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PubMedDate not supplied

Manual materials handling capabilities in non-standard postures.

Research efforts to establish manual materials handling (MMH) capabilities of individuals and populations have been conducted for many years. Most of the previous efforts have explored 'standard postures', utilizing two-handed, symmetric, sagittal plane MMH using unrestricted postures. Recognizing that many industrial MMH activities do not utilize 'standard postures', recent research projects have explored psychophysically determined MMH capacities in a variety of non-standard postures. Among the non-standard postures examined were: twisting while lifting or lowering, lifting and lowering from lying, sitting, kneeling, and squatting positions, and carrying loads under conditions of constricted ceiling heights. This paper presents the results of a series of previous research efforts at Texas Tech University. The results are presented in the form of population capabilities of both males and females for 99 MMH tasks using 'non-standard postures'. The data tables contain means and standard deviations of the data, as well as percentile distributions for the subject populations. Sample sizes for the experimental populations ranged from 45 to 50 subjects of each sex in the first three experiments to 20 subjects of each sex in the fourth set of experiments.

Adolescent↗
PubMed1994

Ergonomic guidelines for the prevention of discomfort of static postures based on endurance data.

This communication aims to show why guidelines to prevent discomfort of static postures can be based on endurance data, and to give insight in the aim and scope of a recent 'work-rest model for static postures' (WR model). The paper is a response to a recent paper of Mathiassen and Winkel (1992) who questioned the usefulness of discomfort and endurance data, and of the WR model for developing guidelines for static postures. It is concluded that discomfort can be considered as an independent evaluation variable for working postures, anchored in European legislation. Discomfort can be predicted from the 'remaining endurance capacity' (REC) because of a known relationship between the REC and discomfort as measured with the Borg rating scale. The WR model estimates at group level the mean REC of a static posture with or without an external force during and immediately after a work-rest schedule. The WR model is meant to assist practitioners in the assessment and optimization of static postures (and external forces) and work-rest schedules in order to avoid high levels of discomfort.

Ergonomics↗
PubMed1999

Effects of keyboard tray geometry on upper body posture and comfort.

The effects of a downward-tilting (DT) keyboard tray on wrist posture, seated posture and self-assessed musculoskeletal discomfort were investigated in a field experiment. Thirty-eight professional office workers were studied. A pretest assessed how they typed using either a conventional keyboard on a desk or on an articulating keyboard tray, and with or without wrist rests. Workers were randomly allocated to a control (n = 15) or test group (n = 23) that used their existing keyboard in a DT system. A post-test was conducted 3 weeks later. Results showed no significant changes in wrist posture, seated posture or reports of musculoskeletal discomfort for the control group, and approximately 50% of typing wrist movements put the hand in a neutral zone. There were significant improvements in wrist posture, seated posture and upper body musculoskeletal discomfort for the test group using the DT system. Over 80% of typing wrist movements put the hand into a neutral zone with the DT arrangement. Reactions to using a conventional keyboard on a DT system were positive.

Adult↗
PubMed1999

Seated work postures for manual, visual and combined tasks.

An awkward and static work posture has been recognized as a risk factor for work-related musculoskeletal problems. The objective of this study was to investigate some of the factors that can influence the posture adopted during work and in particular aspects of the task and how their influence is affected by work height. Three types of task were studied: a peg-hole assembly task, which was largely manual with very little visual component; a visual character identification task; and a combination of the two. Two levels of difficulty were included in each of the manual and visual elements. Postures of the head/neck, trunk and arm were recorded during performance of these tasks. The results showed that type and difficulty of task do influence the posture adopted, and that some of the postural responses (although complex) are predictable so that poor postures could be improved by adjusting task design in addition to workplace layout.

Adult↗
PubMed2002

Effects of exercise-induced fatigue with and without hydration on static postural control in adult human subjects.

Postural instability can be the result of various factors, including fatigue. Although it is well known that exercise-induced fatigue may be responsible for a decrease in performance, its effects on postural control, as well as those of hydration, have been relatively little explored. This study evaluated the effects of fatigue, with and without rehydration, on postural control in 10 healthy subjects who regularly practice sports activities. All subjects were submitted to three types of ergocycle exercises: maximal oxygen uptake (Vo2max) and submaximal exercises in no-hydrated and hydrated conditions at a power corresponding to approximately 60% of the Vo2max of each subject. Static posturographic tests were performed immediately before (control) and after exercises. The postural control performance decreased from the best to the worst: control, hydration, dehydration, and Vo2max. Fast Fourier transformation of the center of foot pressure showed three patterns of amplitude spectral density, with an increase of spectral amplitude for dehydration, more important for Vo2max conditions. Spectral amplitudes for control and hydration conditions were relatively similar. This hierarchy suggests that fatigue mainly alters muscular effectors and sensory inputs, such as proprioception, resulting in poor postural regulation. Moreover, fluid ingestion could be responsible for the preservation of muscular functions and of sensory afferences accurately regulating postural control.

Adult↗
PubMed2001

Interplay of biomechanical constraints and kinematic strategies in selecting arm postures.

In this study, the authors examined the interplay between biomechanics and control strategies in the resolution of excess degrees of freedom at the joint level. Seven participants made aimed arm movements from 30 starting points and several starting postures to targets. Final arm postures for movements to a target exhibited substantial joint angle variation. Through regression modeling and by comparing observed final arm postures with biomechanically plausible postures, the authors identified 3 kinematic strategies: (a) Maintain deviations from the average angle at the starting point to the joint's final posture; (b) make torso rotations that are a fixed proportion of shoulder rotations; and (c) adopt a characteristic combination of 4 wrist-positioning approaches. The results demonstrated that kinematic strategies can account for substantial variance in final arm postures, if one takes into account 2 types of individual differences-those that arise inevitably from biomechanical constraints and those that reflect choices in movement strategy.

Adult↗
PubMed1996

Forward head posture: its structural and functional influence on the stomatognathic system, a conceptual study.

An extensive conceptual analysis to establish the primary role a forward head posture plays in the appearance of some craniomandibular dysfunctions and internal derangements of the temporomandibular joints, associated to craniocervical postural disturbances. The analysis is based on findings contributed by scientific investigations in the field of dentofacial orthopedics and dysfunction. Special emphasis has been put on the influence of forward head posture on the craniofacial growth as it can determine a morphoskeletal and neuromuscular pattern leading to a dysfunctional condition. A correlation is established between Class II Occlusion, forward head posture, and craniomandibular dysfunction. The concept of craniocervical postural position is defined, as well as its close relation to the mandibular postural position.

Adaptation, Physiological↗
PubMed2000

Relationship between craniomandibular disorders and poor posture.

The purpose of this research was to show that a relationship between craniomandibular disorders (CMD) and postural abnormalities has been repeatedly postulated, but still remains unproven. This study was intended to test this hypothesis. Twenty-five CMD patients (mean age 28.2 years) were compared with 25 gender and age matched controls (mean age 28.3 years) in a controlled, investigator-blinded trial. Twelve postural and ten muscle function parameters were examined. Measurements were separated into three subgroups, consisting of those variables associated with the cervical region, the trunk in the frontal plane, and the trunk in the sagittal plane. Within these subgroups, there was significantly more dysfunction in the patients, compared to control subjects (Mann-Whitney U test p < 0.001, p < 0.05, p < 0.01). Postural and muscle function abnormalities appeared to be more common in the CMD group. Since there is evidence of the mutual influence of posture and the craniomandibular system, control of body posture in CMD patients is recommended, especially if they do not respond to splint therapy. Whether poor posture is the reason or the result of CMD cannot be distinguished by the data presented here.

Adult↗
PubMed2003

The influence of premenstrual symptoms on postural balance and kinesthesia during the menstrual cycle.

Recent studies have indicated an increased incidence of female athletic injuries during the luteal phase and the first days of the menstrual period. The purpose of this study was to investigate whether postural sway and knee-joint kinesthesia very during the menstrual cycle, and whether premenstrual syndrome (PMS) influences postural balance and kinesthesia. A total of 13 subjects with regular menstrual cycles participated in the study. Postural sway and kinesthesia were measured in the early follicular phase, in the ovulation phase and in the mid-luteal phase. Postural sway was measured with an ankle disc placed on a Statometer, and kinesthesia was measured with a specially designed device. Menstrual cycle phases were determined by sex hormone analyses in serum and by luteinizing hormone (LH) detection in urine. The diagnosis of PMS was made prospectively using validated daily symptom ratings. Eight of 13 women were classified as having PMS. These women had a significantly greater postural sway (p = 0.002) and a greater threshold for detection of passive motion in the knee joints (p = 0.05) than women without PMS. A tendency (p = 0.06) towards greater postural sway in the mid-luteal phase was detected among women with PMS. This may explain the finding of an increased incidence of athletic injuries in the luteal phase, reported previously.

Adult↗
PubMed1999

Periventricular leucomalacia and preterm birth have different detrimental effects on postural adjustments.

Postural adjustments during sitting on a moveable platform were assessed by means of multiple surface EMGs of neck, trunk and leg muscles and kinematics in three groups of children, aged 1 1/2-4 1/2 years. The first group consisted of 13 preterm children (born at a gestational age of 25-34 weeks), whose neonatal ultrasounds had shown distinct lesions of the periventicular white matter (PWM). The second group was the preterm control group, consisting of 13 preterm children with normal neonatal brain scans, matched to the PWM group with respect to gestational age at birth, birth weight, sex and age of postural assessment. The third group was formed by 13 healthy children born at term and matched to the PWM group with respect to sex and age at examination. In addition to the postural assessment an age-specific neurological examination was carried out. Three of the children of the PWM group developed a cerebral palsy syndrome, nine showed minor neurological dysfunction and one child was neurologically normal. In the preterm control group one child showed minor neurological dysfunction, while the remaining 12 children of this group and all children of the full-term group were neurologically normal. The postural assessment revealed that preterm birth was associated with two types of postural dysfunction. One dysfunction was related to the presence of a PWM lesion and consisted of a limited repertoire of response variation. The other dysfunction was not related to the presence of a PWM lesion, but to preterm birth itself. It consisted of a change in the ability to modulate the postural responses. Preterm children showed a higher sensitivity to platform velocity than full-term children, and they lacked the capacity to modulate EMG amplitude with respect to initial sitting position.

Biomechanical Phenomena↗
PubMed1991

Postural change in blood pressure associated with age and systolic blood pressure. The National Health and Nutrition Examination Survey II.

The prevalence of postural change in blood pressure and its association with age and systolic blood pressure were examined in data from 8,574 White nondiabetic persons aged 25-74 who participated in the second National Health and Nutrition Examination Survey (1976-1980). Postural change in blood pressure was defined as a drop of 20 mm Hg or more on change from supine to seated position. In subjects on no antihypertensive medications (n = 7,316), the prevalence of postural change in blood pressure increased with older age and with higher blood pressure levels, regardless of age. However, systolic blood pressure levels also increased with age. In logistic regression models, level of supine systolic blood pressure was strongly related to postural change in blood pressure (Relative odds (RO) = 1.59, 95% confidence interval (CI) = 1.49, 1.70 for a 10 mm Hg increase in systolic blood pressure) whereas age was not related to postural change in blood pressure (RO for age = 1.07, Cl = .89, 1.19 for a 10-year increase in age). Results were similar for those medicated for hypertension. All results were unchanged by addition of health status indicators, including reports of hospitalization and number of medical conditions, to the model. These data suggest that the age-related increase in the prevalence of postural hypotension previously reported may be partially explained by age-associated increases in systolic blood pressure.

Adult↗
PubMed1996

An interview technique for recording work postures in epidemiological studies. Music-Norrtälje Study Group.

BACKGROUND: The aim of the study was to present and evaluate a work-task-oriented interview technique focusing on the placement of the hands relative to the body and assessing per cent time spent in five standard work postures during a working day. METHODS: The reproducibility of estimated time spent in each work posture was tested by the test-retest method in 32 subjects; 16 were interviewed by the same interviewer and 16 were interviewed by another one at the retest. The validity concerning estimated time spent in th five standard work postures was tested in relation to observations in 58 male blue-collar workers. The mean registration (assessment) time was 6 hours and 15 minutes. RESULTS: No evident differences in the reproducibility depending on same or different interviewers at test and retest could be observed. The linear relationship between times estimated by the interview and by observations was high for four of the work postures: 'sitting' (r = 0.86), 'standing with hands above shoulder level' (r = 0.87), 'between shoulder and knuckle level' (r = 0.75), and 'below knuckle level' (r = 0.93). When the work posture 'standing with hands between shoulder and knuckle level' was divided into 'hands fixed' (r = 0.62) and 'hands not fixed' (r = 0.50) the correlations were weak. Current musculoskeletal complaints did not influence the accuracy of the estimations. CONCLUSIONS: The present task-oriented interview technique may be the best available method to estimate these work postures in a way that requires few resources compared to observations and technical measurements.

Adult↗
PubMed1986

Sequential analyses of postural reactions in nonhandicapped infants.

The purpose of this study was to identify an empirically validated sequence of automatic postural reactions in a sample of 40 nonhandicapped infants. Using a cross-sectional design, we tested infants between the ages of 2 and 10 months for the presence of full and partial righting, equilibrium, and protective reactions. Two types of sequential analyses were performed. The Thurstone absolute scaling technique identified an age-related sequence, and the scalogram technique yielded a measure of the variability of the sequence. The sequence of postural reactions defined in this study is in general agreement with the sequence reported in previous clinical reports, although some differences in ordering are noted. A consistency index of .727 indicated that the sequence of postural reactions had fairly good predictive ability. This study contributes a data-based sequential model of postural reactions and an indication of the degree of sequential variability in the order of emergence of postural reactions in nonhandicapped infants. Definition of the sequence and the observed variability in nonhandicapped infants is an initial step in the understanding of the processes underlying the development of postural reactions.

Child Development↗
PubMed1992

Investigation of evidence for anticipatory postural adjustments in seated subjects who performed a reaching task.

The paradigm for study of anticipatory postural adjustments permits investigation of the coordination of postural and voluntary components of functional movement. The purpose of this study was to investigate whether there were anticipatory postural adjustments for voluntary movement in seated subjects under clinically relevant conditions. Eight neurologically normal subjects performed a reaching task to a target placed at shoulder height, 45 degrees to the right of midline. Onsets and magnitudes of lateral and fore-aft reactive forces associated with the movement and of electromyographic (EMG) activity of the ipsilateral deltoid and external abdominal oblique and contralateral paraspinal muscles were monitored. Conditions of trunk support, reach speed, and distance reached were manipulated. Onsets of deltoid muscle EMG activity preceded onsets of postural muscle (external oblique and paraspinal) EMG activity in 70% of all trials for seated subjects in contrast to reports of EMG activity onset in the postural muscles in advance of the prime mover in standing subjects who performed a similar task. The role of the trunk musculature and the significance of reactive forces in advance of hand movement were equivocal. This study has implications for evaluation of postural instability in persons unable to stand for testing.

Adult↗
PubMed2001

Knee bracing after ACL reconstruction: effects on postural control and proprioception.

PURPOSE: To evaluate the effects an anterior cruciate ligament (ACL) brace has on various measures of knee proprioception and postural control. METHODS: Thirty subjects (mean age 27 +/- 11 yr) having undergone unilateral ACL reconstruction were tested with and without wearing their own custom-fit brace on their involved limb. Proprioception was assessed using joint angle replication tests completed on an isokinetic dynamometer. Postural control was assessed using a series of single-limb standing balance tests completed on a force platform. The balance tests included: 1) standing on the stable platform with eyes open, 2) standing on a foam mat placed over the platform with eyes open, 3) standing on the platform with eyes closed, and 4) standing on the platform after landing from a maximal single-limb forward hop. RESULTS: The brace provided a small but statistically significant improvement in proprioception (mean reduction in error scores between target and reproduced angles = 0.64 +/- 1.4 degrees, P = 0.02). For the postural control tests, there was a significant brace condition by test situation interaction (P = 0.02), with the brace providing a small but statistically significant improvement during the test completed on the stable platform with eyes open (mean reduction in center of pressure path length = 4.2 +/- 8.4 cm, P = 0.02) but not during the other more challenging test situations. Additional post hoc analyses indicated that the relationship between knee proprioception and postural control measures were low and not significant (r = 0.003 to 0.19, P > 0.32), consistent with the suggestion that changes in knee proprioception can occur in the absence of substantial changes in postural control. Also, standing balance tests that challenged the somatosensory contribution to postural control (i.e., those completed on foam, or with eyes closed) were significantly related to single-limb forward hop distances (r = -0.4, P < 0.05), whereas performance during the proprioception test was not (r = 0.1, P > 0.50). CONCLUSIONS: In general, bracing appears to improve performance during tasks characterized by relatively limited somatosensory input but not during tasks characterized by increased somatosenory input. The small magnitude of the improvements, coupled with their apparent lack of carry over to more difficult and functionally relevant tasks, questions the clinical benefit of the present effects of bracing.

Adult↗
PubMed1999

Interaction between voluntary and postural motor commands during perturbed lifting.

STUDY DESIGN: An experimental study was conducted to evaluate the effect of an unexpected postural perturbation during a lifting task. OBJECTIVES: To investigate electromyographic responses in the erector spinae to a postural perturbation, simulating slipping, during an ongoing voluntary lifting movement. It was hypothesized that specific combinations of voluntary movement and postural perturbation present a situation in which injury caused by a rapid switch between conflicting motor commands can occur. SUMMARY OF BACKGROUND DATA: Studies of postural perturbations have mainly focused on behavior during static tasks such as quiet, upright standing. To date, there are no published studies of the effect of a perturbation during an ongoing voluntary lifting movement. METHODS: Subjects standing on a movable platform were exposed to random perturbations while lifting a 20-kg load. Muscle activity was recorded from flexor and extensor muscles of the trunk and hip. Trunk flexion angle in the sagittal plane was recorded with a video system. RESULTS: Perturbations forward were followed by an increased activity in erector spinae superimposed on the background activation present during the lift, indicating that both the voluntary and postural motor programs caused an activation of erector spinae. During backward perturbation, however, there was a sudden cessation of erector spinae activity followed by an extended period of rapid electromyographic amplitude fluctuations while the trunk was flexing, indicating an eccentric contraction of the erector spinae. CONCLUSIONS: This erratic behavior with large electromyographic amplitude fluctuations in the erector spinae after a backward slip during lifting may indicate a rapid switch between voluntary and postural motor programs that require conflicting functions of the back muscles. This may cause rapid force changes in load-carrying tissue, particularly in those surrounding the spine, thus increasing the risk of slip-and-fall-related back injuries.

Adult↗
PubMed2000

Spinal posture during stooped walking under vertical space constraints.

STUDY DESIGN: Simultaneous spine kinematic variables in sewage workers were quantified using a two-dimensional video-based gait analysis system. OBJECTIVES: To identify patterns of spinal posture in a population of sewage workers pushing waste matter through tunnels while walking stooped under various height constraints. SUMMARY OF BACKGROUND DATA: Working with stooped postures is one of several occupational risk factors that have been associated with spinal disorders. However, the specific changes in spinal posture during stooped walking under various height constraints have not been documented. METHODS: A video-based gait analysis system was used to measure spinal posture in 22 sewage workers. Angles of the cervical, thoracic, and lumbar spine in the sagittal plane were assessed during walking with five levels of height constraint, from upright walking to stooped walking under a headroom restriction of 105 cm. Correlations among gait parameters, demographic data, and clinical results were determined. Linear regression analysis was performed to examine which variables have the largest impact on the posture resulting from a given vertical height constraint when age and body height are held constant. RESULTS: Mean angular values changed significantly with increasing headroom restrictions, with increases in cervical and thoracic extension as well as lumbar flexion. The cervical and thoracic angles were best correlated with height constraint, followed by lumbar angle and stride length. The inverse relation between cervical and thoracic angle during upright walking increased with increasing vertical space constraints, whereas the relation between the thoracic and lumbar angles decreased. Subjects with decreased abdominal muscle strength adopted a significantly more kyphotic thoracic posture when walking under headroom constraints than subjects with normal abdominal muscle strength. CONCLUSIONS: Combined walking and pushing under vertical space constraints was associated not only with the expected increased flexion of the lumbar spine, but also with greater extension (i.e., reduced kyphosis) of the thoracic spine.

Adult↗
PubMed2006

Effect of different upright sitting postures on spinal-pelvic curvature and trunk muscle activation in a pain-free population.

STUDY DESIGN: A normative within-subjects single-group study. OBJECTIVE: To compare spinal-pelvic curvature and trunk muscle activation in 2 upright sitting postures ("thoracic" and "lumbo-pelvic") and slump sitting in a pain-free population. SUMMARY OF BACKGROUND DATA: Clinical observations suggest that both upright and slump sitting postures can exacerbate low back pain. Little research has investigated the effects of different upright sitting postures on trunk muscle activation. METHODS: Spinal-pelvic curvature and surface electromyography of 6 trunk muscles were measured bilaterally in 2 upright (thoracic and lumbo-pelvic) sitting postures and slump sitting in 22 subjects. RESULTS: Thoracic, compared to lumbo-pelvic, upright sitting showed significantly greater thoracic extension (P < 0.001), with significantly less lumbar extension (P < 0.001) and anterior pelvic tilt (P = 0.03). Furthermore, there was significantly less superficial lumbar multifidus (P < 0.001) and internal oblique (P = 0.03) activity, with significantly higher thoracic erector spinae (P < 0.001) and external oblique (P = 0.04) activity in thoracic upright sitting. There was no significant difference in superficial lumbar multifidus activity between thoracic upright and slump sitting. CONCLUSIONS: Different upright sitting postures resulted in altered trunk muscle activation. Thoracic when compared to lumbo-pelvic upright sitting involved less coactivation of the local spinal muscles, with greater coactivation of the global muscles. These results highlight the importance of postural training specificity when the aim is to activate the lumbo-pelvic stabilizing muscles in subjects with back pain.

Adult↗