Biodynamic Analysis of the Human Body Subjected to Vibration

2010

Objective: This study aimed to assess the effects of backrest inclination and vibration frequency on muscle activity in a dynamic environment using a musculoskeletal model. Method: The muscle activity modeling method was used to analyze a full body musculoskeletal system of a seated person with a public domain rigid body model in an adjustable car seat. This model was established using AnyBody Modeling System, based on the inverse dynamic approach. And the min/max criterion in dealing with the muscle redundancy problem. Ten healthy subjects were exposed to whole body vibration (WBV) with five frequencies (3, 4.5, 6, 7, and 8 Hz) in the vertical direction in a randomized order on three separate days. The displacement of the seat-pan and head was measured using a hybrid Polaris spectra system to obtain the seat-to-head (STH) transmissibility. Muscle oxygenation was measured using near-infrared spectroscopy. The validity of the model was tested using STH transmissibility and muscle oxygenation. Results: Increased vibration frequency caused high muscle activities of the abdomen and the right leg with a backrest forward inclination angle. The muscle activities of the left leg decreased at a backrest backward inclination except at inclination angles of 15 and 30 . Muscle activity of the lumbar suddenly increased at a backrest inclination angle of 5 and vibration frequency of 5 Hz. Muscle activities were higher under vibration than that without vibration. Conclusion: Vibration frequency significantly affected the muscle activity of the lumbar area. Likewise, the inclination degree of the backrest significantly affected the muscle activities of the right leg and the abdomen. The combination of vibration and forward inclination of the backrest can be used to maximize the muscle activity of the leg, similar to the abdomen and lumbar muscles. Relevance to the industry: The musculoskeletal model established in the present study provides a method that can be used to investigate the biomechanical response of seated drivers to WBV. This model helps protect drivers from occupational injury.

Journal of Sound and Vibration, 2002

WBV-exposures are often linked with forced postures as prolonged sitting, bent forward sitting, or sitting without a backrest. No quantitative data are available to describe the exposure}e!ect relationships for di!erent conditions of seating, posture, and the biological variability of workers. Experiments and subsequent predictions of forces acting within the spine during WBV can help to improve the assessment of the health risk. An experimental study was performed with 39 male subjects sitting on a suspension seat with or with no backrest contact. They were exposed to random whole-body vibration with a weighted r.m.s. value of 0)6 m/s at a relaxed or a forward bending posture. A two-dimensional "nite element model was used for the calculation of the internal spinal load. The model simulates the human response on a suspension driver seat. Individual exposure conditions were considered by including the transfer functions between the seat cushion and the seat base as well as between the backrest and the seat base for the calculation of the vibration input to the buttocks and to the back respectively. The average peak seat transmissibility was higher for the seat with the backrest, but the peak seat-to-head transmissibility was higher for the seat without the backrest for both postures. The peak transmissibilities between the accelerations at the seat base and the compressive forces at L5/S1 were highest for the seat without the backrest during the bending posture. Various biological e!ects can result from identical exposures combined with di!erent backrest contact and postures. The backrest contact and posture conditions should not be neglected in the assessment of health risk caused by whole-body vibration.

Contemporary vehicles have to satisfy high ride comfort criteria. This paper represents an attempt to form criteria for ride comfort improvement of passenger cars. Filed and laboratory investigations on passenger cars have been performed. In field research, dominant vibrations loading were determined by variance analysis of experimental results. The highest loading is in vertical and in fore and in aft direction. These results were base for further laboratory investigations. Purpose of this work was to investigate human behavior under random vibrations. Group of thirty subjects was tested. We have examined the influence of broadband random vibrations on human by Seat To Head Transmissibility (STHT) function. Influence of vertical and fore and aft vibrations on occupants were examined separately. In addition, the influence of multi directional vibration was investigated. Analysis of seat to head transmissibility results showed that in vertical direction seated human body has two resonant frequencies and two resonant frequencies in fore and aft direction under multi directional broadband random vibration. There was high coherency between signals in vertical and fore and aft, direction on the same measuring place and human behavior under multi directional random vibrations can not be approximated by simple superposition of one directional vibration results. Obtained results were base for parameter identification of appropriate biodynamic human model in sitting position. Plane non-linear model was developed. Suggested model showed good corresponding with experimental results.

International Journal of Industrial Ergonomics, 2008

To determine the acute effects of whole-body vibration (WBV) on the sensorimotor system and potentially on the stability of the spine, different biomechanical responses were tested before and after 60 min of sitting, with and without vertical WBV, on four different days. Postures adopted while sitting and the simulated WBV exposure corresponded to large mining load haul dump (LHD) vehicles as measured in the field. Twelve males performed trials of standing balance on a force plate and a sudden loading perturbation test to assess back muscle reflex response, using surface electromyography (EMG). This latter test also allowed to assess if any muscle fatigue occurred as a result of the exposure. First of all, it was shown that back muscle activity while sitting with vibration was significantly higher as compared to back muscle activity while sitting with no vibration. However, WBV per se elicited very few effects on the other outcome variables and thus not supporting our hypothesis that WBV had any effect on spinal stability. Though WBV may not have elicited any effects, new findings have emerged concerning the effect of sitting on muscle fatigue and balance. It was shown that sustaining trunk sitting postures corresponding to mining vehicle operators generate back muscle fatigue. Unexpectedly, standing balance was also improved. The possible explanations and relevance of these findings are discussed. Relevance to industry Occupational groups exposed to WBV while sitting are at increased risk for low back disorders. The results of this study do not support the possible injury pathway linking WBV and back pain via sensorimotor deficits. Unexpectedly, it appears that sitting per se may affect the sensorimotor system but this may only apply to sitting postures corresponding to driving mining vehicles.

Industrial Health, 2010

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.

Applied Ergonomics, 2009

Understanding the behavior of human body under the influence of vibration is of great importance for the optimal motor vehicle system design. Therefore, great efforts are being done in order to discover as many information about the influence of vibration on human body as possible. So far the references show that the major scientific attention has been paid to vertical vibration, although intensive research has been performed lately on the other sorts of excitation. In this paper, the results of the investigation of behavior of human body, in seated position, under the influence of random fore and aft vibration are shown. The investigation is performed by the use of an electro-hydraulic simulator, on a group of 30 healthy male occupants. Experiments are performed in order to give results to improve human body modeling in driving conditions. Excitation amplitudes (1.75 and 2.25 m/s 2 rms) and seat backrest conditions (with and without inclination) were varied. Data results are analyzed by partial coherence and transfer functions. Analyses have been performed and results are given in detail. The results obtained have shown that the human body under the influence of random excitations behaves as a non-linear system and its response depends on spatial position. Obtained results give necessary data to define structure and parameters of human biodynamic model with respect to different excitation and seat backrest position.

MATEC Web of Conferences

This paper analyses the influence of whole-body vibrations on human performance; for this it was investigated how a group of men (20-29 years of age) and a group of woman (21-31 years of age) answered to specific requirements after being subjected to vertical vibrations under controlled laboratory conditions for 10-25 min. The vibrations were generated by a vibrant system with known amplitudes and frequencies. Accelerations were measured with NetdB-complex system for measuring and analysing human vibration and they were found in the range 0.4-3.1m/s 2. The subjects' performances were determined for each vibration level using specific tests. It can be concluded that exposure to vibrations higher than those recommended by ISO 2631 significantly disrupts how subjects responded to tests requirements.

Ergonomics, 2011

This study investigated the effects of reclined backrest angles on cognitive and psychomotor tasks during exposure to vertical whole-body vibration. Twenty participants were each exposed to three test stimuli of vertical vibration: 2-8 Hz; 8-14 Hz and 14-20 Hz, plus a stationary control condition whilst seated on a vibration platform at five backrest angles: 0° (recumbent, supine) to 90° (upright). The vibration magnitude was 2.0 ms −2 root-mean-square. The participants were seated at one of the backrest angles and exposed to each of the three vibration stimuli while performing a tracking and choice reaction time tasks; then they completed the NASA-TLX workload scales. Apart from 22.5° seat backrest angle for the tracking task, backrest angle did not adversely affect the performance during vibration. However, participants required increased effort to maintain performance during vibration relative to the stationary condition. These results suggest that undertaking tasks in an environment with vibration could increase workload and risk earlier onset of fatigue.

International Journal of Vehicle Noise and Vibration, 2014

In this study, the effect of posture, vibration magnitude and frequency on seat-to-head (STH) and back support-tohead (BTH) transfer functions has been studied under vertical sinusoidal vibration. Twelve healthy male subjects were participated in experimental work to measure vertical vibration transmitted to the occupants head in three representative postures (erect, vertical back on and forward lean on table) under three magnitudes of vibration (0.4, 0.8 and 1.2 m/s 2 r.m.s.) in frequency range 1 to 20 Hz. From collected data sets, the effect of vibration magnitude, vibration frequency and postures on STH and BTH transmissibility's and phase has been drawn over the prescribed frequency range. The result suggested that inclusion of all possible variables in optimal design of vehicle seat, suspension and comfort analysis most benefit for better design and analysis. The comparison of experimental and model response reveals that both models matched with mean experimental data sets most closely and the models provide best description about biodynamic response study of seated human subjects under vertical whole body vibration.