Malaysian sitting anthropometry for seat fit parameters

This article presents sitting anthropometry data for Malaysians focusing on seat fit parameters. It offers additional data regarding seat design requirements as there have been only a few efforts made to establish anthropometry data in Malaysia. An analysis using a measurement composed of 16 common and important dimensions in seat design was done with 216 subjects. Data collection was done by using direct measuring methods with standard equipment. Malaysian automobile seat fit parameters, namely backrest width, backrest height, cushion width, and cushion length were established from collected anthropometric dimensions: interscye breadth (5th percentile female and 95th percentile male), sitting shoulder height (5th percentile female), hip breadth (95th percentile female), and buttock–popliteal length (5th percentile female), respectively. From the data collected, this study finds that the fit parameter dimensions are bigger than other Asians' 95th percentile values but smaller than the Filipino and the Thai data being compared in this study. The female 5th percentile values for cushion length and cushion width are the smallest. In addition, two local automobile seats were measured and compared with the data. It was observed that the cushion lengths of both seats were too long for the 5th percentile female of the current data. This study provides seat fit parameters–the most fundamental part of automotive seat design, especially for the Malaysian population. © 2010 Wiley Periodicals, Inc.     

Biomechanical model to predict loads on lumbar vertebra of a tractor operator

A biomechanical model is important for prediction of loads likely to arise in specific body parts under various conditions. The biomechanical model was developed to predict compressive and shear loads at L4/L5 (lumbar vertebra) of a tractor operator seating on seats with selected seat pan and backrest cushion materials. A computer program was written to solve the model for various inputs viz. stature and weight of the tractor operators, choice of operating conditions, and reaction forces from seat pan and backrest cushions. It was observed that maximum compressive and shear forces ranged 943–1367 N and 422–991 N, respectively at L4/L5 of tractor operators steering the tractor with leg and hand control actions and occasionally viewing the implement at back. The compressive forces were maximum (1202–1367 N) with coir based composite seat backrest cushion materials (thickness of 80 mm, density of 47.19 kg/m³) and were minimum (943–1108 N) with high density polyurethane foam (thickness of 44 mm, density of 19.09 kg/m³) for the seats.Relevance to industryThe biomechanical model of a tractor operator is important for theoretical understanding the problem of sitting and is also valuable in prediction of compressive and shear loads at L4/L5 of operator under various operating conditions. It will help in design of tractor seat for operator's comfort.     

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.     

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.     

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.     

Transmission of vertical vibration through a seat: Effect of thickness of foam cushions at the seat pan and the backrest

The perception of vehicle ride comfort is influenced by the dynamic performance of full-depth foam used in many vehicle seats. The effects of the thickness of foam on the dynamic stiffness (i.e., stiffness and damping as a function of frequency) of foam cushions with three thicknesses (60, 80, and 100 mm), and the vibration transmitted through these cushions at the seat pan and the backrest were measured with 12 subjects (6 males and 6 females). With increasing thickness, the stiffness and the damping of the foam decreased. With increasing thickness of foam at the seat pan, the resonance frequencies around 4 Hz in the vertical in-line and fore-and-aft cross-axis transmissibilities of the seat pan cushion and the backrest cushion decreased. For the conditions investigated, it is concluded that the thickness of foam at a vertical backrest has little effect on the vertical in-line or fore-and-aft cross-axis transmissibilities of the foam at either the seat pan or the backrest. The frequencies of the primary resonances around 4 Hz in the vertical in-line transmissibility and the fore-and-aft cross-axis transmissibility of foam at the seat pan were highly correlated. Compared to sitting on a rigid seat pan with a foam backrest, sitting with foam at both the seat pan and the backrest reduced the resonance frequency in the vertical in-line transmissibility of the backrest foam and increased the associated transmissibility at resonance, while the fore-and-aft cross-axis transmissibility of the backrest was little affected. Compared to sitting without a backrest, sitting with a rigid vertical backrest increased the resonance frequency of the fore-and-aft cross-axis transmissibility of the seat pan cushion and increased the transmissibility at resonance.Relevance to industryThe transmissibility of a seat is determined by the dynamic properties of the occupant of the seat and the dynamic properties of the seat. This study shows how the thicknesses of foam at a seat pan and foam at a backrest affect the in-line and cross-axis transmissibilities of the foams at the seat pan and the backrest. The findings have application to the design of vehicle seats to minimise the transmission of vibration to the body.     

Design of combine harvester seat based on anthropometric data of Iranian operators

Harvesting operation with agricultural combines imposes excessive physical loads on the operators and the poorly designed seats may be an important contributory factor in this regard. This aims of this field study were to evaluate the possible mismatch between seat dimensions of existing harvesting combines and anthropometric characteristics of 200 Iranian operators and to propose seat dimensions based on anthropometric principles. The anthropometric dimensions of each individual operator were compared to the relative seat dimensions using the equations proposed in the literature. The results showed a considerable mismatch for different seat dimensions including upper backrest width (100%), seat height (97%), armrest height (83.7%), seat width (52.8%), lower backrest width (40.6%) and seat depth (39.5%). This meant that the existing combine seats were too high, too narrow and too shallow and had armrests and backrests which did not match with body dimensions of the majority of the operators. It was shown that compared to the existing designs, the new proposed dimensions (including seat height = 400 mm, seat width = 450 mm, seat depth = 410 mm, armrest height = 290 mm, backrest height = 420 mm, upper backrest width = 360 mm and lower backrest width = 400 mm) better matched to the operator's anthropometry, with the match percentages ranging from 77% to 100%.Relevance to industryThe design and manufacturing of agricultural machinery should be made based on the anthropometric characteristics of actual users to avoid unnecessary demands on them. This study provide additional data on the operator's anthropometry that can be used as a starting point for designing more appropriate agricultural machinery or used by other researchers in the field.     

Classroom furniture and anthropometric characteristics of Iranian high school students: Proposed dimensions based on anthropometric data

The study evaluated the potential mismatch between classroom furniture dimensions and anthropometric characteristics of 978 Iranian high school students (498 girls, 480 boys), aged 15-18 years. Nine anthropometric measurements (stature, sitting height, sitting shoulder height, popliteal height, hip breadth, elbow-seat height, buttock-popliteal length, buttock-knee length and thigh clearance) and five dimensions from the existing classroom furniture were measured and then compared together (using match criterion equations) to identify any potential mismatch between them. The results indicated a considerable mismatch between body dimensions of the students and the existing classroom furniture, with seat height (60.9%), seat width (54.7%) and desktop height (51.7%) being the furniture dimensions with a higher level of mismatch. The levels of mismatch varied between the high-school grade levels and between genders, indicating their special requirements and possible problems. The proposed dimensions of the classroom furniture more appropriate for the students were given. This additional information on students' anthropometry can be used by local furniture industries as a starting point for designing more appropriate furniture for school children, or used by schools to aid in furniture selection.     

Effects of aircraft seat pitch on interface pressure and passenger discomfort

Seat pitch, defined as the distance from a point on the back of one seat to the same point on the seat in front, is one of the most important factors influencing aircraft seating comfort. This study assessed the influence of different airline seat pitches on subjective ratings of discomfort and body-seat interface contact pressures. This was a laboratory within-subjects study using an aircraft interior mock up to vary seat pitch. Twelve participants completed 1 h of sitting in each of five different seat pitches (28inches, 30inches, 32inches, 34inches, and 36inches). Interface pressure mats measured seat and backrest pressure distribution, subjective rating scales were used to measure overall and local body region discomfort. The results showed that overall body and local body region discomfort ratings tend to be lower when the seat pitch increased from 28 inches to 36 inches (p < 0.05). For pressure variables, the upper back average contact area, upper/lower back average contact pressure, upper/lower back average peak contact pressure, right buttock average contact area, left/right thigh buttock average peak contact pressure, and left buttock average peak contact pressure were significantly affected by seat pitch(p < 0.05). Separate analyses support that seat pitch was more strongly correlated with backrest interface pressure than with seat pan pressure. In conclusion, seat pitch was found to be an important factor associated with body-seat contact pressure and discomfort ratings.     

The effect of an adjustable sitting angle on the perceived discomfort from the back and neck-shoulder regions in building crane operators

In a previous working environment study of building crane operators, it has been found that approximately 70% experienced discomfort from the locomotor system. Comments by the interviewed crane operators indicated that it is, among other things, the forward flexed sitting position during lifts close to the crane that causes discomfort. This investigation sought to apply knowledge from the forestry industry concerning the beneficial effects of improved operator's seats to the work situation of crane operators.

On a construction site with three cranes, an operator's seat with adjustable sitting angle was installed in one of the cranes. Estimation of perceived strain-discomfort in the lumbar region of the back as well as in the neck-shoulder region was assessed according to Borg's scale. Data were collected from the crane operators seated in their ordinary operator's seat, seated in the test seat, and seated in another crane with an ordinary type of seat. The results showed that in 1/3 rd of all lifts, the crane operator was sitting bent-forward with little opportunity for relief via a backrest or armrests. The highest estimated discomfort values in the study were also obtained in an ordinary operator's seat on days with a high proportion of lifts close to the crane. When working in the test seat, none of the subjects gave an estimate higher than 0·5 (discomfort equivalent to very, very weak). An adjustable operator's seat could be a good alternative to a fixed seat, and more tests would be desirable.     

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.     

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.     

Anthropometric criteria for the design of tractor cabs and protection frames

Improved human?–?tractor interface designs, such as well-accommodated operator enclosures (i.e. cabs and protection frames) can enhance operator productivity, comfort and safety. This study investigated farm-worker anthropometry and determined the critical anthropometric measures and 3-D feature envelopes of body landmarks for the design of tractor operator enclosures. One hundred agriculture workers participated in the study. Their body size and shape information was registered, using a 3-D full-body laser scanner. Knee height (sitting) and another eight parameters were found to affect the cab-enclosure accommodation rating and multiple anthropometric dimensions interactively affected the steering wheel and gear-handle impediment. A principal component analysis has identified 15 representative human body models for digitally assessing tractor-cab accommodation. A set of centroid coordinates of 34 body landmarks and the 95% confidence semi-axis-length for each landmark location were developed to guide tractor designers in their placement of tractor control components in order to best accommodate the user population. Finally, the vertical clearance (90?cm) for agriculture tractor enclosure in the current SAE International J2194 standard appeared to be too short as compared to the 99th percentile sitting height of male farm workers in this study (100.6?cm) and in the 1994 National Health and Nutrition Examination Survey III database (99.9?cm) and of the male civilian population in the 2002 Civilian American and European Surface Anthropometric Resource database (100.4?cm).     

Intervention on seat adjustment among drivers of forest tractors

The aim of this study was to clarify the ergonomics of forest tractor drivers' sitting conditions, to study how well drivers had adjusted the seats of forest tractors and to study the short-term effect of the backrest adjustment and the use of accessory lumbar support on neck-shoulder and low-back symptoms of drivers. The subjects in this field study were 100 male forest tractor drivers aged 21–50 years (37 ± 7 years) from central and eastern Finland. The drivers were visited twice, and a two-week intervention on seat adjustment was carried out between the visits. The methods used were interview and assessment of the seat. The height and inclination of the seat, inclination of the backrest and the stiffness of the spring were measured; after the measurements, the technician adjusted the seat. Half of the drivers were given an accessory lumbar support (Camp 21025) and advice concerning its use. Pain, stiffness and fatigue of the low-back and neck-shoulder at the end of the shift were reported to have diminished among nearly all drivers. There were no differences between the intervention groups regardless of whether the inclination of the backrest was adjusted or not or whether the drivers had used the lumbar support or not during the two-week intervention period. Relevance to industryThe results of this study can be taken into account when improvements are made in the ergonomics of the seats of forest tractors.     

Anthropometric criteria for the design of tractor cabs and protection frames

Improved human-tractor interface designs, such as well-accommodated operator enclosures (i.e. cabs and protection frames) can enhance operator productivity, comfort and safety. This study investigated farm-worker anthropometry and determined the critical anthropometric measures and 3-D feature envelopes of body landmarks for the design of tractor operator enclosures. One hundred agriculture workers participated in the study. Their body size and shape information was registered, using a 3-D full-body laser scanner. Knee height (sitting) and another eight parameters were found to affect the cab-enclosure accommodation rating and multiple anthropometric dimensions interactively affected the steering wheel and gear-handle impediment. A principal component analysis has identified 15 representative human body models for digitally assessing tractor-cab accommodation. A set of centroid coordinates of 34 body landmarks and the 95% confidence semi-axis-length for each landmark location were developed to guide tractor designers in their placement of tractor control components in order to best accommodate the user population. Finally, the vertical clearance (90 cm) for agriculture tractor enclosure in the current SAE International J2194 standard appeared to be too short as compared to the 99th percentile sitting height of male farm workers in this study (100.6 cm) and in the 1994 National Health and Nutrition Examination Survey III database (99.9 cm) and of the male civilian population in the 2002 Civilian American and European Surface Anthropometric Resource database (100.4 cm).     

Mismatch between classroom furniture and anthropometric measures in Chilean schools

Children spend about five hours per day sitting down while doing their school work. Considering this as well as the potential inadequate use of school furniture, it is likely that some anatomical-functional changes and problems in the learning process may occur. The aim of this study was to compare furniture sizes within three different schools with the anthropometric characteristics of Chilean students in the Valparaíso region, in order to evaluate the potential mismatch between them. The sample consisted of 195 volunteer students (94 male, 101 female) of the 8th grade, ranging from 12.5 to 14.5 years of age from 3 different schools. Regarding the methodology, 6 anthropometric measures (Stature, Popliteal height, Buttock-popliteal length, Elbow height while sitting, Hip width, Thigh thickness and Subscapular height) were gathered, as well as 8 dimensions from the school furniture. For the evaluation of classroom furniture a match criterion equation was defined. After considering the existing classroom furniture dimensions in each match criterion equation, the anthropometric characteristics of the considered population were compared in order to determine the mismatch between them. Results indicated that seat height, which should be considered as the starting point for the design of classroom furniture, was appropriate for students' popliteal height in only 14% of the 2 out of the 3 schools, and 28% in the third. Seat to desk height was too high and mismatched 99% of the students in one school and 100% in the others. Therefore, it was possible to conclude that the classroom's furniture was inadequate in almost all the analyzed cases and subjects. It is possible that the high mismatch percentage found between furniture and students' anthropometry can be associated to the fact that the acquisition and selection of the furniture was made without any ergonomic concern or criteria.     

The effect of seat back inclination on spine height changes

The effect of backrest inclination on spinal height changes was tested during static sitting and seated whole-body vibrations. The vibration input was sinusoidal with a frequency of 5 Hz and an acceleration of 0.1 g rms. The backrest inclinations tested were 110 degrees and 120 degrees . The 110 degrees backrest caused less shrinkage than did the 120 degrees during static sitting, whereas the opposite was true when vibration was present, although the differences between the backrests were not statistically significant. Only when the results were compared with results from exposure to unsupported sitting were the differences statistically significant for both static sitting and seated vibrations when the 110 degrees backrest was used and for vibration with the 120 degrees backrest. Thus we conclude that an inclined backrest reduces the effects of vibration. More importantly, emphasis should be placed upon seats and seat materials that can attenuate vibration.     

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.     

Mismatch between classroom furniture and anthropometric measures of university students

The appropriate design of tools, equipment and accessories for human body sizes, while meeting the social, cultural, economic and psychological needs of people, provides maximum benefit. This is crucial for students who spend most of their time using school furniture. The aim of the study is to investigate the mismatch between school furniture dimensions and students’ anthropometric measures. Nine anthropometric measures were taken of 225 students (68 female and 157 male) from nine departments of an engineering faculty using a specially designed measurement tool. The mismatch percentages between the existing classroom furniture dimensions and the anthropometric measures were determined using some well-known criterion equations. The results indicated a considerable mismatch: 44.45% for seat height, 100% for seat depth, and 21.28% for desk height. Two types of proposed classroom furniture achieved much higher percentage matches. The match percentages were above 70% for four dimensions for type A and above 95%, except for seat height and width of backrest, for all of the dimensions for both types.Relevance to industryThis study helps in establishing and motivating necessary further studies in classroom ergonomics in university settings.     

Body height change from motor vehicle vibration

Seventeen (17) subjects were exposed to tri-axial vehicle whole-body vibration for approximately 3 h, and measured hourly for body height. The control was the same environment, but no vibration. A broad band predominantly z-axis acceleration (1.6–10 Hz), with a mean level of 0.885 m/s² at the seat, was generated by a semi-truck tractor driven on secondary roads. The dominant one-third octave band of the vibration at the seat was 2 Hz with an acceleration magnitude of 0.521 m/s². At the end of the first hour, the results indicated a subject growth by 1.14 mm when exposed to vibration and a shrinkage of nearly equal amount without vibration. In the second and third hours, subjects followed the natural tendency to shrink under both conditions. At the end of the third hour, the subject height with vibration was 2.23 mm higher than that without vibration.

Relevance to industry

Whole body vibration has been identified as a possible cause for low-back pain problem in professional truck drivers. The body height measure in this study could potentially provide a link between low-back pain and vibration