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Evaluation of a forward-sloping chair
Abstract
A methodology of chair evaluation developed earlier was applied to a novel, forward-sloping chair. Two groups of six subjects each were trained to use the chair and then given an evaluation session of [Formula: see text] . The chair elicited mixed responses, with complaints of leg discomfort from terminal users and of entry and egress from typists. Overall, the chair was no better than conventional chairs and could be worse than well-designed conventional office chairs.
... Discomfort with the use of a conventional seat with a forward slope of 15°P roblems of forward slip, dragging of clothing, and increased weight on the feet (Bendix & Biering-Sorenson, 1983;Bendix, Winkel, & Flemming, 1985;Graf, Guggenbuhl, & Krueger, 1993). Discomfort with the use of a sit kneel seat Dif culty with ingress/egress lack of movement for chair and occupant, discomfort on shins (Drury & Francher, 1985), lack of backrest creating increased erector spinae activity, and kyphosis with use past 10 seconds (Lander, Korbon, DeGood, & Rowlingson, 1987). may be eliminated by elevating the monitor. ...
... This position is likened to the erect posture assumed by horse riders, the degree of hip exion allowing maintenance of the lumbar lordosis despite the lack of backrest ( Mandal 1975( Mandal , 1976. Lack of comfort is re ected by poor subject preference studies comparing the kneel-sit chair with more conventional seating ( Bendix, 1988;Bendix, Winkel, & Flemming, 1985;Drury & Francher, 1985;Lander, Korbon, DeGood, & Rowlingson, 1987 ). However, current designs of forward tilt chairs, including kneel-sit, have addressed these problems ( see Table 4 ), now rendering forward tilt seating a viable and posturally healthy manner of sitting. ...
Prolonged sitting with poor posture is associated with the development of lower
back pain. Ergonomic texts for physiotherapists contain diverging and confusing
views on recommended postures for the lumbar spine when seated that will
promote postural health and optimal functioning of the lumbar spine. A review of
the literature reveals that proponents of both the lordosed and kyphosed lumbar
seated position use similar arguments with contradictory conclusions. The
arguments of those advocating the kyphosed lumbar seated posture are, however,
often anecdotal and unsubstantiated by research. This paper evaluates the
con icting views and concludes that the lordosed seated posture, regularly
interspersed with movement, is the optimal sitting posture and assists in
maintaining lumbar postural health and preventing low back pain.
... The BMC was introduced based on the assumption that a semi-kneeling position can help in the reduction of postural stress, fatigue, and discomfort (Drury & Francher, 1985). A number of studies were performed to demonstrate the overall effect of BMCs using measurements of trunk muscle EMG activity (Bennett, Gillis, Portney, Romanow, & Sanchez, 1989;Lander et al., 1987), pedal cutaneous blood flow (Lander et al., 1987), comfort ratings (Drury & Francher, 1985), and changes in lumbar curvatures (Bennett et al., 1989;Frey & Tecklin, 1986;Lander et al., 1987;Link et al., 1990). ...
... The BMC was introduced based on the assumption that a semi-kneeling position can help in the reduction of postural stress, fatigue, and discomfort (Drury & Francher, 1985). A number of studies were performed to demonstrate the overall effect of BMCs using measurements of trunk muscle EMG activity (Bennett, Gillis, Portney, Romanow, & Sanchez, 1989;Lander et al., 1987), pedal cutaneous blood flow (Lander et al., 1987), comfort ratings (Drury & Francher, 1985), and changes in lumbar curvatures (Bennett et al., 1989;Frey & Tecklin, 1986;Lander et al., 1987;Link et al., 1990). Although the results of some of these studies demonstrated that sitting on the BMC is associated with nearly normal lordosis (Frey & Tecklin, 1986;Link et al., 1990) and increased pedal cutaneous blood flow (Lander et al., 1987), it was also shown that BMC had an adverse effect on the cervical and lumbar paraspinal muscle EMG activity and comfort ratings compared with a standard conventional chair (Lander et al., 1987). ...
The objective of this study was to determine if a forward-tilted seat and the resultant semi-kneeling body position associated with sitting on the Balans Multi Chair (BMC) affect postural control in sitting. Nine healthy subjects were seated on either the BMC or a regular (REG) chair with their arms extended. They were instructed to induce self-initiated body perturbations in four different directions by exerting brief pulses of force against a stationary frame positioned in front of them. Electromyographic (EMG) activities of trunk and leg muscles were recorded before and during the perturbations. The results show that sitting on both types of chairs was associated with anticipatory activation of trunk and upper leg muscles. In contrast, anticipatory activation of distal muscles was observed while sitting only on the REG chair and was absent while sitting on the BMC. The outcome of the study suggests that although the forward-tilting seat and semi-kneeling body position might help in preserving a normal lordosis, it is not associated with anticipatory activation of lower leg muscles, which might reduce the ability of an individual to counteract self-initiated body perturbations. These findings stress the important role of chair designs in the control of sitting posture.
... Relatively recent breakthroughs in seating design are a proof of the fertility of this field of research. Drury and Francher (1985) used the term "conventional" as opposed to the forward sloped chair. Lander, Korbon, DeGood and Rowlingson (1987), comparing popliteal blood flow and muscular activity for seating posture in Balans chair and usual office chair, have used the term "conventional" for the latter. ...
A classification of seating postures is necessary for a systemic approach in chair ergonomics. The methodology used criteria for differentiating and grouping seating variants into categories. Morphological (hip flexion, trunk inclination, lumbar lordosis, and muscular involvement), functional (the relationship with working areas), and cultural criteria (conventional and unconventional) were brought into discussion with arguments for validation. Each valid criterion describes, by its degree of expression, two categories. Cases of particular interest were found, when two or more criteria behave interdependently. The combined categories, defined by several criteria, were used to build up a classification. Discussions resumed conventions and described multi-criteria categories.
... slope and vertical height of the seat. [24][25][26] Anderson and Ortengren 27 examined the effect of backrest angle in supported sitting and found that it has the greatest effect on reducing EMG of the erector spinae. They concluded that increasing the backward lean of the backrest results in less erector spinae activity. ...
Background:
The chair influences the position of the user in relation to his or her devices. Prolonged static sitting is a frequently mentioned risk factor for low back pain. Seat design, thus, plays an important role in the study of human sitting. Quantitative information is needed on what happens to body when one sits in chairs with different seat depth.
Objective:
To determine the myoelectric activity (EMG) of individual lumbar erector spinae muscles after sitting in chairs with different seat pan depth.
Methods:
EMG recordings were taken using surface electrodes placed on the lumbar erector spine muscles of 25 normal, volunteer subjects. EMG recordings for muscle activity were made while the study participants were in a comfortable position and performed the required tasks. The experiments investigated with 3 seat depths according to the 5th, 50th and 95th percentiles of the buttock popliteal length. The recorded EMG data were normalized to the maximal voluntary contraction. The mean EMG recording was calculated for each of the 3 chairs tested. A mixed model was used to assess the differences among the situations.
Results:
A significant (p<0.05) difference was observed between the mean EMG recordings for the 3 tested seat pan depths. EMG activity was higher in seats with the 5th and 95th percentiles compared with that for the seat with 50th percentile of buttock popliteal length depth.
Conclusion:
The seat pan depth used during a comfortable position has a significant effect on the level of myoelectric activity in the lumbar erector spinal muscles. The finding of this study may contribute to our understanding of the biomechanics of sitting.
... Idle Accelerating From Section C, respondents were asked to circle any areas of body parts where they feel discomfort or pain during or after driving on a Nordic body diagram as depicted in Figure 2. Nordic body diagram or a body map is usually found in seat study [4,7,17,18]. As shown in Figure 3, the respondents were required to tick the degree of discomfort that they experienced on fourteen body parts. ...
Satu tinjauan berasaskan soal selidik atas talian telah dijalankan untuk mendapatkan maklumat berkenaan ketidakselesaan pemanduan kenderaan penumpang pemandu Malaysia. Faktor ketidakselesaan yang diselidiki ialah hingar, getaran dan tempat duduk pemandu. Untuk hingar dan getaran, didapati bahawa responden perempuan lebih tidak selesa untuk faktor berkaitan dengan getaran manakala responden lelaki lebih tidak selesa untuk faktor berkaitan hingar. Tiada perbezaan ketara antara ketidakselesaan untuk hingar dan getaran ketika pegun mahupun memecut. Berkenaan ketidakselesaan tempat duduk pemandu, didapati bahawa lebih ramai responden mengalami ketidakselesaan atau kesakitan di bahagian atas belakang. Perbezaan untuk respon ketidakselesaan bagi bahagian badan berlainan antara pemandu lelaki dan perempuan terutamanya disebabkan oleh faktor antropometri. Kedua–dua pemandu lelaki dan perempuan mengalami ketidakselesaan akibat hingar, getaran dan tempat duduk tetapi dengan sensitiviti yang berbeza untuk faktor dan bahagian tubuh yang berlainan. Daripada kajian ini, tiada perbezaan ketara yang dijumpai untuk kesuluruhan ketidakselesaan antara kedua–dua jantina. Meskipun ia berbentuk laporan kendiri, keputusannya adalah selari dengan penemuan daripada kajian–kajian literatur. Kata kunci: Hingar; getaran; tempat duduk pemandu; ketidakselesaan; tinjauan; soal selidik An online questionnaire–based survey was conducted to gather information regarding driving discomfort of Malaysian passengers’ vehicle driver. The discomfort factors investigated were noise, vibration and driver’s seat. For the noise and vibration, it was found that women respondents feel more discomfort for vibration related factors while men respondents feel more discomfort for noise related factors. There was no significant difference between discomfort for noise and vibration during idle or accelerating conditions. Regarding driver’s seat discomfort, it was found that more respondents had experienced discomfort or pain at the upper back. The differences of discomfort responses for different body parts between men and women drivers were mainly caused by anthropometrical factor. Both men and women drivers experience noise, vibration and seat discomfort, however with different levels of sensitivity for different factors and body parts. From this study, no significant difference was found on overall discomfort between genders. Although it is self–reported, the result is in–line with the findings from the literatures. Key words: Noise; vibration; driver seat; discomfort; survey; questionnaire
... Various seats have been designed adopting these principles -most notably, the 'kneeling' chair. Evaluation of such seats has been largely confined to examining user comfort (Drury and Flancher, 1985). Such investigations showed that users of the kneeling chair complained of increased discomfort in the knees, thereby limiting its usefulness. ...
Many upper limb functions are performed in a sitting position. However, if seating is inadequate and poorly designed, back pain and reduced upper limb control may result. This study investigates pelvic posture and performance in an upper limb task.
In total, 15 normal healthy volunteers (aged 18–30 years) were seated in posterior and anterior pelvic tilt positions and performed a simple upper limb task. The parameters measured were electromyography of the lumbar paravertebral muscles, time taken to complete the task and the task error rate. The data were analysed by repeated measures analysis of variance (ANOVA) and post-hoc t tests. The results indicate that, when seated in an anterior pelvic tilt position, the error rate decreased (P=0.013) and the electrical activity increased (P=0.008). The time taken to complete the task was not significantly different.
Since the error rate decreased when seated in the anterior pelvic tilt position, it might be concluded that this posture facilitated task skill. It is suggested that the increase in electrical activity is related to the increased load on the lumbar muscles in maintaining the posture. This study's generalizability is limited, with small subject numbers and the use of a non-functional task. It is, however, a beginning in addressing the interrelationship between the seated posture and skilled upper limb performance.
... The literatures showed previous sitting comfort surveys were based on working chairs meant for offices, industry or schools (Drury and Coury 1982;Drury and Francher 1985;Helander and Zhang 1997). Helander and Zhang (1997) reported that they had used subjective evaluation tools such as General Comfort Rating (GCR) by Shackel et al. (1969), Body Part Discomfort (BPD Scale) by Corlett and Bishop (1976) and Chair Evalua-tion Checklist (CEC) by Zhang et al. (1996) for assessment of chair comfort/discomfort. ...
Subjective evaluation has always been regarded as a branch of social science research. Hence, in scientific and especially engineering points of view, its development is always taken for granted despite the importance of its effects on the design and development decisions. In the past, at least two automotive seat survey questionnaires have been developed with high statistical validity and reliability. Nonetheless, both were not local while subjective perception very much depends on demographic background factors. It is felt that since vehicle seat comfort is an important aspect in a seat design, a local sense should be put into the survey that is used as the subjective tool. The proposed vehicle seat discomfort survey questionnaire was developed in dual languages; English and Malay. Malay language is the national language of Malaysia, where the survey was tested. Beside inputs from literatures, key informant interviews helped in establishing the appropriate terms used as survey items. Three experimental runs on two different seats by 22 paid subjects showed that the developed questionnaire is reliable and valid. Furthermore, criterion validity analysis on the survey and previously developed survey showed significant correlation at 0.01 significance level.
... It is also believed that prolonged sitting (Bendix, 1994;Kelsey and Hardy, 1975) in a slouched or kyphotic posture is closely linked with the incidence of low back pain (Keegan, 1953). Many researchers have investigated the effects of a seat on body posture (Bendix and Beiring-Sorenson, 1983;Branton, 1969;Bridger, 1988;Drury and Francher, 1985;Frey and Tecklin, 1986;Mandal, 1987). Related studies indicate that flat or rearward sloping seats promote lumbar kyphosis, while forward sloping seats preserve the lumbar lordosis. ...
Forward sloping seats are universally accepted based on their increased trunk-thigh angle during sitting. However, these seats are not preferred by some individuals due to reasons such as excessive pressure on knees, difficulties during ingress and egress, and postural fixity during sitting. Some researchers have claimed that forward sloped sitting preserves the lumbar lordosis, thereby making it more comfortable for the sitter. This claim has not been validated across all populations and, therefore, appears to have some disagreement among researchers. In this study, spinal shape during standing and sitting in forward sloping chairs is measured and quantified using a three-dimensional sonic digitizer. Twenty subjects (ten Hong Kong Chinese and ten Indian) have participated in the experiment. Fifteen points on the spine are digitized during standing and sitting in a forward-sloping seat with trunk-thigh angles of 70 degrees, 80 degrees, 90 degrees, 100 degrees, 110 degrees, and 120 degrees. Different measures are used to analyze and differentiate the spinal shape. The correlation between the length of spine during standing and a subject's height is low, but significant. The behavior of the spinal shape change during sitting differs between the populations as shown by the maximum lumbar and maximum thoracic deviations. The Indian subjects seem to approach the standing curvatures in the thoracic region during 30 degrees forward sloping sitting. The Hong Kong Chinese subjects, on the other hand, do not show any resemblance to the standing curvatures during forward sloping sitting. One possible reason could be the differences in arch angle between the two populations. The variations in spinal shape among subjects appear to be similar within a population.
... Hence the seat pan is an important variable in seat design. However, the aspects of a seat pan that have been researched in the past have been somewhat limited to contouring or cushioning in relation to interface pressures and comfort (Gross et al., 1994) and seat pan slope (Bendix and Biering-Sorenson, 1983;Drury and Francher, 1985;Mandal, 1976;Michel and Helander, 1994). Thus, it is not surprising that Renae et al. (1995) found that the seat pan ranked as the number one aspect needing improvement. ...
Even though the seat pan carries most of the weight during sitting, the number of studies investigating the different aspects of the sitting area are limited. Seat depth has been based on anthropometry or the so-called industry practice. The relevance of the widely used seat depth measure is thus questionable. A methodology has been developed to evaluate the useful seat depth for a target population. The methodology is found to be reliable and valid based on both objective and subjective measurements. A chair with an “adjustable” seat depth was designed and developed for this purpose. A total of 30 Chinese students were tested. The objective measure was the seat edge protrusion when seated. Eight seat features were rated using a 5-point scale. The results show that the seat depth's of 30.4 and 38 cm are significantly different, with the seat depth of 38 cm being on the “long side”. In addition, the objective measure of seat edge protrusion indicated that a seat depth of 31–33 cm is adequate for the South China region Chinese population. Based on the subjective ratings and the objective measure developed, it may be concluded that a seat depth of 31–33 cm is appropriate for the same population.Relevance to industryAnthropometry alone is not sufficient for the design of seats. The differing sensitivity in the buttock and thigh areas is an indication that chairs should be designed and selected depending on the population under consideration. The need for having chairs of variable depth has to be recognized especially during long periods of sitting.
... (1990) this was the posture of least constraint of the hip joint with the lumbar spine and pelvis in the middle of their ranges. Sitting on the floor is generally unacceptable in western society and it is interesting to observe that kneeling has recently been implemented in a more acceptable form (the 'Balans' chair) -as a piece of furniture which lifts the user off the floor to desk height (for evaluations of this concept see Drury and Francher, 1985;Frey and Tecklin, 1986;Bridger, 1988). ...
This paper presents a broad review of some fundamental aspects of posture in terms of structure, function and control (including dysfunction and postural behaviour) and attempts to derive implications for ergonomics. It begins by reviewing research on the anatomical basis of the upright bipedal posture in man and its evolutionary development, based on recent fossil discoveries.Relevant aspects of the anatomy of the spine, pelvis and hip are then reviewed together with some developmental aspects of posture and a consideration of postural faults and muscle balance gleaned from the clinical literature. Further clinical aspects are discussed to introduce the concepts of postural control, feedback and postural behaviour. Finally, some aspects of cross-cultural postural variation are briefly reviewed.It is concluded that empirical research on posture and effective workspace design can benefit from a consideration of these fundamental aspects of posture. Much of modern design practice would appear to be built around a limited set of postural stereotypes which are probably culturally biased and do not reflect the true limitations and possibilities of human anatomy. Whether improved designs can be implemented on the basis of these fundamentals is both an empirical question and a challenge to the ingenuity of designers.
... Several authors have described how the form of a seat influences the posture of the body, particularly the spine (for example, Bendix and Beiring-Sorensen, 1983;Bridger, 1988;Drury and Francher, 1985;Frey and Tecklin, 1986;Mandai, 1981Mandai, , 1982. This re-\ search generally indicates that lumbar lordosis tends to be abolished when chairs with flat or rearward-sloping seats are used, whereas chairs with forward-sloping seats tend to preserve the lordosis. ...
Lumbar and thoracic spinal angles of 25 male and 25 female subjects were measured in four sitting postures, with standing angles used as reference. Subjects sat with either 90 deg or 65 deg of hip flexion on either flat or forward-sloping seats. Lumbar kyphosis was greatest when the flat seat/90-deg posture was adopted and least when the sloping seat/65-deg posture was adopted. The opposite was observed for the thoracic angles, and intermediate results were observed for the other two sitting postures. No statistically significant interactions were observed among seat slope, hip flexion, and subject sex. The findings are discussed with reference to the anatomy of sitting and factors influencing pelvic tilt and the implications for the ergonomic design of chairs.
... A number of authors have reported that the effects of forward-sloping chairs on spinal posture (inferred from measurements of the shape of the back) are small or not readily apparent (e.g., Drury and Francher, 1985). Bridger (1988) reported wide variation in subjects' postural adaptation to a forwardsloping chair, citing task variables and individual differences as possible contributory factors. ...
The spinal angles of 25 female subjects were measured in standing and in four different sitting postures with various trunk-thigh angles. Additionally, measurements of hip and lumbar mobility were made in an attempt to relate mobility to spinal curvature in the different sitting postures. Lumbar curvature was observed to decrease as the trunk-thigh angle decreased across the different sitting postures, and reduction in curvature was associated with hip mobility. An exploratory analysis of interrelationships among hip mobility, spinal mobility, and spinal curvature was also carried out. A significant correlation between lumbar and thoracic angular deviations in standing and hip flexion/extension range was obtained. The findings are discussed with reference to theories of sitting posture and the influence of hip joint mobility on postural adaptations to furniture. Further investigations, including studies of male subjects, are indicated.
... Exclusion criteria included past or current back pain, or cardiovascular disease. The session format included: Collection of demographic data An explanation/demonstration of the principles and use of the ETV A supervised 'training period' as used by Drury and Francher (1985) to allow subjects time to adjust to the ETV An evaluation session consisting of a complete wheelchair to showerchair and showerchair to wheelchair transfer using the ETV. This was immediately followed by a structured interview conducted by the researcher to assess safety, comfort and performance. ...
This study evaluated a Patient Handling Device (PHD) called the Elevate and Transfer Vehicle (ETV). The ETV works on the principle of leverage to transfer a patient from one seated position to another. Three types of product evaluation were used: expert appraisal; user trials; and performance tests. Expert appraisal was conducted by a panel of 11 people including an ergonomist, an industrial designer, two engineers, including one employed as an academic in a School of Mechanical, Manufacturing and Medical Engineering, and seven health professionals. The experts evaluated the ETV using a checklist and group discussions. They generally agreed that the advantages of the ETV tested were it's simplicity, the convenient position to adjust clothing for toileting and the need for only one carer. They noted comfort, security of straps, centre of gravity and manoeuvrability as the main areas for improvement. User trials consisted of nine male and nine female volunteer users assigned to carer/patient pairs. Following a training period, each user subjectively evaluated the ETV by structured interview. User trial results indicated ease of use, prevention of back injuries in carers and minimal body contact were advantages of the ETV. The main problems with using the ETV appeared to be the inadequate 'prop' and straps, the 'jolt' and lack of dignity for the patient. Several critical performance tests were conducted to determine compliance to Australian Standards for design. Areas of non-compliance included strength of frame and static stability. The findings suggest that most of the identified problems of the ETV could be overcome with minor design improvements. The general consensus of participants was to keep the design simple, maintain fast transfers and maintain the position of the patient to enable ease of clothing adjustment for toileting.
The concept of androgynous or gender-neutral fashion is known for its distinctive attribute that blends both conventional masculine and feminine design characteristics. In the history of fashion, the notion of androgynous fashion has been evolving since the 1920s, although it was irregular at times. In the postmodern Western cultures, androgynous aesthetic in fashion is increasingly accepted, encouraging the multiplicity of gender expressions. With significant influencers of the generation identifying themselves as gender-neutral and speaking out on the topic, the concept of being gender fluid is catching a lot of attention recently in the international fashion industry. Androgynous fashion is an emergent trend, which reflects in fashion ramps with models showcasing silhouettes and design elements that breakdown gender stereotypes. With this in mind, the current research aims to study androgynous fashion from both conceptual and user-centric perspectives in the Indian context. Data were collected through primary and secondary sources. Relevant secondary data were gathered from various books, research papers and fashion publications to set the conceptual context of the research. Additionally, to gather primary information about the Indian LGBTQ consumers’ perception of androgynous fashion, a questionnaire was circulated amongst young Indian fashion consumers using convenience and snowball sampling methods. The results and analysis of the study reveal the aspirations behind the gender-neutral design genre. This study also brings out the emotional needs of the Indian LGBTQ community members, who are the primary consumers of androgynous aesthetic.
A prospective comparative analysis of the sitting behaviours of two different types of classroom chairs (DIN-ISO-Norm 5970 and BackUp) was done with regard to a more lordotic or kyphotic sitting position. In 26 healthy test subjects, the lordotic and kyphotic curve in the lumbar spine was measured continuously during a sitting test of 45 minutes each on the two different chairs using a strain gauge device fixed to the subject's back. The measuring signal was fed to the A/D conversion interface of a personal computer system for subsequent digital data analysis. Spine curvature scores were analysed to facilitate comparison of the sitting characteristics on the two chair types. In a total of 26 subjects, 6 showed a rather lordotic general sitting position on the BackUp chairs and 15 on the conventional DIN-ISO-Norm 5970 chair whereas no essential difference could be observed in 5 subjects. Altogether, our investigation yielded a more lordotic general sitting position in the conventional rather than on the BackUp system, but without a statistically significant difference (p > 0.05).
Ten ergonomic office chairs, chosen from a sample of eighty-four, were evaluated in an ergonomic field study. Twenty office employees used each of the chairs for one day. The chairs were evaluated using four different methods: a chair feature evaluation checklist, a ranking procedure, general comfort and body part discomfort ratings. The first two methods produced positive results, including significant differences between the chairs. The chair users generally had difficulties in perceiving and expressing their comfort and discomfort associated with the latter two methods. The study identified several distinct features related to chair comfort, including the design of the seat pan, back rest, arm rests and ease of adjustability.
Fuzzy coding vs. crisp coding and then local coding vs. global coding is proposed to transform a quantitative scale into a category scale. Such a transformation technique is seen as the most general one to investigate either heterogeneous but quantitative variables or variables with different scale models (both quantitative and qualitative). A major point of fuzzy coding is that space modalities can be built very early in the statistical analysis process and from a discussion between several specialists. The multiple correspondence analysis (MCA) is proposed to investigate a table where the data come from fuzzy coding; the table rows corresponding to the empirical situations and the columns to the space modalities of the respective variables. Two examples are considered. First, a didactic data set is designed in order to compare the principal component analysis, the MCA with crisp coding and the MCA with fuzzy coding. Second, an example about a sitting posture study is considered in order to show the possibility of achieving relationships between objective and subjective data. The empirical situations correspond to adjustment combinations of the seat, the table and the backrest; the variables are posture indicators and subjective assessments. The main result is that the subjective variables have a much more consistent evolution with the adjustments than the objective ones. Consequently, there is a poor connection between these two sets of variables. The backrest is the furniture setting with the highest influence. From the interpretation of the MCA factor planes, it is possible to find the best and the worst adjustment combinations.
Sitting postures on a knee-support (Balans®) chair and a tiltable chair were investigated with 12 healthy subjects during office work and simulated assembly work. After at least 3 weeks' adaptation to each chair, the subjects were investigated for 1 hour on each chair in stratified sequence. Postures were evaluated by means of a statometric method. Spinal load was further estimated by measuring stature shrinkage over each sitting period. Energy consumption was roughly assessed by pulse measurements. Finally, subjective acceptability was rated by a 5-point scale. Posture effects of the Balans® chair, taken in relation to the tiltable chair, were primarily a forward tilt of the pelvis and a change toward lumbar lordosis. Secondly, the trunk was vertical compared to the slightly backward-inclined position in the tiltable chair. The head was most vertical in the Balans® chair. No effect on spinal shrinkage or pulse was observed. The subjective rating seemed to favour the tiltable chair if used over longer periods. However, the Balans(®) chair may be a good alternative for some seated periods and special tasks.
An investigation was undertaken to determine whether it was possible to achieve equivalent or greater postural improvement, in terms of spinal posture, positional variety and comfort, on a traditional chair modified by design changes to the seat surface to that of a forward sloping chair. Forward sloping chairs have the disadvantage that the body tends to slide forwards off the seat and the possibilities for position change are limited in that leaning backwards is awkward. Theoretically a chair should support a variety of body positions thus allowing the relaxation of alternate groups of muscles (encouraging dynamic seating behaviour). The modified design retains the traditional slightly concave surface for the area under the ischial tuberosities but the front 18 cm is angled downward. Results were obtained using a measuring technique which incorporates the dynamic movement patterns of working people. They indicate that the modified form can be used to achieve similar postural changes to the traditional form when sloped forwards for both assembly work and VDU work. Additionally a wider range of seating positions is adopted on it. Although forward thrust was not reduced the design was rated as more comfortable. This raised questions about whether discomfort is directly related to forward thrust. The issue of table height was also raised.
Chair comfort is a subjective rating, comprising many factors which can be conceptually modelled. It was postulated that the overall comfort perceived by chair users is a function of the relative discomfort in various regions of the body and that the discomfort perceived in the lumbar region is a function of the spinal curvature. The results of two experiments are reported here. In the first experiment, five typical office chairs were evaluated in a field experiment using five subjects. The evaluation procedure used a general comfort rating scale, a body part discomfort rating scale, and a chair feature evaluation checklist. The results showed the body part discomfort ratings of the back regions to be critical in chair comfort. In the second experiment, three chairs were evaluated employing six subjects. The spinal posture of each subject was measured with a METRECOM ® digitizer while standing and seated in each chair type. The results indicate that the backrest curvature, and the thigh-trunk angle (included angle between the seat pan and the back rest) are critical for the overall chair comfort. The implications for the chair designer are discussed.
Large variations in sitting postures and seating are demonstrated in industry. This is largely due to the requirements of the task and the workplace design. Hip and knee angles are important determinators of lumbar posture, and thereby influence the probability of discomfort and disorders of the back. The influence of hip and knee angles on spinal posture was therefore evaluated in sitting and lying on the side. The results showed that hip flexion is 3–8 times more powerful than knee flexion in changing the lumbar curvature. The results are presented in graphs which allow evaluation of seating arrangements in industry to be made in terms of spinal posture and range of spinal motion.
The aim of the study was to investigate the magnitude of spinal shrinkage during video display unit (VDU) work when subjects were sitting on chairs with different design with forward-sloping seats with or without backrest, armrest or knee support and when using a conventional chair with horizontal seat. Three different chairs were investigated: A “Conventional chair” with horizontal seat, B “Ullman chair” with front half of seat sloping forward and back half horizontal, and C “Balans chair” with forward-sloping seat plus knee support. Eight healthy subjects used to professional VDU work volunteered to participate in this field study, which was performed at their own workplaces. The median shrinkage after a three-hour period was 1.3, 1.8 and 3.1 mm for chairs A, B and C, respectively. All subjects shrank more (p < 0.05) when sitting on the chair with knee support (C) than when sitting on the conventional chair. There was no statistically significant difference in shrinkage between chairs A and B, or between chairs B and C.
Ten ergonomic office chairs, chosen from a sample of eighty-four, were evaluated in an ergonomic field study. Twenty office employees used each of the chairs for one day. The chairs were evaluated using four different subjective methods: body part discomfort, general comfort rating, a chair feature evaluation checklist, and a ranking procedure. The chair users generally had difficulties in perceiving and expressing comfort and discomfort which was required in the two first methods. The latter methods produced more informative results including significant differences between the chairs. The study identified several distinct features related to chair comfort including the design of the seat pan, back rest, arm rests, and ease of adjustability.
Many persons over 60 years of age have unique problems sitting on chairs. These problems which are caused by decreased mobility, strength or disease suggest that the chairs should be selected carefully with some scientific basis that incorporates the varying demands of the elderly community. Identification of the proper chair for a particular individual, especially if it has to be low cost and nonmotorized, is a difficult job for institutions, elderly themselves, their families and the furniture industry. Keeping in view these problems a prediction model is developed using established statistical methods to predict comfort of sitting of a particular individual sitting in a particular chair. The study is based on experimental data collected on 18 male and female subjects over the age of 64. The equation uses chair type, body fat %, i.e. above average fat etc., body size, i.e. lean etc., and gender as inputs. The equation was tested on new female and male elderly subjects sitting on two new chairs. The model holds out excellent on the validation despite a low coefficient of determination value obtained for the equation. The paper not only presents a comfort prediction model but also shows a new direction for elderly seating research by employing statistical methods and elderly variables which do not appear in the published literature on elderly seating in the manner presented in this paper. This model will have wide applications especially for practioners (e.g., human factors engineers, occupational therapists, product developers) who need such information in a hurry. This approach also has heuristic value for the researcher in providing guidelines for the testing of other critical variables that may impact on the use of a chair or of other pieces of equipment.
Eight males and eight females participated in a series of simulated 40-minute automobile driving sessions. During each trial, participants sat in one of three contemporary automobile seats or a prototype based on a neutral posture design. Dependent variables were general subjective comfort, subjective body part/area discomfort and performance. General subjective comfort was found to be sensitive to differences between seat types. Females were generally less comfortable in the seats than males, suggesting that the seats better satisfied male than female requirements. Body part discomfort evaluations, for the areas in contact with the seat, were responsive to differences between seat types. Driver performance scores were responsive to gender but not to seat type; female scores were statistically less than those of males and may have been due to the fact that females were generally less comfortable in the suite of seats studied than were males. Correlation analyses indicated that perceptions of general comfort were strongly influenced by comfort experienced in the lower back areas. Driver performance may have been related to perceptions of general comfort due to seat type.
En esta tesis se analizan las técnicas de evaluación ergonómica de asientos que se están utilizando actualmente. Se ha detectado una falta de estudios sobre la relación entre las técnicas que miden parámetros objetivos (posturas, esfuerzos, etc.) y las que utilizan medidas subjetivas (nivel de comodidad, molestias, etc.). El objetivo principal propuesto es abordar el estudio de la relación entre las posturas adoptadas en los asientos y las sensaciones de comodidad experimentadas. Tras analizar las técnicas de medición de posturas existentes, se han realizado diferentes experimentos para poner a punto una nueva técnica de medición de la forma externa de la zona lumbar y la inclinación de la pelvis, que permite el registro continuo de ambos ángulos, y el uso del respaldo sin afectar al comportamiento del sujeto. Se ha comprobado que la técnica desarrollada tiene precisión y repetibilidad superiores a las de otras técnicas convencionales. Se ha desarrollado también un procedimiento de localización de las vértebras a nivel de la piel que no requiere de conocimientos anatómicos específicos y se ha comprobado la relación existente entre ángulos de cuerpos vertebrales y ángulos en piel, validando así la técnica de medición a nivel de la piel. Para abordar el objetivo principal, se han realizado ensayos con diferentes sillas y sujetos durante los que se ha registrado de forma continua la postura lumbar, la inclinación de la pelvis y el uso del respaldo, además de diversas sensaciones de comodidad (general, por zonas del cuerpo). Con los resultados obtenidos, se ha podido analizar el comportamiento espontáneo de los sujetos en tareas de oficina, y se han identificado las formas básicas de sentarse en función del uso del respaldo. Se han estudiado diferentes parámetros de movilidad y posturas medias, así como el efecto del respaldo sobre ellos. Se ha analizado también la relación entre las diferentes sensaciones de comodidad, comprobando que las molestias en la zona lumbar son las más influyentes en las sensaciones de comodidad general. El análisis de la relación entre los parámetros posturales y las molestias corporales indica que los grandes cambios de postura, en especial de la pelvis, son buenos indicadores de las situaciones de incomodidad. Por el contrario, los pequeños movimientos frecuentes alrededor de las posturas estables, y también las posturas con una ligera flexión lumbar y la pelvis más inclinada hacia atrás mejoran la comodidad.
Sumario: This paper reports aspects of the evaluation of industrial seating: seat requirements; dimensional requirements; biomechanical requirements; sitting time; the evaluation of seating; dimensional evaluations; ingress and egress, observational methods; subjective methods; cross-modality matching (CMM); posture changes and stability; changes in stature; comprehensive evaluation procedure
The amount of spontaneous movement during seated office work was estimated by analysing the tilting movements of a tiltable office chair. Both movement frequency and amplitude range were considered. The seat inclinations and subjective acceptability were also recorded.
The seat was moved more frequently and with a greater range when adjusted 6 cm above popliteal level compared to 1 cm below, or when the backrest was pushed anteriorly or posteriorly compared to a middle position. The greatest acceptability occurred with the highest seat adjustment and the backrest in the middle position. Typing or desk-work influenced movement to a similar extent.
Sitting postures were observed in four different work spaces that were designed using combinations of a conventional chair, a forward-sloping chair, and a horizontal or sloping work surface. Subjects sat at each of the work spaces while a lateral view of posture was recorded using a video camera. The slumped posture typically reported in the literature was observed when the conventional work space was used. When the sloping chair was used, postures exhibited less trunk flexion. When the sloping work surface was used, less neck flexion and a more upright trunk were observed. Although the differences between the work spaces were small, the sloping furniture was perceived to be more comfortable than the conventional furniture.
Possible differences in spinal stress were evaluated during forward-reaching movements from chairs with, respectively, fixed backward-inclining, forward-inclining, and tiltable seat. Twenty-four healthy subjects, 12 female and 12 male, performed rhythmical sagittal movements with pins over a 40-cm distance. The posture in an upright and in a forward position was described by means of seven variables, measured by an inclinometer. Posture changes between these positions were then compared for the three types of chairs. No significant influence from the chairs on posture changes was observed. Thus, no variation in spinal stress can be anticipated during forward-reaching movements in any of the three types of chair. The discussion also presents a current status regarding tiltable and fixed forward-inclining seats.
The purpose of this study was to determine the differences in the electromyographic (EMG) activity of the posterior musculature of the trunk while subjects were first seated on a conventional chair, and then while the chair surface was inclined anteriorly to 100 and 110 deg. Twenty healthy subjects had electrodes applied lateral to the spinous processes of C6, T10, and L3 while EMG was monitored every other minute for 15 minutes. All subjects assumed each posture and used a keyboard to operate an interactive computer terminal. Before analysis, all data were processed by root-mean-square circuit and normalized to the EMG from maximum voluntary contractions. Analyses of variance showed significant differences (p < 0.0005) between postures; the EMG activity was found to be less with greater inclination of the chair seat.
One of the major problems in applying ergonomics, as experienced during 25 years of consultancy and lecturing, lies in the fact that emphasis is laid either on the technology or on the field of human shortcomings of a physical or psychosocial nature. While each approach has its place in the man-machine system, they should not be treated separately but be integratedErgonomics is more than the optimization of work places and environment, of tools and machines, and of the safety of workers: it means putting an optimally healthy person into an optimal working situation. A system that embraces simultaneously the condition of the worker, with focus on health, safety and well-being, and the work and work situation, will produce optimal impact. Consumers, scientists, designers and ergonomists should be taught to be more critical in their approach to daily contact with the technical world. Examples are given of gaps in the man-work relationship. Even the recognition of the existence of such gaps may contribute to a more effective and beneficial application of ergonomics
The purpose of the study was to compare muscular activity levels and sitting posture displayed by 10 children (mean age = 4.7 years) when performing tracing tasks while seated at a traditional work station (level desk top, 5 degrees backward sloping seat) and at an ergonomically designed work station (15 degrees sloping desk top, 15 degrees forward sloping seat). EMG profiles of latissimus dorsi (LD), erector spine (ES), and superior trapezius (ST) were sampled using Medi-trace disposable surface electrodes for 10 min on the non-dominant side. Muscle activity was sampled (1000 Hz) every 2 min for 5000 ms while the subjects performed the tracing tasks at each station. Raw EMG signals of the five trials for each muscle were processed by removing signal offset, full-wave rectification, and integration. The subjects' posture was monitored from a lateral view using a Panasonic VHS video camera while the children were seated at each work station. Neck flexion angle and the angle between the torso and thigh (hip angle) were manually sampled from the video images each 1 min as an indication of the posture adopted by the subjects during the tracing tasks. Use of t-tests for dependent means indicated that there was no significant difference in either mean ES or ST muscle activity as a function of work station design. However, subjects demonstrated significantly less LD activity when seated at the ergonomic work station (mean = 20.9 V ms) compared with the traditional work station (mean = 24.4 V ms, t = -2.88, p = 0.018).(ABSTRACT TRUNCATED AT 250 WORDS)
This paper discusses the possible causes of musculoskeletal pain in VDT workers and outlines strategies to minimize it. The paper reviews workstation, chair, and keyboard design, and makes recommendations to improve user comfort. Also discussed is worker selection, training, posture, conditioning, and rest breaks. Short term musculoskeletal discomfort is experienced by many VDT operators in the telecommunications industry and chronic disability may result in the long term. It is important that the ergonomist and office manager work together to improve the working conditions in this important occupational area.
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.
Anthropometric data of Hong Kong schoolchildren have been collected and analysed in order to develop recommendations for the design of chairs and tables for use in Hong Kong Government coeducational schools. The anthropometric data for Hong Kong have been compared with data from a Western population (United Kingdom) and another Asian population (Japan). Five sizes of chair and table combinations have been proposed to accommodate six primary and seven secondary forms (pupils aged from 6 to 18 years). The recommended design dimensions, based on the anthropometric characteristics of the Hong Kong target populations, are discussed in relation to recommendations from previous research in this area.
Back pain is now recognised to occur early in childhood and is associated with high prevalence rates when estimated by survey. This review paper considers the risk factors associated with back pain in children aged 11-14 years, and particularly those present in a school setting. The risk factors most significantly associated with back pain are primarily characteristics of the individual with less strong associations with factors present in the school environment. The majority of intervention studies undertaken in a school setting have focussed on the effect of school furniture on posture and comfort and were of short-term duration. There is a need for further research in order to achieve a better understanding of the risk factors present in a school environment and to address ways to reduce the currently recognised perceived problem of back pain among school children. A strategy for an evidence-based longitudinal intervention study is proposed, with the content outlined under the headings: policy, school equipment and furniture, individual and family.
Pupils were photographed by automatic camera during a four-hour examination. All of them were bent far over their tables in an unacceptable manner. An experiment was conducted to determine what height the pupils themselves preferred. Without exception, they preferred to sit much higher, which automatically placed them in a sitting position with a straight back. Revised design of furniture corrected the posture problem. It was concluded that the table should be at least half the person's height (80-90 cm for older pupils) and that the chair should be at least one-third the person's height (50-60 cm for older pupils). The seat should be capable of sloping forward 10-15 deg, and the forward sliding tendency counteracted by a small, fixed cushion. The tabletop should slope backward 10-15 deg.
A technique is described which enables the distribution of discomfort in the body, and its change during the work poriod, to he recorded. The recorded data indicate points of inadequate man-machine compatibility as well as permitting the evaluation of the effectiveness of machine designs. When used in conjunction with moasures of production performance the technique provides direct evidence of the benefits of orgonomic changes. Its use is illustrated in relation to a study of spot welders.
A methodology for evaluating a single chair, rather than making a comparison among chairs, was developed from previous chair studies. The methodology was found to be rapid and effective when applied to a prototype chair, giving information to the manufacturer on overall comfort and good and bad points in the design. Testing took place on three tasks and showed that chair comfort is influenced by the task as well as the chair.
Modern furniture in schools, factories and offices is constructed in such a way that no one can use it properly. Each day people sit for many hours hunched over their tables in postures extremely harmful to the back. No one should be surprised that more than half of the population today is complaining of backache. In no other field of human activity is a similar gap between theory and reality found. A closer study of 'normal' sitting postures will explain why nobody is able to sit in the 'ideal' position. First of all, the eye in this position is at a distance of 50-60 cm from the book or working material and the axis of vision is horizontal. In addition, this posture requires at least 90 degrees flexion of the hip joint, yet the normal human being can only bend 60 degrees . A considerably better sitting posture can be obtained if the table is tilted about 10 degrees . In this way the book is brought closer and at a better angle to the eye. The worst bending of the neck is thus avoided. Furthermore, the seat can, with advantage, be tilted 20 degrees forward to reduce the flexion of the lumbar region. By both these means the extra 30 degrees flexion, which is the most strenuous part of flexion, is avoided.
Alterations of the lumbar curve
- Keegan