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PubMed2004

Effect of hip and ankle muscle fatigue on unipedal postural control.

Fatigue and deficits in postural control may predispose musculoskeletal injury. The purpose of this study was to examine the effects of fatigue at the hip and ankle during frontal plane movements on postural control during single-leg stance. Thirteen healthy volunteers completed two testing sessions 1 week apart consisting of isokinetic fatigue of the frontal plane movers of either the ankle or hip with measures of static unipedal postural control taken before and after fatigue. Postural control was assessed during three 30-s trials of unilateral stance with eyes open before and after the fatigue protocol at each testing session. Mean center of pressure (COP) excursion velocity in the sagittal and frontal planes was compared between pre- and post-fatigue across the two joints. Fatigue of the hip musculature led to postural control impairments in the frontal and sagittal planes, while fatigue of the ankle musculature did not significantly impair postural control in either plane. Our results suggest that there is a greater effect of localized fatigue of the frontal plane movers of the hip compared to the ankle on maintenance of a postural control in single-leg stance.

Adult↗

PubMed2004

The reliability of quantifying upright standing postures as a baseline diagnostic clinical tool.

OBJECTIVE: To assess the reliability of posture across and within subjects, specifically the repeatability of spinal angles determined by digitization of images in the anterior, posterior, and sagittal views. DESIGN: A repeated measure design was used in which subjects were required to attend 3 sessions, each consisting of 3 trials. Photographs of the anterior, posterior, and lateral views of normal, relaxed upright standing were taken during each trial. Landmarks were digitized and cervical, thoracic, and lumbar angles were calculated with respect to a vertical reference line. SUBJECTS: Fourteen healthy and active subjects (7 male subjects and 7 female subjects) were recruited from a university student population. All had been free of low back pain during the previous 6 months. RESULTS: When comparing mean angles, no significant differences were detected for any angle in any view. However, large variability within subjects was observed, likely leading to the lack of significance found with respect to the main factors in the analysis of variance (ANOVA). Large coefficients of variance (CVs) reflect the substantial intrasubject variability, as well as poor to moderate agreement indicated by intraclass correlation coefficients (ICCs). There were no apparent trends indicating that gender affected repeatability of posture. CONCLUSIONS: The poor repeatability of postures documented using the studied method brings into question the validity of this postural analysis approach for either diagnostic use or tracking changes in response to treatment. Users of such postural analysis tools should interpret postural deviations from a vertical reference with caution, as there are many inherent factors that can contribute to the variability of these measured postures.

Adult↗

PubMed2006

Lumbar spine reposition sense: the effect of a 'slouched' posture.

Proprioceptive control is considered important for spinal stability and prevention of injury. However there is evidence that proprioceptive structures, that are reflexive and viscoelastic, are challenged by commonly adopted 'slouched' postures. The aim of this study was to investigate the effect of such postures on proprioceptive control. The reliability of a flexible electrogoniometer was established (ICC=0.89). Using a repeated measures design (n=32, 80% power detecting 0.5 degrees difference at 95% significance) subjects repositioned their lumbar spine immediately (3 s) and following 300 s in a 'slouched' posture, with a 15-min interval in between. Results showed a significantly reduced lumbar spine reposition sense following 300 s in a 'slouched' posture as compared with 3 s in a 'slouched' posture (P<0.001), mean difference 3.92 degrees (SD 4.35). Based on this sample, there was evidence that a 'slouched' posture, of 5 min duration, would increase reposition error by more than 2.35 degrees and less than 5.48 degrees (n=32, CI 95%). These findings support the practice of postural education to reduce potential to proprioceptive loss and injury. The electrogoniometer shows potential for use in clinical practice.

Adolescent↗

PubMed2005

Hand posture modulates cortical finger representation in SII.

Somatosensory magnetic fields evoked by electrical stimuli of the thumb or the index finger were recorded using a whole head magnetoencephalography (MEG) system in 10 subjects performing different finger postures, open hand posture and close hand posture for picking up a small object. The mean Euclidean distances between the ECD (equivalent current dipole) locations for the thumb and index finger in the secondary somatosensory cortex (SII) across the subjects were 8.5 +/- 2.1 mm in the close hand posture and 11.2 +/- 2.6 mm in the open hand posture. The distance was significantly shorter in the close hand posture (paired t test, P = 0.002, n = 8). However, the distances of the P38m and P60m components in the primary somatosensory cortex (SI) were not significantly different between the two hand postures (P38m: 13.4 +/- 5.6 mm in the open and 13.5 +/- 3.9 mm in the close; P60m: 12.4 +/- 2.6 mm in the open and 16.2 +/- 5.3 mm in the close). This shortening of the spatial distance between the cortical finger representations suggests a similarity in humans of the rapid changes in the dynamics of cortical circuits reported in animal studies. In addition, the overlap of the cortical finger representations, which might be suggested by the shortening of the distance between the ECDs in SII, is likely to play a role in information integration between sensory inputs from the thumb and index finger.

Adult↗

PubMed2006

Effect of early lead exposure on the maturation of children's postural balance: a longitudinal study.

This prospective study investigated the impact of early exposure to lead on the maturation of children's postural balance. The effect of lead exposure on age-associated maturation of postural balance was investigated on 91 children from the Cincinnati Lead Study (CLS) with a 5-year geometric mean lead concentration in blood of 11.66 microg/dL (range 3.89-28.33 microg/dL) by re-assessing their postural balance approximately every 20 months starting at mean age of 6.6 years through mean age of 12.1 years. The results presented in this paper provide evidence that low to moderate lead exposure in early childhood has a measurable and statistically significant impact on the maturation of postural balance. In comparison to less exposed children, of those in the higher lead group showed an impaired postural balance response. The results from this study suggest that children with early childhood lead exposure may need additional time to approach (or "catch up" with) their maturational postural balance status. As these subjects are now adults in their early to mid-twenties, poor postural balance may impact their daily living tasks and pose a higher risk of potential injuries at home and work.

Aging↗

PubMed2001

Marker-less systems for tracking working postures--results from two experiments.

Two experiments are performed to examine the usability of different marker-less approaches in image analysis and computer vision for automatic registration of OWAS (Ovako working posture analysing system) postures from video film. In experiment 1, a parametric method based on image analysis routines is developed both for separating the subject from its background and for relating the shapes of the extracted subject to OWAS postures. All 12 analysed images were correctly classified by the method. In experiment 2 a computer neural network is taught to relate postures of a subject to OWAS postures. When the network was trained with 53 images the rest of the set of 138 images was correctly classified. The experiments described in this paper show promising results regarding the use of image analysis and computer vision for tracking and assessing working postures. However, further research is needed including tests of different human models, neural networks, and template matching for making the OWAS method more useful in identifying and evaluating potentially harmful working postures.

Humans↗

PubMed2002

A comparison between analysis time and inter-analyst reliability using spectral analysis of kinematic data and posture classification.

This study compares the time needed to analyze data and the inter-analyst variability using observational posture classification vs. spectral analysis of upper limb kinematic measurements made using an electrogoniometer for selected industrial jobs. Eight trained analysts studied four jobs using both methods. An incomplete fixed block experimental design was used, whereby each analyst used one method for each job. The four jobs included (1) punch press operation, (2) packaging, (3) parts hanging, and (4) construction vehicle operation. The posture classification analysis method involved visually classifying tipper extremity joint angles into specific zones relative to the range of motion for every one-third second (10 frames) of videotape. Spectral analysis required the analysts to identify cycle break points. The electrogoniometer signals were synchronized with each cycle, and power spectra for each joint were computed. The average difference in RMS joint deviation among analysts was 0.9 (SD = 0.61 degrees) for spectral analysis and 7.1 (SD = 2.53 degrees) for posture classification. The average difference in mean joint angle was 0.8 (SD = 0.59 degrees) for spectral analysis and 11.4 (SD = 1.58 degrees) for posture classification. Repetition frequency differed an average of 0.05 Hz (SD = 0.054 Hz) for spectral analysis and 0.07 Hz (SD = 0.058 Hz) for posture classification. Posture classification took a factor of 6.3 more time than cycle break point assignment for spectral analysis. Even considering the additional time needed for sensor attachment for direct measurement, posture classification took an average factor of 1.29 more time than spectral analysis using electrogoniometer data.

Biomechanical Phenomena↗

PubMed1998

Postural control systems in developmental perspective.

How can the adult postural organisation be elucidated using an ontogenetic approach, and what questions can be raised about ontogenesis starting from the organisation of adult posture? These questions will be addressed taking three aspects of postural organisation. The first is the internal representation of erect posture, including the role played by the various sensory inputs in this representation. The second aspect relates to the variables which are controlled during erect posture: is it the body orientation with respect to the vertical or the localisation of the centre of gravity with respect to the feet which is controlled? The third aspect concerns the coordination between posture, equilibrium and movement, focusing on the role played by an internal representation of the external world and its interactions with the body segments in organising the anticipatory postural adjustments. The central organisation of coordinated control will also be considered. Each of these aspects will be discussed in relation to ontogenetic considerations.

Humans↗

PubMed1997

The ground reaction forces of postural adjustments during skilled reaching in unilateral dopamine-depleted hemiparkinson rats.

Rats with unilateral dopamine (DA) depletions (hemiParkinson analogue rats) produced by intracerebral 6-hydroxydopamine injection are impaired in using the contralateral (bad) limbs for postural adjustments. This article examines whether the bad limbs are impaired in applying the forces required to initiate postural adjustments that anticipate and accompany voluntary movements. The rats were trained to reach for food using their good paw while standing on small platforms, each of which measured force changes produced by an individual limb. In one condition the force platforms were aligned to support the limb placement of normal rats and in the second they were aligned to permit the DA-depleted rats to use a compensatory reaching stance. It was found that the bad limbs of the DA-depleted rats produced normal supporting reactions but did not initiate adjustments in posture. Postural adjustments were initiated with the good limbs and preceded rather than accompanied the reaching movements. When constrained to use the posture of normal rats, the DA-deplete rats could not reach successfully, but when allowed to adjust their stance to increase reliance on the good limbs, reaching performance improved. Measures of ground reaction forces confirm that DA-depleted rats can support posture but cannot initiate postural adjustments with their impaired limbs.

Adaptation, Physiological↗

PubMed2001

Spinal posture and prior loading history modulate compressive strength and type of failure in the spine: a biomechanical study using a porcine cervical spine model.

OBJECTIVE: The purpose of this study was to investigate the effect of posture and loading history on the compressive strength and site of failure in the spine. DESIGN: An in vitro experiment was performed using a porcine cervical model that provided a homogeneous population of young healthy spines. BACKGROUND: The distribution of stresses amongst the many load bearing tissues of the spine is altered throughout the day by posture and the history of loading, but it is not clear how this modulates tissue damage or the risk of injury. METHODS: 48 porcine cervical spines were harvested and dissected into motion segments containing two vertebrae and the intervening disc (C3/4 and C5/6). Compressive loads and rotational torques (flexion/extension) were applied so that the effects of four loading histories (hydrated, neutral dehydration, flexed dehydration, superhydrated) and two failure postures (neutral, flexed) could be examined. Levels of dehydration were based on those reported over the course of a day. Dissection techniques and X-rays were used to document tissue damage. RESULTS. Specimens had a lower yield point (43--63%) and ultimate compressive strength (23--47%) when in a flexed posture than when in a neutral posture. When injured in a neutral posture, superhydrated specimens had a lower strength (22--29%) than dehydrated specimens. Loading history also modulated the site of failure. CONCLUSIONS: The spine may be more prone to injury early in the morning when the discs are at their greatest level of hydration and/or when they are in a fully flexed posture.

Animals↗

PubMed2002

The relationship between clinical measurements of lower extremity posture and tibial translation.

OBJECTIVE: The purpose of this investigation was to determine if postures of the lower extremity were related to the amount of anterior tibial translation. DESIGN: Regression model of lower extremity postural measures used to predict the amount of tibial translation for a sample of convenience. BACKGROUND: Retrospective studies have indicated a link between certain lower extremity postures and prediction of anterior cruciate ligament injury status. What is not clear is whether these lower extremity postures cause, or occur as a result of anterior cruciate ligament injury. METHODS: Genu recurvatum, the thigh-foot angle, and navicular drop measures were obtained from the right leg of 43 uninjured college-aged subjects. Tibial translation was determined using a KT-1000 arthrometer. Gender related differences were determined with independent t-tests. Step-wise regression was performed to assess the relationship between postural measures and subject gender, and tibial translation. RESULTS: Very good to excellent inter- and intra-rater reliability was found for the postural measures. There was greater tibial translation (P=0.01) in females. The final regression model indicated a moderate relationship between sex of the subject, navicular drop and tibial translation (r=0.551). Genu recurvatum and thigh-foot angle were not significant predictors of tibial translation. CONCLUSIONS; We concluded that foot pronation has a greater impact on the amount of tibial translation than genu recurvatum and torsion of the lower leg in anterior cruciate intact subjects. RELEVANCE: Static clinical measures of lower extremity posture are commonly taken as predictors of outcome (both performance and injury). There may be little association between these static measures and dynamic performance.

Adult↗

PubMed2001

A sequence of postural muscle excitations precedes and accompanies isometric ramp efforts performed while sitting in human subjects.

The purpose of this study was to explore how the muscles which control postural body segments are activated during bilateral isometric ramp pushes exerted with the upper limbs by seated subjects. The paradigm under study presents the advantage that the subject is in a quasi-static posture, and since upper limbs are stretched out, the dynamic phenomena, which might occur, can only originate from the rest of the body, which means from the postural chain. A dynamometer was used to measure the horizontal force, Fx, exerted on the bar, and a custom-designed force-plate was used to measure global reaction forces (Rx) and displacement of the centre of pressure (Xp) along the antero-posterior axis. Electromyograms (EMGs) were picked up by bipolar surface electrodes from 14 muscles crossing the lower limb, pelvis, trunk and upper limb joints. It was shown that transient push efforts require monotonous EMG increase in postural as well as in focal muscles. The EMG sequence starts with the postural muscles and ends with the focal ones. The postural EMG sequence is anticipatory. It is concluded that the EMG sequence is programmed according to the task parameters, and that its role is to counteract in advance the perturbing effect of the effort, in order to allow the effort to be performed efficiently. It is suggested that excitation between the postural muscles is distributed according to their biomechanical role in relation to the supports.

Biomechanical Phenomena↗

PubMed2000

The occurrence rate and correlation factors of thumb-in-palm posture in newborns.

Bilateral fisting of hands, including adduction and infolding of the thumbs (cortical thumbs), is an expected finding in term infants. Clinically, the cortical thumb position is a transient and normal, but not general, hand posture in newborns. The aim of this study was to analyze the rate of occurrence and the factors possibly affecting the cortical thumb (thumb-in-palm) posture in term newborns. We enrolled 197 low-risk term newborns and observed the posture of their hands once daily from the day of birth for 3 consecutive days. The occurrence rates of the thumb-in-palm posture of the right hand on the first, second, and third days were 62.8%, 60.9%, and 50%, respectively, and those of the left hand were 60.3%, 55.8% and 53.2%, respectively. There was a significant reduction on a day-to-day basis in the right hand and an insignificant reduction in that of the left hand. Factors including sex, gestation age, birth weight, method of delivery, and alertness were analyzed, and no relationship was evident between these factors and the occurrence rates of the cortical thumb posture. Our observations suggest that the cortical thumb posture is indeed a predominant hand posture in our hospital, yet it is not a general phenomenon in all term newborns.

Age Factors↗

PubMed1999

Fifteen-year reproducibility of natural head posture: A longitudinal study.

Natural head posture continues to be widely used as the logical reference position for the evaluation of craniofacial morphology. The basic underlying premise is that the long-term clinical reproducibility (variability) of natural head posture is significantly less than the variability of conventional reference planes with respect to the vertical. This study reports the 15-year longitudinal reproducibility of natural head posture. Twenty Chinese adults in Hong Kong, who had initial natural head posture radiographs at age 12 years, were followed up and had repeated cephalograms after 15 years. The method error (reproducibility) after 15 years was 2.2 degrees, which compared favorably with the 5-year reproducibility (method error = 3.0 degrees ) and the 5 to 10 minutes reproducibility (method error = 1.9 degrees ). The individual variability of natural head posture reproducibility increased slightly over time. After 15 years the variance of natural head posture (4.8 degrees [= 2.2(2)]) remains significantly less than the variance of intracranial reference planes to the vertical (25 degrees to 36 degrees ). Cephalometric analyses based on natural head posture therefore remain valid over time.

Adult↗

PubMed1997

Exercise physiology principles applied to vocal performance: the improvement of postural alignment.

Postural alignment is not an inherent trait. Proper alignment is acquired through training postural muscle groups. This training is based on scientific principles associated with improving the physiological parameters of muscle mechanics. The purpose of this report is to describe and demonstrate the application of exercise physiology training principles to the improvement of postural alignment, which may enhance vocal performance. Specific exercise principles are explained and key concepts highlighted. Selected exercises for training postural muscles are presented to assist in establishing techniques that result in the expected adaptations. The application of training principles to postural muscles has been shown to improve postural alignment by strengthening synergistic muscles and establishing a balance between the agonistic and antagonistic activity of these muscles. Since posture has been well established as an important component of vocal performance, the application of these principles to vocal training seems to warrant the attention of vocal trainers and performers.

Exercise↗

PubMedDate not supplied

Changes in postural risk and general health associated with a participatory ergonomics education program used by heavy video display terminal users: a pilot study.

To determine if a brief, participatory ergonomics education program was associated with changes in work posture and general health of heavy video display terminal (VDT) users, 23 full-time VDT users participated in an on-site, small-group, 60-minute ergonomics education session and 1 week later an individual 15-minute follow-up session at their workstation. Posture was assessed by a blinded tester who scored videotape records to complete the Postural and Repetitiveness Risk Factors Index (PRRI), and general health status was assessed via self-administered Short-Form 36 Health Survey (SF-36) questionnaire before the intervention and again 5 weeks later. Five weeks after the 60-minute session, PRRI scores were 19% lower than were preintervention scores (p < 0.01), indicating lower postural risk. SF-36 physical (2% higher) and mental (4% higher) component scores were not statistically different, however, before and after intervention (p > 0.05). Although the participatory ergonomics education program was associated with improved work posture (PRRI scores) after 5 weeks, general physical and mental health (SF-36 scores) did not change within this time period. These results suggest that a participatory ergonomics program, which is of short duration and minimally disruptive to the normal workplace routine, may have a rapid effect on improving work posture. Although awkward posture is thought to be a risk factor for work-related musculoskeletal disorders, multigroup and long-term randomized trials are required to establish the effectiveness of participatory ergonomics programs in reducing the incidence and severity of musculoskeletal disorders associated with heavy VDT use.

Adult↗

PubMed2000

Human oscillatory brain activity within gamma band (30-50 Hz) induced by visual recognition of non-stable postures.

Our principal finding from this study is that there were changes at the level of brain electrical activity (EEG) during cognitive tasks while subjects were instructed to visually recognize non-stable postures of a computer animated human body model. In particular, there was clear enhancement of the amplitude within the gamma band (30-50 Hz) activity associated with visual recognition of non-stable postures at fronto-central and parietal areas in all subjects. The Morlet's wavelet transform was applied to examine the change of time-frequency (TF) energy within a range of 1-70 Hz frequencies range as a function of experimental tasks. There was a high energy burst within the 35-45 Hz TF cluster at fronto-central and parietal areas when subjects visually recognized non-stable postures. Experimental evidences were provided demonstrating that EEG activity recorded during visual recognition of non-stable postures was related to specific judgement of postural instability. In a series of control experiments, additional evidences were provided to justify the specific sensitivity of EEG 40-Hz activity to the act of visual recognition of postural instability. The contamination of muscle activity in the reported EEG results during perceptual tasks was also ruled out. Our findings are consistent with the notion of existence of specialized neural detectors (predictors) for specific postures and goal-oriented behavior. However, the functional significance and precise cognitive and neurophysiological mechanisms predicting the existence of these detectors remain to be explored.

Adolescent↗

PubMed1999

Ankle and hip postural strategies defined by joint torques.

Previous studies have identified two discrete strategies for the control of posture in the sagittal plane based on EMG activations, body kinematics, and ground reaction forces. The ankle strategy was characterized by body sway resembling a single-segment-inverted pendulum and was elicited on flat support surfaces. In contrast, the hip strategy was characterized by body sway resembling a double-segment inverted pendulum divided at the hip and was elicited on short or compliant support surfaces. However, biomechanical optimization models have suggested that hip strategy should be observed in response to fast translations on a flat surface also, provided the feet are constrained to remain in contact with the floor and the knee is constrained to remain straight. The purpose of this study was to examine the experimental evidence for hip strategy in postural responses to backward translations of a flat support surface and to determine whether analyses of joint torques would provide evidence for two separate postural strategies. Normal subjects standing on a flat support surface were translated backward with a range of velocities from fast (55 cm/s) to slow (5 cm/s). EMG activations and joint kinematics showed pattern changes consistent with previous experimental descriptions of mixed hip and ankle strategy with increasing platform velocity. Joint torque analyses revealed the addition of a hip flexor torque to the ankle plantarflexor torque during fast translations. This finding indicates the addition of hip strategy to ankle strategy to produce a continuum of postural responses. Hip torque without accompanying ankle torque (pure hip strategy) was not observed. Although postural control strategies have previously been defined by how the body moves, we conclude that joint torques, which indicate how body movements are produced, are useful in defining postural control strategies. These results also illustrate how the biomechanics of the body can transform discrete control patterns into a continuum of postural corrections.

Adult↗