Validity of self-reporting and video-recording for measuring knee-straining work postures

The aim of this study was to compare the validity of self-reporting and video-recording as methods of measuring the duration of knee-straining work postures, and to evaluate the reproducibility of timings of the video-recordings. Thirty-nine carpenters and 33 floorlayers were video-filmed while working, and were asked immediately afterwards to quantify the amount of time spent in knee-straining positions. The investigators recorded the periods of knee-straining work with a stopwatch during playback of the video-film, and the agreement between the two investigators' measurements was studied in 13 pairs of measurements. The video-observation method was very effective for timing knee-strain work. Furthermore, Spearman's correlation coefficient (0.88) indicated a good association between observed and self-reported knee-straining work. Estimation of self-reported knee-straining work collected by interview showed good correlation with measurements of video-recordings. When judging the repeatability of timings of knee-straining work from the video-recordings, a high level of agreement was seen between the two observers in the 13 dual measurements of time spent in knee-straining work positions.     

Validity of self-reported duration of work postures obtained by interview

The aim of the study was to validate interview data concerning the duration of four work postures (1) sitting, (2) standing/walking with hands above shoulder level, (3) standing/walking with hands between shoulder and knuckle level, and (4) standing/walking with hands below knuckle level. The self-reported time spent in each posture was tested in relation to observations and technical measurements in 20 subjects during two full working days. The linear relationships between self-reports and observations were strong for the three postures; sitting (r²=0.55), hands above shoulder level (r²=0.58) and hands below knuckle level (r²=0.69). Thus, using this interview technique, self-reports concerning time spent in (1) sitting, (2) standing/walking with hands above shoulder level and, (3) standing/walking with hands below knuckle level may be accurate enough for studying these work postures in epidemiological studies.     

Test-retest repeatability of the Strain Index

Fifteen raters individually, and in five teams of three, evaluated the test-retest repeatability of published data collection and rating methods of the Strain Index by analyzing 61 job video files twice over a 5-month period. Raters estimated average and peak hand forces, measured Duration of Exertion, cycle time, and exertions per job cycle, calculated percent Duration of Exertion and Efforts per Minute, and assigned ratings for five of the six Strain Index task variables. Twelve additional jobs were analyzed to determine Strain Index Score and hazard classification. Intraclass correlation (ICC) coefficients for task variable ratings and accompanying data ranged from 0.66 to 0.95 for both individuals and teams. The Strain Index Score ICC(2,1) for individuals and teams were 0.56 and 0.82, respectively. Intra-rater reliability for the hazard classification was 0.81 for individuals and 0.88 for teams. The results indicate that the Strain Index has good test-retest reliability.     

Test-retest reliability and concurrent validity of a web-based questionnaire measuring workstation and individual correlates of work postures during computer work

INTRODUCTION: "Ergonomic" questionnaires are widely used in epidemiological field studies to study the association between workstation characteristics, work posture and musculoskeletal disorders among office workers. Findings have been inconsistent regarding the putative adverse effect of work postures. Underestimation of the true association might be present in studies due to misclassification of subjects to risk (i.e. exposed to non-neutral working postures) and no-risk categories (i.e. not exposed to non-neutral working postures) based on questionnaire responses. The objective of this study was to estimate the amount of misclassification resulting from the use of questionnaires. METHODS: Test-retest reliability and concurrent validity of a newly developed questionnaire was assessed. This questionnaire collects data on workstation characteristics and on individual characteristics during computer work (i.e. work postures, movements and habits). Pictures were added where possible to provide visual guidance. The study population consisted of 84 office workers of a research department. They filled out the questionnaire on the Internet twice, with an in-between period of 2 weeks. For a subgroup of workers (n=38), additional on-site observations and multiple manual goniometer measurements were performed. RESULTS: Percentage agreement ranged between 71% and 100% for the test-retest analysis, between 31% and 100% for the comparison between questionnaire and on-site observation, and between 26% and 71% for the comparison between questionnaire and manual goniometer measurements. For 9 out of 12 tested items, the percentage agreement between questionnaire and manual goniometer measurements was below 50%. CONCLUSIONS: The questionnaire collects reliable data on workstation characteristics and some individual characteristics during computer work (i.e. work movements and habits), but does not seem to be useful to collect data on work postures during computer work in epidemiological field studies among office workers.     

基于VB的UCAM系列应变仪测控软件设计

为解决在我国结构测量领域广泛应用的UCAM-70A应变测量系统存在的缺乏合适的上位机测控软件导致测量及后处理效率低下的技术问题,通过对UCAM-70A技术手册的研究和串口侦测手段,掌握其串口通讯协议规则,运用Visual Basic编程工具结合第三方表格控件及数据库组件开发了基于PC机的上位机测控软件,实现了便捷的参数设置、高效的测量与后处理功能,极大地提升了测量及后处理效率及数据可靠性。并通过对UCAM-60B等其它系列应变仪通讯协议的比较研究,对软件的通讯协议部分作局部修改后可广泛适用于UCAM系列应变仪,该软件设计方法及成果在结构监测领域具有借鉴及推广应用价值。     

Repeatability of measurement in determining stature in sitting and standing postures

The aim of this study was to determine the effect of sitting and standing postures on the repeatability of a stadiometer designed to detect small variations in spinal length. Two groups of ten healthy subjects, with no previous or known history of back problems, participated in this study. One group was measured in the standing posture, while the other group was measured in a sitting posture. All subjects gave informed consent to participate in this study. Subjects had a set of landmarks defining the spinal contour marked on their backs and then stood in the stadiometer for three series of ten measurements to be performed. At the end of each measurement, the subjects were requested to move away from and then be repositioned in the stadiometer. Subjects improved the repeatability across the measurement series. At the end of the second measurement series, all subjects presented mean standard deviations of 0.43±0.08 mm (range 0.300.50 mm) in the standing posture. In the sitting posture, deviations of less than 0.05 mm were obtained only at the end of the third measurement series (0.48±0.08 mm; range 0.340.62 mm), suggesting that this posture required three measurement series before repeatable measurements could be assured rather than two in the standing posture.     

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.     

Biomechanical aspects of occupational neck postures during dental work

A typical occupational risk factor for developing neck symptoms is prolonged flexion of the cervical spine. The present aim was to determine joint moments and muscle activity of the neck during forward flexion of the cervical spine to evaluate the load in the neck region. Three dimensional video (3-D) and surface electromyography (EMG) from the splenius muscles were recorded in two common work postures. Using a 3-D static link segment model, moments at the atlanto-occipital (A-O) joint and the seventh cervical-first thoracal (C7-T1) joint were estimated. Maximal extension moments were estimated from maximal neck extension strength. Extension moments at the C7-T1 joint were significantly higher for a highly flexed position (45% of max) compared to a moderately flexed position (32% of max), but remained unchanged at the A-O joint (40% of max). The mean RMS amplitude was 9% of maximal EMG in both positions (no bilateral differences). This difference between mechanical load and muscle load indicates that EMG may seriously underestimate the total loads of the tissue. Lateral flexion influenced the lateral flexion moment while rotation did not influence the rotation moment. The study demonstrates the importance of quantification of joint loads in occupational risk assessment of the neck.

Relevance to industry

3-D biomechanical calculations provide information on the mechanical load during work. Because EMG may underestimate total tissue load, calculations of joint moments in combination with information on muscle activity and strength are necessary to estimate different tissue loading of significance for overall risk identification.     

Using Kinect™ sensor in observational methods for assessing postures at work

This paper examines the potential use of Kinect™ range sensor in observational methods for assessing postural loads. Range sensors can detect the position of the joints at high sampling rates without attaching sensors or markers directly to the subject under study. First, a computerized OWAS ergonomic assessment system was implemented to permit the data acquisition from Kinect™ and data processing in order to identify the risk level of each recorded postures. Output data were compared with the results provided by human observers, and were used to determine the influence of the sensor view angle relative to the worker. The tests show high inter-method agreement in the classification of risk categories (Proportion agreement index = 0.89 κ = 0.83) when the tracked subject is facing the sensor. The camera's point of view relative to the position of the tracked subject significantly affects the correct classification of the postures. Although the results are promising, some aspects involved in the use of low-cost range sensors should be further studied for their use in real environments.     

Effect of alternating postures on cognitive performance for healthy people performing sedentary work

Prolonged sitting is a risk factor for several diseases and the prevalence of worksite-based interventions such as sit-to-stand workstations is increasing. Although their impact on sedentary behaviour has been regularly investigated, the effect of working in alternating body postures on cognitive performance is unclear. To address this uncertainty, 45 students participated in a two-arm, randomised controlled cross-over trial under laboratory conditions. Subjects executed validated cognitive tests (working speed, reaction time, concentration performance) either in sitting or alternating working postures on two separate days (ClinicalTrials.gov Identifier: NCT02863731). MANOVA results showed no significant difference in cognitive performance between trials executed in alternating, standing or sitting postures. Perceived workload did not differ between sitting and alternating days. Repeated measures ANOVA revealed significant learning effects regarding concentration performance and working speed for both days. These results suggest that working posture did not affect cognitive performance in the short term.

Practitioner Summary: Prior reports indicated health-related benefits based on alternated (sit/stand) body postures. Nevertheless, their effect on cognitive performance is unknown. This randomised controlled trial showed that working in alternating body postures did not influence reaction time, concentration performance, working speed or workload perception in the short term.     

Inter- and intra-tester reliability when measuring seated spinal postures with inertial sensors

Prolonged awkward sitting postures may be associated with neck or back pain, but it is often unclear which specific postures cause most problems and which mechanisms that may underlie the pain. In order to increase the knowledge in this field, it seems crucial first of all to be able to analyse, in depth, different seated spinal postures. A problem is however the lack of reliable and direct measurement methods of the posture, especially for sitting. Recently developed systems with inertial sensor attached along the spine have potential for this purpose. The aim of the present study was therefore to test the reliability of using such a system to assess various seated postures.     

Implementation programme of the Swedish ordinance concerning work postures and working movements

Ergonomically-rclated occupational injuries have been increasingly recognized in Sweden. The official injury statistics show that ergonomically-related injuries accounted for about 20% of all reported occupational injuries (ISA 1985). On 1 January 1984 an ordinance concerning work postures and working movements was passed. It was built upon and is a complement to the Work Environment Act of 1978. There are in Sweden about 400 labour inspectors in 19 regional Labour Inspectorates, to ensure among other things that rules concerning the occupational environment are complied with at the workplace level. Sweden has a working population of about 4 million people. To implement the above-mentioned ordinance, a 2-year implementation programme was set up. The labour inspectors first identified major areas with severe non-ergonomic working conditions, in all areas of work. Six typical work situations were then selected and the inspectors were asked to pay special attention to them, and to intensify their efforts on these work situations, during a 10-month period. Eighteen months after the ordinance came into effect, the implementation programme and the labour inspectorate input was evaluated. The preliminary results showed an overall increase in ergonomic awareness. The ordinance was distributed in about 120000 copies, and the labour inspectors found it to be a useful tool in their work. Citations concerning ergonomics had increased considerably during this period.     

Physiological strain during kitchen work in relation to maximal and task-specific peak values

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO₂) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO₂ and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO₂ for the male and the female subjects during kitchen work was 0.65±0.16 l min^-1. This corresponded to 24% of VO_2max and to 41% of VO_2peak during arm-cranking. The difference was significant (p<0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min^-1. It corresponded to 55% of HRmax and 67% of HR during arm-cranking (p<0.05). The present study shows that the peak relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO_2peak instead of the VO_2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.     

A user interface specification for a program debugging and measuring environment

A high level of complexity is involved in program dynamics. A number of tools have been developed to assist the programmer in mastering this complexity in the various phases of software development. However, these tools are specifically oriented towards the monitoring of particular aspects of program behaviour. This paper presents the results of a systematic attempt at defining the user interface to an environment for program debugging, program performance evaluation and program structure analysis. This environment can be used to implement many common debugging techniques, and to evaluate important program performance indexes and program structure statistics. It supports both sequential and concurrent block-oriented high-level languages.     

The investigation and evaluation of work and workplaces

Most workplaces and jobs demonstrate a mis-match in relation to the workers involved with them. To assess this we must measure the work loads, the workplace characteristics, the work performance, the interactions of these with the workers and the consequences for them. Changes are devised as a result of these measures, and insofar as the measures fall short of the comprehensive list above, then the modifications may be sub-optimal as important aspects are not taken into account. The results of the changes, too, need a similar comprehensive assessment.

The paper will follow through the process of investigating industrial workplaces. It will briefly introduce techniques developed for assessing a range of aspects and how they lead to the development of changes. The view of the worker as a total person will be supported by proposals for the combined evaluation of the task, the workplace etc and the state and effects of the social environment, with suggestions for their economic evaluation.     

Work postures and strain of workers in nordic forest work: A selective review

In this paper, ergonomic characteristics of forest work and particularly the strain related to work postures are reviewed. Both in manual and mechanized forest work, working postures play an important role, separately and combined with other strain factors. The combined effect mmay be worse than those of single factors. Examples of such combinations include bad work postures in conjunction with heavy lifting while cutting or during maintenance of machines and whole-body vibration and repetitive steering work while operating machines. The situation becomes even more complicated when the whole work environment is taken into consideration. Work postures often contribute to strains that have far-reaching effects, but have no immediate impact on the worker's behaviour or injury rates. Even in highly mechanized forest work, problems still exist despite extensive development of cabs. Some new technical and design solutions have recently been introduced.     

Non-invasive measurement of three dimensional joint angles: Development and evaluation of a computer-aided system for measuring working postures

A new system was developed to analyze work posture in order to measure the three-dimensional body angles required as inputs to a biomechanical strength prediction model. This system was non-invasive and required no interference with work activities. Videotape was used at the job site to establish a permanent record of postural activity and a computer-aided digitization system was used to measure body angles in the laboratory.

An experiment using five subjects and ten work postures was performed to investigate the nature and significance of measurement errors when using the new system. The results of this experiment revealed that, in general, subjects were able to distinguish different work postures; and that inter-subject bias was not significant. Measurement error was small for most joint angles and could be reduced further by enhancements to the system hardware. The system was found to be a useful tool for determining three-dimensional body angles when direct measurements are infeasible.     

Assessment of work postures and movements using a video-based observation method and direct technical measurements

The aim was to study postures and movements during repetitive work using video-based observations and direct technical measurements (inclinometers and goniometers). A total of 21 healthy women from a poultry processing plant volunteered. Neck flexion > 20 degrees was registered during 92% of the recorded time with the observation method, while the corresponding value measured with the inclinometer was 65%. Different reference positions and different measured variables apparently contributed to the differences between the methods. Mean wrist position was measured to be 0 degrees in flexion-extension and 19 degrees in ulnar deviation. Differences between the methods in the registered hand positions were small. The number of repetitive movements/minute and mean power frequency (MPF) of the electrogoniometer data was significantly related, showing both variables to be relevant measures of repetitiveness. In conclusion, the observation method and the technical measurements supplemented each other well. A reduction in class categories was suggested for future observation methods.     

A method for measuring work interference in surgical teams

To enhance surgical systems we need to manage the performance of the teams that comprise them. To do this we must measure the properties and processes of teams and account for the demands and conditions of their work. Recent research shows that observation is a potentially valuable method of measurement, but its potential application in surgery remains unclear. In this study of laparoscopic cholecystectomy, an observer applied observational measures of teamwork in the operating theatre and recorded intra-operative interference from observed distraction and interruption. Results showed that it was feasible to observe a broad scope of teamwork and to reveal the frequency and source of work interference. However, the measures were necessarily selective and so limited in their analysis of the conditions and events that might interfere with the collective work in surgery. Such measures may however prove useful when applied in conjunction with other methods of measurement and utilised as performance feedback data.