Seated work postures for manual,visual and combined tasks

An awkward and static work posture has been recognized as a risk factor for workrelated 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.     

Factors affecting posture for machine sewing tasks: the need for changes in sewing machine design

Sewing machinists suffer from musculoskeletal problems, which have been attributed to poor working postures as well as to the repetitive hand and arm movements. Their posture is constrained by both the visual and the manual aspects of the task, and the design of the sewing machine and table have a considerable influence on the posture adopted. The potential for improvement of industrial sewing machines was investigated in a study of the effects of two design parameters (table inclination and view of the needle). It was shown that both trunk posture and head/neck flexion could be improved significantly by altering these design parameters. Trunk posture was found to be strongly related to the manual aspects of the task, and could be improved by altering the working positions for the arm. Head posture was most influenced by the view of the task/needle and could be improved by improving the visual condition for the task.     

Evaluating posture behavior during seated tasks

A method was developed to evaluate posture behavior of the trunk, neck, eye, and upper extremity in three-dimensional space during the performance of static, seated tasks. Body postures were measured using an ultrasonic measurement system to determine the Cartesian coordinates of joints and the angles between adjacent limbs. Posture preferences for a variety of visual and manual tasks were then determined.

Pilot studies using three subjects performing visual and right-handed tasks showed that the postures were affected by target location, body size, and target size. These experiments suggest that the preferred horizontal location of visual targets is within 10° of the sagittal plane of the head. The preferred vertical location of visual targets is 10° to 35° below the seated eye height. For manual reaches, the target-to-shoulder distance should be at least one-third the length of the upper extremity to avoid extreme elbow flexion. In addition, the seat pan should swivel and should allow a person to move fore and aft in order to adjust to a comfortable work posture.     

The validity of visual observation to assess posture in a laboratory-simulated,manual material handling task

A wide range of methods to evaluate posture in work situations relies on simple, unaided visual observation. In the present study the validity of visual observation to assess posture in a dynamic job was evaluated. Postural aspects were observed and recorded during a manual materials handling job simulated in a laboratory. The results from these observations, concerning gross body posture, torso flexion, arms and legs position, and load to be handled, were compared to the results obtained by direct opto-electronic recording. The agreement on a sample-to-sample basis (expressed by Cohen's k) was poor for the variables torso flexion (mean value for tc = 0.38), position of arms (tc = 0.43) and legs (tc = 0.46) and load to be handled (tc — 0.50) and acceptable only for the gross body posture (k = 0.79). Moreover, for each variable except gross body posture, the crude distributions of all observations and recordings across categories (irrespective of time) were significantly different. The results demonstrate that the observations are not valid. It is concluded mat dynamic work situations require less simple, more time consuming methods (e.g., analyzing film or video records of the job) than a posture registration method based on direct visual observation.     

Posture,discomfort and performance in a VDT task

Improvements in workplace, working posture, and discomfort need to be justified in terms of improvements in performance. Previously, a visual inspection task has been investigated. The objective of the current study was to demonstrate the interactions between workplace, work duration, discomfort, working posture, as well as performance in a 2-h typing task. Three levels of keyboard heights were used to change working posture (e.g. joint angles and postural shifts), and thus presumably discomfort (e.g. rating of perceived discomfort and body part discomfort), and performance (e.g. typing speed, error rate and error correction rate). The results indicated that the hypothesized posture-comfort-performance interrelationships were partially supported. Keyboard height had effects on working posture adopted. As in previous studies, the rate of postural shift was a good indication of discomfort in a VDT task. Discomfort and postural shift rate had adverse effects on performance (e.g. error rate). However, these effects on error rate may not be strong.     

Posture, discomfort and performance in a VDT task

Improvements in workplace, working posture, and discomfort need to be justified in terms of improvements in performance. Previously, a visual inspection task has been investigated. The objective of the current study was to demonstrate the interactions between workplace, work duration, discomfort, working posture, as well as performance in a 2-h typing task. Three levels of keyboard heights were used to change working posture (e.g. joint angles and postural shifts), and thus presumably discomfort (e.g. rating of perceived discomfort and body part discomfort), and performance (e.g. typing speed, error rate and error correction rate). The results indicated that the hypothesized posture-comfort-performance interrelationships were partially supported. Keyboard height had effects on working posture adopted. As in previous studies, the rate of postural shift was a good indication of discomfort in a VDT task. Discomfort and postural shift rate had adverse effects on performance (e.g. error rate). However, these effects on error rate may not be strong.     

Visual display height

We examined the influence of backrest inclination and vergence demand on the posture and gaze angle that workers adopt to view visual targets placed in different vertical locations. In the study, 12 participants viewed a small video monitor placed in 7 locations around a 0.65-m radius arc (from 65 degrees below to 30 degrees above horizontal eye height). Trunk posture was manipulated by changing the backrest inclination of an adjustable chair. Vergence demand was manipulated by using ophthalmic lenses and prisms to mimic the visual consequences of varying target distance. Changes in vertical target location caused large changes in atlanto-occipital posture and gaze angle. Cervical posture was altered to a lesser extent by changes in vertical target location. Participants compensated for changes in backrest inclination by changing cervical posture, though they did not significantly alter atlanto-occipital posture and gaze angle. The posture adopted to view any target represents a compromise between visual and musculoskeletal demands. These results provide support for the argument that the optimal location of visual targets is at least 15 degrees below horizontal eye level. Actual or potential applications of this work include the layout of computer workstations and the viewing of displays from a seated posture.     

Divided attention in experienced young and older drivers: lane tracking and visual analysis in a dynamic driving simulator.

A simulated driving task that required the simultaneous execution of two continuous visual tasks was administered to 12 healthy young (mean age 26.1 years) and 12 healthy older (mean age 64.4 years) experienced and currently active drivers. The first task was a compensatory lane-tracking task involving a three-dimensional road display. The second task was a timed, self-paced visual analysis task involving either a vocal or manual binary response to dot patterns projected within the road display. Using adaptive tasks, single-task difficulty was individually adjusted for each subject. To control for individual differences in attention allocation strategy, the dual task was performed according to three different sets of instructions based on the relative importance of each task. Compared with young adults, older adults showed a significantly decreased ability to divide attention. This effect was apparent in lane tracking and in the accuracy of visual analysis. The impairment of divided attention was less pronounced in the vocal condition than in the manual one. This suggests that difficulty in integrating responses may be an important determinant of poor dual-task performance in old age.     

An observation of adults with visual impairments carrying out copy-typing tasks

Increasing numbers of people with a visual impairment are using computers to access information. This study examines the behaviours of 10 visually impaired adults carrying out a copy-typing task. Momentary time sampling methods were used to examine how the participants conducted the task. Four different aspects were observed: functions performed, line of vision, technology used, and posture. Postures were further analysed using RULA (McAtamney and Corlett 1993). Recommendations were presented to each participant and their feedback was obtained. All participants exhibited examples of inefficient working habits and potentially problematic posture. Feedback from them indicated that most participants were not aware of some of the issues raised and the extent to which their work was affected. Although participants had unique individual profiles, general issues were apparent across the group. These included poor touch-typing, rare use of short cut keys, and a lack of adjustment of equipment, furniture, and copy material. While many of these behaviours are common in normally sighted computer users, the presence of a visual impairment means that compensatory strategies often result in greater negative impact upon postures adopted. Key recommendations included more proactive and creative strategies for improving skills and work techniques and adjusting positions of equipment and furniture. Importantly these must be individualised because of the idiosyncratic nature of the visual impairment. Participants positively acknowledged the recommendations provided. Nevertheless there is responsibility at the level of the institution to provide necessary equipment and training to enable the individual to affect change.     

An observation of adults with visual impairments carrying out copy-typing tasks

Increasing numbers of people with a visual impairment are using computers to access information. This study examines the behaviours of 10 visually impaired adults carrying out a copy-typing task. Momentary time sampling methods were used to examine how the participants conducted the task. Four different aspects were observed: functions performed, line of vision, technology used, and posture. Postures were further analysed using RULA (McAtamney and Corlett 1993). Recommendations were presented to each participant and their feedback was obtained. All participants exhibited examples of inefficient working habits and potentially problematic posture. Feedback from them indicated that most participants were not aware of some of the issues raised and the extent to which their work was affected. Although participants had unique individual profiles, general issues were apparent across the group. These included poor touch-typing, rare use of short cut keys, and a lack of adjustment of equipment, furniture, and copy material. While many of these behaviours are common in normally sighted computer users, the presence of a visual impairment means that compensatory strategies often result in greater negative impact upon postures adopted. Key recommendations included more proactive and creative strategies for improving skills and work techniques and adjusting positions of equipment and furniture. Importantly these must be individualised because of the idiosyncratic nature of the visual impairment. Participants positively acknowledged the recommendations provided. Nevertheless there is responsibility at the level of the institution to provide necessary equipment and training to enable the individual to affect change.     

Influence of reading format on reading activity under uniaxial whole body vibration

In a railway vehicle, the vibrations are transmitted to the passengers through the various interfaces such as floor, seat, backrest etc. These vibrations affect the passenger comfort as well as their performance to do any work such as reading, writing, typing etc. In the present work, effects of vibration magnitude, direction of vibration, postures and reading formats have been studied on the reading activity. Thirty healthy male subjects have performed reading task, one at a time. All subjects were exposed to uni-axial whole body vibration in 1–20 Hz frequency range at 0.5, 1 and 1.5 m/s² rms vibration magnitude. The experimental task involved reading a paragraph under the different 54 experimental conditions (three magnitude, three direction, two posture and three reading format). The task performance has been evaluated in terms of time taken by the subjects to read a given paragraph and also the subjective evaluation of perceived difficulty on Borg's CR 10 scale. Perceived difficulty and performance degradation in reading have been found to increase with the increase in vibration magnitude in each direction of vibration. The perceived difficulty and performance degradation in reading have been observed to be higher in the fore-&-aft direction in with-backrest posture. In vertical and lateral vibration, perceived difficulty and performance degradation have been higher in without-backrest posture compare to with-backrest posture. The perceived difficulty and performance degradation have been lower for the triple-column format.     

A comparison of risk assessment of single and combination manual handling tasks: 3. Biomechanical measures

Anecdotal evidence suggests organisations experience difficulty assessing the risk in manual handling tasks. One reason for this difficulty may be that many common tasks are a combination of lift, lower, push, pull and carry tasks. No prior reports of attempts to assess the risk in combination tasks using biomechanical measures could be found. The aim of the study was to compare the risks assessed in single manual handling tasks with those in combination tasks. Nine male and nine female students performed combination and single handling tasks. The force applied by subjects to a box was recorded and, together with kinematic data on subject posture collected via video, used in a twodimensional dynamic model to estimate the lumbar compression force and lumbar shear force. The hand force, peak lumbar compression force and peak lumbar shear force for each combination task were each compared with the same variable for the single tasks which comprised the combination, using repeated measured analysis of variance with specific contrasts. In at least one of the twelve comparisons performed for each dependent variable, the combination task value was significantly different to the single task value. It is concluded that the risk in combination manual handling tasks can not be accurately assessed by using estimates based on biomechanical measures of single tasks.     

The effects of multifocal refractive lenses on occipital extension and forward head posture during a visual task

The purpose of this study was to determine if a change in forward head posture and occipital extension occurred in participants who wore multifocal lenses vs. those persons with non-multifocal lenses while performing an 8-min visual reading task on a visual display unit (VDU). Forty-two healthy human participants were recruited for this study. Thirty-three participants completed the study. Fourteen participants wore multifocal lenses and 19 wore frames with non-multifocal lenses. To evaluate the degree of change of forward head posture and occipital extension digital photographs of cervical posture were taken at four different time intervals: prior to performing the reading task and at 3, 5 and 8 min during the reading task. The digital photographs were analysed utilizing a computer program. Two one-way ANOVA were utilized to determine the degree of change of forward head posture and occipital extension between groups. A significant difference was identified between groups for changes in degrees of forward head posture while performing a visual reading task on a VDU. However, no significant difference between groups was found for occipital extension while performing the same task. Multifocal wearers exhibit greater degrees of change in forward head posture and occipital extension than non-multifocal wearers. These postural changes may place them at a greater risk for musculoskeletal disorders and headaches.     

Comparing standing posture and use of a sit-stand stool: Analysis of vascular,muscular and discomfort outcomes during simulated industrial work

Sit-stand stools are available for use in industrial settings, but there is a lack of quantitative evidence demonstrating benefits for lower limb, back and/or neck/shoulder outcomes. In this paper we describe an experiment conducted to compare and contrast posture and time-related differences in muscular and vascular outcomes during 34 min of manual repetitive work performed in either standing or sit-standing work posture. We measured vascular parameters in the lower limbs, and muscular parameters in the trunk and neck/shoulder, and discomfort in the three regions as participants accomplished a repetitive box-folding task. Results show that blood flow in the foot (p = 0.022) and ankle mean arterial pressure (p < 0.001) were greater during standing. Left gluteus medius and external oblique activation was higher during standing, while sit-standing work resulted in higher levels of co-activation between the left erector spinae and external oblique muscle pair (p = 0.026). Neck/shoulder muscle activity was not significantly different between the conditions. Reported discomfort did not differ significantly for the trunk and neck/shoulder region, but standing resulted in higher level of reported discomfort in the lower limb. The sit-stand posture used in this experiment appears to prevent the undesirable lower limb outcomes associated with static standing work posture.Relevance to industryThis work demonstrates quantitative evidence to support the potential use of a sit-stand stool for industrial work operations, at least over relatively short durations.     

Impact of training standard complexity on inspection performance

Research in the area of visual inspection has shown that various factors influence inspection performance. Task factors have been identified as one of the primary classes of factors influencing the complexity of inspection tasks. If inspection task complexity is to be reduced it is essential to understand the influence of various task factors and prescribe interventions based on the impact of these factors. Moreover, historical work in this area has shown that the greater the difficulty of a vigilance task, the more engaged operators may become. Therefore, this research studies the influence of the following task factors: number of defect types, defect standard complexity, defect probability, and defect distribution on both the visual search and decision‐making components of a contact lens inspection task. This study was conducted using a computer simulation of a real world contact lens inspection task using 28 student subjects. Performance was measured on both the visual search and decision‐making components of the task. The results revealed a negative influence of defect standard complexity and a positive influence of defect probability on both the visual search and decision‐making components of the inspection task. © 2006 Wiley Periodicals, Inc. Hum Factors Man 16: 109–132, 2006.     

The effects of multifocal refractive lenses on occipital extension and forward head posture during a visual task

The purpose of this study was to determine if a change in forward head posture and occipital extension occurred in participants who wore multifocal lenses vs. those persons with non-multifocal lenses while performing an 8-min visual reading task on a visual display unit (VDU). Forty-two healthy human participants were recruited for this study. Thirty-three participants completed the study. Fourteen participants wore multifocal lenses and 19 wore frames with non-multifocal lenses. To evaluate the degree of change of forward head posture and occipital extension digital photographs of cervical posture were taken at four different time intervals: prior to performing the reading task and at 3, 5 and 8 min during the reading task. The digital photographs were analysed utilizing a computer program. Two one-way ANOVA were utilized to determine the degree of change of forward head posture and occipital extension between groups. A significant difference was identified between groups for changes in degrees of forward head posture while performing a visual reading task on a VDU. However, no significant difference between groups was found for occipital extension while performing the same task. Multifocal wearers exhibit greater degrees of change in forward head posture and occipital extension than non-multifocal wearers. These postural changes may place them at a greater risk for musculoskeletal disorders and headaches.     

An investigation of children's posture and discomfort during computer use

This study investigated schoolchildren's posture and discomfort while working at computers. Sixty-eight children (mean age 9.5 years) were observed at school during normal computer sessions lasting 15-25 min. Rapid upper limb assessment (RULA) was used to evaluate posture, and a body discomfort chart (BDC) and a modified visual analogue scale (VAS) were used to record site and intensity of discomfort. Computer tasks were noted and in accordance with RULA, postures were classified as Action Level (AL) 1 (acceptable) to 4 (needs immediate change). Most children adopted postures at an unacceptable level while working at computers. None of the postures were in AL 1; 60% were in AL 2; 38% were in AL 3; and 2% were in AL 4. Posture became worse over time. Poor posture was associated with discomfort, but it is not clear if it was related to the sitting posture or to the computer use. Children who reported discomfort had a higher mean RULA grand score (5.0) than those who did not report discomfort (4.4). The type of computer task influenced the children's posture. RULA proved generally to be a suitable method for evaluating children's posture.     

An experimental evaluation of instantaneous self-assessment as a measure of workload

Instantaneous self-assessment (ISA) is a technique that has been developed as a measure of workload to provide immediate subjective ratings of work demands during the performance of primary work tasks such as air traffic control. This paper reports a study that compared the results of ISA with those gathered from other established workload evaluation techniques; subjective ratings collected at the end of the task, mean heart rate and heart rate variability, and error in the primary task of tracking. ISA ratings were found to be correlated significantly with the post-task ratings of workload, heart rate variability, and task performance. Generally each of the techniques was sensitive to variations in task difficulty. However, performance on the primary tracking task was found to be poorer during periods when ISA responses were required, regardless of whether they were spoken or manual responses. This finding suggests that the usefulness of the technique is limited in comparison to less intrusive measures of workload.     

What do we mean by a ‘working posture’?

Abstract

No clear definition of ‘posture’ can be found in ergonomics literature. It may be regarded as the configuration of the body's head, trunk and limbs in space or as a ‘quasistatic biomechanical alignment’ (Rohmert and Mainzer 1986), depending on whether the particular context in which it is used is anatomical or biomechanical. The functional aspects of posture are highlighted by the definition of a ‘position adopted because it is appropriate for the task being performed’ (Corlett 1981). Yet, in any work situation, functional, geometric, and biomechanical aspects are as integral to the concept of posture as they are to the consequences for performance and comfort. A simple task posture model, describing the relationships between the various factors which influence working postures, is presented as an aid to workplace design, and two examples are given to show how the model can be applied to die demands of particular types of task. An analysis is also made of the factors involved in the exertion of force, including physiological, environmental, personal, and task factors, in order to give a better understanding of the influences of task and workplace on strength capability.     

Electromyography of the thigh muscles during lifting tasks in kneeling and squatting postures

Underground coal miners who work in low-seam mines frequently handle materials in kneeling or squatting postures. To assess quadriceps and hamstring muscle demands in these postures, nine participants performed lateral load transfers in kneeling and squatting postures, during which electromyographic (EMG) data were collected. EMG activity was obtained at five points throughout the transfer for three quadriceps muscles and two hamstring muscles from each thigh. ANOVA results indicated that EMG data for nine of 10 thigh muscles were affected by an interaction between posture and angular position of the load lifted (p < 0.001). Muscles of the right thigh were most active during the lifting portion of the task (lifting a block from the participant's right) and activity decreased as the block was transferred to the left. Left thigh muscles showed the opposite pattern. EMG activity for the majority of thigh muscles was affected by the size of the base of support provided by different postures, with lower EMG activity observed with a larger base of support and increased activity in postures where base of support was reduced (p < 0.05). Thigh EMG activity was lowest in postures with fully flexed knees, which may explain worker preference for this posture. However, such postures are also associated with increased risk of meniscal damage. STATEMENT OF RELEVANCE: Kneeling and squatting postures are sometimes used for manual lifting activities, but are associated with increased knee injury risk. This paper examines the EMG responses of knee extensors/flexors to lifting in these postures, discusses the impact of posture and kneepads on muscle recruitment and explores the implications for work in such postures.