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PubMed2005

Action simulation for others is not constrained by one's own postures.

Does the brain use the same mechanism to simulate both our own and other persons' actions? If it does, then one's current posture should influence action simulation for others, depending on whether current and imagined postures differ. To test this prediction, 20 observers sat upright or bent forward while evaluating the reaching range of a model that had been photographed in similar postures. Posture congruency did not influence performance but decisions were faster and more accurate when the simulation required fewer posture changes. These results begin to reveal the processes that transform visual inputs into motor predictions for others. Implications of the present findings for our understanding of the so-called "mirror system" are discussed.

Adult↗

PubMed2006

Parietal updating of limb posture: an event-related fMRI study.

The posterior parietal cortex (PPC) is thought to integrate different kinds of sensory information (e.g., visual, auditory, somatosensory) to produce multiple representations of space that are each associated with different types or combinations of action; such as saccadic eye movements and reaching or grasping movements of the upper limb. Lesion studies in monkeys and in humans have shown that reaching movements to visually defined and to posturally defined targets can be dissociated from one another; indicating that different regions of the parietal cortex may code the same movement in either extrinsic (visual) or intrinsic (postural) coordinates. These studies also suggest that regions within the posterior parietal cortex play an important role in maintaining an accurate and up-to-date representation of the current postural state of the body (the body schema). We used event-related functional magnetic resonance imaging (fMRI) to investigate those brain areas involved in maintaining and updating postural (i.e., non-visual) representations of the upper limb that participate in the accurate control of reaching movements. We show that a change in the posture of the upper-limb is associated with a significant increase in BOLD activation in only one brain region--the superior parietal cortex, particularly the medial aspect (precuneus). We note that this finding is consistent with the suggestion, based upon human neurological investigations and monkey electrophysiology, that this region of the PPC may participate in the dynamic representation of the body schema, and is the most likely location for damage leading to errors in visually guided reaching to non-foveated target locations. We also note that this brain area corresponds to a region of PPC recently identified as the human homologue of the Parietal Reach Region (PRR) observed in the monkey brain that has been thought to represent reaching movements in eye-centred coordinates.

Adult↗

PubMed2004

Effects of intensity and locus of painful stimulation on postural stability.

Stimulation of small diameter afferents can influence motor behavior. Little is known about how a prolonged painful stimulation of these small afferents may affect essential motor behavior such as the maintenance of an erect stance. The present study documents the effects of 10-s weak, moderate and extreme painful stimulations applied to the dorsum of the feet on the postural stability. Also, the moderate painful stimulation was applied to the metacarpal heads to determine if a painful stimulation to a limb not involved in the maintenance of the erect stance affects the postural control mechanisms. Increasing the intensity of the painful stimulation applied to the feet yielded larger postural oscillations whereas stimulation to the hands did not affect the control of posture. This suggests that the painful stimulation mainly affected the postural control mechanisms via sensorimotor processes rather than via cognitive resources related to the perception of pain.

Adult↗

PubMed1997

Subjective vertical and postural activity.

Three experiments were conducted to test the effect of postural information, resulting from the active control of balance, on the perception of the vertical. Subjects were required to adjust a luminous rod in two different visual contexts: in the dark or within a tilted visual frame. In these experiments, postural activity was manipulated by placing observers either in a situation of slight postural imbalance (Experiment 1) or in a situation of postural immobilization (Experiment 2). In both situations performance was compared with a control condition in which subjects were standing upright freely (Experiment 1) or sitting unconstrained (Experiment 2). Results showed no main effect of active posture or of immobilization on the visual perception of the vertical. In the third experiment, subjects were supine with their Z body axis perpendicular to the plane of the luminous rod. Thus, body orientation relative to gravity was modified and motor activity reduced. In this position, the physical vertical was perceived quite accurately in a dark environment. Moreover, in the titled frame condition, the supine body position clearly improved vertical judgements. These results are discussed in relation to the ecological theory of orientation.

Humans↗

PubMed2000

A comparison of different postures for scaffold end-frame disassembly.

Overexertion and fall injuries comprise the largest category of nonfatal injuries among scaffold workers. This study was conducted to identify the most favourable scaffold end-frame disassembly techniques and evaluate the associated slip potential by measuring whole-body isometric strength capability and required coefficient of friction (RCOF) to reduce the incidence of injury. Forty-six male construction workers were used to study seven typical postures associated with scaffold end-frame disassembly. An analysis of variance (ANOVA) showed that the isometric forces (334.4-676.3 N) resulting from the seven postures were significantly different (p < 0.05). Three of the disassembly postures resulted in considerable biomechanical stress to workers. The symmetric front-lift method with hand locations at knuckle height would be the most favourable posture; at least 93% of the male construction worker population could handle the end frame with minimum overexertion risk. The static RCOF value resulting from this posture during the disassembly phase was less than 0.2, thus the likelihood of a slip should be low.

Accidental Falls↗

PubMed2001

Validity of fixed-interval observations for postural assessment in construction work.

While observing six simulated construction tasks in the field, trained analysts recorded arm, trunk and leg postures categorically with two fixed-interval observational protocols. Observations were compared to measurements obtained with an electronic postural assessment system coupled with video analysis. The electronic postural assessment system consisted of electronic inclinometers to measure upper arm posture, knee flexion and trunk flexion, coveralls to house the inclinometer wiring, and an eletrogoniometric system to measure trunk lateral bending and twisting. Video analysis included frozen-frame analysis that corresponded to the moment of observation and simulated real-time analysis. Measurements were made on five male participants who each performed three tasks representative of construction laborers' work. Agreement among the observational and reference methods was generally high, although significant differences in measured frequency of exposure existed for knee flexion, trunk lateral bending and trunk twisting. The results suggest that, under appropriate conditions, discrete observations can be used to obtain reasonably accurate estimates of exposure frequency for broad categories of certain body postures.

Humans↗

PubMed2001

LUBA: an assessment technique for postural loading on the upper body based on joint motion discomfort and maximum holding time.

This paper presents a technique for postural loading on the upper body assessment (LUBA). The proposed method is based on the new experimental data for composite index of perceived discomfort (ratio values) for a set of joint motions, including the hand, arm, neck and back, and the corresponding maximum holding times in static postures. Twenty male subjects participated in the experiment designed to measure perceived joint discomforts. The free modulus technique of the magnitude estimation method was employed to obtain subjects' discomforts for varying joint motions. The developed postural classification scheme was based on the angular deviation levels from the neutral position for each joint motion. These were divided into groups with the same degree of discomforts based on the statistical analysis. Each group was assigned a numerical discomfort score relative to the perceived discomfort value of elbow flexion, which exhibited the lowest level among all joint motions investigated in this study, and, therefore, was set as a reference point. The criteria for evaluating stresses of working postures were proposed based on the four distinct action categories, in order to enable practitioners to apply appropriate corrective actions. The proposed scheme can be used for evaluating and redesigning static working postures in industry.

Adult↗

PubMed2002

The use of the portable ergonomic observation method (PEO) to monitor the sitting posture of schoolchildren in the classroom.

Contrary to common belief, back pain amongst young people is a frequent phenomenon. Epidemiological studies have found high prevalence rates of back pain amongst schoolchildren. The investigation reported here aims to validate children's self-reporting and the observation of sitting postures to establish the intensity, duration and frequency of exposure in the classroom. The sitting postures of 18 children were recorded using three methods, the portable ergonomic observation method (PEO), video analysis and self-report. The three methods were compared. PEO was significantly correlated with video analysis of the sitting postures after development of the method. Self-report was not significantly correlated with video analysis of the sitting postures. Therefore PEO was selected as the main observation tool in further analysis of children's sitting posture in schools in South-East England as part of a large research programme investigating back pain amongst schoolchildren.

Adolescent↗

PubMed1998

Influence of screen and copy holder positions on head posture, muscle activity and user judgement.

A study was conducted on eight subjects, in order to investigate the influence of head posture with regards to the screen and copy holder position, the activity of cervical muscles and the subjective judgement given by the subjects. A total of eleven different positions (exercises) of screen and copy holder were investigated. Four different screen positions were examined in the upright (middle) sitting posture and three different screen positions were investigated in the backward sitting posture. In addition, four different positions of the copy holder were examined in the upright sitting posture. Head posture and muscle activity were continuously measured in each exercise for a duration of 5 min. At the end of each exercise, the subjects were asked how they judged the position of the screen and/or the copy holder in comparison with other positions. The results show that preference is to be given to a screen position in which the vision axis is horizontal or inclined slightly downwards. The copy holder should be arranged at one side of the screen.

Adult↗

PubMed2000

Total head excursion and resting head posture: normal and patient comparisons.

OBJECTIVE: To determine whether significant differences existed between normal and patient groups on three postural measurements: anterior-posterior total head excursion (THE), resting head posture in sitting (RHPsit), and resting head posture in standing (RHPstd). SUBJECTS: Forty-two healthy subjects, 13 men and 29 women between the ages of 20 and 60 years, were matched to 42 patients according to gender and age. DESIGN: Measurements of THE, RHPsit, and RHPstd were taken for each subject. Patients were measured during their initial evaluation and had neck pain as a primary or secondary complaint. RESULTS: A two-way multivariate analysis of variance followed by two-way analyses of variance showed that normal subjects had a significantly (p<.05) greater THE than did the patients and that men (patients and controls) scored significantly higher (p<.05) than women (patients and controls) on both THE and RHPstd. CONCLUSION: Clinical assessment of patients with cervical pain should focus on cervical mobility rather than resting head posture. Head/neck posture is different for males and females and they should not be judged by the same standard.

Adult↗

PubMed1997

Variations in foot breadth: effect on aspects of postural control during one-leg stance.

OBJECTIVE: To test the hypothesis that changing body weight toward the narrower rearfoot or the wider forefoot causes a decrease or increase in the amount of center of pressure (CoP) displacement per unit of foot tilt (EQ), and to examine the effect on postural control. DESIGN: Experimental, within-subject design with one controlled variable. SETTING: A biomechanics laboratory of a university department of biomedical physics and technology. SUBJECTS: Ten healthy, young subjects. MAIN OUTCOME MEASURES: The sagittal plane position of the CoP (Y) reflecting foot loading, EQ, and horizontal ground reaction forces (Fx) representing postural control. RESULTS: Shifting body weight to the rearfoot or forefoot decreases (d) or increases (i) Y (Pd = .002, Pi = .000) and EQ (Pd = .018, Pi = .064). In both cases Fx (Pd = .008, Pi = .098) increased and postural control deteriorated. CONCLUSIONS: Shifting body weight to the rearfoot or forefoot decreases or increases EQ. Besides the changes in EQ encountered here, other factors are held responsible for the deterioration of postural control. The absence or presence of changes in Y can be used to exclude or include the presence of an effect of EQ or these unknown factors on postural control.

Adult↗

PubMed1997

Changes in postural sway and performance of functional tasks during rehabilitation after traumatic brain injury.

OBJECTIVE: To investigate changes in postural sway while standing, walking parameters, and performance of functional tasks during rehabilitation in a group of traumatic brain injury (TBI) patients. DESIGN: Descriptive. SETTING: Inpatient brain injury rehabilitation unit. PARTICIPANTS: Thirteen subjects undergoing rehabilitation after severe TBI. OUTCOME MEASURES: Two assessments were performed, 2 to 6 weeks apart that included the following: postural sway in three stance conditions; temporal and spatial parameters of walking; functional assessments of walking, standing up, reaching while standing, and stair climbing. RESULTS: There were significant reductions in postural sway in all stance conditions (p < .05) and significant increases in velocity of walking (p < .05), stride length (p < .01), and left and right step lengths (p < .01). Performance on all functional tasks improved (p < .05) except for functional reach. There were no significant correlations between changes in postural sway and changes in walking parameters or functional assessments. CONCLUSION: This study demonstrated significant improvements in postural sway, walking parameters, and functional tasks during a relatively short period of rehabilitation after severe TBI. Improvements in standing balance appear to be independent of improvements in walking performance, suggesting that different mechanisms underlie improved control of these tasks.

Adolescent↗

PubMed2001

Effects of backpacks on students: measurement of cervical and shoulder posture.

The aims of this pilot study were to determine whether the weight of a backpack, its position on the spine or time carried affected adolescents cervical and shoulder posture. Standing posture measured from the sagittal and frontal planes of 13 students was recorded photographically under several load carrying conditions. Cervical and shoulder position angles were calculated and compared. Results revealed that both backpack weight and time carried influenced cervical and shoulder posture. Forward head posture increased when carrying a backpack, especially one with a heavy load. Carrying a backpack weighing 15% of body weight appeared to be too heavy to maintain standing posture for adolescents. These findings have implications for future load carrying studies in adolescents.

Adolescent↗

PubMed1997

Spatial zones for muscle coactivation and the control of postural stability.

It is hypothesized that, depending on the motor task, the angular range of a joint may be subdivided into zones in which agonist and antagonist muscles are coactive, only one group of muscles is active or neither group is active. It is further hypothesized that central commands may change the size and location of these spatial zones. We investigated whether spatial zones are used by the nervous system and how they may be changed to provide postural stability of the elbow. We compared responses to sudden unloading of the elbow flexors in neurologically normal subjects with those in patients with postural control deficits due to unilateral hemispheric and/or subcortical lesions. By studying responses in patients, we sought to determine whether the specification of zones of agonist/antagonist muscle coactivation ("coactivation zones") may be essential for postural stability. At an initial elbow angle (130 degrees; full extension is 180 degrees), flexors were pre-activated by compensating an initial load which was equal to approximately 30% of the subject's maximal isometric voluntary contraction effort. Subjects were instructed not to correct the arm displacement elicited by a sudden decrease in the load. Data from 10 trials were collected at each of 4-6 final load levels (separated by 1.5-2 Nm) in order to map out the relationship between torque and angle in each subject. The procedure was repeated from a more flexed initial position of the elbow (100 degrees). EMG activity from two elbow flexors and two elbow extensors, as well as torque, velocity and joint position were recorded. Healthy control subjects and patients with mild clinical symptoms had coactivation zones or small silent zones around the final positions established after unloading. In these subjects, final positions of the limb were stable. Voluntary movement, i.e., transition of the limb from one initial position to another, was associated with a change in the location of the zone in articular space. The presence of large silent zones in patients with moderate or severe symptoms was correlated with postural instability and oscillations about the final position of the arm after unloading. The comparison of results from healthy and hemiparetic subjects implies that the central specification of the size and the location of a coactivation zone may be fundamental for the control of posture and movement.

Adult↗

PubMed1984

Hand posture in writing: possible artifacts from self report.

Seven hundred forty undergraduate students were asked to report the hand posture they used during writing and the presence or absence of left-handedness in the immediate family. Drawings were provided of prototypical "normal" and "inverted" posture and subjects were also given the option of reporting that their hand posture was somewhere between the two illustrated positions. The incidence of reporting "between" was 17% for left-handers and 46% for right-handers. These results suggest that experimenters should exercise caution when categorizing subjects on the basis of self-report forms that include only two choices: normal posture and inverted posture.

Adult↗

PubMed1996

Anticipatory postural adjustments during self-initiated perturbations of different magnitude triggered by a standard motor action.

The purpose of the study was to define whether anticipatory postural adjustments scale with the magnitude of a self-triggered postural perturbation when a standard motor action triggers the perturbation. Standing subjects generated vertical forces of different magnitude with their extended arms against a bar connected through a rigid cord to the floor. They released the bar with a standard bilateral shoulder abduction. Anticipatory postural adjustments were seen as changes in the level and/or timing of the background activation of postural muscles. Muscles of the dorsal part of the legs and of the trunk demonstrated an anticipatory decrease in the level of activation, commonly leading to its complete disappearance. There was no relation between the magnitude of the unloading and the timing of the changes in the background activity of these muscles. Muscles of the frontal part of the legs and of the trunk demonstrated an anticipatory increase in their activity whose timing and amplitude correlated positively with the magnitude of the perturbation. We conclude that anticipatory postural adjustments can be scaled with respect to the magnitude of a self-triggered perturbation.

Adult↗

PubMed2000

Do quadrupeds require a change in trunk posture to walk backward?

Previous studies on cats walking backward have indicated that they adopt a presumably adaptive posture characterized by extreme dorsiflexion of the lumbar spine. Because humans do not show any marked postural changes during backward walking, we questioned whether the posture exhibited by cats during backward walking was in fact adaptive and whether it was typical of quadrupeds. We therefore compared forward and backward walking in three treadmill-trained dogs and found reduced temporal parameters during backward walking and a marked reduction in wrist palmar-flexion during the swing phase of a backward step, but no change in trunk posture. We suggest that the aberrant posture exhibited by cats during backward walking is more related to ethological factors than to biomechanical ones.

Adaptation, Physiological↗

PubMed1998

Resonance behaviour of the seated human body and effects of posture.

Understanding of the resonance behaviour of the human body is important in the identification of vibration frequencies and body postures associated with back problems. In this study, experimental modal analysis was applied to whole-body vibration. Eight subjects were exposed to vertical random vibration while adopting three different postures on a rigid seat without a backrest. Motions of the spine, pelvis and viscera in the mid-sagittal plane were derived from skin-mounted accelerometers; head responses were measured using a bite-bar. Eight modes of vibration response were extracted below 10 Hz. A principal resonance of the human body at about 5 Hz consisted of an entire body mode, in which the skeleton moved vertically due to axial and shear deformations of buttocks tissue, in phase with a vertical visceral mode, and a bending mode of the upper thoracic and cervical spine. A bending mode of the lumbar and lower thoracic spine was found with a pitching mode of the head in the next higher mode located close to the principal mode. The second principal resonance at about 8 Hz corresponded to pitching modes of the pelvis and a second visceral mode. When subjects changed posture from erect to slouched, the natural frequency of the entire body mode decreased, resulting in a decrease in the principal resonance frequency. Shear deformation of buttocks tissue increased in the entire body mode due to the same change of posture. The complex body motions suggest that any forces causing injury from whole-body vibration will not be well-predicted by biodynamic models incapable of representing the appropriate body motions and the effects of body posture. It seems likely that the greatest risk of back problems will arise from the bending deformations of the spine.

Adult↗