Liesbeth Groenesteijn

Comparison of four specific dynamic office chairs with a conventional office chair: Impact upon muscle activation, physical activity and posture

Prolonged and static sitting postures provoke physical inactivity at VDU workplaces and are therefore discussed as risk factors for the musculoskeletal system. Manufacturers have designed specific dynamic office chairs featuring structural elements which promote dynamic sitting and therefore physical activity. The aim of the present study was to evaluate the effects of four specific dynamic chairs on erector spinae and trapezius EMG, postures/joint angles and physical activity intensity (PAI) compared to those of a conventional standard office chair. All chairs were fitted with sensors for measurement of the chair parameters (backrest inclination, forward and sideward seat pan inclination), and tested in the laboratory by 10 subjects performing 7 standardized office tasks and by another 12 subjects in the field during their normal office work. Muscle activation revealed no significant differences between the specific dynamic chairs and the reference chair. Analysis of postures/joint angles and PAI revealed only a few differences between the chairs, whereas the tasks performed strongly affected the measured muscle activation, postures and kinematics. The characteristic dynamic elements of each specific chair yielded significant differences in the measured chair parameters, but these characteristics did not appear to affect the sitting dynamics of the subjects performing their office tasks.

Effects of differences in office chair controls, seat and backrest angle design in relation to tasks.

In this study the influence of chair characteristics on comfort, discomfort, adjustment time and seat interface pressure is investigated during VDU and non-VDU tasks: The two investigated office chairs, both designed according to European and Dutch standards are different regarding: 1) seat cushioning and shape, 2) backrest angle and 3) controls. Thirty subjects in total, both male and female, participated in two experiments: twenty in the first and ten in the second. Significant differences are found for ease of adjustment and adjustment time of controls, independent of the tasks. Related to tasks, a significant difference was found for the backrest range of motion. For non-VDU tasks a larger range of backrest motion was preferred by 70% of the subjects. The chair design differences were most clear for comfort and adjustment time of controls, followed by comfort of backrest angle. No differences are found between seat pan comfort and discomfort, first impressions and peak interface pressure.

Identifying predictors of comfort and discomfort in using hand tools

The aim of the study was to identify predictors of comfort and discomfort in using hand tools. For this purpose, the comfort questionnaire for hand tools (CQH) was developed based on the results of a previous study. In the current study, four screwdrivers were evaluated on comfort (expected comfort at first sight and comfort after short time use) using the CQH and discomfort (local perceived discomfort). The results showed that expected comfort at first sight was predicted by aesthetics. Additionally, functionality and physical interaction, and adverse body effects were the major predictors of overall comfort after short time use. Discomfort was predicted by adverse body effects only. It is concluded that comfort and discomfort in using hand tools have partly the same underlying factors: discomfort feelings also affect the comfort experience.

Changing from batch to flow assembly in the production of emergency lighting devices

Current assembly enterprises are under a lot of pressure, as they are faced with increasing volume demands and product variations, needs for shorter delivery times and cost reduction. This pressure is likely to increase the pressure on individual workers. In many small to medium-sized enterprises (SMEs), we observe that traditional assembly concepts are no longer fulfilled. These are challenged to find other concepts to meet todays demands. In a company where emergency lighting devices are assembled in batches (large series of products are assembled step by step), we applied a participatory and integrative approach to set up a mixed flow assembly system including ergonomically designed work stations. In this paper, we describe the approach and the effects which were studied by a within-subject design. We observed an increase of 44% in productivity and a reduction in order lead time of 46%. The time that workers spent to added-value activities increased significantly from 74% to 92%, without any increase in postural and experienced loads. Instead, the workers experienced significantly less overall fatigue at the end of the day in the new situation. The results show the potential benefits of the approach for the many SMEs where products are assembled in batches and faced with the problem of meeting current production demands.

The effects of precision demands during a low intensity pinching task on muscle activation and load sharing of the fingers

High precision demands in manual tasks can be expected to cause more selective use of a part of the muscular synergy involved. To test this expectation, load sharing of the index finger and middle finger was investigated during a pinching task. Myoelectric activation of lower arm and neck-shoulder muscles was measured to see if overall level of effort was affected by precision demands. Ten healthy female subjects performed pinching tasks with three levels of force and three levels of precision demands. The force level did not significantly affect the relative contribution of the index and middle finger to the force. Higher precision demands, however, led to higher contribution of the index finger to the pinch force. Consequently, a more selective load of the forearm and hand occurs during tasks with high precision demands. The variability of the force contribution of the fingers increased during the task. No effects of precision demand on the activation of forearm and neck-shoulder muscles were found. Force level did affect the EMG parameters of several muscles. The effects were most apparent in the muscles responsible for the pinch force, the forearm muscles. Activation of these muscles was higher at higher force levels. In the trapezius muscle at the dominant side EMG amplitudes were lower at the high pinch force compared to the low force and median force conditions.

New ways of working: a proposed framework and literature review

The drive towards new ways of working is of great relevance to our modern world. Many companies and organizations have introduced aspects of this new approach in recent years, while many others are on the verge of doing so. The new way of working consists of a large variety of measures enabling flexibility in time and place Expectations are often high: those who embrace such innovations aim to reduce operating costs and create more productive employees. However, it is worth asking whether these expectations are realistic. To date, very little research has been done on how the introduction of new ways of working affects operational objectives. This article is aimed to provide an overview of the available knowledge of the effects of the new way of working concept through scientific research and by developing a clearly defined framework. Some of the most important findings are outlined.

Predicting passenger seat comfort and discomfort on the basis of human, context and seat characteristics: a literature review

Abstract This literature review focused on passenger seat comfort and discomfort in a human–product–context interaction. The relationships between anthropometric variables (human level), activities (context level), seat characteristics (product level) and the perception of comfort and discomfort were studied through mediating variables, such as body posture, movement and interface pressure. It is concluded that there are correlations between anthropometric variables and interface pressure variables, and that this relationship is affected by body posture. The results of studies on the correlation between pressure variables and passenger comfort and discomfort are not in line with each other. Only associations were found between the other variables (e.g. activities and seat characteristics). A conceptual model illustrates the results of the review, but relationships could not be quantified due to a lack of statistical evidence and large differences in research set-ups between the reviewed papers. Practitioner Summary: This literature review set out to quantify the relationships between human, context and seat characteristics, and comfort and discomfort experience of passenger seats, in order to build a predictive model that can support seat designers and purchasers to make informed decisions. However, statistical evidence is lacking from existing literature.

Effects of using dynamic office chairs on posture and EMG in standardized office tasks

In the paper a measuring system for the comparative posture and EMG analysis of office chairs is presented. With the system four specific dynamic office chairs that promote dynamic sitting and therefore aim to prevent musculoskeletal disorders (MSD), were analyzed in comparison to a reference chair in two different standardized tasks (intensive mouse use and sorting files). Exemplary results of the ongoing study suggest that postures and the electrical activities of the erector spinae and trapezius muscles depend more on the tasks performed than on the use of a particular type of office chair. This still has to be proved by statistical analysis.

Using both qualitative and quantitative types of research to design a comfortable television chair

This paper reports on a design and evaluation of a chair in which users can sit comfortably while watching a television screen. The design of this chair is based on requirements that were gathered from three studies with end-users in which their needs and wishes for this chair are explored. These three types of research study show that the chair to be designed should enable users to sit in a large variety of positions and support the body where it requires it. This means that the head, back, arms and legs should be supported in various positions. A full-scale prototype of this chair was built and evaluated with end-users. This evaluation shows that the designed chair enables users to sit in a large variety of positions. A moving arm support and an adjustable feet support contribute to different sitting positions. The designed chair is also rated as comfortable but the position of the head support and the lumbar support need better positioning. The study also shows that the three experiments used to gather end-user information were very valuable to arrive at a better design.

Activities, postures and comfort perception of train passengers as input for train seat design

Working in the train is a part of new ways of working. However, the ideal working position is unknown. Moreover, the ideal position for leisure and relaxing is also unknown. This article defines what activities train passengers mainly perform and which corresponding postures are seen. Based on the observations on actual train rides, four main activities could be identified: Reading, Staring/sleeping, Talking and Working on laptop. Working on laptop was the activity with the longest duration and talking had the shortest duration. Associated with these four activities, a top eight of different postures were observed. Except for headrest comfort, comfort scores were not significantly different between activities. The top eight corresponding postures combined with comfort scores showed that per activity different postures were observed and the comfort scores varied in relation to the combination of posture and activity. Nearly for all activities, the majority of passengers preferred adjustability options to fit the seat to the performed activity. Practitioner Summary: The article is created for insight into activities, postures and comfort of seated train passengers. The results of this study can be used for designing comfortable seating in the transportation industry (train passengers, bus and aircraft seats) and for semi-public spaces to enable optimal support for the user in its activities.