Effect of vibration magnitude, vibration spectrum and muscle tension on apparent mass and cross axis transfer functions during whole-body vibration exposure

Twelve seated male subjects were exposed to 15 vibration conditions to investigate the nature and mechanisms of the non-linearity in biomechanical response. Subjects were exposed to three groups of stimuli: Group A comprised three repeats of random vertical vibration at 0.5, 1.0 and 1.5 m s⁻² r.m.s. with subjects sitting in a relaxed upright posture. Group B used the same vibration stimuli as Group A, but with subjects sitting in a ‘tense’ posture. Group C used vibration where the vibration spectrum was dominated by either low-frequency motion (2–7 Hz), high-frequency motion (7–20 Hz) or a 1.0 m s⁻² r.m.s. sinusoid at the frequency of the second peak in apparent mass (about 10–14 Hz) added to 0.5 m s⁻² r.m.s. random vibration. In the relaxed posture, frequencies of the primary peak in apparent mass decreased with increased vibration magnitude. In the tense posture, the extent of the non-linearity was reduced. For the low-frequency dominated stimulus, the primary peak frequency was lower than that for the high-frequency dominated stimulus indicating that the frequency of the primary peak in the apparent mass is dominated by the magnitude of the vibration encompassing the peak. Cross-axis transfer functions showed peaks of about 15–20% and 5% of the magnitudes of the peaks in the apparent mass for x- and y-direction transfer functions, respectively, in the relaxed posture. In the tense posture, cross-axis transfer functions reduced in magnitude with increased vibration, likely indicating a reduced fore-aft pitching of the body with increased tension, supporting the hypothesis that pitching contributes to the non-linearity in apparent mass.     

The apparent mass of the seated human exposed to single-axis and multi-axis whole-body vibration

Most workplaces where workers are exposed to whole-body vibration involves simultaneous motion in the fore-and-aft (x-), lateral (y-) and vertical (z-) directions. Previous studies reporting the biomechanical response of people exposed to vibration have almost always used single-axis vibration stimuli. This paper reports a study where apparent masses of 15 subjects were measured whilst exposed to single-axis and tri-axial whole-body vibration. Each subject was exposed to 28 vibration conditions comprising every combination of single-axis and tri-axial vibration with magnitudes of 0.4 and 0.8 ms(-2) r.m.s. in each direction, once with backrest contact and once without backrest contact. Results show that increasing the magnitude of vibration in directions orthogonal to that being measured affects the apparent mass, causing a reduction in the resonance frequency as the total magnitude of vibration increases. It is demonstrated that the apparent mass resonance frequency is a function of the total vibration magnitude in all axes rather than a function of the vibration magnitude in the direction being measured. It is also shown that, for individuals, the frequency of the peak in the apparent mass in one direction is not related to the frequency of the peak in another direction. It is concluded that more complex biomechanical models are required in order to simulate human response to multi-axis vibration.     

Identification of the head-neck complex in response to trunk horizontal vibration

A method is proposed for identifying the head-neck complex (HNC) in the seated human body when it is exposed to the trunk horizontal (fore-and-aft) vibration. It is assumed that the HNC only has the anteroposterior (flexion/extension) motion in the sagittal plane. An electrohydraulic vibrator is used as a source of vibration. To generate the trunk horizontal vibration, the trunk of the seated subject is fixed to the seatback. The subjects are exposed to the random vibration at a magnitude of 1.60 ms^-2 rms (root-mean-square) for 50 s. The coherence and frequency response function are then obtained in the frequency range 0.5–3 Hz. The results show that the HNC behavior is quasilinear with a resonance frequency between 1 and 1.4 Hz. Accordingly, a two-dimensional single-inverted pendulum is considered as a model for the HNC. The frequency domain identification method is then used to estimate the unknown parameters, including the HNC viscoelastic and inertia parameters. The model is examined in a time domain using the random vibration. Good agreement is obtained between experimental and simulation results, indicating the reliability of the proposed method.     

Modeling of human reactions to whole-body vibration

A computer-automated approach for studying the human body vibration is presented. This includes vertical, horizontal, and torsional vibration. The procedure used is based on Finite Segment Modeling (FSM) of the human body, thus treating it as a mechanical structure. Kane's equations as developed by Huston et al. are used to formulate the governing equations of motion. The connective tissues are modeled by springs and dampers. In addition, the paper presents the transient response of different parts of the body due to a sinusoidal forcing function as well as an impulse function applied to the lower torso in the vertical direction.     

Non-linearities in apparent mass and transmissibility during exposure to whole-body vertical vibration

The causes of low back pain associated with prolonged exposure to whole-body vibration are not understood. An understanding of non-linearities in the biomechanical responses is required to identify the mechanisms responsible for the dynamic characteristics of the body, to allow for the non-linearities when predicting the influence of seating dynamics, and to predict the adverse effects caused by various magnitudes of vibration. Twelve subjects were exposed to six magnitudes, 0.25-2.5ms(-2) rms, of vertical random vibration in the frequency range 0.2-20Hz. The apparent masses of the subjects were determined together with transmissibilities measured from the seat to various locations on the body surface: the upper and lower abdominal wall, at L3, over the posterior superior iliac spine and the iliac crest. There were significant reductions in resonance frequencies for both the apparent mass and the transmissibilities to the lower abdomen with increases in vibration magnitude. The apparent mass resonance frequency reduced from 5.4-4. 2Hz as the magnitude of the vibration increased from 0.25-2.5ms(-2) rms. Vertical motion of the lumbar spine and pelvis showed resonances at about 4Hz and between 8 and 10Hz. When exposed to vertical vibration, the human body shows appreciable non-linearities in its biodynamic responses. Biodynamic models should be developed to reflect the non-linearity.     

Non-linear characteristics in the dynamic responses of seated subjects exposed to vertical whole-body vibration

The effect of the magnitude of vertical vibration on the dynamic response of the seated human body has been investigated. Eight male subjects were exposed to random vibration in the 0.5 to 20 Hz frequency range at five magnitudes: 0.125, 0.25, 0.5, 1.0 and 2.0 ms(-2) r.m.s. The dynamic responses of the body were measured at eight locations: at the first, fifth, and tenth thoracic vertebrae (T1, T5, T10), at the first, third, and fifth lumbar vertebrae (L1, L3, L5) and at the pelvis (the posterior-superior iliac spine). At each location, the motions on the body surface were measured in the three orthogonal axes within the sagittal plane (i.e., the vertical, fore-and-aft, and pitch axes). The force at the seat surface was also measured. Frequency response functions (i.e., transmissibilities and apparent mass) were used to represent the responses of the body. Non-linear characteristics were observed in the apparent mass and in the transmissibilities to most measurement locations. Resonance frequencies in the frequency response functions decreased with increases in the vibration magnitude (e.g. for the vertical transmissibility to L3, a reduction from 6.25 to 4.75 Hz when the vibration magnitude increased from 0.125 to 2.0 ms(-2) r.m.s.). The transmission of vibration within the spine also showed some evidence of a non-linear characteristic. It can be concluded from this study that the dynamic responses of seated subjects are clearly non-linear with respect to vibration magnitude, whereas previous studies have reported inconsistent conclusions. More understanding of the dependence on vibration magnitude of both the dynamic responses of the soft tissues of the body and the muscle activity (voluntary and involuntary) is required to identify the causes of the non-linear characteristics observed in this study.     

Dynamics of the head-neck complex in response to the trunk horizontal vibration: modeling and identification

Although many studies exist concerning the influence of seat vibration on the head in the seated human body, the dynamic response of the head-neck complex (HNC) to the trunk vibration has not been well investigated. Little quantitative knowledge exists about viscoelastic parameters of the neck. In this study, the dynamics of the HNC is identified when it is exposed to the trunk horizontal (fore-and-aft) vibration. The frequency response functions between the HNC angular velocity and the trunk horizontal acceleration, corresponding to four volunteers, are obtained in the frequency range of 0.5 Hz to 10 Hz. A fourth-order mathematical model, derived by considering a double-inverted-pendulum model for the HNC, is designed to simulate the dynamic response of the HNC to the trunk horizontal vibration. The frequency domain identification method is used to determine the coefficients of the mathematical model of the HNC. Good agreement has been obtained between experimental and simulation results. This indicates that the system, similar to the designed fourth-order model, has mainly two resonance frequencies. The viscoelastic parameters of the neck, including the spring and damping coefficients, are then obtained by use of the optimization method.     

Influence of vibration training on energy expenditure in active men

The aim of the present study was to analyze the effect of whole-body vibration on energy expenditure, as well as on exercise intensity, during and immediately after a typical set of exercises for muscle hypertrophy in physically active subjects. Seventeen male university students (mean age 18.3 +/- 0.24 years) volunteered to perform 2 different training exercises: half squat (HS), and half squat with vibration (HSV). Both exercises were performed by all subjects on the vibration platform (with vibration only for HSV), the sequence order being assigned randomly. Energy expenditure (EE), respiratory exchange ratio, perceived exertion (PE), and heart rate were recorded for baseline, exercise, and short-recovery conditions. Training consisted of 5 sets of 10 repetitions of HS and HSV, with a 2-minute recovery interval between sets. Analysis of variance with repeated measurements and Bonferroni correction, as well as effect size were used for statistical calculations. Results indicated that EE and PE were significantly higher in the HSV group, during both exercise and recovery. Heart rate did not differ significantly between groups. Thus, it would appear that HS strength training could be rendered more energy-efficient through the addition of vibration. Moreover, it would be feasible to introduce vibration exercises into regular training programs, particularly those whose key objective is muscle hypertrophy along with fat reduction.     

Acute effect of whole-body vibration on electromechanical delay and vertical jump performance

Objectives:To determine if a change in vertical jump performance from acute whole-body vibration can be explained by indirectly assessing spindle sensitivity from electromechanical delay.Methods:Using a counter-balanced design, twenty college-aged participants performed whole-body vibration (WBV) and control treatments. WBV included 10 intervals (26 Hz, 3.6 mm) of 60 s in a half-squat followed by 60 s of rest. After 5 intervals, participants rested for 6-minutes before commencing the final 5 intervals. For the control, the exact same protocol of whole-body vibration was performed but without vibration. Electromechanical delay and vertical jump were assessed at baseline, during the 6-minute rest period and immediately after whole-body vibration and control.Results:There were no differences between treatments, for both electromechanical delay (F(2, 38)=1.385, p=0.263) and vertical jump (F(2, 38)=0.040, p<0.96). Whole-body vibration had no effect on vertical jump performance.Conclusion:The current whole-body vibration protocol is not effective for acute vertical jump or electromechanical delay enhancement. Also, since there was no effect on electromechanical delay, this suggests that whole-body vibration did not enhance muscle spindle sensitivity for the parameters examined.     

Experimental Evidence of the Tonic Vibration Reflex during Whole-Body Vibration of the Loaded and Unloaded Leg

Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spinal and supraspinal neurophysiological mechanism termed the tonic vibration reflex (TVR). However, TVR has not been experimentally demonstrated during low-frequency WBV, therefore this investigation aimed to determine the expression of TVR during WBV.  Whilst seated, eight healthy males were exposed to either vertical WBV applied to the leg via the plantar-surface of the foot, or Achilles tendon vibration (ATV) at 25Hz and 50Hzfor 70s. Ankle plantar-flexion force, tri-axial accelerations at the shank and vibration source, and surface EMG activity of m. soleus (SOL) and m. tibialis anterior (TA) were recorded from the unloaded and passively loaded leg to simulate body mass supported during standing.  Plantar flexion force was similarly augmented by WBV and ATV and increased over time in a load- and frequency dependent fashion. SOL and TA EMG amplitudes increased over time in all conditions independently of vibration mode. 50Hz WBV and ATV resulted in greater muscle activation than 25Hz in SOL when the shank was loaded and in TA when the shank was unloaded despite the greater transmission of vertical acceleration from source to shank with 25Hz and WBV, especially during loading. Low-amplitude WBV of the unloaded and passively loaded leg produced slow tonic muscle contraction and plantar-flexion force increase of similar magnitudes to those induced by Achilles tendon vibration at the same frequencies. This study provides the first experimental evidence supporting the TVR as a plausible mechanism underlying the neuromuscular response to whole-body vibration.     

The apparent mass of the human body exposed to non-orthogonal horizontal vibration

Apparent masses of 15 male and 15 female subjects have been measured during exposure to various directions of horizontal vibration. Twenty vibration conditions were used in the experiment. In each of five directions (0, 22.5, 45, 67.5 and 90° to the mid-sagittal plane) subjects were exposed to random vibration in the frequency range of 1.5–20 Hz at 0.25, 0.5 and 1.0 m s⁻² r.m.s. The five remaining conditions were selected to give measurements whereby the magnitude of the x-component of the vibration was fixed and the y-component changed and vice-versa. Two peaks were observed in the apparent masses. The first peak occurred at about 3 Hz and reduced in frequency with increases in vibration magnitude. The frequency of the first peak also reduced as the direction of vibration changed from 0 to 90°. The magnitude of the peak increased as the vibration magnitude and direction increased. The second peak occurred at about 5 Hz and decreased in both frequency and magnitude with increases in vibration magnitude. There was no change in the frequency of the second peak with vibration direction, although the magnitude of the peak decreased as the angle of vibration to the mid-sagittal plane increased. Increasing the magnitude of the x-component of vibration whilst using a fixed y-component changed the magnitude of the first peak but did not change the frequency of the first or any characteristics of the second peak. In contrast, increasing the y-component of vibration whilst using a fixed x-component changed the frequencies and magnitudes of both peaks. Predictions of the response at 45° by applying the principle of superposition to data measured at 0 and 90° showed that the response of the body with direction was not linear. This implies that the apparent mass in non-orthogonal axes cannot be predicted from the apparent masses measured in orthogonal directions.     

The effects of whole-body vibration on human biodynamic response

The objective of vibration research at the Armstrong Laboratory includes the expansion and improvement of the measurement, quantification, analysis, and modeling of human vibration response. The driving-point impedance and transmissibility techniques have been expanded and are rigorously applied in the research efforts. Driving-point impedance is defined as the ratio between the transmitted force and input velocity at the point of load application. Transmissibility is typically defined as the ratio between the acceleration level measured at some location on the body and the input acceleration at the seat. These two ratios are used to assess the magnitude and frequency location of resonance behaviors where maximum motions occur in the body. From these data, analytical models are developed which can simulate the motions and coupling behaviors, and predict the stiffness and damping characteristics of the affected anatomical structures. The ultimate goal of the research is to provide new and improved data and modeling capability for revising exposure standards and for developing equipment design guidelines and criteria for improving tolerance and reducing physiological consequences. This paper describes the results of recent studies conducted to identify the biodynamic behavior of major anatomical structures affected by seated whole-body vibration, to develop an analytical model for simulating human vibration response, and to apply the model to evaluate the effects of seat cushion materials on the transmission/attenuation pathways.     

Reductions in finger blood flow in men and women induced by 125-Hz vibration: association with vibration perception thresholds

Vibration of one hand reduces blood flow in the exposed hand and in the contralateral hand not exposed to vibration, but the mechanisms involved are not understood. This study investigated whether vibration-induced reductions in finger blood flow are associated with vibrotactile perception thresholds mediated by the Pacinian channel and considered sex differences in both vibration thresholds and vibration-induced changes in digital circulation. With force and vibration applied to the thenar eminence of the right hand, finger blood flow and finger skin temperature were measured in the middle fingers of both hands at 30-s intervals during seven successive 4-min periods: 1) pre-exposure with no force or vibration, 2) pre-exposure with force, 3) vibration 1, 4) rest with force, 5) vibration 2, 6) postexposure with force, and 7) recovery with no force or vibration. A 2-N force was applied during periods 2-6 and 125-Hz vibration at 0.5 and 1.5 ms(-2) root mean square (r.m.s.; unweighted) was applied during periods 3 and 5, respectively. Vibrotactile thresholds were measured at the thenar eminence of right hand using the same force, contact conditions, and vibration frequency. When the vibration magnitude was greater than individual vibration thresholds, changes in finger blood flow were correlated with thresholds (with both 0.5 and 1.5 ms(-2) r.m.s. vibration): subjects with lower thresholds showed greater reductions in finger blood flow. Women had lower vibrotactile thresholds and showed greater vibration-induced reductions in finger blood flow. It is concluded that mechanoreceptors responsible for mediating vibration perception are involved in the vascular response to vibration.     

The effects of movement velocity during squatting on energy expenditure and substrate utilization in whole-body vibration

The purpose of this study was to examine whether and how cycle time duration affects energy expenditure and substrate utilization during whole-body vibration (WBV). Nine men performed 3 squatting exercises in execution frequency cycles of 6, 4, and 2 seconds to 90 degrees knee flexion with vibration (Vb+) (frequency was set at 30 Hz and the amplitude of vibration was 4 mm) and without vibration (Vb-) during 3 minutes, each with an additional load of 30% of the subject's body weight. A 2-way analysis of variance for VO2 revealed a significant vibration condition main effect (p < 0.001) and a cycle time duration effect (p < 0.001). When differences were analyzed by Fisher's LSD test, cycle time duration of 2 seconds was significantly different from 4 and 6 seconds, both in Vb+ and Vb-. Total energy expenditure (EE(tot)), carbohydrate oxidation rate (EE(cho)), and fat oxidation rate (EE(fat)) demonstrated a significant vibration condition main effect (EE(tot): p < 0.01; EE(cho): p < 0.001; EE(fat): p < 0.001) and cycle time duration main effect (EE(tot) and EE(cho): p < 0.001; EE(fat): p < 0.01). EE(tot), EE(cho), and EE(fat) post hoc comparisons indicated that values for the 2-second test significantly differed from 4 and 6 seconds when compared in the same vibration condition. VO2 and EE values were greater in Vb+ than in Vb- conditions with the same cycle time duration. Our study confirms that squatting at a greater frequency helps to maximize energy expenditure during exercise with or without vibration. Therefore, cycle time duration must be controlled when vibration exercise is prescribed.     

Effects of vibration intensity on lower limb joint moments during standing

Muscle activity and joint moment of the lower limbs can provide different information about the stimulation of controlled whole-body vibration (CWBV) on human body. Previous studies investigated the immediate effects of the intensity of CWBV on enhancing lower-limb muscle activity. However, no study has examined the possible influence of CWBV intensity on joint loading. It remains unexplored how CWBV intensity impacts joint loading. This study was carried out (1) to quantify the effects of CWBV intensity in terms of vibration frequency and amplitude on the lower limb joint moments and (2) to examine the relationship between leg joint moments and vibration intensity characterized by the platform’s acceleration, that is determined by frequency and amplitude, during standing among young adults. Thirty healthy young adults participated in this study. Each participant experienced nine vibration intensity levels dependent upon the frequency (10, 20, and 30 Hz) and amplitude (1, 2, and 3 mm) while standing on a side-alternating vibration platform. Their body kinematics and vertical reaction forces between the feet and platform were collected. Inverse dynamics was employed to calculate the resultant moment for the ankle, knee, and hip joints in the sagittal plane. Our results revealed that the root-mean-square moment significantly increases with increasing vibration frequency or amplitude for all three joints. Further, all joint moments are strongly and positively correlated with the platform acceleration.     

Effects of tibialis anterior vibration on postural control when exposed to support surface translations

The sensory re-weighting theory suggests unreliable inputs may be down-weighted to favor more reliable sensory information and thus maintain proper postural control. This study investigated the effects of tibialis anterior (TA) vibration on center of pressure (COP) motion in healthy individuals exposed to support surface translations to further explore the concept of sensory re-weighting. Twenty healthy young adults stood with eyes closed and arms across their chest while exposed to randomized blocks of five trials. Each trial lasted 8?s, with TA vibration either on or off. After 2?s, a sudden backward or forward translation occurred. Anterior–posterior (A/P) COP data were evaluated during the preparatory (first 2?s), perturbation (next 3?s), and recovery (last 3?s) phases to assess the effect of vibration on perturbation response features. The knowledge of an impending perturbation resulted in reduced anterior COP motion with TA vibration in the preparatory phase relative to the magnitude of anterior motion typically observed during TA vibration. During the perturbation phase, vibration did not influence COP motion. However, during the recovery phase vibration induced greater anterior COP motion than during trials without vibration. The fact that TA vibration produced differing effects on COP motion depending upon the phase of the perturbation response may suggest that the immediate context during which postural control is being regulated affects A/P COP responses to TA vibration. This indicates that proprioceptive information is likely continuously re-weighted according to the context in order to maintain effective postural control.     

Acute effects of whole-body vibration on muscle activity, strength, and power

The purpose of this study was to investigate the effects of a single bout of whole-body vibration on isometric squat (IS) and countermovement jump (CMJ) performance. Nine moderately resistance-trained men were tested for peak force (PF) during the IS and jump height (JH) and peak power (PP) during the CMJ. Average integrated electromyography (IEMG) was measured from the vastus medialis, vastus lateralis, and biceps femoris muscles. Subjects performed the 2 treatment conditions, vibration or sham, in a randomized order. Subjects were tested for baseline performance variables in both the IS and CMJ, and were exposed to either a 30-second bout of whole-body vibration or sham intervention. Subjects were tested immediately following the vibration or sham treatment, as well as 5, 15, and 30 minutes posttreatment. Whole-body vibration resulted in a significantly higher (p < or = 0.05) JH during the CMJ immediately following vibration, as compared with the sham condition. No significant differences were observed in CMJ PP; PF during IS or IEMG of the vastus medialis, vastus lateralis, or biceps femoris during the CMJ; or IS between vibration and sham treatments. Whole-body vibration may be a potential warm-up procedure for increasing vertical JH. Future research is warranted addressing the influence of various protocols of whole-body vibration (i.e., duration, amplitude, frequency) on athletic performance.     

Acute vibration increases alpha2C-adrenergic smooth muscle constriction and alters thermosensitivity of cutaneous arteries.

The vascular symptoms of hand-arm vibration syndrome, including cold-induced vasospasm, are in part mediated by increased sensitivity of cutaneous arteries to sympathetic stimulation. The goal of the present study was to use a rat tail model to analyze the effects of vibration on vascular function and alpha-adrenoceptor (AR) responsiveness. Rats were exposed to a single period of vibration (4 h, 125 Hz, constant acceleration 49 m/s2 root mean square). The physical or biodynamic response of the tail demonstrated increased transmissibility or resonance at this frequency, similar to that observed during vibration of human fingers. Morphological analysis demonstrated that vibration did not appear to cause structural injury to vascular cells. In vitro analysis of vascular function demonstrated that constriction to the alpha1-AR agonist phenylephrine was similar in vibrated and control arteries. In contrast, constriction to the alpha2-AR agonist UK14304 was increased in vibrated compared with control arteries, both in endothelium-containing or endothelium-denuded arteries. The alpha2C-AR antagonist MK912 (3 x 10(-10) M) inhibited constriction to UK14304 in vibrated but not control arteries, reversing the vibration-induced increase in alpha2-AR activity. Moderate cooling (to 28 degrees C) increased constriction to the alpha2-AR agonist in control and vibrated arteries, but the magnitude of the amplification was less in vibrated compared with control arteries. Endothelium-dependent relaxation to acetylcholine was similar in control and vibrated arteries. Based on these results, we conclude that a single exposure to vibration caused a persistent increase in alpha2C-AR-mediated vasoconstriction, which may contribute to the pathogenesis of vibration-induced vascular disease.     

Effects of vibration training in reducing risk of slip-related falls among young adults with obesity

This study examined the effects of controlled whole-body vibration training on reducing risk of slip-related falls in people with obesity. Twenty-three young adults with obesity were randomly assigned into either the vibration or placebo group. The vibration and placebo groups respectively received 6-week vibration and placebo training on a side-alternating vibration platform. Before and after the training, the isometric knee extensors strength capacity was measured for the two groups. Both groups were also exposed to a standardized slip induced by a treadmill during gait prior to and following the training. Dynamic stability and fall incidences responding to the slip were also assessed. The results indicated that vibration training significantly increased the muscle strength and improved dynamic stability control at recovery touchdown after the slip occurrence. The improved dynamic stability could be resulted from the enhanced trunk segment movement control, which may be attributable to the strength increment caused by the vibration training. The decline of the fall rates from the pre-training slip to the post-training one was greater among the vibration group than the placebo group (45% vs. 25%). Vibration-based training could be a promising alternative or additional modality to active exercise-based fall prevention programs for people with obesity.     

Effects of isolated and combined exposures to whole-body vibration and noise on auditory-event related brain potentials and psychophysical assessment

Auditory event-related brain potentials (ERP) in response to two different tone stimuli (1.1 kHz or 1 kHz, 80 dB, 50 ms; given by headphones at a regular interstimulus interval of 5 s with a probability distribution of 70:30) were recorded from 12 healthy male subjects (Ss) during four different conditions with two repetitions: A-60 dBA white noise (wN), no whole-body vibration (WBV); B-60 dBA wN plus sinusoidal WBV in the az-direction with a frequency of 2.01 Hz and acceleration of 2 m.s-2 root mean square; C-80 dBA wN, no WBV; D-80 dBA wN plus WBV. Each condition consisted of two runs of about 11 min interrupted by a break of 4 min. During the break with continuing exposure, but without auditory stimuli, Ss judged the difficulty of the tone-detection task and intensity of noise by means of cross-modality matching (CMM). Vibration-synchronous activity in the electrocardiogram was eliminated by a subtraction-technique. Noise caused an attenuation of the N1 and P2 amplitudes and prolongation of P3 latencies. The WBV did not cause systematic ERP effects. Condition B was associated with higher N1 and smaller P3 amplitudes. The factor "condition" had a significant effect on the peak latencies of P3 to target stimuli and the task difficulty judged by CMM. Both effects exhibited significant linear increases in the sequence of conditions A, B, C, D. For the evaluation of exposure conditions at work, it can be suggested that noise has a strong systematic effect which can be enhanced by WBV.(ABSTRACT TRUNCATED AT 250 WORDS)