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At least 19 recordsLinked to original sources
PubMed2000

Interactions between posture and locomotion: motor patterns in humans walking with bent posture versus erect posture.

Human erect locomotion is unique among living primates. Evolution selected specific biomechanical features that make human locomotion mechanically efficient. These features are matched by the motor patterns generated in the CNS. What happens when humans walk with bent postures? Are normal motor patterns of erect locomotion maintained or completely reorganized? Five healthy volunteers walked straight and forward at different speeds in three different postures (regular, knee-flexed, and knee- and trunk-flexed) while their motion, ground reaction forces, and electromyographic (EMG) activity were recorded. The three postures imply large differences in the position of the center of body mass relative to the body segments. The elevation angles of the trunk, pelvis, and lower limb segments relative to the vertical in the sagittal plane, the ground reaction forces and the rectified EMGs were analyzed over the gait cycle. The waveforms of the elevation angles along the gait cycle remained essentially unchanged irrespective of the adopted postures. The first two harmonics of these kinematic waveforms explain >95% of their variance. The phase shift but not the amplitude ratio between the first harmonic of the elevation angle waveforms of adjacent pairs was affected systematically by changes in posture. Thigh, shank, and foot angles covaried close to a plane in all conditions, but the plane orientation was systematically different in bent versus erect locomotion. This was explained by the changes in the temporal coupling among the three segments. For walking speeds >1 m s(-1), the plane orientation of bent locomotion indicates a much lower mechanical efficiency relative to erect locomotion. Ground reaction forces differed prominently in bent versus erect posture displaying characteristics intermediate between those typical of walking and those of running. Mean EMG activity was greater in bent postures for all recorded muscles independent of the functional role. The waveforms of the muscle activities and muscle synergies also were affected by the adopted posture. We conclude that maintaining bent postures does not interfere either with the generation of segmental kinematic waveforms or with the planar constraint of intersegmental covariation. These characteristics are maintained at the expense of adjustments in kinetic parameters, muscle synergies and the temporal coupling among the oscillating body segments. We argue that an integrated control of gait and posture is made possible because these two motor functions share some common principles of spatial organization.

Adult↗
PubMed2003

Effects of local fatigue of the lower limbs on postural control and postural stability in standing posture.

Postural stability and postural control were studied before and after a fatigue protocol of soleus muscles. Postural stability was assessed by the centre of gravity motion, which was computed from the motion of the centre of pressure, evaluating the postural control. Ten healthy male subjects were asked to stand as still as possible with eyes open before and after the fatigue protocol, performed in a sitting position. Fatigue was assumed on the basis of a shortening of the exertion time of the soleus muscles at 60% of their maximal voluntary contraction. Results of the whole group showed that fatigue modified postural control but did not change postural stability. The same results were observed only for some subjects. However, these results indicate an increase of the neuromuscular activity in high frequencies.

Adult↗
PubMed1999

Postural hypotension and postural dizziness in patients with non-insulin-dependent diabetes.

BACKGROUND: Postural hypotension with a decline of 20 mm Hg or more in systolic blood pressure on standing is considered a potentially dangerous hypotensive response. Postural dizziness is often strongly associated with postural hypotension. However, there is conflicting evidence, and previous studies have been confined to the elderly, not specifically to patients with diabetes. Thus, we evaluated the association between postural hypotension and postural dizziness, and determined the factors most likely related to postural hypotension in patients with diabetes. METHODS: The subjects were 204 consecutive noninsulin-dependent patients with diabetes and 408 age- and sex-matched control subjects. Postural hypotension was defined as a decline of 20 mm Hg or more in systolic blood pressure 1 minute after standing. Postural dizziness was any feelings of dizziness, lightheadedness, or faintness that occurred while standing during the examination. RESULTS: The prevalence of postural hypotension and postural dizziness in patients with diabetes was higher than in control subjects. Those patients with both diabetes and postural hypotension were older and had higher supine systolic blood pressures and higher plasma glycosylated hemoglobin and fasting glucose levels. They had higher prevalence of postural dizziness, hypertension, and cerebrovascular disease, and lower standing systolic blood pressures than those without postural hypotension. They also were more often being treated with antihypertensive agents. Only 32.8% of patients with diabetes with postural hypotension suffered from postural dizziness. Postural dizziness, hypertension, cerebrovascular disease, and plasma glycosylated hemoglobin levels were independently associated with postural hypotension in patients with diabetes. CONCLUSIONS: Postural dizziness, glycemic control, hypertension, and cerebrovascular disease were important determinants of postural hypotension in patients with diabetes. Postural hypotension was associated with postural dizziness, but it cannot be determined clinically just from the presence of postural dizziness because the sensitivity for diagnosis of postural hypotension is low.

Aged↗
PubMed1992

Postural hypotension and postural dizziness in elderly women. The study of osteoporotic fractures. The Study of Osteoporotic Fractures Research Group.

BACKGROUND: Postural hypotension and dizziness are common findings in elderly individuals. Although postural hypotension and postural dizziness are often perceived to be strongly associated entities, evidence to support this view in sparse. In addition, there is a lack of knowledge regarding the relationship of postural hypotension and postural dizziness to potential clinical outcomes, such as falls, syncope, and restricted activity. METHODS: We utilized a cross-sectional examination to study the prevalence and correlates of postural hypotension (drop in systolic blood pressure of greater than or equal to 20 mm Hg after 1 minute of standing) and postural dizziness (self-reported dizziness on standing) in 9704 nonblack, ambulatory women aged 65 years and older enrolled in the multicenter Study of Osteoporotic Fractures. First, we examined postural hypotension and postural dizziness as outcomes of risk factors that included medical conditions, medications, and physical findings. Then, we examined falls, syncope, and impaired functional status as outcomes of postural hypotension and postural dizziness. RESULTS: Postural hypotension and postural dizziness were common findings, noted in 14% and 19% of subjects, respectively. However, they were not highly correlated with each other and did not share the same risk factors or associated outcomes. Postural dizziness was more strongly associated than was postural hypotension with history of falling (age-adjusted odds ratios, 1.32 vs 1.02), history of syncope (1.94 vs 1.35), and impaired functional status (1.95 vs 0.76). CONCLUSION: Assessment of dizziness on standing appears to be more important than measurement of postural blood pressure change in ascertaining functional status and risk of falls and syncope in elderly individuals. Future prospective studies of postural dizziness are needed to confirm its value as a predictor of clinical outcomes.

Aged↗
PubMed2000

Postural control is scaled to level of postural threat.

This study investigated control of posture when standing at different surface heights above ground level. Alterations in surface height were used to modify threat to postural control. Sixty-two healthy adults (mean+/-S.D.=20.3+/-1.3 years) stood quietly on a force plate 40 cm (LOW threat), 100 cm (MEDIUM threat) or 160 cm (HIGH threat) above ground level. Each standing trial was performed with eyes open for 120 s. Postural threat was presented in ascending (n=31) or descending (n=31) order with the first threat condition in each series (LOW threat for ascending group, HIGH threat for descending group) repeated. This manipulation allowed for an examination of set effects (i.e. prior experience of postural threat) on postural control. The results demonstrated scaling of postural control variables to level of postural threat. Amplitude of centre of pressure (COP) displacement decreased and frequency of COP displacement increased linearly as postural threat increased from LOW to HIGH. The central nervous system progressively tightened control of posture as postural threat increased. Initial exposure to the HIGH or LOW threat condition influenced postural control differently. The group who received the HIGH threat condition first (descending) demonstrated increased amplitude of COP displacement in the anterior-posterior direction compared with the group who received the LOW threat condition first (ascending). A 'first trial' effect was observed when standing for two consecutive trials but only at the LOW threat condition. Decreased amplitude and increased frequency of COP displacement were observed on the first trial compared to the second trial. The results of this study demonstrated that control of posture is influenced not only by the threat to posture but also by the order in which the threat to posture is experienced.

Accidental Falls↗
PubMed1994

Modification of postural responses and step initiation: evidence for goal-directed postural interactions.

1. In this study, the interaction between anticipatory postural adjustments for step initiation and automatic postural responses to an external perturbation were investigated by having subjects initiate a voluntary forward step while perturbed by a backward surface translation, which caused forward sway of the body. The postural adjustments for step initiation act to move the body center of mass (COM) forward, whereas the automatic postural responses act to move the COM backward to restore stance equilibrium. Because the postural behaviors are in opposition, we asked whether a temporal hierarchy exists in which automatic postural responses are executed to restore equilibrium and followed by stereotypic postural adjustments for step initiation, or whether the interaction between these two postural behaviors is more dynamic. 2. Lower extremity electromyographs (EMGs), ground reaction forces, and kinematics were recorded from 10 subjects during three conditions: to quantify the anticipatory postural adjustments for step initiation, subjects stepped forward as soon as they felt a proprioceptive cue; to quantify the automatic postural responses to perturbation, subjects maintained stance equilibrium in response to a backward surface translation under both feet; and to quantify the interaction between the postural adjustments for the voluntary step and the automatic responses to the perturbation, subjects were exposed to a backward surface translation and instructed to step forward as soon as they felt the platform begin to move. 3. The anticipatory adjustments for step initiation included tibialis activation [stance limb = 163 +/- 28 (SE) ms; swing limb = 173 +/- 33 ms] and soleus inhibition resulting in center of foot pressure (COP) moving backward and lateral toward the swing limb to propel the COM forward over the stance limb. Subsequently, activation of the swing limb gastrocnemius resulted in heel-off. In contrast, the automatic postural adjustments for maintenance of stance equilibrium during a backward surface translation included activation of soleus and gastrocnemius (104 +/- 23 ms and 115 +/- 14 ms, respectively) resulting in a symmetrical forward displacement of the COP that moved the COM back to its original position with respect to the feet. 4. When a forward step was initiated in response to the translation, the automatic postural responses were reduced in amplitude bilaterally in soleus and in the stance limb gastrocnemius. When present the postural response occurred at the same latency when the goal was to initiate a step as when the goal was to maintain standing.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2000

Cephalic version by postural management for breech presentation.

BACKGROUND: It is possible that maternal posture may influence fetal position. Many postural techniques have been used to promote cephalic version. OBJECTIVES: The objective of this review was to assess the effects of postural management of breech presentation on measures of pregnancy outcome. SEARCH STRATEGY: The Cochrane Pregnancy and Childbirth trials register and Controlled Trials Register were searched. Date of last search: February 1999. SELECTION CRITERIA: Randomised and quasi-randomised trials comparing postural management with pelvic elevation for breech presentation, with a control group. DATA COLLECTION AND ANALYSIS: Eligibility and trial quality were assessed by both reviewers. MAIN RESULTS: Three studies involving a total of 192 women were included. Postural management was associated with a non-significant trend towards fewer non-cephalic births (relative risk 0.90, 95% confidence interval 0. 73 to 1.12). No differences were detected for caesarean sections or Apgar scores below seven at one minute. REVIEWER'S CONCLUSIONS: There is not enough evidence to evaluate the use of postural management for breech presentation.

Breech Presentation↗
PubMed2002

Is the prioritization of postural control altered in conditions of postural threat in younger and older adults?

Background. The purpose of this study was to determine if the prioritization of postural control over secondary task performance is altered in younger and older adults under different conditions of postural threat. Methods. Fifteen healthy older adults (mean age = 69.53 +/- 5.78) and 15 younger adults (mean age = 22.00 +/- 2.17) performed Brooks' Spatial Letter Task (BST) while standing in four conditions of postural threat. Galvanic skin conductance (GSC) was collected to measure changes in physiological arousal. BST task duration was used to measure changes in cognitive performance, and center of pressure (COP) area was used to determine changes in postural stability across each of the testing conditions. A prioritization index was calculated based on the relative change in BST and COP across testing conditions. This measure was used to quantify changes in the relationship between postural control and secondary task performance under conditions of postural threat. Results. Measures of GSC increased in younger and older adults in response to conditions of increased postural threat. Prioritization index scores revealed that a greater number of older adults than younger adults prioritized postural control over secondary task performance under conditions of increased postural threat. Conclusions. Environmental contexts that alter postural threat may lead to modifications in the prioritization between postural control and secondary task performance among older adults. This relationship may have implications for postural control under situations that do not afford deterioration in secondary task performance.

Adult↗
PubMed2000

A reliable technique for the assessment of posture: assessment criteria for aspects of posture.

BACKGROUND: The purposes of this study were: a) to describe assessment criteria for 10 separate aspects of posture; b) to describe the development and use of a qualitative posture rating scale based on the above; and c) to establish the reliability of the assessment technique. METHODS: Experimental design. Observation and photographic record of the posture of a sample of adolescent males. Reliability determined using two observations separated by a period of seven days. PARTICIPANTS: 114 adolescent males (age, 15-17 yrs) randomly selected from two post-primary schools. MEASURES: Ten different aspects of posture assessed according to defined criteria. Assessments made from four photographs: anterior, posterior, lateral and oblique views. RESULTS: Through examination of the photographs a qualitative postural assessment scale was developed. This consisted of three categories for each aspect of posture, corresponding to: good posture, moderate defect, and severe defect. Definite assessment criteria for each of the 10 aspects of posture have been described. The above has resulted in an assessment procedure in which the reproducibility of the posture scores exceeded 85 % for all aspects assessed. CONCLUSIONS: Definite criteria for the examination of 10 different aspects of posture have been described and clear diagrams representing good posture, moderate and severe defects have been produced. The reproducibility of the assessment procedure described makes it suitable for investigating the relationships between posture and other health variables such as musculo-skeletal disorders.

Adolescent↗
PubMed1999

Are automatic postural responses in patients with Parkinson's disease abnormal due to their stooped posture?

Abnormal automatic postural responses are thought to contribute to balance impairment in Parkinson's disease. However, because postural responses are modifiable by stance, we have speculated that some postural abnormalities in patients with Parkinson's disease are secondary to their stooped stance. We have studied this assumption by assessing automatic postural responses in 30 healthy subjects who were instructed either to stand upright or to assume a typical parkinsonian posture. During both conditions, subjects received 20 serial 4 degrees 'toe-up' rotational perturbations from a supporting forceplate. We recorded short-latency (SL) and medium-latency (ML) responses from stretched gastrocnemius muscles and long-latency (LL) responses from shortened tibialis anterior muscles. We also assessed changes in the center of foot pressure (CFP) and the center of gravity (COG). The results were qualitatively compared to a previously described group of patients with Parkinson's disease who, under these circumstances, typically have large ML responses, small LL responses and insufficient voluntary postural corrections, accompanied by a slow rate of backward CFP displacement and an increased posterior COG displacement. The stooped posture resulted in unloading of medial gastrocnemius muscles and loading of tibialis anterior muscles. Onset latencies of stretch responses in gastrocnemius muscles were delayed in stooped subjects, but the onset of LL responses was markedly reduced. Amplitudes of both ML and LL responses were reduced in stooped subjects. Prestimulus COG and, to a lesser extent, CFP were shifted forwards in stooped subjects. Posterior COG displacement and the rate of backward CFP displacement were diminished in stooped subjects. Voluntary postural corrections were unchanged while standing stooped. These results indicate that some postural abnormalities of patients with Parkinson's disease (most notably the reduced LL responses) can be reproduced in healthy subjects mimicking a stooped parkinsonian posture. Other postural abnormalities (most notably the increased ML responses and insufficient voluntary responses) did not appear in stooped controls and may contribute to balance impairment in Parkinson's disease.

Adult↗
PubMed2001

Transitions in a postural task: do the recruitment and suppression of degrees of freedom stabilize posture?

In this study, we examined flexibility in postural coordination by inducing transitions between postural patterns. Previous work demonstrated that the postural control system produces two task-specific postural patterns as a function of the frequency of support surface translation. For slow translation frequencies (<0.5 Hz), subjects ride on the platform reminiscent of upright stance (ride pattern), and for fast frequencies (> or =0.75 Hz) subjects actively fixed the head and trunk in space (head fixed pattern) during anterior-posterior platform motion. To study the adaptation of the postural control system, we had subjects stand on a support surface undergoing increases (from 0.2 to 1.0 Hz in 0.1-Hz steps) and decreases (from 1.0 to 0.2 Hz in 0.1-Hz steps) in translation frequency with the eyes open and closed. Kinematic measures of sagittal plane body motion revealed a gradual transition between these two postural patterns as a function of frequency scaling. In both the increasing and decreasing frequency conditions with visual input, center of mass displacements gradually decreased and increased, respectively, whereas upper-trunk (and head) displacement decreased gradually within the ride pattern until a head fixed pattern was observed without any significant changes in displacement for translation frequencies at and above 0.6 Hz. Without visual input, the scaling of the ride pattern was similar except the transition to the head fixed pattern never emerged with increasing frequency; instead, a less stable pattern exhibiting slow drift in head-trunk anterior-posterior motion (drift pattern) was observed at and above 0.5 Hz oscillations. The stability of the head fixed pattern at fast frequencies was clearly dependent on visual input suggesting that vision was more critical for trunk and head control in space at high than low translation frequencies. Head velocity was kept constant, and lower with vision, as translation frequency (and velocity) changed suggesting a head velocity threshold constraint across postural patterns. The gradual transition from the ride to the head fixed pattern was made possible by the recruitment of available degrees of freedom in the form of ankle, then knee, and then hip joint motion. In turn, the transition from the head fixed or drift pattern was made possible by the gradual suppression of available degrees of freedom in the form of reducing hip, then knee, and then ankle motion. The gradual change in postural kinematics without instabilities and hysteresis suggests that the ability to recruit and suppress biomechanical degrees of freedom allows the postural control system to gradually change postural strategies without suffering a loss of stability. The results are discussed in light of possible self-organizing mechanisms in the multisensory control of posture.

Adult↗
PubMed2000

Measures of postural stability are not predictors of recovery from large postural disturbances in healthy older adults.

OBJECTIVES: To determine, in healthy older adults, the relationship between postural steadiness, stability limits, and the ability to recover balance from three postural disturbances requiring anteriorly directed stepping responses. DESIGN: Analysis of multiple motor tasks in a cross-sectional sample of healthy older adults. SETTING: A biomechanics research laboratory. PARTICIPANTS: Fifty women and 29 men aged 65 or older, all healthy, living in the community, participated in this study. Subjects were examined by a geriatrician to identify the presence of exclusionary factors. MEASUREMENTS: Anterior-posterior and medial-lateral excursion distances of the center of pressure during quiet standing (postural steadiness), static leaning (static stability limits), and dynamic swaying (dynamic stability limits) were determined from ground reaction forces measured by a strain gauge forceplate. Within the same group of subjects, the maximum angle of forward lean from which a subject could recover with a single step, the ability to recover balance in response to an accelerated support surface, and the ability to recover balance after being tripped were determined. RESULTS: Recovery from the three types of postural disturbances were found to be statistically independent. The postural steadiness and the stability limit variables were only weakly correlated. Postural steadiness and stability limits were not related to the maximum recoverable angle of lean. The average medial-lateral center of pressure speed during the postural steadiness test was significantly slower for those who failed to recover after tripping than for the subjects who recovered successfully. However, a logistic regression model failed to achieve statistical significance, suggesting that the difference may not be functionally important. The anterior-posterior static stability limits were significantly larger for subjects who recovered successfully than for those who failed to recover during the accelerated support surface test. Although logistic regression suggested that a reduced anterior-posterior stability limit represents a risk factor for failure to recover during this task, only nine of 28 failures could be properly classified, thus diminishing the functional importance of this finding. CONCLUSIONS: Because recovery following postural disturbances could not generally be predicted from measures of postural stability, these findings suggest that these measures of postural stability are of limited utility in identifying potential anteriorly directed fallers in healthy older adults.

Aged↗
PubMedDate not supplied

Effects of side-posture positioning and side-posture adjusting on the lumbar zygapophysial joints as evaluated by magnetic resonance imaging: a before and after study with randomization.

OBJECTIVE: To test the a priori hypothesis that one of the positive mechanisms of action of chiropractic side-posture manipulation (adjusting) of the lumbar spine is to separate, or gap, the zygapophysial (Z) joints. DESIGN: Before and after study with randomization. SETTING: Chiropractic college clinic and magnetic resonance imaging (MRI) facility. PARTICIPANTS: Sixteen healthy student volunteers (8 men and 8 women) ages 22 to 29 years with no history of significant low back pain. Nineteen volunteers were screened, with 3 disqualified from the study. Subjects were randomized into 4 groups, each with 2 men and 2 women. INTERVENTIONS: Lumbar side-posture spinal adjusting (manipulation) and side-posture positioning. MAIN OUTCOME MEASURES: Comparison of anterior to posterior measurements of the Z joints from MRI scans taken before and after side-posture spinal adjusting and before and after side-posture positioning, and a rigorous subjective evaluation protocol of the Z joints by 3 radiologists blinded to the randomized groups. MAIN RESULTS: Observers making measurements were blinded to what group subjects were placed in and whether they were measuring first or second scans; radiologists were blinded to what group subjects were assigned. Differences were found between the groups. Those receiving side-posture spinal adjusting and remaining in side posture showed the greatest increase in gapping (0.7 mm vs 0.0 mm for controls). CONCLUSIONS: Lumbar side-posture spinal adjusting produced increased separation (gapping) of the zygapophysial joints. Side-posture positioning also produced gapping, but less than that seen with lumbar side-posture adjusting. A larger clinical trial should be performed to further define the results of this study.

Adult↗
PubMed2001

Postural discomfort and perceived exertion in standardized box-holding postures.

To help in the design or redesign of workplaces it would be helpful to know in advance the postural stress consequences of a wide range of body postures. This experiment evaluated 168 postures chosen to represent those in the Ovako Working-posture Analysing System (OWAS) using Rated Perceived Exertion (RPE) and Body Part Discomfort (BPD) measures. The postures comprised all combinations of three arm postures, four back postures, seven leg postures and two forces (weights of held boxes). Twelve male subjects held each posture for a fixed duration (20 s) before providing RPE and BPD ratings. Analysis of the ratings gave highly significant main effects, with the major driver being the object weight. As each factor was varied, the largest effect was on the body region corresponding to that factor. A simple main-effects-only additive model explained 91% of the variance of RPE means for the postures.

Adult↗
PubMed1980

Influence of a diagonal postural pattern on parameters of movement and associated postural adjustment in the cat.

The aim of this study was to investigate the influence of initial posture on the latency and amplitude of a movement and the postural adjustment associated with it. The movement studied was a limb flexion induced by stimulation of the motor cortex in chronically implanted cats. Only weak stimulations were used and the motor activity was mainly isometric, which facilitated the quantification of responses, analysed by measuring vertical forces exerted at the level of each limb. The initial posture consisted of the diagonal force pattern induced by stimulation of another cortical site corresponding to a different limb. The choice of this cortical site depended on the desired direction of force changes for the initial posture, i.e. either in the same direction as those accompanying the movement or in the opposite direction. The conditioning stimulation leading to the initial posture was triggered only when the computer analysing postural parameters showed a stable and balanced posture. Within the limits of the experimental method utilized, the following results have been established: 1. The latency of onset of the test movement and its associated postural adjustment were independent of initial posture. 2. The peak forces recorded were constant for a given stimulation intensity, and independent of initial force values. This shows that the amplitudes of force variations depend on the initial values: in the case of a low initial value the force variation must be greater to reach the same extreme value as in the case of a high initial value. Thus, the same stimulus intensity can induce different motor activities depending on the initial conditions.

Animals↗
PubMed1990

Observations of working postures in garages using the Ovako Working posture Analysing System (OWAS) and consequent workload reduction recommendations.

The working postures of mechanics (n = 84) in 42 garages were observed using the Ovako Working posture Analysis System (OWAS). During observation, both working postures and work activities were recorded. A computer program was developed for the data analyses. Using this program it is possible to calculate the working posture load for each work activity and the contribution of a specific activity to the total working posture load. This is a substantial extension of the original OWAS method. Five out of 19 observed postures of the body members were classified as Action Category 2, which suggests they were slightly harmful to the musculoskeletal system and likely to cause discomfort. Of the so-called typical working postures, 31.9% was classified in Action Category 2, suggesting that during a substantial part of the working day typical working postures occur which are at least slightly harmful to the musculoskeletal system. Moreover, those work activities principally causing the workload to fall in OWAS' higher Action Categories were identified. For each of these three work activities an alternative work method was observed. The data show that in all three work activities the use of a vehicle lift reduces the number of poor working postures thereby reducing the load on the musculoskeletal system.

Accidents, Occupational↗
PubMed1995

Directional specificity of postural muscles in feed-forward postural reactions during fast voluntary arm movements.

Healthy subjects performed bilateral fast shoulder movements in different directions while standing on a force platform. Anticipatory postural adjustments were seen as changes in the electrical activity of postural muscles as well as displacements of the center of pressure and center of gravity. Postural muscle pairs of agonist-antagonist commonly demonstrated triphasic patterns starting prior to the first electromyographic (EMG) burst in the prime-mover muscle. Proximal postural muscles demonstrated the largest anticipatory increase in the background activity during movements in one of the two opposite directions (forward or backwards). These changes progressively decreased when movements deviated from the preferred direction and frequently disappeared during movements in the opposite direction. The patterns in distal muscles varied across subjects and could demonstrate larger anticipatory changes during movements forward and backwards as compared to movements in intermediate directions. Bilateral addition of inertial loads to the wrists did not change the general anticipatory patterns, while making some of their features more pronounced. Anticipatory postural adjustments were followed by later changes in the activity of postural muscles, also reflected in the mechanical variables. Changes in leg joint angles revealed a "hip-ankle strategy" during shoulder flexions and an "ankle strategy" during shoulder extensions. The study demonstrates different behaviors of proximal and distal muscles during anticipatory postural adjustments in preparation for fast arm movements. We suggest that the proximal muscles produce a general pattern of postural adjustments, while distal muscles take care of fine adjustments that are more likely to vary across subjects.

Adult↗
PubMed1998

Static posture tests for the assessment of postural instability after virtual environment use.

The aim of this experiment was to measure the effect of immersion in a virtual environment (VE) on postural stability and examine the relationship between postural stability and self-reported simulator sickness. Forty healthy subjects were exposed to 20 min of immersion in an interactive VE with restricted user movement. The VE was viewed on a head mounted display (HMD) and the subject remained standing throughout the immersion period. Two static postures, normal stance and tandem romberg, were recorded before immersion, immediately after immersion and again at 10 min postimmersion. Performance in each posture was simultaneously measured by recording time that the posture could be maintained and mm path length of body sway over a 30-s period. The results demonstrated differences in the sensitivity of postural stability measurement techniques and variations in inter- and intraindividual responses to measures. Sway magnetometry measured a significant increase in postural instability in normal stance after VE immersion. None of the other measures were sensitive to this change. Postimmersion reports of simulator sickness symptoms indicate that the VE stimulus was provocative and correlation was found between reports of simulator sickness and balance-related symptoms. However, no association between self-reported symptoms and performance measures of postural instability was found.

Adolescent↗