Vertical Whole-body Vibration Research Articles

Feasibility of a Sprague-Dawley Rat Model for Investigating the Effects of Seated Whole-body Vibration.

Vehicular whole-body vibration (WBV) can have long-term adverse effects on human quality of life. Animal models can be used to study pathophysiologic effects of vibration. The goal of this study was to assess animal cooperation and well-being to determine the feasibility of a novel seated rat model for investigating the effects of WBV on biologic systems. Twenty-four male Sprague-Dawley rats were used. The experiment consisted of an acclimation phase, 2 training phases (TrP1 and TrP2), and a testing phase (TeP), including weekly radiographic imaging. During acclimation, rats were housed in pairs in standard cages without vibration. First, experimental (EG; n = 18) and control group 1 (C1; n = 3) rats were placed in a vibration apparatus without vibration, with increasing duration over 5 d during TrP1. EG rats were exposed to vertical random WBV that was increased in magnitude over 5 d during TrP2 until reaching the vibration signal used during TeP (15 min, 0.7 m·s-2 root mean square, unweighted). C1 rats were placed in the vibration apparatus but received no vibration during any phase. Control group 2 (C2; n = 3) rats remained in the home cages. Cooperation was evaluated with regard to rat-apparatus interactions and position compliance. Behavior, weight, and fecal glucocorticoid metabolite concentrations (fGCM) were used to evaluate animal well-being. We observed good cooperation and no behavioral patterns or weight loss between phases, indicating little or no animal stress. The differences in fGCM concentration between groups indicated that the EG rats had lower stress levels than the control rats in all phases except TrP1. Thus, this model elicited little or no stress in the conscious, unrestrained, seated rats.

The impact of accelerometer location and frequency weightings on the prediction of pleasantness ratings for vertical whole-body vibrations on an aircraft seat bench

Noise and vibration are two physical factors that can reduce the perceived comfort of passengers during a flight. In this application context, vibrations are often measured using accelerometers placed at the seat rail or with a seat pad between the seat surface and the buttock of a sitting person. To develop pleasant aircraft cabin environments, it necessary to know which measurement location best reflects subjective ratings and whether the application of a frequency weighting as proposed in the ISO 2631 standard is beneficial. In this study, 40 participants rated the pleasantness of sinusoidal whole-body vibrations in the vertical direction while seated on a typical aircraft seat bench and listening to a synthetic broadband aircraft cabin noise over headphones. The vibration signals covered seven frequencies and four vibration levels and ratings were made on a verbally anchored scale. The results showed that an increase in vibration level leads to more unpleasant ratings for each of the tested frequencies, independent of the accelerometer position. Although the ISO frequency weighting underpredicts the ratings for high frequencies in both cases, applying it to the seat rail measurements seems to reflect the pleasantness ratings better than the seat pad measurements proposed in the ISO 2631 standard.

Influence of foot excitation and shin posture on the vibration behavior of the entire spine inside a seated human body

Due to ethical issues and simplification of traditional biomechanical models, experimental methods and traditional computer methods were difficult to quantify the effects of foot excitation and shin posture on vibration behavior of the entire spine inside a seated human body under vertical whole-body vibration. This study developed and verified different three-dimensional (3D) finite element (FE) models of seated human body with detailed anatomical structure under the biomechanical characteristics to predict vibration behavior of the entire spine inside a seated human body with different foot excitation (with and without vibration) and shin posture (vertical and tilt posture). Random response analysis was performed to study the transmissibility of the entire spine to seat under vertical white noise excitation between 0 and 20 Hz at 0.5 m/s2 r.m.s. The results showed that although the foot excitation could reduce the fore-aft transmissibility in the cervical spine (23% reduction), it could significantly increase that in the lumbar spine (52% increase), which resulted in complex alternating stresses at lumbar spine and made the lumbar spine more vulnerable to injury in long-term vibration environment. Moreover, the shin tilt posture made the maximum fore-aft transmissibility in the lumbar spine move to the upper lumbar spine. The study provided new insights into the influence of foot excitation and shin posture on the vibration behavior of the entire spine inside a seated human body. Foot excitation exposed the lumbar spine to complex alternating stresses and made it more vulnerable to injury in long-term whole body vibration.

Discomfort estimation for vertical whole-body vibration in the aircraft cabin considering the duration and static sitting comfort

This paper investigated the discomfort caused by vertical whole-body vibration (WBV) over 20 minutes using data recorded at the front, middle, and rear seats of the passenger cabin in civil aviation during a cruising flight. Twenty-four subjects experienced each stimulus at 0.5 ms−2 r.m.s. and judged discomfort at various moments (i.e., 1/6, 5, 10, 15, and 20 min) using a category-ratio method. The difference in discomfort due to high-frequency vibration components vanished after 10 min. Based on Stevens’ power law, a method is developed to estimate long-term vertical WBV discomfort by considering the static discomfort and an interaction coefficient between vibration and static discomfort as parameters. The proposed estimation method showed high accuracy with determination coefficients (R 2) higher than 0.97 and good linearity with values of growth rates 0.95, 1 and 0.95 for the vertical WBV discomfort at the front, middle and rear seat positions in the aircraft cabin.

Pleasantness ratings for vertical whole-body vibration on an aircraft seat and relevant body parts involved

Noise and vibration are two physical factors which can reduce the perceived comfort of passengers in an aircraft during flight. In this study, 40 participants rated the pleasantness of 28 sinusoidal whole-body vibrations in the vertical direction, which differed in frequency and acceleration level while seated on a typical aircraft seat bench. The results showed significant main effects for frequency and level as well as an interaction of the two factors and an interaction between frequency and gender. Using body-maps, the pleasantness ratings could be linked to those parts of the body that were underlying the judgments. In a second experiment, the same 40 participants judged whether noise or vibration should be attenuated for comfort improvement for the same 28 signals. Logistic regression functions fitted to the results enable an estimate of the percentage of people preferring vibration reduction as a function of frequency and vibration level.

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.

Global-guidance chaotic multi-objective particle swarm optimization method for pneumatic suspension handling and ride quality enhancement on the basis of a thermodynamic model of a full vehicle

In this paper, the parameters of the validated suspension system model of a full-vehicle are tuned through design sensitivity analyses, and then Multi-Objective Particle Swarm Optimization (MOPSO) is used to enhance vehicle ride comfort, which is the vertical whole-body vibrations, and handling features, that is, roll motion and road holding, simultaneously. The parameters of this thermodynamic-based pneumatic suspension system model are comprised of the air spring reservoir volume, orifice resistance, initial volume, and pressure of the pneumatic springs. To enhance the convergence rate, computational times, and diversity of the swarm particles, we have incorporated chaotic dynamics into the MOPSO using the Logistic Map chaotic method to initialize the population and also employed the leader-based global guidance techniques to conduct the potential solutions in each iteration. The analysis of the proposed modeling and optimization results show that the suspension system has been reasonably boosted in terms of vehicle handling and ride comfort. Quantitatively, the RMS acceleration and pitch angle has been reduced by about 71% and 57%, respectively, showing a substantial improvement in passenger comfort. Furthermore, the proposed approach caused an increase in tire road-holding force by about 148% and a reduction of roll angle by 33% which results in an enhancement in vehicle handling, boosting vehicle driving safety.

Short-term effects of side-alternating Whole-Body Vibration on cognitive function of young adults.

Recent research in rodents and humans revealed that Whole-Body Vibration (WBV) is beneficial for cognitive functions. However, the optimal WBV conditions are not established: contrary to vertical WBV, side-alternating WBV was not investigated before. The present study investigated the short-term effects of side-alternating WBV in standing and sitting posture on specific cognitive function of young adults. We used a balanced cross-over design. Sixty healthy young adults (mean age 21.7 ± 2.0 years, 72% female) participated. They were exposed to three bouts of two-minute side-alternating WBV (frequency 27 Hz) and three control conditions in two different sessions. In one session a sitting posture was used and in the other session a standing (semi-squat) posture. After each condition selective attention and inhibition was measured with the incongruent condition of the Stroop Color-Word Interference Test. WBV significantly (p = 0.026) improved selective attention and inhibition in the sitting posture, but not in the standing posture. The sitting posture was perceived as more comfortable, joyous and less exhaustive as compared to the standing posture. This study demonstrated that side-alternating WBV in sitting posture improves selective attention and inhibition in healthy young adults. This indicates that posture moderates the cognitive effect of WBV, although the effects are still small. Future studies should focus on the working mechanisms and further optimization of settings, especially in individuals who are unable to perform active exercise.

Biomechanical responses of the human lumbar spine to vertical whole-body vibration in normal and osteoporotic conditions

BackgroundThe prevalence of osteoporosis is continuing to escalate with an aging population. However, it remains unclear how biomechanical behavior of the lumbar spine is affected by osteoporosis under whole-body vibration, which is considered a significant risk factor for degenerative spinal disease and is typically present when driving a car. Accordingly, the objective of this study was to compare the spine biomechanical responses to vertical whole-body vibration between normal and osteoporotic conditions. MethodsA three-dimensional finite-element model of the normal human lumbar spine-pelvis segment was developed using computed tomographic scans and was validated against experimental data. Osteoporotic condition was simulated by modifying material properties of bone tissues in the normal model. Transient dynamic analyses were conducted on the normal and osteoporotic models to compute deformation and stress in all lumbar motion segments. FindingsWhen osteoporosis occurred, vibration amplitudes of the vertebral axial displacement, disc bulge, and disc stress were increased by 32.1–45.4%, 25.7–47.1% and 23.0–42.7%, respectively. In addition, it was found that for both the normal and osteoporotic models, the response values (disc bugle and disc stress) were higher in L4–L5 and L5–S1 intervertebral discs than in other discs. InterpretationOsteoporosis deteriorates the effect of whole-body vibration on lumbar spine, and the lower lumbar segments might have a higher likelihood of disc degeneration under whole-body vibration.

Equivalent magnitude-dependent discomfort under vertical vibration up to 100 Hz

The effect of vibration magnitude on frequency-dependence of discomfort of human body is always overlooked with respect to the comfort equivalence contours, particularly for high-magnitude vibration in wideband frequency. In this study, the magnitude effect of vertical vibration on discomfort of human body is investigated experimentally. Nineteen male subjects are involved in the jury test of vibration discomfort in the vertical direction with 2–5 m/s2 in magnitude up to 100 Hz. It is shown that the growth rate of discomfort may exceed 1 due to the high-magnitude vibration employed. In this condition that the rate varies around 1, the Stevens’ power law is not capable to properly represent the relationship between the subjective discomfort and the vibration magnitude. It means the equivalent comfort contours are not only dependent on the frequency range but also related to the vibration magnitude. Frequency weightings of vibration discomfort are influenced by the excitation magnitude. Practitioner summary: The occupant comfort to vertical whole-body vibration is affected by vibration magnitude. This study provides the effect of vibration magnitude on frequency-dependence of discomfort to whole-body vibration. It is suggested to propose variable frequency weightings for vibration discomfort evaluation under different magnitudes to achieve better comfort design.

Effects of whole-body vibration at different periods on lumbar vertebrae in female rats.

The current study aimed to investigate the effects of whole-body vibration (WBV) before and after ovariectomy on lumbar vertebrae, and to observe whether the positive effects of WBV before and after ovariectomy on lumbar vertebrae in rats could be maintained after vibration stopped. Three-month-old female rats were divided into four groups (n=45/group): control (CON), ovariectomy (OVA), WBV before ovariectomy (WBV-BO), and WBV after ovariectomy (WBV-AO) groups. For 1-8 weeks, WBV-BO group was subjected to vertical WBV. At the 9th week, the rats in WBV-BO, WBV-AO, and OVA groups were ovariectomized. During 11-18 weeks, WBV-AO group was subjected to vibration. For 19-26 weeks, no intervention was done for rats. The lumbar vertebrae were examined by Micro-CT, compressive test, creep test, and microindentation test. At the 8th week, the displacement of the L1-L2 annulus fibrosus in WBV-BO group was 18% smaller compared with CON group (p<0.05). At the 18th week, the elastic modulus of the L5 vertebral body in WBV-BO and WBV-AO groups was 53% and 57% higher than that in CON group, respectively (p<0.05); the displacement of the L1-L2 annulus fibrosus in WBV-BO group was 25% smaller than those in the other groups (p<0.05). At the 26th week, there was no significant difference in the displacement of the L1-L2 annulus fibrosus between WBV-BO group and other groups (p>0.05); the elastic modulus of the L5 vertebral body had no significant difference between WBV-AO group and CON group (p>0.05). Our results demonstrated that WBV before ovariectomy effectively prevented disc degeneration with significant effects up to 8 weeks after ovariectomy. The vertebral mechanical properties could be significantly improved by WBV after ovariectomy, but the residual effect did not maintain after WBV stopped.

Vertical and Side-Alternating Whole Body Vibration Platform Parameters Influence Lower Extremity Blood Flow and Muscle Oxygenation

This study directly compared blood flow and oxygenation during six treatment parameters used with vertical and side alternating whole body vibration (WBV). Twenty-seven healthy adults were randomized into the vertical or side-alternating (vibration type) WBV group. Participants completed three WBV sessions a week apart, 5 sets of 1 min on/off, at 3 conditions (Vertical: 30 Hz and 4 mm, 40 Hz and 2 mm, 45 Hz and 4 mm; Side-alternating: 10 Hz and 4 mm, 18 Hz and 3 mm and 26 Hz and 2 mm). Blood flow velocity and popliteal artery diameter, muscle oxygenation, skin temperature, heart rate and blood pressure were assessed. Muscle oxygenation was significantly increased for all vibration frequencies and types following two minutes of WBV (14.78%, p = 0.02) and continued until immediately after the cessation of WBV (24.7%, p &lt; 0.001). WBV also increased heart rate (23.9%, p &lt; 0.001) and systolic blood pressure (8.9%, p &lt; 0.001) regardless of frequency and vibration type. Side-alternating and vertical WBV increased muscle oxygenation and heart rate in healthy participants completing an isometric squat. Muscle oxygenation was not increased until the second vibration set indicating the amount of time spent on the platform may have a significant effect on increases in blood flow.

The Effects of Whole-Body Vibration and Head Supported Mass on Performance and Muscular Demand

For military rotary-wing aircrew, little is known about the interactive effects of vibration exposure and the addition of head supported mass (HSM) on target acquisition performance, head kinematics, and muscular demand. Sixteen healthy male participants wore an aviator helmet with replica night vision goggles and completed rapid aiming head movements to acquire visual targets in axial and off-axis movement trajectories while secured in a Bell-412 helicopter seat mounted to a human-rated shaker platform. HSM configuration (with or without a counterweight (CW)) and vertical whole-body vibration (WBV) conditions (vibration or no vibration exposure) were manipulated as independent variables. WBV exposure degraded target acquisition performance and lengthened time to peak velocity of head movements. For yaw peak velocity in the axial movement trajectory, peak velocity was 9.9%, 11.6%, and 8.4% higher in the noCW + WBV condition compared to the CW + WBV, CW + noWBV, and noCW + noWBV conditions, respectively.

Perception thresholds for whole-body vibrations on an airplane seat

The comfort during a flight on an aircraft is important for passengers. Like many other physical factors, vibrations of the airplane may negatively affect comfort. To understand the impact of vibration on comfort, it is important to know in which way the vibrations transmitted through the seat affects the perception of whole-body-vibrations. In this study, perception thresholds for vertical sinusoidal whole-body vibrations with frequencies between 20 Hz and 75 Hz were determined on a vibration platform with a typical economy class aircraft seat bench. Acceleration levels were recorded with accelerometers placed at the right rear seat rail and inside a seat cushion between the seat surface and the participant. The results show a distinct frequency dependency of the detection thresholds when measured at the seat rail. When taking the difference between the two measurement positions into account and describing the thresholds by the acceleration levels at the seat cushion, the determined perception thresholds are nearly frequency independent up to 50 Hz. This finding is in good agreement with literature data suggesting that the specific experimental setup does not play a big role in this frequency range. Differences above 50 Hz might be explained by the additional armrests in the present study.

Frequency dependence of vertical whole-body vibration perception - is your car rattling or humming?

Humans perceive whole-body vibration in many daily life situations. Often they are exposed to whole-body vibration in combination with acoustic events. Sound and vibration usually stems from the same source, for example concerts or travelling in vehicles, such as automobile, aircrafts, or ships. While we can describe acoustic stimuli using psychoacoustic descriptors such as loudness or timbre, the description human perception of whole body vibration frequently has been reduced to comfort or quality in the past. Unlike loudness or timbre, comfort and quality are dependent on the overall context. Especially in vehicles expectations might differ lot between different vehicle classes. Previous studies have evaluated a large range of suitable descriptors for whole-body vibrations that are independent of context. They suggest that certain descriptors are driven to a large extend by the frequency content of the vibration. This study systematically investigates the influence of frequency content on the perception of whole-body vibration varying frequency content and intensity of the vibrations. The results verify the frequency dependence of specific descriptors and identify the respective frequency ranges.

Mechanism associated with the effect of backrest inclination on biodynamic responses of the human body sitting on a rigid seat exposed to vertical vibration

Drivers and passengers in vehicles usually sit with their backs supported with a backrest. Sitting with a backrest in vehicles can affect the biodynamic responses of the human body and sitting comfort. Understanding the effect of back support on the biodynamic responses can assist in improving vehicle ride comfort. This study was designed to identify the mechanism associated with the effect of backrest inclination on the apparent masses measured at the seat pan and the backrest during vertical whole-body vibration based on experiment and modelling. The apparent masses of 14 subjects sitting on a rigid seat with various backrest inclination angles of 0º, 10º, 20º and 30º during exposure to vertical vibration at 0.5 ms−2 r.m.s. between 0.5 and 20 Hz were measured at the seat pan and the backrest. A biodynamic model previously developed by the authors was updated to include the interaction between the back of the human body and the seat backrest to represent the measured responses for each subject . The effect of backrest inclination on the biodynamic response and on the model parameters were identified. It was found that as the backrest inclination increased, the resonance frequency in the vertical in-line apparent mass measured at the seat pan increased, and the resonance frequency in the fore-and-aft cross-axis apparent mass measured at the seat pan decreased, while the resonance frequency in the normal apparent mass measured at the backrest was not changed. Statistical analysis found that with increasing backrest inclination, the vertical stiffness of the soft tissues at the ischial tuberosities, middle thighs and front thighs, as well as the stiffness at the lumbar joint tended to decrease, while the fore-and-aft stiffness and the damping of the soft tissues at the ischial tuberosities tended to increase. Analysis with the model of the median apparent masses of the 14 subjects disclosed the vibration modes of the body containing the fore-and-aft sliding motion of the pelvis and thighs, the vertical motion of the body on the soft tissue beneath the ischial tuberosities and thighs, and the bending motion of the spine. With the vertical backrest, the fore-and-aft and vertical motions of the pelvis and thighs were coupled together. As the backrest inclination increased, this coupling decreased and the coupling between the vertical motion of the pelvis and the bending of the spine increased.

Prediction of the influence of vertical whole-body vibration on biomechanics of spinal segments after lumbar interbody fusion surgery

BackgroundPrevious studies have shown that for healthy spine, cyclic loading encountered due to whole-body vibration exposure generated higher responses in spinal tissues than static loading. However, how whole-body vibration affects spine biomechanics after interbody fusion surgery is poorly understood. This study aimed at comparing the effects of vibration loading on spinal segments between postsurgical and healthy lumbar spines. MethodsA validated finite element model of healthy human lumbosacral spine was modified to simulate interbody fusion at L4–L5 level considering the statuses immediately after surgery (before bony fusion) and after bony fusion. Biomechanical responses at its adjacent levels for the healthy and fusion models to a sinusoidal axial vibration load of ±40 N and the corresponding static axal loads (−40 N and 40 N) were computed using transient dynamic and static analyses, respectively. FindingsFor both healthy and fusion models, vibration amplitudes of the predicted responses were significantly higher than the corresponding changing amplitudes under static loads. Specifically, the increasing effect of vibration load in disc bulge, disc stress and intradiscal pressure at L3–L4 level reached 255.9%, 215.0% and 224.4% for the healthy model, 157.4%, 177.8% and 171.8% for the fusion model (before bony fusion), 141.9%, 152.6% and 160.1% for the fusion model (after bony fusion). InterpretationAlthough whole-body vibration is still more dangerous for the lumbar spine after interbody fusion surgery than static loading, the sensitivity of adjacent segment in postsurgical spine to vibration loading is decreased compared with healthy spine, especially when reaching to bony fusion.

Spatiotemporal gait parameter changes due to exposure to vertical whole-body vibration.

Vertical whole-body vibration (vWBV) during work, recreation, and transportation can have detrimental effects on physical and mental health. Studies have shown that lateral vibration at low frequencies (<3 Hz) can result in changes to spatiotemporal gait parameters. There are few studies which explore spatiotemporal gait changes due to vertical vibration at higher frequencies (> 3 Hz). This study seeks to assess the effect of vWBV on spatiotemporal gait parameters at a greater range of frequencies (≤ 30 Hz). Stride Frequency (SF), Stride Length (SL), and Center of Pressure velocity (CoPv) was measured in seven male subjects (23 ± 4 years, 1.79 ± 0.05 m, 73.9 ± 9.7 kg) during In-Place Walking and nine male subjects (29 ± 7 years, 1.78 ± 0.07 m, 77.8 ± 9.9 kg; mean ± SD) during Treadmill Walking while exposed to vWBV. Load cells measured ground reaction forces during In-Place Walking and sensorized insoles acquired under-foot pressure during Treadmill Walking. Statistical tests included a one-way repeated-measures ANOVA, post-hoc two way paired T-tests, statistical power (1-β), correlation (R2), and effect size (Cohen's d). While statistical significance was not found for changes in SF, SL, or Mean CoPv, small to large effects were found in all measured spatiotemporal parameters of both setups. During Treadmill Walking, vWBV was correlated with a decrease in SF (R2 = 0.925), an increase in SL (R2 = 0.908), and an increase in Mean CoPv (R2 = 0.921) and Max CoPv (R2 = 0.952) with a significant increase (p < 0.0083) in Max CoPv at frequencies of 8 Hz and higher. Study results demonstrated that vWBV influences spatiotemporal gait parameters at frequencies greater than previously studied.

Perturbation effect of noise on overall feeling of discomfort from vertical whole-body vibration in vibro-acoustic environment

The human discomfort from combined noise and vibration has been investigated with a new perspective. The concept in perturbation effect has been adopted to formulate a new novel predictive model of human discomfort from noise and vibration. A psycho-physics experiment has been designed to identify the perturbation effect which caused by noise stimulus. The experiment involved twelve (12) subjects. Each subject was imposed in random order with a total of 42 combinations of seven (7) levels of noise (X, 61, 71, 77, 84, 87, 89 dBA) where the X is no noise stimulus, and six (6) levels of vibration dose values (V1 = 0.2079, V2 = 0.3242 V3 = 0.6388 V4 = 0.8803 V5 = 1.4947 and V6 = 1.8624 m/s1.75). Initially, the subject would be imposed with a reference combination of noise and vibration which was assumed to have a value of 100. The assigned combination for reference was chosen at sound exposure level, LAE of 71 dB(A) and the vibration dose value, VDV of 0.2079 ms−1.75. Then the subject was imposed with other combinations of noise and vibration in a duration of 5 s and 5 s break in between the stimuli combination. After each exposure to each combination of noise and vibration, the subject is required to state the discomfort caused by the noise and vibration in the form of a number relative to the reference stimuli of 100. The subject was asked to be seated in a relaxed position, holding a handphone and used it to record all the response values after each stimulation. The finding suggested that the discomfort from vibration can be predicted with equation ψv=170.6082avdv0.6662 and the overall discomfort from noise and vibration is given by ψv−n=ψv+ψvε where the ε is the perturbation effect caused by noise stimulus.

Posterior Lumbar Interbody Fusion Versus Transforaminal Lumbar Interbody Fusion: Finite Element Analysis of the Vibration Characteristics of Fused Lumbar Spine

Previous studies have investigated biomechanical characteristics of the lumbar spine after different types of lumbar interbody fusion surgery under static loadings. However, very few have dealt with the whole-body vibration (WBV) condition that is typically present in vehicles. The aim of this study was to compare the influence of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) on dynamic responses of the fused lumbar spine to vertical WBV. The PLIF and TLIF procedures with bilateral pedicle screw fixation at L4-L5 level were simulated by modifying a previously validated intact lumbar L1-S1 finite element model. The PLIF and TLIF models were subjected to a sinusoidal vertical load with a compressive follower preload, and computed for transient dynamic analysis. The obtained dynamic responses for the models at the fused and adjacent levels were collected and compared. The results showed that the contact force between endplate and cage was higher in the PLIF model than in the TLIF model, indicating that PLIF allowed for higher compressive load across the anterior structure. At fused L4-L5 level, the TLIF led to a higher stress in the endplate and posterior BPSF system than the PLIF. At adjacent L3-L4 level and L5-S1 level, the computed dynamic responses, in terms of stress and deformation, for the PLIF and TLIF models showed very few differences. This study may be helpful to quantify dynamic mechanical properties of the fused lumbar spine, and better understand biomechanical differences between the PLIF and TLIF procedures during vibration.