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Designing one seat for multi-sitters and multi-activities is challenging especially in a very restrained aircraft economy class cabin. In this paper, the effects of seat parameters and sitters' anthropometric dimensions on seat profile and optimal compressed seat pan surface were studied using a newly built multi-adjustable experimental seat. The 'optimal' seat pan contact surface was obtained by controlling the height of 52 cylinders so that the normal contact force was distributed to all cylinders as evenly as possible. With 13 other motorized adjustments controllable by a computer, individual seat profile in the symmetry plane such as seat height, seat pan length, seat pan angle, lumbar protrusion and headrest position were also studied. Data were collected from 36 men and women of varying body size testing 40 seat configurations. Parametric models were obtained for predicting seat profile and optimal compressed seat pan seat surface in function of seat pan and back rest angles for two sitting postures. It is expected that the proposed parametric models provide necessary reference values in seat development for a better fit of a target population of sitters with large varying body size. [ABSTRACT FROM AUTHOR]

This study investigated changes in task-induced trunk sway of quay crane operators during a four-hour shift performed in a dedicated simulator as an indicator of postural control system effectiveness. Using a pressure sensitive mat placed on the seat pan, center-of-pressure (COP) time series were acquired and processed to calculate sway area, path length and COP displacements and velocities. The results show a well-defined linear trend for sway path and area, with significant increases starting from 65 to 155 min of work respectively. This indicates non-optimized trunk control most likely originated by the combination of physical and cognitive workload and suggests a possible role of long-term monitoring of trunk sway of crane operators as a useful tool in detecting non-optimized movements potentially associated with deteriorating performance. [ABSTRACT FROM AUTHOR]

Whereas in the past dental stools typically facilitated a 90° hip angle, a number of currently available alternative designs allow for a more extended hip posture. The present study investigated the influence of different stool types on muscle activity and lumbar posture. Twenty five participants completed a simulated dental procedure on a standard stool, a saddle and the Ghopec. The latter stool comprises a seat pan consisting of a horizontal rear part for the pelvis and an inclinable sloping down front part for the upper legs, with a vertically and horizontally adjustable back rest. Lumbar posture was most close to neutral on the Ghopec, whereas sitting on a standard/saddle stool resulted in more flexed/extended postures respectively. Sitting with a 90° angle (standard stool) resulted in higher activation of back muscles while sitting with a 125° angle (saddle and Ghopec) activated abdominal muscles more, although less in the presence of a backrest (Ghopec). To maintain neutral posture during dental screening, the Ghopec is considered the most suitable design for the tasks undertaken. [ABSTRACT FROM AUTHOR]

Measurements of the transmission of vibration from the floor beneath a seat to interfaces between the seat and the human body are used to characterise the dynamic performance of the seat. Most studies of seat transmissibility concern the transmission of vertical vibration through seat pan cushions, but fore-and-aft vibration at a seat pan and backrest can also cause discomfort. This study investigated the transmission of fore-and-aft vibration through a car seat to surfaces on the seat pan cushion, the backrest cushion and the headrest, and also to the seat frame at these three locations. The study sought to understand the influences of the seat frame and the cushion foam and to provide data for dynamic modelling of the seat. The fore-and-aft transmissibility of the seat was measured with 12 human subjects and an SAE J826 manikin, using 120-s periods of fore-and-aft random vibration (0.25-40 Hz) at three magnitudes (0.4 m/s2 r.m.s., 0.8 m/s2 r.m.s. and 1.2 m/s2 r.m.s.). With the manikin, there were three resonances (at 3.5 Hz, 12 Hz and 20 Hz) in the transmissibilities from the seat base to the seat pan frame and the seat pan cushion, and to the backrest frame and the backrest cushion. With the human subjects, the transmissibilities from the seat base to all six locations on the seat showed a principal resonance around 4 Hz. With increasing magnitude of the vibration, the principal resonance frequency in all the seat transmissibilities decreased. It is concluded that fore-and-aft resonances in the seat transmissibilities, especially to the backrest, are likely to affect vibration discomfort. There are large differences between the fore-and-aft transmissibility of a seat with a manikin and those with human subjects, consistent with the human body having dynamics very different from those of a rigid mass. Non-linearities in the seat transmissibilities with the manikin and with the human subjects may be explained by non-linearity in the biodynamics of the body and the responses of the seat and the manikin. [ABSTRACT FROM AUTHOR]

Nowadays, an increasing amount of time is spent seated, especially in office environments, where sitting comfort and support are increasingly important due to the prevalence of musculoskeletal disorders. The aim of this study was to develop a methodology for chair-specific sensor mat calibration, to evaluate the interconnections between specific pressure parameters and to establish those that are most meaningful and significant in order to differentiate pressure distribution measures between office chairs. The shape of the exponential calibration function was highly influenced by the material properties and geometry of the office chairs, and therefore a chair-specific calibration proved to be essential. High correlations were observed between the eight analysed pressure parameters, whereby the pressure parameters could be reduced to a set of four and three parameters for the seat pan and the backrest respectively. In order to find significant differences between office chairs, gradient parameters should be analysed for the seat pan, whereas for the backrest almost all parameters are suitable. [ABSTRACT FROM AUTHOR]

Highlights: [•] Burst fractures of the lumbar spine occur during non-horizontal crash forces. [•] Seat pan deformation demonstrates an axial load to the L-spine in frontal crashes. [•] Major L-spine fractures have increased in late model vehicles with bucket seats. [•] Belted occupants are at greater odds for L-spine burst fractures in a frontal crash. [•] An increase in age greatly increases the odds for L-spine fractures in a frontal crash. [ABSTRACT FROM AUTHOR]

This study investigates the effects of a dynamic seat pan design on sitting biomechanics, perceived pain and seat movement compared to a control. Thirty male participants were recruited for two experimental sessions consisting of a 2-h sitting exposure (standardized typing task). Spine angles, back muscle activity, perceived pain and calf circumference were measured pre and post exposure. Sitting in the dynamic condition resulted in lower pain ratings (p = 0.031), decreased calf circumference (p < 0.001), lower average seat pressure (p < 0.001), and greater seat contact area (p = 0.003) compared to the control. Spine angles and low back EMG for all 6 muscles showed no significant differences between chair conditions. These results suggest this dynamic seat pan design is effective at decreasing several negative components associated with sitting for the occupant. Future work should examine the longer-term effects of dynamic office chair features in the field setting with a more generalizable population. [ABSTRACT FROM AUTHOR]

Ride comfort in vehicles can be affected by seat properties. While previous studies focused on the vertical whole-body vibration, this study was designed to understand the influence of the foam thickness at the seat pan and at the backrest on seat transmissibilities with fore-and-aft vibration. Twelve subjects sitting with or without a vertical backrest were exposed to random fore-and-aft vibration between 1 and 15 Hz with the magnitude of 0.5 ms-2 r.m.s.. It was found that there was no significant difference in the primary resonance frequencies in the fore-and-aft in-line and vertical cross-axis transmissibilities to the seat pan and to the backrest. The resonance frequency in the fore-and-aft in-line transmissibilities to the seat pan and the backrest decreased with increasing thickness of foam at the seat pan and the backrest. Altering the thickness of foam at the seat pan was more effective than changing that at the backrest. [ABSTRACT FROM AUTHOR]

This paper investigates whether spring-foam technology in an aircraft seat-pan can reduce weight and at the same time provide equal or better comfort. Firstly, through literature studies and using an iterative design process a prototype seat-pan was designed and developed using spring-foam technology. The (dis)comfort of this seat was compared with a standard aircraft seat-pan. Twenty two participants were asked to sit in each seat for 90 min, completing a questionnaire every 15 min. At the end of each seating session pressure map recordings were made of the seat-pans. The results showed that the prototype seat-pan has on average a significantly higher comfort for the first 30 min and at a 60 min recording than the standard seat-pan. The discomfort and long term comfort were not significantly influenced. The pressure distribution on the prototype seat-pan was significantly closer to an ideal pressure distribution than a conventional seat-pan. In addition, the prototype seat-pan had a significantly larger contact area and lower average pressure. The seat-cushion weighs 20% less than the conventional seat-cushion. The study indicates that a seat-pan design using spring-foam technology can be lighter and more comfortable than conventional foam cushion materials. It is recommended to optimize the prototype seat further and conduct long term (dis)comfort studies with a broader variation in subjects' age. [ABSTRACT FROM AUTHOR]

Many factors affect the comfort of automotive seats including pressure distribution, vibration, temperature, and backrest inclination. However, one aspect of seating that has not been well studied is leg splay; splay is a rotation at the hips which causes the knees to move outward. The work presented here identified the ranges of "comfortable" splay in different styles of seats and related changes in seating pressure due to leg splay. Sixteen midsized male participants were tested in six seats: a flat control, three mid-sized sedan, a sports car, and a pickup truck. Participants sat with two leg conditions: 1) shoulder width apart and 2) rotating their legs to splay to a self-identified, comfortable position. For each test, the participant placed his left leg on a foot support and right leg on a depressible pedal to mimic a driving position. In each posture, leg angle and seat pan pressures were collected. Of the seats tested, the flat wooden seat had the highest possible splay (24.5°). The three sedan seats had similar splay angles (16.1-18.5°). The lowest splay values were in the sports car seat (8.96°) and truck seat (7.46°). This reduction in splay was attributed to the more aggressive bolsters in the sports car and a higher seat design position in the pickup truck seat. Following participant splay the pressures in the seat bolsters increased while the pressure in the left thigh and left buttocks regions decreased. By determining the comfortable ranges of splay and how pressure distribution is affected, seat designers and automobile manufacturers can use these data when evaluating seat designs and occupant positioning. [ABSTRACT FROM AUTHOR]