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.     

Evaluation of a new work seat for industrial sewing operations: results of three field studies

A newly developed work seat for industrial sewing operations was compared with a traditional sewing work seat to evaluate the effectiveness of design features. The new seat was designed with special seat-pan and backrest features to accommodate the musculoskeletal geometry of a low sit-stand posture. The seat-pan consisted of a pelvic support which supported the ischial tuberosities and areas behind them, and a thigh support which maintained the thighs at a 15 degrees downward angle, resulting in a 105 degrees trunk-thigh angle. The backrest consisted of a lumbar support which preserved lumbar lordosis and a thoracic support which supported the upper back during backward leaning. The traditional work seat was similar to an office chair (i e, a large horizontal seat-pan and a wide backrest) with the exception of having a higher than normal seat-height. This investigation consisted of three studies to compare the seats: (1) A user comfort and acceptance experiment which compared the initial psychophysical responses of 50 industrial sewers when introduced to the new seat; (2) a backrest usage experiment which compared the duration of backrest use among 10 industrial sewers; and (3) a follow-up experiment to evaluate chair preference after extended use of the new seat. The results of the user comfort and acceptance experiment found that the new work seat had greater comfort and user preference; the results of the backrest usage experiment found that the new seat had greater backrest use than the traditional seat; the results of the follow-up experiment found that the preference for the new seat was maintained over time and not due to a Hawthorne Effect.     

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 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.     

Background to sitting at work: research-based requirements for the design of work seats

The body's responses to sitting are complex and involve the anatomy and physiology of the sitter as well as the structure of the seat, the desk and the environment. In the light of recent research, the major reactions of the spine, the muscles and the spinal discs are discussed. Their interactions when adopting sitting postures are described. Reasons are given why certain sitting postures are to be preferred. The mechanisms that may give rise to muscle and disc damage, as well as back pain, as a result of adverse sitting postures are outlined. The design consequences of the research are then presented, showing how the seat shape arises from the previously described data. The influence of backrest design on sitting comfort and in the reduction of loading on the body is shown. Finally, a brief discussion of the influences from the work surface illustrates how the combination of seat and workplace can reduce the risks of injury by mitigating body loadings over the working day.     

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.     

Equivalent comfort contours for vertical seat vibration: effect of vibration magnitude and backrest inclination

This study determined how backrest inclination and the frequency and magnitude of vertical seat vibration influence vibration discomfort. Subjects experienced vertical seat vibration at frequencies in the range 2.5-25 Hz at vibration magnitudes in the range 0.016-2.0 ms(-2) r.m.s. Equivalent comfort contours were determined with five backrest conditions: no backrest, and with a stationary backrest inclined at 0° (upright), 30°, 60° and 90°. Within all conditions, the frequency of greatest sensitivity to acceleration decreased with increasing vibration magnitude. Compared to an upright backrest, around the main resonance of the body, the vibration magnitudes required to cause similar discomfort were 100% greater with 60° and 90° backrest inclinations and 50% greater with a 30° backrest inclination. It is concluded that no single frequency weighting provides an accurate prediction of the discomfort caused by vertical seat vibration at all magnitudes and with all backrest conditions. PRACTITIONER SUMMARY: Vertical seat vibration is a main cause of vibration discomfort for drivers and passengers of road vehicles. A frequency weighting has been standardised for the evaluation of vertical seat vibration when sitting upright but it was not known whether this weighting is suitable for the reclined sitting postures often adopted during travel.     

Visual display height

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

The effect on sitting posture of a desk with a 10 degree inclination for reading and writing

A pilot study was carried out on 10 subjects to examine the effect that a desk with a 10 degree inclination had on their sitting posture while reading and writing. A continuous recording of the subjects head and trunk positions was made. Each subject was studied during two periods of 1.5 h on different days. The subject worked at a flat desk on the first day and at a desk with a 10 degree inclination on the second. On average, the position of the head in the sagittal plane was found to be 6 degrees more erect and the position of the trunk 7 degrees more erect when working at a desk with a 10 degree inclination than when working at a flat desk. The maximal decrease in load observed on the cervical spine was 35% and on the thoracic spine 95%. The angle between the head and the trunk did not change significantly when using an inclined desk. Differences in posture in the frontal plane were not observed in this study.     

Background to sitting at work: research-based requirements for the design of work seats

The body's responses to sitting are complex and involve the anatomy and physiology of the sitter as well as the structure of the seat, the desk and the environment. In the light of recent research, the major reactions of the spine, the muscles and the spinal discs are discussed. Their interactions when adopting sitting postures are described. Reasons are given why certain sitting postures are to be preferred. The mechanisms that may give rise to muscle and disc damage, as well as back pain, as a result of adverse sitting postures are outlined. The design consequences of the research are then presented, showing how the seat shape arises from the previously described data. The influence of backrest design on sitting comfort and in the reduction of loading on the body is shown. Finally, a brief discussion of the influences from the work surface illustrates how the combination of seat and workplace can reduce the risks of injury by mitigating body loadings over the working day.     

Trunk posture and load on the trapezius muscle whilst sitting at sloping desks

Abstract

Sitting posture in relation to three different desk slopes of 45,22 and 0° (horizontal) was examined by statometry on 10 subjects who were reading. With increasing desk slope the cervical as well as the lumbar spine were extended, and the head and trunk changed towards a more upright posture. Electromyography (EMG) from the descending part of the trapezius muscle was also recorded during both reading and writing. This muscular load was low and did not change with varying desk slopes for any of the two tasks. A rating for acceptability, performed for both tasks on each desk inclination, favoured a steep slope of the desk for reading, while the opposite was favoured for writing. The study suggests that the reading matter should be placed on a sloping desk, and the paper used for writing on the horizontal tabletop between the desk and the person.     

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.     

The effect on sitting posture of a desk with a 10° inclination for reading and writing

Abstract

A pilot study was carried out on 10 subjects to examine the effect that a desk with a 10° inclination had on their sitting posture while reading and writing. A continuous recording of the subjects head and trunk positions was made. Each subject was studied during two periods of 1·5 h on different days. The subject worked at a flat desk on the first day and at a desk with a 10° inclination on the second. On average, the position of the head in the sagittal plane was found to be 6° more erect and the position of the trunk 7° more erect when working at a desk with a 10° inclination than when working at a flat desk. The maximal decrease in load observed on the cervical spine was 35% and on the thoracic spine 95%. The angle between the head and the trunk did not change significantly when using an inclined desk. Differences in posture in the frontal plane were not observed in this study.     

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.     

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.     

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.     

The effect on sitting posture of a desk with a ten-degree inclination using an adjustable chair and table

By means of continuous recording of the positions of the trunk and head, an investigation was carried out to examine the effect of the Erasmus office-desk - a desk with a 10 degrees inclination - on sitting posture whilst reading and writing, sitting in an adjustable chair at an adjustable table. The posture assumed by a person who is doing mixed reading and writing work at a table with the Erasmus office-desk is more upright than the posture of the same person doing the same work without the desk. This applies for both the head and the trunk. The average position of the trunk was changed from 26.0 degrees to 18.2 degrees when working with the desk placed on the table. The moment of force caused by gravity is proportional to the sine of the angle. Therefore the change of angle results in a decrease of the average moment of force on the back at L5-S1 of 29%. The largest individual decrease found was 86%. The average change of the position of the head was changed from 38.5 degrees to 29.6 degrees , resulting in an average decrease of the moment of force, on C7-T1, of 21%. The largest individual decrease was 51%. Lateroflexion of the back was less often assumed when the subjects were using the desk. The posture assumed by the subjects when they were doing writing work only was generally more upright when working at a desk with a 10 degrees inclination than when working at a flat desk. Marked differences were found between the postures of the subjects. The change of posture while using the desk also showed marked differences for each subject individually.     

The influence of backrest angles on the passenger neck comfort during sleep in the economy class air seat without head support

The purposes of this study were to characterize the influence of seat back angle variations on the neck comfort of sleeping passengers without a pillow and provide suggestions for the design of economy-class seats. In this study, 17 subjects were subjected to a sleep experiment to test the effect of the backrest angle on head and neck rotation and the fatigue level of the neck muscles. The results showed that a reclined backrest (positioned at 110°) caused greater rotation of the head and neck and greater fatigue of the neck muscles than a vertical backrest. Additionally, the higher was the subject's head extended above the top of the backrest, the more complicated the head and neck rotation was and the more intense the stretching of muscles was. We conclude that, when sleeping in a sitting position without head support, passengers were more likely to experience neck muscle fatigue with the reclined backrest than with the vertical backrest. Passenger height was also found to be an important factor contributing to head and neck fatigue. On the basis of the experimental results, we offer suggestions for the design of backrests to improve passengers' sleeping experience. Our research and suggestions provide a new path for innovation in the design of economy-class seats and could help to improve the travel experience.