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At least 1,675 records · Page 93Linked to original sources
PubMed2003

Effect of sitting posture on 3-dimensional scapular kinematics measured by skin-mounted electromagnetic tracking sensors.

OBJECTIVE: To determine the effect of trunk sitting posture on scapular kinematics during humeral elevation by using skin-mounted electromagnetic tracking sensors. DESIGN: Repeated-measures design contrasting scapular kinematics in 2 different sitting postures. SETTING: A biomechanics laboratory in Hong Kong with a real-time, 3-dimensional electromagnetic tracking device for measuring movements of the scapula. PARTICIPANTS: A sample of 16 healthy adults (12 women, 4 men; age, 21.6+/-3.92y) with full, pain-free shoulder range of motion and no history of shoulder pathology. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Movements of the scapula were measured while each subject performed humeral elevation in an upright seated position and a slouched seated position. RESULTS: In both postures, posterior tip, lateral and upward rotation of the scapula, and lateral rotation of the humerus were observed during humeral elevation. When the slouched posture was adopted, there were significant decreases in the posterior tip and lateral rotation of the scapula, but there was no significant change in the magnitude of the upward rotation of the scapula. CONCLUSION: Increased thoracic kyphosis significantly alters the kinematics of the scapula during humeral elevation.

Adult↗
PubMed1998

Zona fasciculata-like histotype and aldosterone response to upright posture are not related in aldosterone-producing adenomas.

Two distinct subtypes of patients with primary aldosteronism due to aldosterone-producing adenomas (APA), based on different aldosterone responses to angiotensin, have been identified. We evaluated the relationship between adrenal zona fasciculata-like histotype and response of plasma aldosterone to upright posture in a series of patients with APA. Twenty-five patients were retrospectively divided in two groups according to aldosterone response to posture, i.e., a first group without postural change of aldosterone (n = 19) and a second group with at least 30% aldosterone increase after standing (n = 6). The percentage of zona fasciculata-like cells was calculated at histology in all adenoma tissues removed at adrenalectomy. The two groups of patients were similar in sex, age, systolic/diastolic blood pressure, supine/upright plasma renin activity, supine/upright aldosterone, tumor size. No differences between the two groups were observed as to zona fasciculata-like (84 +/- 3% vs 71 +/- 9%, P NS) and non-zona fasciculata-like cells percentage in adenoma tissues. No inverse correlation was found in either group between the percentage change from supine to upright aldosterone and the percentage of zona fasciculata-like cells. Aldosterone and cortisol responses to ACTH testing were similar in the two groups. Our results indicate that the two subtypes of primary aldosteronism based on different postural responses of aldosterone are not due to a different prevalence of zona fasciculata-like histotype in APA.

Adenoma↗
PubMed1989

Posture during head turning in pre-term infants: a longitudinal study of 15 low-risk infants of 32-36 weeks of conceptional age.

As part of a longitudinal study of spontaneous behaviour from 32-36 weeks of conceptional age, body posture was studied during spontaneous head movements in 15 low-risk pre-term infants. At the moment of an active head position in the midline, the most frequently observed posture was a symmetrical one in which the arms were fully flexed and the legs partly extended. With regard to the arm position no clearly developmental trend was noted. With regard to the leg position an increase of the partly flexed position of the limbs related to conceptional age was found. The observed postures during activity in our study showed a cephalocaudal acquisition of flexor tone. A symmetrical posture, when the head is in the midline, may be a sign of normality in pre-term infants.

Gestational Age↗
PubMed2002

A simplified conceptual model of the human cervical spine for evaluating force transmission in upright static posture.

OBJECTIVE: To develop a simplified graphical model appropriate for the evaluation of proposed theoretical force transmission mechanisms in the upright static cervical spine. The model is used to demonstrate in a visual format the underlying mechanical principles contributing to an optimal mechanical configuration of the cervical spine in upright posture. The model is also used to explore the relative mechanical efficiency of 2 different force transmission methods. METHOD: A graphical model was developed to illustrate relevant force vectors acting on the head and neck in upright posture. This model was used to calculate theoretical static loading on the structures of the neck under various loading conditions resulting from specific configurations of passive elements and active supportive muscle effort. RESULTS: From the information gained from the model, a theorized optimal mechanical configuration and theorized role of various components of the cervical spine in static upright posture is presented. The model is used to test the mechanical validity of a concurrent force system with intersegmental muscle force rather than the parallel force system presented in the literature. The alternate models are examined in relation to their predictions and theoretical implications with respect to force transmission in the cervical spine. CONCLUSION: A simplified model has been developed that facilitates the graphical representation of forces involved in maintaining static upright posture in the human cervical spine. The model is used to explore the optimal spinal configuration of the major mechanical components of the neck.

Biomechanical Phenomena↗
PubMed2002

Maximal bite force and its associations with spinal posture and craniofacial morphology in young adults.

Maximal bite force (MBF) and its associations with craniofacial morphology and spinal posture were studied in a group of young adults (46 M and 38 F) aged 21 to 23 years. MBF was recorded in molar and incisal regions. Sagittal spinal posture was measured by spinal pantography and trunk asymmetry at thoracic and lumbar levels by a forward-bending test. Craniofacial variables and posture of the cervical spine were examined from lateral cephalograms taken in a natural head position. No statistically significant correlations existed between MBF and spinal posture, but significant correlations did exist between MBF and craniofacial variables, especially in women.

Adult↗
PubMed2000

Abnormalities of post-caloric nystagmus induced by postural change.

Post-caloric nystagmus, the reverse secondary phase of caloric nystagmus after the cessation of primary-phase nystagmus, can easily be elicited by postural change. It has been related to the mechanism of vestibular adaptation, and exaggerated responses have been shown in some neurological disorders. Post-caloric nystagmus induced by postural change was analyzed in normal young adults (16 ears), elderly people (age > or = 65 years, 18 ears), patients with central lesions (40 ears) and patients with peripheral vestibulopathy (25 ears). The duration, maximum frequency and maximum slow-phase velocity of the primary phase of caloric nystagmus and of post-caloric nystagmus were documented. The duration, frequency and velocity ratios of post-caloric to primary-phase nystagmus were calculated. The results showed that post-caloric nystagmus induced by postural change was observed in 14 ears (88%) of normal young adults, 10 ears (56%) of elderly patients, 31 ears (78%) of patients with central lesions and 22 ears (88%) of patients with peripheral lesions. The duration and slow-phase velocity ratios for the central lesion group were found to be relatively higher than those for the control group (p < 0.05). A significant positive correlation between the intensities of post-caloric and primary-phase nystagmus was found in all groups except in the central lesion group. Abnormalities of post-caloric nystagmus induced by postural change may occur in the form of exaggerated response or failure of elicitation, which were observed with various central neuro-otological lesions and as a result of the aging process.

Adult↗
PubMed2003

Influence of neck proprioception on vibration-induced postural sway.

OBJECTIVE: Several reports have shown that the direction of the postural responses induced by vestibular stimulation is affected by the positions of the neck and torso. The aim of this study was to investigate whether the postural responses to vibratory proprioceptive stimulation of the calf muscles are affected by the position of the head and thus by proprioceptive and vestibular information from the neck and head. MATERIAL AND METHODS: Ten normal subjects were exposed to vibratory proprioceptive stimulation of the calf muscles when the head was maintained in five different positions: in a neutral position facing forwards, with the head turned to the right or left sides or with the head tilted backwards or forwards. Body movements were evaluated by analyzing the anteroposterior and lateral torques induced towards the supporting surface. RESULTS: The analysis showed that only the anteroposterior body sway was significantly affected by the position of the head. The anteroposterior postural responses were primarily increased during the tests with the head tilted backwards or forwards, whereas the postural responses were unaffected by head torsion towards the sides. The lateral responses were primarily affected by vision and not by the position of the head. CONCLUSIONS: The findings suggest that the responses evoked by vibratory proprioceptive stimulation of the calf muscles may be affected by different mechanisms, either by purely proprioceptive information or by an interaction between proprioceptive and vestibular information. Moreover, the increasing difference between the test conditions over time suggests that fatigue of the neck muscles may be one of the factors affecting the responses induced by the perturbations.

Adult↗
PubMed2003

The effects of posture on forearm muscle loading during gripping.

The purpose of this study was to quantify the response of the forearm musculature to combinations of wrist and forearm posture and grip force. Ten healthy individuals performed five relative handgrip efforts (5%, 50%, 70% and 100% of maximum, and 50 N) for combinations of three wrist postures (flexed, neutral and extended) and three forearm postures (pronated, neutral and supinated). 'Baseline' extensor muscle activity (associated with holding the dynamometer without exerting grip force) was greatest with the forearm pronated and the wrist extended, while flexor activity was largest in supination when the wrist was flexed. Extensor activity was generally larger than that of flexors during low to mid-range target force levels, and was always greater when the forearm was pronated. Flexor activation only exceeded the extensor activation at the 70% and 100% target force levels in some postures. A flexed wrist reduced maximum grip force by 40-50%, but EMG amplitude remained elevated. Women produced 60-65% of the grip strength of men, and required 5-10% more of both relative force and extensor activation to produce a 50 N grip. However, this appeared to be due to strength rather than gender. Forearm rotation affected grip force generation only when the wrist was flexed, with force decreasing from supination to pronation (p < 0.005). The levels of extensor activation observed, especially during baseline and low level grip exertions, suggest a possible contributing mechanism to the development of lateral forearm muscle pain in the workplace.

Adult↗
PubMed2005

Postural perturbation and muscular response following sudden release during symmetric squat and stoop lifting.

Squat and stoop lifting have been examined in some detail, but limited data exist regarding the sudden release of load during such lifting. Ten participants performed squat and stoop lifting trials with loads of 20, 40, 60 and 80N, and sudden release was randomly included in one of the lifting cycles. Postural perturbation was recorded via centre of pressure displacement using a force platform and the electromyographic response of trunk and lower limb muscles was recorded. Results indicated that irrespective of lifting posture, an 'ankle' response strategy to sudden release was elicited, where the anterior muscles of the lower limb contracted first, followed by the anterior trunk muscles, relaxation of the posterior trunk muscles and, finally, relaxation of the posterior lower limb muscles. The latency of muscles responding by contraction tended to decrease slightly with increasing load for both postures, while the latency of muscles responding by relaxation increased, resulting in increased trunk muscle co-contraction durations. The postural disturbance appeared to be greater for squat lifting than stoop lifting at the higher loads of 60 and 80N, as the centre of pressure moves significantly closer to the posterior limit of static stability (the line joining the heels).In terms of stability and muscular response, squat lifting may not be the most appropriate strategy if a sudden release of loads greater than approximately 50N is likely.

Adult↗
PubMed1991

Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures.

Eight healthy, male underground coal miners (mean age = 36.9 yrs +/- 4.5 SD) participated in a study examining psychophysically acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted head-room conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60 cm). All tasks were 10 min in duration and were performed under a 1.22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11.3% lower when kneeling as compared to stooping. Subjects selected 3.5% more weight in asymmetric tasks, and lifted 5.0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3.5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8.2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.

Adult↗
PubMed1991

Biomechanical evaluation of lift postures in adult Koli female labourers.

Three lift-postures, back straight and knees bent, back bent and knees straight and squatting were evaluated biomechanically based on data from 100 Koli female labourers, when lifting loads from the floor to hold them at knee height. The maximum weight was lifted with the back bent and the knees straight which is a posture commonly used by Indian labourers for lifting a load. Squatting (a posture used by Indians for performing household chores) produced the least physical strain in terms of moment and moment ratio (moment per kilogramme of load lifted). Consequently, squatting was found to be the best posture for lifting a load, specifically for the Indian labourers who are accustomed to squatting when working.

Adult↗
PubMed1993

Effects of seated posture on erector spinae EMG activity during whole body vibration.

The purpose of this study was to evaluate the electromyographic (EMG) response of the erector spinae to whole body vibration in three different unsupported seated postures: neutral upright, forward lean, and posterior lean. Subjects were 11 healthy college-age men. EMG was collected using bipolar surface electrodes placed bilaterally over the erector spinae at the L4 level. A modified chair with attached accelerometer was affixed to an induction type vibrator. Subjects were vibrated vertically at 4.5 Hz and 6.21 m.s-2 RMS. Data were collected in each of the three postures for 30 s pre- and post-vibration and for 2 min during vibration. Mean EMG values were determined for each sampling period and compared using ANOVA. The mean value for anterior lean was significantly larger (p < 0.05) than that for posterior lean and neutral. EMG data analysed by triggered averaging showed a phase-dependent response to the vibratory cycle for the forward leaning and neutral upright postures. The results of this study indicate that the magnitude of the vibration synchronous response of the erector spinae musculature is dependent upon body posture. This response may be an important factor in the onset of muscular fatigue and the increased incidence of back disorders among individuals exposed to whole body vibration.

Adult↗
PubMed1994

Continuous measurement of lumbar posture using flexible electrogoniometers.

Continuous measurement of changing limb segment angle is possible using a recently introduced flexible electrogoniometer but, unfortunately, the magnitude of linear displacements occurring during flexion and extension of the trunk has prevented its use as a measure of spinal mobility and posture. To overcome this limitation, a specially constructed, lightweight, aluminium carriage has been developed to allow free linear travel of the electrogoniometer, while maintaining the angle recorded between the thoracolumbar junction and the sacrum. The reliability and practicability of this new approach for recording changes in lumbar posture have been investigated. Following bench tests and operator training, measurements of maximal flexion and extension of the lumbar spine were repeated on 12 subjects. The extent of sagittal mobility was compared with measures from a fluid-filled inclinometer and a flexicurve. Analysis of the data showed that the use of the aluminium carriage did not markedly influence the accuracy of the electrogoniometer, and the technique as modified was found to be comparable with standard techniques for estimating the extent of lumbar sagittal flexibility. A field based study, involving four garage mechanics, was undertaken to examine the usability and acceptability of the electrogoniometer technique for continuous measurements. Lumbar curvature was monitored continuously for a two hour period during the course of the mechanics' working day. Dedicated software provided angle-time plots from which it was established that extreme flexed or extended postures were maintained only for relatively short periods; projection to an eight hour shift would indicate that a total of approximately 40 min is spent in extension beyond 10 degrees and flexion beyond 50 degrees. The technique has the potential to provide quantitative information on lumbar posture necessary for non-invasive, biomechanical investigations of spinal loading. It will be particularly useful for both sporting and occupational ergonomics field-studies.

Adult↗
PubMed1994

Dynamic biomechanical modelling of symmetric and asymmetric lifting tasks in restricted postures.

This article describes investigations of dynamic biomechanical stresses associated with lifting in stooping and kneeling postures. Twelve subjects volunteered to participate in two lifting experiments each having two levels of posture (stooped or kneeling), two levels of lifting height (350 or 700 mm), and three levels of weight (15, 20, or 25 kg). One study examined sagitally symmetric lifting, the other examined an asymmetric task. In each study, subjects lifted and lowered a box every 10 s for a period of 2 min in each treatment combination. Electromyography (EMG) of eight trunk muscles was collected during a specified lift. The EMG data, normalized to maximum extension and flexion exertions in each posture, was used to predict compression and shear forces at the L3 level of the lumbar spine. A comparison of symmetric and asymmetric lifting indicated that the average lumbar compression was greater in sagittal plane tasks; however, both anterior-posterior and lateral shear forces acting on the lumbar spine were increased with asymmetric lifts. Analysis of muscle recruitment indicated that the demands of lifting asymmetrically are shifted to ancillary muscles possessing smaller cross-sectional areas, which may be at greater risk of injury during manual materials handling (MMH) tasks. Model estimates indicated increased compression when kneeling, but increased shear forces when stooping. Increasing box weight and lifting height both significantly increased compressive and shear loading on the lumbar spine. A multivariate analysis of variance (MANOVA) indicated complex muscle recruitment schemes--each treatment combination elicited a unique pattern of muscle recruitment. The results of this investigation will help to evaluate safe loads for lifting in these restricted postures.

Adult↗
PubMed1995

Ranking of static non-neutral postures around the joints of the upper extremity and the spine.

Constrained body postures are usually cited as the major cause of musculoskeletal static loading. Thus, the main goal of the present study was to develop a ranking system for the stressfulness of the non-neutral static postures around the wrist, elbow, shoulder, neck and lower back. This was based on the ratings of perceived discomfort. Sixteen men participated in the study. The results indicated that static postural stresses yielded varying effects on the discomforting rating levels. On the basis of these preliminary findings, a ranking system was developed for the stressfulness of non-neutral postures around the joints of the upper extremity and the spine.

Adult↗
PubMed1995

Postural adaptations to workbench modifications in standing workers.

Surveys have shown that many workers operate under conditions that require constrained standing. The aim of this study was to investigate postural adaptations in constrained standing to facilitate the development of design guidelines for standing workspaces. Standing postures were observed in six different workspaces that were designed using combinations of task distance (which was either constrained or unconstrained) and foot position (which was constrained, unconstrained or employed a footrest). Subjects at work were recorded stereophotogrammetrically and postural variables were obtained in three dimensions. Postural adaptation to increased task distance was found to be characterized by increased trunk flexion and increased hip flexion while adaptation to close work was found to be characterized by increased neck flexion and increased thoracic kyphosis. Constrained foot position resulted in increased hip flexion accompanied by increased plantar flexion. Although use of the footrest resulted in some reduced lumbar lordosis, it increased trunk flexion and was not associated with significantly less discomfort than any of the other workspaces.

Adaptation, Physiological↗
PubMed1999

Postural muscle responses in the spinal cord injured persons during forward reaching.

To compensate for postural muscle function loss spinal cord injured (SCI) people have to use parts of the sensorimotor system which are still intact. In this study, postural control was investigated in high and low thoracic SCI people and in able-bodied controls, using a bimanual forward-reaching task. Muscle activity was recorded bilaterally from the erector spinae (ES) at level L3, T9 and T3, latissimus dorsi (LD), ascending part of the trapezius muscle (TPA), serratus anterior (SA), sternocostal head of the pectoralis major (PM) and the oblique abdominal muscles (OA) by means of surface electromyography. Sitting balance was monitored by measuring the changes in the location of the centre of pressure (CP) using a force platform. Muscle activity analyzed in different phases of the movement showed that SCI people adopt different postural adjustments to face the balance changes due to the reaching movement. SCI people make alternative use of non-postural muscles like the LD and TPA to maintain their sitting balance.

Adaptation, Physiological↗
PubMed2003

Does weight-shifting exercise improve postural symmetry in sitting in people with hemiplegia?

BACKGROUND: Weight-shifting exercise was empirically practised in correcting the biased posture of people with stroke-induced hemiplegia. OBJECTIVES: (1) Evaluate the loading symmetry at the buttock-seat interface as a reflection of a postural defect in sitting. (2) Investigate if weight-shifting exercises could correct the postural problem of people with hemiplegia. DESIGN: Control group design. PARTICIPANTS: 16 subjects with hemiplegia after stroke and 14 healthy individuals. PROCEDURES: Subjects were assessed for buttock-seat interface loading while in erect sitting using a seat pressure mapping system. Subjects with stroke then practised one session of weight-shifting exercise followed by a reassessment. RESULTS: The subjects with hemiplegia, particularly those with right hemisphere lesion, had more load borne at the buttock ipsilateral to the side of stroke lesion. The weight-shifting exercise did not produce an immediate improvement on the loading asymmetry. CONCLUSION: The exercise would require further investigation to clarify its benefits in treating postural problems after stroke.

Adult↗