Development of a work seat for industrial sewing operations: results of a laboratory study

A hydraulically adjustable chair with seven independent variables - seat height, seat angle, seat rocking, seat swivel, back-rest distance, back-rest height and back-rest angle-was constructed to evaluate comfort and biomechanical factors relevant to the design of a chair for industrial sewing operations. The purpose of this investigation was to determine which of these factors were significant. Four assessment methods: overall body discomfort, localized body discomfort, electromyography (EMG) and height reduction (vertebral disc shrinkage) were used to evaluate these seven independent variables. Two female subjects attended eight 6 hour experimental sessions. The results indicate that to accommodate 90% of the female population, the seat height should be adjustable in the range 51 to 61 cm, the back-rest distance should be adjustable in the range 10 to 15 cm (measured from the centre of the back-rest to the centre of the seat-pan), the back-rest height should be fixed at 25 cm (measured from the centre of the back-rest to the centre of the seat-pan), and the seat should be allowed to swivel freely.     

A parametric investigation on seat/occupant contact forces and their relationship with initially perceived discomfort using a configurable seat

The present work investigates the contact forces between sitters and seat as well as their correlations with perceived discomfort. Twelve different economy class aeroplane seat configurations were simulated using a multi-adjustable experimental seat by varying seat pan and backrest angles, as well as seat pan compressed surface. Eighteen males and 18 females, selected by their body mass index and stature, tested these configurations for two sitting postures. Perceived discomfort was significantly affected by seat parameters and posture and correlated both with normal force distribution on the seat-pan surface and with normal forces at the lumbar and head supports. Lower discomfort ratings were obtained for more evenly distributed normal forces on the seat pan. Shear force at the seat pan surface was at its lowest when sitters were allowed to self-select their seat-pan angle, supporting that a shear force should be reduced but not zeroed to improve seating comfort.

Practitioner Summary: The effects of seat-pan and backrest angle, anthropometric dimensions and sitting posture on contact forces and perceived discomfort were investigated using a multi-adjustable experimental seat. In addition to preferred seat profile parameters, the present work provides quantitative guidelines on contact force requirement for improving seating comfort.     

Office task effects on comfort and body dynamics in five dynamic office chairs

In the present study, we investigated the effect of office tasks on posture and movements in field settings, and the comfort rating for chair characteristics and correlation with type of task. The tasks studied were: computer work, telephoning, desk work and conversation. Postures, movements, chair part inclinations and comfort rating data were collected from 12 subjects. Computer work showed the lowest physical activity, together with upright trunk and head position and low backrest inclination. Conversation shows the highest activity of head legs and low back together with the highest cervical spine extension. In contrast, desk work provoked the most cervical spine flexion and showed the second lowest activity. The telephoning tasks showed medium activity and the highest kyphosis. Conversation showed the highest backrest inclination. Positive comfort relations were found for computer work and a "swing system" chair, for telephoning and an active longitudinal seat rotation, and for desk work and a chair with a three-dimensionally moveable seat.     

Effect of lumbar support on seating comfort predicted by a whole human body-seat model

Automobile seat greatly affects the ride comfort of drivers in a prolonged driving. Not only the layout parameters of automobile seats, such as seat height, cushion inclination angle, backrest inclination angle, etc, but also the backrest surface related with lumbar support all affect the seating comfort. The human body-seat system includes the three-dimensional data of body based on anatomy and anthropometry, three-dimensional data of seat and adjustable assembly interaction between body and seat based on human body kinematics. Body height and driving posture are adjusted in POSER software, then the solid model of human skin, skeleton and muscle are created in ANSA software, and the integrated model of body-seat system is created in ABAQUS software. The adjustment of the lumbar support parameters is achieved by setting boundary condition of lumbar support region of seats. The finite element model of human body-seat system is validated by comparison to available literature results. At last the finite element model is applied to analyze the effect of lumbar support parameters of seats on the interaction between body and seat under the action of gravity. The pressure value and distribution, contact area, total force of backrest and intervertebral disc stress are obtained. The result shows that the optimal thickness of seat's lumbar support size for the seating comfort is 10 mm after comprehensive comparison and evaluation.Relevance to industry: This study investigated the effects of lumbar support on seating comfort, and can be used to protect the lumbar health. The modeling and simulation method can be applied for the optimization design of vehicle seats.     

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.     

Effects of backrest design on biomechanics and comfort during seated work

The purpose of this study was to examine the effects of backrest configuration on seatpan and backrest pressure, spinal posture, and comfort. Thirty volunteers (15 male, 15 female) typed a standardized text passage while seated at a computer workstation in five backrest configurations: chair only, chair with a supplementary backrest, and with each of three lumbar pad thicknesses. Pressure, lumbar and cervical angles were collected during 15-min trials. Subjective data were collected during each trial and at the end of the entire protocol. The addition of a supplementary backrest to a standard chair reduced peak and average pressure on the back by 35% and 20%, respectively (P<0.02). Lumbar lordosis was observed only when lumbar pads were used, being greatest with the large pad. Participants preferred backrest configurations that had lower pressure on the back and less lordotic lumbar posture (backrest only or 3 cm lumbar pad), regardless of anthropometrics. Comfort was rated highest in conditions that would not necessarily be considered biomechanically ideal. Further delineation between specific comfort and objective seating variables is required to effectively reduce and prevent low back pain.     

The Influence of Various Seat Design Parameters: A Computational Analysis

Nowadays, low back pain becomes a common healthcare problem. Poor or unsuitable seat design is related to the discomfort and other healthcare problems of users. The aim of this study is to investigate the influence of seat design variables on the compressive loadings of lumbar joints. A basis that includes a musculoskeletal human body model and a chair model has been developed using LifeMOD Biomechanics Modeller. Inverse and forward dynamic simulations have been performed for various seat design parameters. The results show that the inclination of backrest and seat pan may or may not decrease the compressive spinal joint forces, depending on other conditions. The medium‐level height and depth of seat pan and the medium‐level and high‐level height of backrest are found to cause the minimum compressive loads on lumbar joints. This work contributes to a better understanding of sitting biomechanics and provides some useful guidelines for seat design.     

The impact of office chair features on lumbar lordosis,intervertebral joint and sacral tilt angles: a radiographic assessment

Abstract

Background: The purpose of this study was to determine which office chair feature is better at improving spine posture in sitting. Method: Participants (n = 28) were radiographed in standing, maximum flexion and seated in four chair conditions: control, lumbar support, seat pan tilt and backrest with scapular relief. Measures of lumbar lordosis, intervertebral joint angles and sacral tilt were compared between conditions and sex. Results: Sitting consisted of approximately 70% of maximum range of spine flexion. No differences in lumbar flexion were found between the chair features or control. Significantly more anterior pelvic rotation was found with the lumbar support (p = 0.0028) and seat pan tilt (p < 0.0001). Males had significantly more anterior pelvic rotation and extended intervertebral joint angles through L1–L3 in all conditions (p < 0.0001). Conclusion: No one feature was statistically superior with respect to minimising spine flexion, however, seat pan tilt resulted in significantly improved pelvic posture.

Practitioner Summary: Seat pan tilt, and to some extent lumbar supports, appear to improve seated postures. However, sitting, regardless of chair features used, still involves near end range flexion of the spine. This will increase stresses to the spine and could be a potential injury generator during prolonged seated exposures.     

Active sitting with backrest support: Is it feasible?

Abstract

Ergonomics science recommends office chairs that promote active sitting to reduce sitting related complaints. Since current office chairs do not fulfill this recommendation, a new chair was developed by inverting an existing dynamic chair principle. This study compares active sitting on the inverted chair during a simulated computer-based office task to two existing dynamic office chairs (n?=?8). Upper body stability was analysed using Friedman ANOVA (p?=?.01). In addition, participants completed a questionnaire to rate their comfort and activity after half a working day.

The inverted chair allowed the participants to perform a substantial range of lateral spine flexion (11.5°) with the most stable upper body posture (≤11?mm, ≤2°, p?≤?.01). The results of this study suggest that the inverted chair supports active sitting with backrest support during computer-based office work. However, according to comfort and activity ratings, results should be verified in a future field study with 24 participants.

Practitioner Summary: This experimental laboratory study analyses the feasibility of active sitting with a backrest support during common office work on a new type of dynamic office chair. The results demonstrate that active sitting with a backrest support is feasible on the new but limited on existing chairs.     

Application of Zen sitting principles to microscopic surgery seating

This paper describes the application of an alternative seating concept for surgeons that reflects the research of Zen sitting postures, which require Zazen meditators to maintain fixed postures for long durations. The aim of this alternative approach is to provide sitters with a seat pan with sacral support(1) that provides a more even distribution of seat pressures, induces forward pelvic rotation and improves lumbar, buttock and thigh support. This approach was applied to the development of a chair for microscopic surgery. The experimental chair is a seat pan that closely matches the three-dimensional contours of the user's buttocks. Seat comfort was evaluated by comparing both changes in pelvic tilt and seat pressure distributions using Regionally-Differentiated Pressure Maps (RDPM) with subjective ratings of surgeons while operating in prototype and conventional chairs. Findings include that the sacral support of the prototype chair prevents backward pelvic rotation, as seen in zazen (Zen sitting postures). Preliminary data suggests that the prototype provided greater sitting comfort and support for constrained operating postures than did the conventional chair. These findings support the selective application of concave-shaped seat pans that conform to users' buttocks and reflect Zen sitting principles.     

Free shoulder space requirements in the design of high backrests

The objective of this study was to determine the influence of scapular support on the effects of lumbar support and to prove that a high and straight backrest is inappropriate. In literature the importance of a lumbar support is noted, although data about optimal dimensions is an under-researched topic and in earlier studies on force distribution and muscle activity the backrest had a fixed form. The lumbar support is needed to maintain the lumbar lordosis but no studies deal with the question of the precise dimensions of the backrest at shoulder level. With a specially designed apparatus, forces on shoulder and seat were measured separately, and the force on the pelvis calculated, while varying seat and backrest inclination within the range from 0° to 17°. Seat-to-backrest angle (at the level of lumbar support) was kept constant at 90°. The distance between the tangent to the lumbar support and the parallel tangent to the scapular support was varied from 0, 2, 4, 6 and 8 cm. This distance is called the free shoulder space. Electromyography was measured at the erector spinae at the levels of the L1, T8 and T5 vertebrae. For all seat angles, a free shoulder space of d=0 cm resulted in the highest back muscle activity. In agreement with the biomechanical model, EMG activity reduced with an increase of seat tilt and increase of free shoulder space. With increasing free shoulder space, a larger part of the total backrest force was carried by the lumbar support. This study shows that a high and straight backrest overrules lumbar support. Offering free shoulder space of at least 6 cm reduces back muscle activity and allows for lumbar support.     

Free shoulder space requirements in the design of high backrests

The objective of this study was to determine the influence of scapular support on the effects of lumbar support and to prove that a high and straight backrest is inappropriate. In literature the importance of a lumbar support is noted, although data about optimal dimensions is an under-researched topic and in earlier studies on force distribution and muscle activity the backrest had a fixed form. The lumbar support is needed to maintain the lumbar lordosis but no studies deal with the question of the precise dimensions of the backrest at shoulder level. With a specially designed apparatus, forces on shoulder and seat were measured separately, and the force on the pelvis calculated, while varying seat and backrest inclination within the range from 0 degrees to 17 degrees. Seat-to-backrest angle (at the level of lumbar support) was kept constant at 90 degrees. The distance between the tangent to the lumbar support and the parallel tangent to the scapular support was varied from 0, 2, 4, 6 and 8 cm. This distance is called the free shoulder space. Electromyography was measured at the erector spinae at the levels of the L1, T8 and T5 vertebrae. For all seat angles, a free shoulder space of d=0 cm resulted in the highest back muscle activity. In agreement with the biomechanical model, EMG activity reduced with an increase of seat tilt and increase of free shoulder space. With increasing free shoulder space, a larger part of the total backrest force was carried by the lumbar support. This study shows that a high and straight backrest overrules lumbar support. Offering free shoulder space of at least 6 cm reduces back muscle activity and allows for lumbar support.     

Spinal shrinkage with three different types of chair whilst performing video display unit work

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.     

Review of anthropometric considerations for tractor seat design

Tractor driving imposes a lot of physical and mental stress upon the operator. If the operator's seat is not comfortable, his work performance may be poor and there is also a possibility of accidents. The optimal design of tractor seat may be achieved by integrating anthropometric data with other technical features of the design. This paper reviews the existing information on the tractor seat design that considers anthropometry and biomechanical factors and gives an approach for seat design based on anthropometric data. The anthropometric dimensions, i.e. popliteal height sitting (5th percentile), hip breadth sitting (95th percentile), buttock popliteal length (5th percentile), interscye breadth (5th and 95th percentile) and sitting acromion height (5th percentile) of agricultural workers need to be taken into consideration for design of seat height, seat pan width, seat pan length, seat backrest width and seat backrest height, respectively, of a tractor. The seat dimensions recommended for tractor operator's comfort based on anthropometric data of 5434 Indian male agricultural workers were as follows: seat height of 380 mm, seat pan width of 420–450 mm, seat backrest width of 380–400 mm (bottom) and 270–290 mm (top), seat pan length of 370±10 mm, seat pan tilt of 5–7° backward and seat backrest height of 350 mm.

Relevance to industry

The approach presented in this paper for tractor seat design based on anthropometric considerations will help the tractor seat designers to develop and introduce seats suiting to the requirements of the user population. This will not only enhance the comfort of the tractor operators but may also help to reduce the occupational health problems of tractor operators.     

Adaptation and sensitivity to postural change in sitting

We used 3 psychophysics methods to determine perceptible changes in seat height, seat pan angle, and backrest angle using an experimental chair. In the method of adjustment, the chosen chair settings were affected by the initial setting. For example, a high initial setting of the seat height led to a high selected setting and a low setting led to a low value. The difference between settings was referred to as not noticeable difference (NND). The method of limits was used to determine acceptable chair settings using verbal limits such as "too high" and "too low." Using the method of constant stimuli, just noticeable differences (JNDs) were determined for chair height (1.5 cm), seat pan angle (1.2 degrees) and backrest angle (1.7 degrees). The corresponding values for NNDs and verbal limits were about twice as large: chair height (2.5 cm), seat pan angle (4 degrees) and backrest angle (3 degrees). NNDs and verbal limits are unobtrusive measures that are considered more valid than JNDs, which exaggerate the need for adjustability. The results have practical implications for the design of office chairs.     

Human–seat interface analysis of upper and lower body weight distribution

The human–seat interfaces were analyzed to determine the differential distribution of the body weight to the components of seat. Fifteen volunteers were tested on a simulated seat system with two piezoelectric force platforms, one placed as chair seat pan and the other placed on the floor surface as footrest. The seated configurations included back inclines (75° and 80°), upright (90°) and reclines (95°, 105° and 115°), absence or presence of armrest (adjusted at 62–68 cm of height), forward and backward sloping of the seat pan, and supported and unsupported back. The armrest and backrest assemblies were isolated from the force platforms. The difference in the body weight (kgf) to the sum of forces recorded at seat pan and feet yielded the extent of weight transferred to other features (e.g., backrest and armrest). The weight distributed at seat was 10–12% less at back inclines (p<0.01) as compared to upright unsupported sitting. With the backrest reclined beyond 95°, the weight at seat gradually decreased by 9% at 115° recline. The load distributed at feet varied narrowly; however, it was significantly greater (p<0.01) at upright supported back, compared to unsupported back. The height of the armrest was optimized at 68 cm, since the weight distribution at seat pan consistently reduced by 12% at that height, as compared to the absence of armrest (F_(4,524)=8.80, p<0.05). The suggested height of the armrest corresponded to 40% of the body stature of the selected volunteers. The load distributed at feet was 18% greater with the presence of armrest, indicating that a part of the weight of the upper leg fell on the seat pan, when the armrest was absent. The weight fell on the seat in slouch posture was 5% less than in upright sitting, while the weight at feet was marginally higher in slouch than in upright posture. The study maintained that the horizontal as well as 5° forward slope of the seat might be the preferred choice, since the load distributed at seat was highest at backward sloping seat for all conditions of supported and unsupported back. The study reaffirms that the backrest and armrest have conjoint influence in reducing the load distributed at seat, which in turn might help in mitigating stress on the spinal and other paraspinal structures.

Relevance to Industry

The human–seat interface analysis and understanding of body weight distribution to the components of seat may be beneficial for ergo-design application in optimizing parameters for chair configurations that provide comfort and safety to the user.     

Vibration and comfort HI. Translational vibration of the feet and back

The effects on discomfort of the frequency and direction of the translational vibration of a footrest and flat firm backrest have been studied in two experiments. At frequencies in the range 2.5-63 Hz, the first experiment determined the levels of fore-and-aft, lateral and vertical vibration of the feet of seated subjects which caused them discomfort equivalent to that from 0.8 m/s² r.m.s. 10 Hz vertical vibration of a firm flat seat. The levels of fore-and-aft, lateral and vertical vibration at the back of a seat which were equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined in the second experiment. The vibration of the feet or back occurred without simultaneous vibration at the seat.

Individual and group equivalent comfort contours are presented. It is concluded that the data provide a useful initial indication of the relative contribution of foot and back vibration to discomfort. Equivalent comfort contours for foot vibration were similar for all three directions of vibration. The contours for vibration of the back show a high sensitivity to fore-and-aft vibration. The results obtained from two additional studies show that vibration from a backrest and other variations in seating conditions can influence subject comfort.     

Sitting comfort in an aircraft seat with different seat inclination angles

Passengers' comfort experience during flights is important in choosing their flights. The focus of this study is passengers’ perceived comfort in different climbing angles during ascent. Twenty-six participants were invited to experience three inclination angles including 3°, 14° and 18° in a Boeing 737 cabin. The angle of 3° was used to simulate cruising stage and the other two were used to simulate different climbing angles. Participants experienced each setting for 20 min where the perceived comfort, their heart rate variability(HRV), and their body contact pressure values on the backrest and seat pan were recorded with questionnaires, HRV bands and pressure mats respectively. The results indicate a preference of 14° inclination angle resembling the cruising angle (3°) and having the slowest moving speed of the center of pressure (COP) on both the backrest and seat pan.     

An evaluation of comfort of a bus seat

The aim of this research was to evaluate the comfort of a passenger seat for a new type of bus. A fuzzy set model of a multistage comfort scale (MCS) was adopted for the assessment of comfort, together with the techniques of human back shape and EMG measurements as well as posture analysis. The subjects were 30 university students. It is concluded that MCS is a rapid but comprehensive evaluation method for single chair evaluation. The overall rating of MCS is 0.532, which is acceptable under the conditions of the prototype evaluation. The seat profile fits better with the back curve of subjects who had higher comfort rating in the way that the upper profile of the seat coincides with the human back curve and the lower part of the profile intersects the human back curve in the lumbar region; here the human back curves were measured in the slumped sitting posture. There was a significant difference in the EMGs of back muscles between the two sitting postures (sitting upright and the slumped sitting posture) at all the seat heights.     

The determination of pressures and patterns for the male human buttocks and thigh in sitting utilizing conductive foam

Pressures and patterns for twelve male human buttocks and thighs in sitting in three different shaped seat pans were determined. Pressure was determined by multiple transducers situated geometrically on a conductive foam blanket which measured changes in resistance with an ohm meter as pressure was applied. The three chair seat pans consisted of a small round surgeons type stool, a standard biomechanic secretarial shaped chair, and a neutral posture chair which was a unique combination of a forward-sloping cultivator seat and an English saddle with wrap around leg trough support. Trunk-thigh posture angles of 90 and 127 deg for each chair were evaluated. The location of the maximum pressure points for all chair posture treatments had generally small tight patterns whose locations where consistent with the locations of the ischial tuberosities. The mean pressure was found to vary inversely with the total area. Thus, as the seat pan surface area decreased in total area in contact with the buttock-thigh, the larger the mean pressure became. Mean pressure values were also found to be in the same rank order and relative magnitude to subjective comfort for the buttock-thigh, conducted in related experiments on the chair-posture treatments. The neutral posture chair was found to reduce buttock-thigh maximum pressure from 118.94 mmHg (2.3 psi) to 62.06 mmHg (1.2 psi) and to reduce mean pressure by more than 50%.