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.     

Estimation of various sitting postures using a load-cell-driven monitoring system

Maintaining correct sitting posture is highly likely by simply informing seated people of their current sitting postures. Few studies have simultaneously applied load distribution measurements and sitting posture feedback to measure bodily pressure distribution. Commercialization of sitting posture monitoring systems has been difficult due to high cost. This study tested a system that measures load on the seat pan and load transferred to the backrest using four load cells installed on the seat pan. Three body weight ratios were calculated and differences in body weight ratios were tested among six sitting postures. The results were considered highly reliable based on strong correlations among three instruments’ results despite differences in force plate and dead load between the results of the monitoring system and the load-measuring system. The findings encourage commercialization and future research that includes gender and physical characteristic differences.     

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.     

Effects of seat slope and hip flexion on spinal angles in sitting

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.     

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.     

Lipoatrophia semicircularis and the relation with office work.

The relation between lipoatrophia semicircularis (LS--band-like circular depressions and isolated atrophy of the subcutaneous fatty tissue on the anterior thighs and sitting posture or pressure on the seat surface of office chairs was investigated in an office environment. A questionnaire was presented to 21 subjects and electromyographic measurements, video analysis and pressure measurements were performed. Remarkable posture differences between the LS group and the group without LS were found: less use of the lumbar support of the chair, static sitting postures and a too high seat surface of the office chair were characteristics of the subjects with LS. These observations were confirmed by higher pressure measurements for the subjects with LS. In addition, highly significant pressure differences were found between different chairs.     

The effect of posture and vibration magnitude on the vertical vibration transmissibility of tractor suspension system

The efficiency of suspension seat can be influenced by several factors such as the input vibration, the dynamic characteristics of the seat and the dynamic characteristics of the human body. The objective of this paper is to study the effect of sitting postures and vibration magnitude on the vibration transmissibility of a suspension system of an agricultural tractor seat. Eleven (11) healthy male subjects participated in the study. All subjects were asked to sit on the suspension system. Four (4) different sitting postures were investigated – i) “relax”, ii) “slouch”, iii) “tense”, and iv) “with backrest support”. All subjects were exposed to random vertical vibration in the range of 1–20 Hz, at three vibration magnitudes - 0.5, 1.0 and 2.0 m/s² r.m.s for 60 s. The results showed that there were three pronounced peaks in the seat transmissibility, with the primary resonance was found at 1.75–2.5 Hz for every sitting postures. The “backrest” condition had the highest transmissibility resonance (1.46), while the “slouch” posture had the highest Seat Effective Amplitude Transmissibility (SEAT) values (64.7%). Changes in vibration magnitude for “relax” posture from 0.5 to 2.0 m/s² r.m.s resulted in greater reduction in the primary resonance frequency of seat transmissibility. The SEAT values decreased with increased vibration magnitude. It can be suggested that variations in posture and vibration magnitude affected the vibration transmission through the suspension system, indicating the non-linear effect on the interaction between the human body and the suspension system.Relevance to industry: Investigating the posture adopted during agricultural activities, and the effects of various magnitudes of vibration on the suspension system's performance are beneficial to the industry. The findings regarding their influence on the human body may be used to optimize the suspension system's performance.     

Seated buttock contours: a pilot study of Australian senior high-school students

Both posture and comfort of a chair are influenced by the contour and characteristics of the seat. Knowledge of seat contours of a student population could thus be useful in the design of school chairs. This study investigated seated buttock contours of senior high-school students in order to determine: (a) their general characteristics, (b) the effect of gender and sitting posture and (c) the relationship between the contours and selected anthropometric variables (stature and mass). A contour measurement device was developed and used to measure buttock contours in five sitting postures (typing, sitting up, sitting back, slumping and writing). Buttock contours were quantified by constructing anterior-posterior (AP) and lateral profiles from which six discrete profile dimension measurements were made. AP and lateral profiles were found to have a consistent shape across all participants. Five out of six profile dimensions were significantly different between genders, with just one significantly different between sitting postures (typing and sitting back). Correlations between anthropometric measures and profile dimensions were relatively low (r < 0.34) with no clear patterns evident. Overall results of this study suggest that buttock contours are influenced by gender to a greater extent than sitting posture.     

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.     

Design and implementation of a system for body posture recognition

Under Ambient Intelligence auspice, many researchers have studied the area of context recognition such as location, users’ identity and activities, and other parameters related to users’ situation in the environment. One aspect of context that is pertained to the users’ situation is body posture of a sitting person. The aim of this paper is the design and development of a novel Aware Chair system that recognizes sitting body postures. The Aware Chair is based on digital sensors mounted on the sitting and back area of the chair. The chair is tested using 50 people with different gender, body mass, and height. The design details of the system as well as test results are presented in this paper.     

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

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

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

Effects of vehicle interior geometry and anthropometric variables on automobile driving posture

The effects of vehicle package, seat, and anthropometric variables on posture were studied in a laboratory vehicle mockup. Participants (68 men and women) selected their preferred driving postures in 18 combinations of seat height, fore-aft steering wheel position, and seat cushion angle. Two seats differing in stiffness and seat back contour were used in testing. Driving postures were recorded using a sonic digitizer to measure the 3D locations of body landmarks. All test variables had significant independent effects on driving posture. Drivers were found to adapt to changes in the vehicle geometry primarily by changes in limb posture, whereas torso posture remained relatively constant. Stature accounts for most of the anthropometrically related variability in driving posture, and gender differences appear to be explained by body size variation. Large intersubject differences in torso posture, which are fairly stable across different seat and package conditions, are not closely related to standard anthropometric measures. The findings can be used to predict the effects of changes in vehicle and seat design on driving postures for populations with a wide range of anthropometric characteristics.     

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.     

A comparison of sitting posture adaptations of pregnant and non-pregnant females

The postural differences between seated pregnant and non-pregnant subjects were studied, and the effects of various sitting workstation designs were assessed. Five pregnant and five non-pregnant subjects participated in this study. The experimental variables were the table-chair-vertical-distance (35 cm and 30 cm) and the seat-inclination-angle (0°, +10° and +20°). The seated working postures of the last 10 min of a 50-min sitting session were videotaped and analyzed using a 2D motion analysis system. Postural differences were observed between the pregnant and non-pregnant groups which may be attributed to the changes and/or mechanisms associated with pregnancy. The increased size of the abdomen requires more room in front of the body; in the pregnant subjects this was obtained by holding the upper-arm further from the body, inclining the upper trunk more anterior, and extending the hip more. A seat with a sloping angle of 10° was found to reduce the biomechanical loading on the lower back and in subjective ratings from both groups, was preferred over the other seat angles.

Relevance to industry

Pregnant women make up a small but significant part of the workforce. Changes in body form and working posture due to pregnancy change the effective working envelope and increase the biomechanical loads on the musculoskeletal system resulting in an increase in the risk of lower-back pain. This study examined the posture adaptations and the effects of workstation design on pregnant and non-pregnant subjects.     

Analysis of sitting comfortability of driver's seat by contact shape

Abstract

In order to evaluate sitting comfort qualitatively, a flexible and very thin sensor was developed to measure the contact shape between a seated man and the seal surface. Each tape has twenty strain guages on it at regular intervals, and the fourteen tape sensors were arranged on the bottom and back surface of the experimental driver's seat. The contact shapes and postures in thirty two male drivers were measured with two types of seal cushion and sitting posture: free and recommended. Sensory evaluation was made for each experimental condition. The results of the interrelation between the characteristics of the surface deformation, the parameters of body build, sitting posture and feeling of comfort shows that the comfort of each morphological fitting does not correspond to one special and single parameter from those physical factors, but is represented by a function with many parameters related to the deformation, posture and body build. By using these relations, a sensory model for the prediction of the sitting comfort was constructed.     

EMG analysis of sitting work postures in women

Based on EMG analysis on six middle-aged women, seven sitting work postures were compared with reference to relaxed standing position. The muscles included in the investigation are pectoralis major, levator scapulae, deltoideus, latissimus dorsi, upper fibres of the trapezius, erector spinae, vastus medialis and lateralis, rectus femoris and gastrocnemius muscles. The commoner sitting postures examined were sitting on the floor with crossed legs, sitting on the floor with right leg bent at the knee, sitting on the floor with left leg bent at the knee, squatting with both legs bent at the knee without any back support, sitting on a plank of 10 cm height with both legs bent at the knee, sitting on the floor with legs extended, and sitting upright on a stool of 40 cm height. The relative load on the muscles was highest in the case of sitting on the floor with the right leg bent at the knee. However, less muscle activity was noted when sitting on the floor with the legs extended, a posture commonly adopted by women performing various domestic and other activities.     

基于人机尺寸驱动的座椅设计系统

针对各类座椅产品,分析了其设计参数与人体坐姿与尺寸之间的关联关系,根据人机工程学知识和人体测量标准建立了标准化人体尺寸数据库和参数化人体模型。在Unigraphics平台上利用OpenGrip工具开发了人机尺寸驱动的座椅设计系统,实现了通过操作人体模型来自动生成符合人机性能要求的座椅产品,提高了设计师的工作效率并保证了所设计产品的合理人机性能。     

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.     

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.     

A Review of :“Leu Accidents du Travail.” By JACQUES LEPLAT et XAVIER CUNY. (Paris: Presses Universities de France, 1974.( [Pp.128. £0·00.

Police officers spend large amounts of time performing duties within a police cruiser and report a high prevalence of musculoskeletal problems. This study evaluated the effects of driver seat and duty belt design on posture, pressure and discomfort. Ten male and 10 female university students attended two sessions involving simulated driving in a standard police seat (CV) and an active lumbar support (ALS) seat. Participants wore a full duty belt (FDB) or reduced duty belt (RDB) in each seat. Lumbar postures, driver-seat and driver-duty belt pressures and perceived discomfort were measured. Gender × Seat interactions were found for pelvic (p = 0.0001) and lumbar postures (p = 0.003). Females had more lumbar flexion than males and were more extended in the ALS seat (?9.8 ± 11.3°) than CV seat (?19.8 ± 9.6°). The FDB had greater seat pressure than the RDB (p < 0.0001), which corresponded to increased pelvis discomfort. This study supports the use of an ALS seat and RDB to reduce injury risk associated with prolonged sitting in police officers.

Practitioner Summary: Police officers report a high prevalence of musculoskeletal problems to the lower back, associated with prolonged driving and further investigation is needed to reduce injury risk. This simulated driving study investigated seat and duty belt configuration on biomechanical measures and discomfort. Seat design had the greatest impact, regardless of gender and males benefited more from a reduced belt configuration.