PRA could be detected as early as 20--25 days after renal transplantation, and appeared with increasing frequency as time elapsed. 4. There was a significant inverse correlation (r = -0.794, P less than 0.001) between the postural changes of PRA and those of mean arterial pressure. 5. These results suggest that in patients with renal homotransplantation the postural increase of PRA can only partly be due to circulating catecholamines or the sympathetic nervous system and may be explained by inverse changes in the mean arterial pressure.

Adolescent↗

PubMed2001

Effect of rearfoot orthotics on postural sway after lateral ankle sprain.

OBJECTIVE: To investigate the effects of different rearfoot orthotics on postural sway during unilateral stance after lateral ankle sprain. DESIGN: Repeated-measures 3-factor analysis of variance on postural sway length and velocity in the frontal and sagittal planes with factors being stance leg (injured, uninjured), session (within 3 d, 2 wk, 4 wk postinjury), and condition (6 orthotic conditions). SETTING: University biomechanics laboratory. PATIENTS: Fifteen collegiate athletes with acute, unilateral first- or second-degree lateral ankle sprain. INTERVENTIONS: Balance testing was performed under 6 conditions: (1) shoe only, (2) molded Aquaplast orthotic, (3) lateral heel wedge, (4) 7 degrees medially posted orthotic, (5) 4 degrees laterally posted orthotic, and (6) neutral orthotic. MAIN OUTCOME MEASURES: Postural sway length and postural sway velocity in the frontal and sagittal planes. RESULTS: Significant main effects were found for side and session, but not orthotic condition, for all 4 dependent variables. Postural sway length and velocity were greater on the injured limbs as compared with the uninjured limbs during the first 2 sessions but not during the third session. None of the orthotics significantly reduced postural sway compared with the shoe-only condition after lateral ankle sprain. CONCLUSIONS: Rearfoot orthotics, irrespective of design or posting, were ineffective at improving postural sway after lateral ankle sprain.

Adult↗

PubMed2002

Electromyographic activity of the trunk extensor muscles: effect of varying hip position and lumbar posture during Roman chair exercise.

OBJECTIVE: To evaluate the effect of hip position and lumbar posture on the surface electromyographic activity of the trunk extensors during Roman chair exercise. DESIGN: Descriptive, repeated measures. SETTING: University-based musculoskeletal research laboratory. PARTICIPANTS: Twelve healthy volunteers (7 men, 5 women; age range, 18-35y) without a history of low back pain were recruited from a university setting. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Surface electromyographic activity was recorded from the lumbar extensor, gluteal, and hamstring musculature during dynamic Roman chair exercise. For each muscle group, electromyographic activity (mV/rep) was compared among exercises with internal hip rotation and external hip rotation and among exercises by using a typical lumbar posture (nonbiphasic) and a posture that accentuated lumbar lordosis (biphasic). RESULTS: For the lumbar extensors, electromyographic activity during exercise was 18% greater with internal hip rotation than external hip rotation (P< or =.05) and was 25% greater with a biphasic posture than with a nonbiphasic posture (P< or =.05). For the gluteals and hamstrings, there was no difference in electromyographic activity between internal and external hip rotation or between biphasic and nonbiphasic postures (P >.05). CONCLUSION: The level of recruitment of the lumbar extensors can be modified during Roman chair exercise by altering hip position and lumbar posture. Clinicians can use these data to develop progressive exercise protocols for the lumbar extensors with a variety of resistance levels without the need for complex equipment.

Adolescent↗

PubMed2001

The influence of initial resting posture on range of motion of the lumbar spine.

The aim of this study was to investigate the influence of initial resting posture on range of motion of the lumbar spine in 18 normal subjects. Subjects resting posture and active range of motion was measured using the CA-6000 Spinal Motion Analyser (OSI, USA) in five test positions, namely in flat standing and with a variety of heel raises. Analysis showed that there was no significant correlation between subject's normal resting posture and active range of motion. However, when subjects resting posture was artificially altered with heel raises, significant effects on the active range of motion were demonstrated. Increasing heel height significantly influenced resting posture in the sagittal plane only. As heel height increased, the lumbar lordosis decreased and a significant reduction in the range of lumbar spine flexion (P<0.001) was observed. Simulating pelvic asymmetry influenced resting posture in the frontal plane and significant effects on the range of lateral flexion (P<0.05) were observed. These results have important clinical implications in terms of using range of motion of the lumbar spine as an examination tool and suggest that studies using range of motion as an outcome measure should consider initial resting posture.

Adult↗

PubMed2003

Repeatability over time of posture, radiograph positioning, and radiograph line drawing: an analysis of six control groups.

BACKGROUND: There is debate concerning the repeatability of posture over time, radiograph positioning repeatability, and radiograph line drawing reliability. These ideas seem to negate the use of before-and-after spinal radiographic imaging to detect and correct vertebral subluxations. OBJECTIVE: To review the results of control groups in 6 clinical control trials with before-and-after radiographic measurements taken days, weeks, months, or years apart to accept or reject the hypothesis that radiographic analysis procedures are not repeatable, reliable, or reproducible. DATA SOURCES: Six published control groups from original data. Other data were obtained from searches on MEDLINE, CHIROLARS, MANTIS, and CINAHL on radiographic reliability, posture, and positioning. RESULTS: Comparison of initial and follow-up radiographic data for 6 control groups indicate that measured angles and distances between initial and follow-up radiograph measurements on lateral and anterior to posterior radiographs are not significantly different when utilizing Chiropractic Biophysics radiographic procedures. In 48 out of 50 measurements, the differences between initial and follow-up radiographs are less than 1.5 degrees and 2 mm. These measurements indicate that posture is repeatable, radiographic positioning is repeatable, and radiographic line drawing analysis for spinal displacement is highly reliable. The scientific literature on these topics also indicates the repeatability of posture, radiographic positioning, and radiographic line drawing. CONCLUSIONS: Posture, radiographic positioning, and radiographic line drawing are all very reliable/repeatable. When Chiropractic Biophysics standardized procedures are used, any pre-to-post alignment changes in treatment groups are a result of the treatment procedures applied. These results contradict common claims made by several researchers and clinicians in the indexed literature. Chiropractic radiologic education and publications should reflect the recent literature, provide more support for posture analysis, radiographic positioning, radiographic line drawing analyses, and applications of posture and radiographic procedures for measuring spinal displacement on plain radiographs.

Biomechanical Phenomena↗

PubMed2001

Technical note: repeatability of measurement in determining stature in sitting and standing postures.

The aim of this study was to determine the effect of sitting and standing postures on the repeatability of a stadiometer designed to detect small variations in spinal length. Two groups of ten healthy subjects, with no previous or known history of back problems, participated in this study. One group was measured in the standing posture, while the other group was measured in a sitting posture. All subjects gave informed consent to participate in this study. Subjects had a set of landmarks defining the spinal contour marked on their backs and then stood in the stadiometer for three series of ten measurements to be performed. At the end of each measurement, the subjects were requested to move away from and then be repositioned in the stadiometer. Subjects improved the repeatability across the measurement series. At the end of the second measurement series, all subjects presented mean standard deviations of 0.43 +/- 0.08 mm (range 0.30-0.50 mm) in the standing posture. In the sitting posture, deviations of less than 0.05 mm were obtained only at the end of the third measurement series (0.48 +/- 0.08 mm; range 0.34-0.62 mm), suggesting that this posture required three measurement series before repeatable measurements could be assured rather than two in the standing posture.

Adult↗

PubMed2006

A memory-based model for planning target reach postures in the presence of obstructions.

Existing posture prediction and motion simulation models generally lack the capability of simulating human obstruction avoidance during target reach. This compromises the utility of digital human models for ergonomics, as many design problems involve interactions between humans and obstructions. To address this problem, this paper presents a novel memory-based posture planning (MBPP) model, which plans reach postures that avoid obstructions. In this model, the task space is partitioned into small regions called cells. For a given human figure, each cell is linked to a memory that stores various alternative postures for reaching the cell. When a posture planning problem is given in terms of a target and an obstruction configuration, the model examines postures belonging to the relevant cell, selects collision-free ones and modifies them to exactly meet the hand target acquisition constraint. Simulation results showed that the MBPP model is capable of rapidly and robustly planning reach postures for various scenarios.

Biomechanical Phenomena↗

PubMed1992

Decrease in back strength in asymmetric trunk postures.

The extension force against resistance was recorded in 23 postures for 12 subjects to find explanations for the decrease in back strength in asymmetric postures. A reduction in muscle force in asymmetric postures was found up to 40%, but was strongly dependent on the plane in which asymmetry occurred, and on the posture to which it referred. A quantitative relationship between the forces exerted in different asymmetric postures is discussed, as a basis for formulating universal ergonomic guidelines for optimal working postures. The reduction in force in different asymmetric postures can be explained by length of the muscle, the activation of the muscle, and the moment angle of the muscle.

Adult↗

PubMed1994

Head posture measurements among work vehicle drivers and implications for work and workplace design.

An increased risk of musculoskeletal disorders, e.g. from the neck region, has been found among professional drivers of work vehicles. The purpose of this study was to identify causes of postural load and implications for vehicle design and work tasks. A second purpose was to develop the methods for measurement and analysis of head postures. Field measurements of head postures for drivers of fork lift trucks, forestry machines, and cranes were carried out. The equipment used was an electric goniometer measurement system, containing a mechanical transmission between the head and the upper trunk. Methods for data presentation and quantification were developed. The results showed that rotatable and movable driver cabins improved head postures and viewing angles substantially. Narrow window frame structures and large, optimally-placed windows were also advantageous. The steering wheel, controls, and a high backrest restricted shoulder rotation, which increased head rotation in unfavourable viewing angles. Improved workspace layouts and work organization factors such as job enlargement decreased the influence of strenuous postures. The results also showed that head postures should be analysed in two or three dimensions simultaneously, otherwise the postures taken will be underestimated in relation to the maximal voluntary movement.

Adult↗

PubMed1994

The effects of computer interface design on human postural dynamics.

The main objective of this study was to examine the effects of human-computer interface design on postural dynamics, i.e., changes in working postures and postural discomfort exhibited by operators of the computer-based remote bar coding (RBC) system. In addition, the effects of different work/rest schedules on postural dynamics were evaluated. Twelve subjects participated in the laboratory experiment, which consisted of twelve scenarios utilizing two cognitive task requirement factors, i.e., (1) information presentation mode, defined through the letter image preview on the computer screen (none or one preview image); and (2) the information processing mode, defined through the specific keying method (key all characters or key 5 digits only). The third experimental factor was the work/rest schedule (50 min work/10 min break, 2 h of work/15 min break, or flexible schedule). The results showed that requirements of human-computer interface design significantly affected the operators' postural dynamics. It was concluded that not only the physical, organizational, or psychosocial work environment characteristics, but also the cognitive task characteristics are important for assessment of postural effects in the VDT work. The relationship between interface design, mental workload and postural dynamics should be carefully considered in future studies aimed at optimizing the human-computer data entry tasks.

Adult↗

PubMed1994

The validity of visual observation to assess posture in a laboratory-simulated, manual material handling task.

A wide range of methods to evaluate posture in work situations relies on simple, unaided visual observation. In the present study the validity of visual observation to assess posture in a dynamic job was evaluated. Postural aspects were observed and recorded during a manual materials handling job simulated in a laboratory. The results from these observations, concerning gross body posture, torso flexion, arms and legs position, and load to be handled, were compared to the results obtained by direct opto-electronic recording. The agreement on a sample-to-sample basis (expressed by Cohen's kappa) was poor for the variables torso flexion (mean value for kappa = 0.38), position of arms (kappa = 0.43) and legs (kappa = 0.46) and load to be handled (kappa = 0.50) and acceptable only for the gross body posture (kappa = 0.79). Moreover, for each variable except gross body posture, the crude distributions of all observations and recordings across categories (irrespective of time) were significantly different. The results demonstrate that the observations are not valid. It is concluded that dynamic work situations require less simple, more time consuming methods (e.g., analyzing film or video records of the job) than a posture registration method based on direct visual observation.

Adult↗

PubMed1994

Standing working posture compared in pregnant and non-pregnant conditions.

During pregnancy, an increase in body weight occurs together with changes in body weight distribution and in fit between body dimensions and workplace layout. These changes may cause alterations in working posture which may, in turn, have adverse consequences for the biomechanical load on the musculoskeletal system and so increase the risk of musculoskeletal disorders. Using photographic posture registration, the standing working posture was studied in 27 women during the last stage of pregnancy and after delivery (the experimental group). The women performed an assembly task while standing at various workplace layouts. The postural differences between the pregnant condition and the non-pregnant condition were studied and the effect of the various workplace layouts assessed. Ten non-pregnant controls were also studied twice to establish the effect of the time interval between the measuring occasions. We found that the women of the experimental group stood further from the work surface in the pregnant condition compared to the non-pregnant condition, the hips were positioned more backwards, and, in order to reach the tesk, they increased the flexion of the trunk, increased the anteflexion of the upper arms, and extended the arms more. At the workplace layout in which the work surface height was self-selected, the postural differences due to pregnancy were smallest or even absent, compared to the postural differences in the other workplace layouts studied. Ergonomists and workers in occupational health services should be alert to the consequences for the biomechanical load on the musculoskeletal system and the risk of development of health complaints caused by postural changes due to pregnancy. An adjustable workplace layout may prevent some problems.

Adult↗

PubMed1997

Age Group Differences in Postural Adjustments Associated With a Stepping Task.

In this study, differences among age groups in the postural adjustments associated with a stepping task were identified. Twenty subjects from each of 3 age groups, children (8-12 years), young adults (25-35 years), and older adults (65-73 years), performed the task in 2 movement contexts: place and step. In place, the subject simply lifted the foot and placed it on the step. In step, the subject lifted the foot, placed it on the step, and stepped up onto the step. Latencies of postural and focal muscle activation were determined by using surface electromyography and pressure switches. Center of pressure (CP) data were obtained by using a force platform. Subjects in all 3 age groups consistently demonstrated postural adjustments before movement initiation. Children displayed longer postural latencies than young adults as well as disproportionately large values for CP path length. Older adults showed prolonged postural-focal latencies and decreased CP excursions compared with the 2 younger age groups. These results suggest that maturation of coordination between posture and movement may not be fully complete in 8- to 12-year-olds and that increased restraint characterizes the performance of postural adjustments in healthy persons over 65 years of age.

center of pressure↗

PubMed2001

Kinematic and postural characteristics of sprint running on sloping surfaces.

The aim of this study was to identify the kinematic and postural characteristics associated with sprint running on uphill and downhill slopes of 3 degrees and on a horizontal surface. Eight male physical education students were filmed while sprinting maximally on an uphill-downhill platform under each of three conditions: (a) uphill at 3 degrees, (b) downhill at 3 degrees and (c) horizontal. Running speed, step rate, step length, step time, contact time, flight time and selected postural characteristics of the step cycle were analysed. Running speed was 9.2% faster (P < 0.05) during downhill and 3.0% slower (P < 0.05) during uphill compared with horizontal sprint running. During downhill and uphill sprint running, step length was the main contributor to the observed changes in running speed. It increased by 7.1% (P < 0.05) for downhill sprint running and was associated with significant changes in posture at touchdown and take-off. During uphill sprint running, step length decreased by 5.2% (P < 0.05), which was associated with significant changes in posture and reduced flight distance. Given the interaction between the acute changes in step length and posture when sprinting on a sloping surface, our findings suggest that such changes in posture may detract from the specificity of training on such surfaces. The chronic effects of training on such slopes on the kinematics and posture of horizontal sprint running are currently unclear.

Adult↗

PubMedDate not supplied

On the cognitive penetrability of posture control.

Postural sway increases with age. The decreased stability associated with postural sway often has been related to the reduced peripheral sensibility in the visual, vestibular, and proprioceptive systems. We examined whether the micropostural adjustments necessary for maintaining balance also require some cognitive processing. Young and older subjects were submitted to an auditory reaction time task while maintaining an upright posture on a force platform. The auditory stimuli were presented randomly when subjects were in a central or in an eccentric less stable postural position in four conditions of vision/surface. If the postural adjustments require some cognitive processing, a more eccentric position of the center of foot pressure (COP) would require more attention than a stable position of the COP because when an eccentric position is identified, a corrective response subsequently needs to be selected, programmed, and executed. The visual and surface conditions were altered to determine if additional attentional resources need to be allocated to the postural task when there is a reduction of the sensory information available. Results showed that as the sensory information decreased, the postural task became increasingly difficult for the elderly and required more of their attentional capacity (as indexed by increases in reaction time).

Acoustic Stimulation↗

PubMed1989

Radiographic measurements of intervertebral foramina of cervical vertebra in forward and normal head posture.

Forward head posture has long since been associated with a number of clinical problems treated by the fields of physical therapy and dentistry. The consistent and longstanding difficulty in the diagnosis and treatment of these conditions has been a lack of a clear understanding of the anatomical and biomechanical conditions that underly forward head posture. It has been reported that there is a narrowing of the cervical interspaces in forward head posture with the greatest change being between C4-5 and C5-6. These observations were made by viewing lateral radiographic films, yet the size of the foramina can only be viewed using oblique views. This study used oblique radiographic views of the intervertebral foramina to determine if there is a difference in the size of the intervertebral foramina in the forward head posture versus the normal head posture. The intervertebral foramina of the cervical vertebra were found to be larger in the forward head posture from levels C3 to T1. These results conflict with previous observations, suggesting that additional research is needed to assist in determining the underlying mechanisms responsible for the pain associated with forward head posture.

Cervical Vertebrae↗

PubMed2001

Postural instability and acute mountain sickness during exposure to 24 hours of simulated altitude (4300 m).

Short exposures to severe or moderate hypoxia can have detrimental effects on postural stability. We hypothesized that continuous 24-h exposure to simulated 4300-m altitude (446 mmHg) would adversely affect postural stability and that this change in postural stability would be related to the severity of acute mountain sickness (AMS). On two different studies with similar experimental designs, postural instability was measured after approximately 3 and approximately 24 h of exposure using a computer-controlled unstable platform system in a total of 19 volunteers on three consecutive, 30-sec tests: eyes open (EO), eyes closed (EC), and a dynamic test involving tracking a circular moving object. Compared to baseline sea-level results, increases in postural instability were obtained with the EO test after 2 to 3 h (30%, p = 0.002) and 23 to 24 h (21%, p = 0.036) of altitude exposure. Similar increases were obtained on the EC test: 2 to 3 h (25%, p < 0.001) and 23 to 24 h (31%, p < 0.001). Although absolute instability values were higher on the EC test, the ratio EC/EO and the relative temporal changes with altitude exposure were similar. There were no significant altitude-stability effects on the target-tracking task. Sixty-three percent of the subjects (12 of 19) exhibited significant AMS (> 0.7 ESQ-C score) at some point during the 24-h exposure. No statistically significant correlations were obtained between the ESQ-C and any of the postural instability tests. These results indicate that postural stability is adversely affected during a 24-h exposure to 4300 m; however, there does not appear to be a correlation with the incidence or severity of AMS.

Adolescent↗