Back Support Conditions Research Articles

Gender and Anthropometric Effects on Seat-to-Head Transmissibility Responses to Vertical Whole-Body Vibration of Humans Seated on an Elastic Seat

This study investigated the effects of gender and ten different anthropometric parameters on the vertical vibration transmission from seat to the head of the body seated on an elastic seat. The seat-to-head transmissibility (STHT) responses in the vertical and fore-aft directions of 58 participants (31 males and 27 females) were measured under three levels of vertical vibration (root mean square acceleration: 0.25, 0.50, and 0.75 m/s2) in the 0.50–20 Hz range, when sitting on a viscoelastic seat with and without a vertical back support, and with hands on a steering wheel. Apart from the important effects of elastic coupling between the body and seat, the results show distinctly different vertical and fore-aft STHT responses from the two genders. Moreover, the gender effect was strongly coupled with back support and excitation conditions. The primary resonance frequencies of male subjects were higher than those of female subjects, while the peak vertical STHT magnitudes were comparable. Owing to the strong coupled effects of gender and anthropometric dimensions, the study is designed to reduce the coupling by considering datasets for subjects with comparable chosen dimensions. Among the various anthropometric dimensions considered, the body mass and fat mass revealed strong influences on the primary resonance frequency, which was similar for male and female subjects with comparable body mass index and body fat mass. The vertical STHT magnitude of the two genders with the same lean body mass was also nearly identical. The peak fore-aft STHT magnitudes of the male subjects were notably higher than those of the female subjects with comparable anthropometric dimensions with the exception of the body mass.

Differences in oscillometric blood pressure readings between unsupported and supported back conditions.

Appropriate body posture is important for accurate blood pressure (BP) measurement. However, the impact of an unsupported back on BP readings is currently controversial. This study included 224 subjects (18-86 years old, 54.5 ± 15.5 years old, 105 males). BP was measured with an oscillometric BP device randomly following one of two protocols for back support conditions: (1) supported-unsupported-supported-unsupported, or (2) unsupported-supported-unsupported-supported. The average of the two systolic BP (SBP) and diastolic BP (DBP) readings in the same position was recorded as the final BP value. The differences in BP between the unsupported and supported back conditions were calculated as delta BP. Moreover, the percentage variation in BP (PV) was calculated with the formula delta BP/BP with an unsupported back. Multivariable regression analysis evaluated the impact of age, sex, hypertension history and supported BP level on PV. The SBP/DBP levels measured with an unsupported back were slightly higher than those when the back was supported (132.7 ± 19.5/79.6 ± 12.9 mmHg vs. 130.3 ± 20.0/78.5 ± 14.3 mmHg), and the delta SBP (2.3 mmHg) was statistically significant. The multivariable regression analysis showed that age was a positive factor but supported SBP level as a negative factor for systolic PV, while age and supported DBP level were positive factors, but hypertension history was a negative factor for diastolic PV. For a group participant, the mean difference in oscillometric SBP/DBP in the unsupported back position was 2.3/1.0 mmHg higher than that in the supported back position.

Gender and anthropometric effects on whole-body vibration power absorption of the seated body

The gender and anthropometric effects on vibration absorbed power characteristics of the seated body are investigated through measurements with 31 males and 27 females considering two different back support conditions, and three levels of vertical vibration (0.25, 0.50, and 0.75 m/s2 rms acceleration) in the 0.5–20 Hz frequency range. The absorbed power responses for the males and females revealed strong gender effect, which could be mostly related to differences in body mass of the two groups. Subsequent analyses were conducted considering different datasets grouped corresponding to three ranges of the body mass-, build-, and stature-related parameters for both the males and females. Notable differences were evident in the absorbed power responses of the males and females with comparable anthropometric dimensions. Males revealed significantly higher peak and total absorbed power responses compared to the females of comparable anthropometric dimensions, except for the lean body mass. The differences, however, were relatively small in the data for males and females of comparable body mass. The peak power for the females, invariably, occurred at a lower frequency than that for the males. The total absorbed power responses revealed some degree of correlations with the body mass, lean body mass, body fat, and hip circumference ( r2>0.60), irrespective of the back support condition and excitation magnitude for both the genders.

Effect of lumbar support on human-head movement and discomfort in whole-body vibration

BACKGROUND: It is well known that prolonged sitting can elicit low back pain as a result of the abnormal shape of the spine. This problem becomes worse in whole-body vibration environments where a rocking motion of the pelvis can occur and may amplify the vibration motion transmitted to the lumbar spine. OBJECTIVE: Although the use of lumbar supports is common in static environments, little is known about how the use of such supports changes the biodynamic response and discomfort of the person in whole-body vibration environments. METHODS: The motion at the head and the discomfort of ten participants were recorded under five back-support conditions, including three commercially available lumbar supports. RESULTS:The results indicated significantly lower head motion and discomfort ( p< 0.05) with the use of the lumbar supports than with a simple flat backrest. CONCLUSIONS: All lumbar supports used in this study combined the advantages of reduced head motion and reduced discomfort during whole-body vibration.

Seated body apparent mass response to vertical whole body vibration: Gender and anthropometric effects

The gender and anthropometric effects on apparent mass characteristics of the seated body exposed to vertical vibration are investigated through laboratory measurements. The study was conducted on 31 male and 27 female subjects, exposed to three levels of vertical vibration (0.25, 0.50 and 0.75 m/s2 rms acceleration) in the 0.50 to 20 frequency range, while seated without a back support and against a vertical back support. The apparent mass responses were analyzed by grouping datasets in three ranges of mass-, build- and stature-related parameters for the male and female subjects. Comparisons of responses of male and female subjects with comparable anthropometric properties showed distinctly different biodynamic responses of the two genders. The primary resonance frequency of male subjects was significantly (p < 0.001) higher than the female subjects of comparable body mass but the peak magnitude was comparable for both the gender groups. The male subjects showed greater softening with increasing excitation magnitude compared to the female subjects, irrespective of the sitting condition. The male subjects showed significantly higher peak magnitude response than those of the female subjects for the same anthropometric properties, except for the total and lean body mass. The peak magnitude was linearly correlated with the body mass, body mass index, body fat and hip circumference (r2 > 0.7), irrespective of the back support and excitation conditions for both the genders. Relevance to the industryThe apparent mass responses of the human body exposed to whole-body vibration form an essential basis for an understanding of mechanical-equivalent properties of the body, developments in frequency-weightings for assessment of exposure risks and anthropodynamic manikins for assessment of seats. The effects of gender and anthropometric parameters on the AM response are vital for seeking better seat designs, and anthropodynamic manikins for assessments of seating for male as well as female workers.

점토지반내의 IER 지주식 흙막이의 실험적 고찰

기존의 흙막이 공법의 문제점을 보완하고 개선하기 위해서 새로이 고안한 공법이 지주식 흙막이공법이다. 지주식 흙막이 공법은 전면지주와 배면지주를 사항으로 설치하여 일체화시킨 가시설 공법으로, 배면지주의 설치로 인해 전면지주에 작용하는 토압을 효과적으로 분산시켜 가시설의 구조적인 안정성을 증대시킨 공법이다. 본 연구에서는 점토지반의 실내모형실험을 통해 배면지주의 설치 여부와 지주 하부의 고정 조건 등을 달리하여 지주식 흙막이 공법의 역학적 특성을 확인하였다. 실내모형실험결과 배면지주의 설치로 인해 IER 벽체의 수평변위가 효과적으로 감소하는 것으로 분석되었으며, 배면지주의 간격 및 고정 조건에 따른 효과가 분석되었다. Inclined Earth Retaining Structure Method (IER Method), was developed in order to improve the mechanical properties of the existing earth retaining method. IER consists of two supports, which are front and back supports. In the IER method, back support is very effective for the reduction of the earth pressure acting on the front support. In this study, the effects of back support and fixing conditions of lower ends of supports are analysed by laboratory model tests in clay. The test results show that back support reduces the Leteral displacement of IER effectively, and according to the results the effect of interval and fixing condition of back support was analysed.

Apparent mass and head vibration transmission responses of seated body to three translational axis vibration

The apparent mass and seat-to-head vibration transmissibility response functions of the seated human body were investigated under whole-body vibration exposures to fore-aft (x), lateral (y), and vertical (z) applied individually and simultaneously. The experiments were performed with 9 adult male subjects to measure the biodynamic responses to single and uncorrelated three-axis vibration with and without hands and back supports under different magnitudes of random vibration in the 0.5–20Hz frequency range. The apparent mass and the head vibration transmission responses were derived using two different frequency response function estimators based upon the cross- and auto-spectral densities of the response and excitation signals, denoted as H1 and Hv estimators, respectively. The two methods resulted in identical single-axis responses but considerably different responses under multi-axis vibration. The responses derived from the Hv estimator revealed significant coupling effects of three-axis vibration, which could be directly related to contributions of cross-axis responses observed under single-axis vibration, particularly those attributed to sagittal plane motion of the upper body. Such coupling effect, however, was not evident in the three-axis responses derived using the commonly used H1 estimator. The results also revealed significant effects of hands and back support conditions on the coupling effects of multiple axis vibration and the measured responses. The results suggest that biodynamic responses of the seated body exposed to simultaneous three-axis vibration, commonly encountered in work vehicles, differ considerably from the widely reported responses to individual axis vibration. A better understanding of the seated human body responses to uncorrelated three-axis whole-body vibration could be developed using the power-spectral-density based Hv estimator. Relevance to industryThe seated body biodynamic responses to multi-axis whole-body vibration and knowledge of coupling in the responses are essential for developing more efficient analytical models of the seated human body for applications in vehicular seating design and dynamics, and for deriving improved frequency-weighting for exposure assessment.

Ergonomically Designed Kneeling Chair Influence on Adolescent Idiopathic Scoliosis

Ergonomically design is very important for younger body growth healthy. According to the anthropometry which include the differences between adults and teenagers, and the motion of normal behavior and daily domain that influence of sitting situation, which designed for teenagers can get special design that fit for the younger in age stage developmental. Using this virtual simulation technique can detect the design of more product modeling whether accord with human body posture virtual scene lumber curvature, thus obtains the more effectiveness about posture of the human body according to Ergonomically design and back support condition. This method will greatly improve the comfortableness with prolonged sitting, and reduce low-back pain caused by poor chair design. Function of the back support system can affect muscles tension and guard against Adolescent idiopathic scoliosis.

Analyses of biodynamic responses of seated occupants to uncorrelated fore-aft and vertical whole-body vibration

The apparent mass and seat-to-head-transmissibility response functions of the seated human body were investigated under exposures to fore-aft ( x ), vertical ( z ), and combined fore-aft and vertical ( x and z ) axis whole-body vibration. The coupling effects of dual-axis vibration were investigated using two different frequency response function estimators based upon the cross- and auto-spectral densities of the response and excitation signals, denoted as H 1 and H v estimators, respectively. The experiments were performed to measure the biodynamic responses to single and uncorrelated dual-axis vibration, and to study the effects of hands support, back support and vibration magnitude on the body interactions with the seatpan and the backrest, characterized in terms of apparent masses and the vibration transmitted to the head. The data were acquired with 9 subjects exposed to two different magnitudes of vibration applied along the individual x- and z- axis (0.25 and 0.4 m/s 2 rms), and along both the axis (0.28 and 0.4 m/s 2 rms along each axis) in the 0.5–20 Hz frequency range. The two methods resulted in identical single-axis responses but considerably different dual-axis responses. The dual-axis responses derived from the H v estimator revealed notable effects of dual-axis vibration, as they comprised both the direct and cross-axis responses observed under single axis vibration. Such effect, termed as the coupling effect, was not evident in the dual-axis responses derived using the commonly used H 1 estimator. The results also revealed significant effects of hands and back support conditions on the coupling effects and the measured responses. The back support constrained the upper body movements and thus showed relatively weaker coupling compared to that observed in the responses without the back support. The effect of hand support was also pronounced under the fore-aft vibration. The results suggest that a better understanding of the seated human body responses to uncorrelated multi-axis whole-body vibration could be developed using the power-spectral-density based H v estimator.

Apparent Mass and Seat-to-head Transmissibility Responses of Seated Occupants under Single and Dual Axis Horizontal Vibration

The apparent mass and seat-to-head-transmissibility response functions of the seated human body are investigated under exposures to fore-aft (x), lateral (y), and combined fore-aft and lateral (x and y) axis whole-body vibration. The experiments were performed to study the effects of hands support, back support and vibration magnitude on the body interactions with the seat pan and the backrest, characterised in terms of fore-aft and lateral apparent masses and the vibration transmitted to the head under single and dual-axis horizontal vibration. The data were acquired with 9 subjects exposed to two different magnitudes of vibration applied along the individual x- and y- axis (0.25 and 0.4 m/s(2) rms), and along both the-axis (0.28 and 0.4 m/s(2) rms) in the 0.5 to 20 Hz frequency range, and analyzed to derive the biodynamic responses. A method was further derived to obtain total seated body apparent mass response from those measured at the backrest and the seatpan. The results revealed coupled effects of hands and back support conditions on the responses, while the vibration magnitude effect was relatively small. For a given postural condition, the biodynamic responses to dual-axis vibration could be estimated from the direct- and cross-axis responses to single-axis vibration, suggesting weakly nonlinear behaviour.

Influence of Support Conditions on Vertical Whole-body Vibration of the Seated Human Body

The vibration transmission to the lumbar and thoracic segments of seated human subjects exposed to whole body vibration of a vehicular nature have been mostly characterised without the back and hand supports, which is not representative of general driving conditions. This non-invasive experimental study investigated the transmission of vertical seat vibration to selected vertebrae and the head along the vertical and fore-aft axes of twelve male human subjects seated on a rigid seat and exposed to random vertical excitation in the 0.5-20 Hz range. The measurements were performed under four different sitting postures involving combinations of back support conditions and hands positions, and three difference magnitudes of vertical vibration (0.25, 0.5 and 1.0 m/s(2) rms acceleration). The results showed significant errors induced by sensor misalignment and skin effects, which required appropriate correction methodologies. The averaged corrected responses revealed that the back support attenuates vibration in the vertical axis to all the body locations while increasing the fore-aft transmissibility at the C7 and T5. The hands position generally has a relatively smaller effect, showing some influences on the C7 and L5 vibration. Sitting without a back support resulted in very low magnitude fore-aft vibration at T5, which was substantially higher with a back support, suggestive of a probable change in the body's vibration mode. The effect of back support was observed to be very small on the horizontal vibration of the lower thoracic and lumbar regions. The results suggest that distinctly different target body-segment biodynamic functions need to be defined for different support conditions in order to represent the unique contribution of the specific support condition. These datasets may then be useful for the development of biodynamic models.

Relationship between measured apparent mass and seat-to-head transmissibility responses of seated occupants exposed to vertical vibration

The “to-the-body” and “through-the-body” biodynamic response functions of the seated human body exposed to vertical vibration are measured and analyzed in an attempt to identify relationships between the apparent mass and seat-to-head transmissibility measures. The experiments involved 12 male subjects exposed to three magnitudes of whole-body vertical random vibration (0.25,0.5,1.0 m/s 2 rms acceleration) in the 0.5–15 Hz frequency range, and seated with three back support conditions (none, vertical and inclined), and two different hands positions (hands in lap and hands on the steering wheel). The vertical apparent mass and seat-to-head transmissibility responses were acquired during the experiments, where the head acceleration was measured using a light and adjustable helmet-strap mounted accelerometer. The results showed that both the measured responses show good agreements in the primary resonances, irrespective of the back support condition, while considerable differences between the normalized apparent mass and seat-to-head transmissibility could be seen in the secondary resonance range for the two back supported postures. The seat-to-head transmissibility responses are further shown to be relatively sensitive to back supported postures compared with that of apparent mass responses. Relatively stronger effects of hands position were observed on the seat-to-head transmissibility responses compared with the apparent mass responses under back supported conditions. From the results, it is further concluded that seat-to-head transmissibility emphasizes the biodynamic response in the vicinity of the secondary resonance compared to the apparent mass. The seat-to-head transmissibility measure is thus considered to be more appropriate for describing seated body response to higher frequency vibration.

Determination of reference values of apparent mass responses of seated occupants of different body masses under vertical vibration with and without a back support

The biodynamic response of human body seated without a back support and exposed to vertical whole-body vibration have been standardized in ISO 5982 and DIN 45676 in terms of driving-point mechanical impedance and apparent mass. A comparison of ranges defined in two standards, however, reveal considerable differences in both the magnitude and phase. Greater differences are more evident for the three body mass groups, which suggests the lack of adequate reference values of biodynamic responses of seated human subjects of different body masses. In this experimental study, the biodynamic responses of seated humans within three different body mass ranges are characterized under different magnitudes of vibration and three different sitting postures in an attempt to define reference values of apparent mass for applications in mechanical-equivalent model development and anthropodynamic manikin design. Laboratory measurements were performed with adult male subjects of total body mass in the vicinity of 55, 75 and 98 kg (nine subjects for each mass group) seated with and without an inclined back support and exposed to three different magnitudes of white-noise vertical vibration (0.5, 1.0 and 2.0 m/s 2 unweighted rms acceleration) in the frequency range between 0.5 and 20 Hz. The measured data were analyzed to derive the mean magnitude and phase responses for the three body masses, posture and excitation conditions. The mean magnitude responses of subjects within three mass groups were compared with idealized ranges defined in ISO 5982 and mean values described in DIN 45676 for no back support condition. The results revealed significant differences between the mean measured and standardized magnitudes, suggesting that the current standardized values do not describe the biodynamic responses of seated occupant of different masses even for the back not supported condition. The mean measured responses revealed most important effect of body mass, irrespective of the sitting posture. The reference values of apparent mass responses of seated body subject to vertical whole-body vibration are thus defined for three mass groups and different back support conditions that may be considered applicable for ranges of excitations considered. The responses of the body seated without a back support, also revealed notable influences of excitation magnitude, particularly on the primary peak frequencies.

Energy Absorption of Seated Occupants Exposed to Horizontal Vibration and Role of Back Support Condition

Absorbed power characteristics of seated human subjects under fore-aft (x-axis) and lateral (y-axis) vibration are investigated through measurements of dynamic interactions at the two driving-points formed by the body and the seat pan, and upper body and the backrest. The experiments involved: (i) three back support conditions (no back support, and back supported against a vertical and an inclined backrest); (ii) three seat pan heights (425, 390 and 350 mm); and three magnitudes (0.25, 0.5 and 1.0 m/s2 rms acceleration) of band limited random excitations in 0.5-10 Hz frequency range, applied independently along the x- and y- axes. The force responses, measured at the seat pan and the backrest are applied to characterize total energy transfer reflected on the seat pan and the backrest. The mean responses suggest strong contributions due to back support, and direction and magnitude of vibration. In the absence of a back support, the seat pan responses dominated in lower frequency bands centered at 0.63 and 1.25 Hz under both directions of motion. Most significant interactions of the upper body against the back support was observed under fore-aft vibration. The addition of back support caused the seat pan response to converge to a single primary peak near a higher frequency of 4 Hz under x- axis, with only little effect on the y-axis responses. The back support serves as an additional source of vibration to the occupant and an important constraint to limit the fore-aft movement of the upper body and thus relatively higher energy transfer under. The mean responses were further explored to examine the Wd frequency-weighting used for assessing exposure to horizontal vibration. The results show that the current weighting is suited for assessing the vibration exposure of human subjects seated only without a back support.

Effect of Back Support Condition on Seat to Head Transmissibilities of Seated Occupants under Vertical Vibration

The seat-to-head transmissibility (STHT) of seated human subjects has been investigated through measurements of vertical seat vibration transmitted to the head in both vertical and fore-and-aft directions. The experiment was performed using 12 adult male subjects exposed to whole-body vertical random vibration in the 0.5–15 Hz frequency range. The effects of back support conditions on the transmitted vibration were investigated by considering three back support conditions (No back support, vertical back support, and inclined back support), and two different hands positions (hands in lap and hands on the steering wheel) while exposed to three magnitudes of excitation (0.25, 0.5 and 1.0 m/s2 rms acceleration). A helmet-strap-mounted accelerometer mounting system was designed to measure the head acceleration motions along the three translational axes. The results attained from ANOVA suggested a strong influence of the back support condition on the magnitude of both the vertical and fore-and-aft STHT. The results also revealed the nonlinear response of the seated body with respect to the excitation magnitude, while the effect of hands position was judged to be insignificant.

The role of seat geometry and posture on the mechanical energy absorption characteristics of seated occupants under vertical vibration

The power absorption characteristics of 27 male and female seated subjects, exposed to vertical vibration in the 0.5–40 Hz frequency range, are characterized under different sitting postures. The measurements are performed for a total of 36 different sitting postural configurations realized through variations in hands position (in lap and on steering wheel), seat heights (510, 460 and 410 mm), and seat design factors involving pan (0° and 7.5°) and backrest (0° and 12°) orientations, and different back support conditions. The measured data, expressed in terms of the vertical absorbed power density, are analyzed to study the effects of sitting posture on the biodynamic response under whole-body vertical vibration. An indirect method of computing absorbed power from the apparent mass response is formulated and validated using the directly measured absorbed power data. The measured data were analyzed to study the dependence of vibration energy absorption on various factors related to anthropometry (body mass, fat and mass index), seat geometry and sitting postures. The strong linear dependence between the absorbed power and the body mass and body mass index were revealed over the frequency range considered. The results clearly validate that the power absorption strongly depends upon the magnitude of whole-body vibration. Both the absorbed power near the primary resonance and the total power increase nearly quadratically with the exposure level. The hands in lap sitting posture yields to higher power absorption, irrespective of the back support condition. The sitting with a backrest reduces the energy dissipation at low frequencies and increases the energy absorption at frequencies above resonance, irrespective of the hands position, while the influence of seat pan inclination is negligible within the range of angles investigated. Relevance to industry The biodynamic responses of seated occupants exposed to whole-body vibration have been mostly investigated in terms of apparent mass characteristics, which show negligible contributions due to exposure level. Considering that the severity of vibration exposure is related to the level and duration of exposure, the apparent mass responses cannot be used for assessment of the associated risks. Alternatively, the absorbed power characteristics of the seated vibration exposed occupants show strong dependence on the level of exposure. Moreover, the absorbed power response characteristics could be applied to obtain an estimate of the cumulative energy dissipated by the exposed body over a given exposure duration. The absorbed power can thus serve as a measure for assessing the health and safety risks associated with exposure to whole-body vertical vibration. The energy dissipation by the vibration-exposed body is further influenced by the sitting posture and seat design factors. The knowledge of the seat design factors and some of the anthropometric factors on the energy dissipation is thus vital to realize better seat designs.

Influence of Back Support Conditions on the Apparent Mass of Seated Occupants under Horizontal Vibration

The response characteristics of seated human subjects exposed to fore-aft (x-axis) and lateral (y-axis) vibration are investigated through measurements of dynamic interactions between the seated body and the seat pan, and the upper body and the seat backrest. The experiments involved: (i) three different back support conditions (no back support, and upper body supported against a vertical and an inclined backrest); (ii) three different seat pan heights (425, 390 and 350 mm); and three different magnitudes (0.25, 0.5 and 1.0 m/s2 rms acceleration) of band limited random excitations in the 0.5-10 Hz frequency range, applied independently along the fore-aft and lateral directions in an uncoupled manner. The body force responses, measured at the seat pan and the backrest along the direction of motion, are applied to characterize the total body apparent mass (APMS) reflected on the seat pan, and those of the upper body reflected on the backrest. Unlike the widely reported responses of seated occupants under vertical vibration, the responses to horizontal vibration show strong effect of excitation magnitude. The large displacements at lower frequencies cause considerable rotations of the upper body, and the knees and ankles, particularly when seated without a back support, which encouraged the occupants to continually shift larger portion of the body weight towards their feet. This together with the strong dependence on the excitation magnitude resulted in considerable inter-subject variability of the data. The addition of a back support causes stiffening of the body to limit the low frequency rocking motion of the upper body under x-axis motion, while considerable dynamic interactions with the backrest occur. The mean apparent mass (APMS) responses measured at the seat pan and the backrest suggest strong contributions due to the back support condition, and the direction and magnitude of horizontal vibration, while the role of seat height is important only in the vicinity of the resonant frequencies. In the absence of a back support, the seat pan responses predominate at a lower frequency (near 0.7 Hz) under both directions of motion, while two secondary peaks in the magnitude also occur at relatively higher frequencies. The addition of back support causes the seat pan response to converge mostly to a single primary peak, resulting in a single-degree-of-freedom like behavior, with peak occurring in the 2.7-5.4 Hz range under x-axis, and 0.9-2.1 Hz range under y-axis motions, depending upon the excitation magnitude and the back support condition. This can be attributed to the stiffening of the body in the presence of the constraints imposed by the backrest. A relaxed posture with an inclined backrest, however, causes a softening effect, when compared to an erect posture with a vertical backrest. The backrest, however, serves as another source of vibration to the seated occupant, which tends to cause considerably higher magnitude responses. The considerable magnitudes of the apparent mass response measured at the seat back under fore-aft motions suggest strong interactions with the backrest. Such interactions along the side-to-side motions, however, are relatively small. The results suggest that the biodynamic characterization of seated occupants exposed to horizontal vibration requires appropriate considerations of the interactions with the backrest.

Effects of sitting postures on biodynamic response of seated occupants under vertical vibration

The biodynamic response characteristics of 13 male and 14 female seated subjects, exposed to vertical vibration, are characterized under different postural conditions. The measurements are performed for a total of 36 different sitting postural configurations realized through variations in hands position (in lap and on steering wheel), three seat heights (510, 460 and 410 mm), and seat design factors involving two different pan orientations (0° and 7.5°) and three different back support conditions (no support, and support with vertical and inclined backrest). The measured data, expressed in terms of the vertical apparent mass (APMS), are analyzed to study the effects of sitting posture on the biodynamic response under whole-body vertical vibration. Owing to the complex dependence of apparent mass response on the body mass, the statistical analyses are performed with body mass as a covariant. The results suggest that the hands in lap posture yields larger primary resonant frequency and considerably higher APMS magnitude response in the vicinity of primary resonant frequency than the hands on the steering wheel posture, when the back is supported with an inclined backrest. The apparent mass magnitudes at frequencies above the primary resonance tend to increase when the back is supported irrespective of the hands position. A higher seat height yields higher peak magnitude response which is attributed to relatively larger portion of the body mass supported by the seat, while the influence of seat pan inclination is observed to be negligible for range of inclination investigated. Relevance to industry The apparent mass of seated occupants exposed to whole body vibration yields significant information on human response to vibration, and forms the basis for developing analytical models representing the seated human body, and for potential applications in assessment of coupled occupant system and design of automotive seat. The knowledge of influence of various design and operating factors, and some of the anthropometric factors is vital to realize better seat design.