Low-frequency Whole-body Vibration Research Articles

Coupled occupant-suspension-seat system analysis and vehicle-specific design optimization

A suspension seat is generally designed to achieve attenuation of low frequency whole-body vibration for a broad range of vehicles. Owing to the strong dependence of its vibration isolation performance on the nature of vibration excitation, an optimal performance could be realized via optimal tuning of suspension for specific classes of vehicles. In this study, a coupled occupant suspension seat model is developed and analyzed to identify optimal design parameters for different classes of vehicles. The multibody dynamic model of the air suspension seat is formulated considering kineto-dynamics of the suspension system and the elastic motion-limiters. The component models, namely, air spring with auxiliary air volume, hydraulic damper, and cushion, are identified from the laboratory-measured static and dynamic characteristics. A two-degree-of-freedom occupant model, is integrated to the suspension seat model to account for contribution due to occupant biodynamics. Model validity is examined using the laboratory-measured responses with a rigid load and a human occupant of similar body weight, and analyzed for different body weights and excitation spectra. The results suggest strong dependency of the suspension resonance frequency on nonlinear behavior of the air spring and the seated body mass. The model is subsequently employed to identify optimal coordinates of the air spring to achieve nearly constant natural frequency for a broad range of body masses. Furthermore, the model is used to identify optimal linkage and suspension design parameters with an objective to minimize the SEAT (Seat Effective Amplitude Transmissibility) for different spectral classes of earth moving machines defined in the ISO-7096 standard, while limiting the suspension travel. It is shown that the optimal coordinates of air spring could yield nearly constant natural frequency for different body weights, while damper could help limit the suspension travel, in addition to notable reductions in SEAT, ranging from 9% to 31% for different spectral classes of vehicles.

Low-frequency whole-body vibration can enhance cartilage degradation with slight changes in subchondral bone in mice with knee osteoarthritis and does not have any morphologic effect on normal joints.

To evaluate the effects of low frequency whole-body vibration (WBV) on degeneration of articular cartilage and subchondral bone in mice with destabilization of the medial meniscus (DMM)induced osteoarthritis(OA) and mice with normal knee. Ten-week-old C57BL/6J male mice received DMM on right knees, while the left knees performed sham operation. There were six groups: DMM, SHAM DMM, DMM+WBV,SHAM DMM+WBV, DMM+ NON-WBV and SHAM DMM+NON-WBV. After four weeks, the knees were harvested from the DMM and SHAM DMM group. The remaining groups were treated with WBV (10 Hz) or NON-WBV. Four weeks later, the knees were harvested. Genes, containing Aggrecan(Acan) and CollagenⅡ(Col2a1), Matrix Metalloproteinases 3 and 13(MMP3,13), TNFα and IL6, were measured and staining was also performed. OA was graded with OARSI scores, and tibial plateaubone volume to tissue volume ratio(BV/TV), bone surface area to bone volume ratio (BS/BV), trabecular number(Tb.N) and trabecular thickness separation(TS) between groups were analyzed. Increased OARSI scores and cartilage degradation were observed after WBV. BV/TV, Tb.N and TS were not significant between the groups. Significant reductions were observed in MMP3, MMP13, Col2a1, Acan, TNFα and IL6 in the DMM+WBV compared to SHAM DMM+WBV group. BV/TV, BS/BV, Tb.N, TS and OARSI scores were not significantly changed in the left knees. IL6 expression in the SHAM DMM+WBV group was significantly increased compared with the SHAM DMM+ NON-WBV group, while Col2a1, Acan and MMP13 expression decreased. WBV accelerated cartilage degeneration and caused slight changes in subchondral bone in a DMM-induced OA model. WBV had no morphologic effect on normal joints.

High-frequency whole-body vibration activates tonic vibration reflex.

The aim of this research was to examine whether high-frequency whole-body vibration activates the tonic vibration reflex (TVR). The experimental study was conducted with seven volunteers (mean age: 30.8±3.3 years; range, 26 to 35 years) between December 2021 and January 2022. To elicit soleus TVR, high-frequency (100-150 Hz) vibration was applied to the Achilles tendon. High-frequency (100-150 Hz) whole-body vibration and low-frequency (30-40 Hz) whole-body vibration were applied in quiet standing. Whole-body vibration-induced reflexes were recorded from the soleus muscle using surface electromyography. The cumulative average method was used to determine the reflex latencies. Soleus TVR latency was 35.6±5.9 msec, the latency of the reflex activated by high-frequency whole-body vibration was 34.8±6.2 msec, and the latency of the reflex activated by low-frequency whole-body vibration was 42.8±3.4 msec (F(2, 12)=40.07, p=0.0001, ƞ2 =0.87). The low-frequency whole-body vibration-induced reflex latency was significantly longer than high-frequency whole-body vibration-induced reflex latency and TVR latency (p=0.002 and p=0.001, respectively). High-frequency whole-body vibration-induced reflex latency and TVR latency were found to be similar (p=0.526). This study showed that high-frequency whole-body vibration activates TVR.

Post-stroke low-frequency whole-body vibration improves cognition in middle-aged rats of both sexes.

Low-frequency whole-body vibration (WBV; 40 Hz), a low impact form of exercise, intervention for a month following moderate transient middle-cerebral artery occlusion (tMCAO) reduces infarct volume and improves motor function in reproductively senescent, middle-aged female rats. Since post-stroke cognitive decline remains a significant problem, the current study aims to investigate the efficacy of WBV in ameliorating post-tMCAO cognitive deficits and to determine the underlying putative mechanism(s) conferring benefits of WBV in middle-aged rats. Middle-aged rats of both sexes were randomly assigned to tMCAO (90 min) or sham surgery followed by exposure to either WBV (twice a day for 15 min each for 5 days a week over a month) or no WBV treatment groups. Following the last WBV treatment, rats were tested for hippocampus-dependent learning and memory using a water maze followed by harvesting brain and blood samples for histopathological and inflammatory marker analyses, respectively. Results show that post-tMCAO WBV significantly lessens cognitive deficits in rats of both sexes. Post-tMCAO WBV significantly decreased circulating pro-inflammatory cytokines and increased serum levels of irisin, a muscle-derived hormone that may play a role in brain metabolism and inflammation regulation, which suggests putative beneficial mechanisms of WBV.

Whole-Body Vibration Associated with Strength Training on the Lower-Limb Blood Flow and Mobility in Older Adults with Type 2 Diabetes: A Study Protocol for a Randomized Controlled Trial.

Vascular endothelium insults caused by high serum glucose levels affect the oxygen supply to tissues, via the microvascular endothelium, resulting in an increased perfusion heterogeneity. These insults may lead to the underuse of blood capillaries, while other vessels are overused and effectively overload their oxygen supply capacity, which eventually causes damages to distal parts of the peripheral nervous system. Therefore, the proprioceptive and exteroceptive feedback information will be gradually lost and contribute to a mobility reduction. This study aims to assess the efficacy of whole-body vibration (WBV) associated with strength training (ST) on lower-limb blood flow and mobility in older adults with type 2 diabetes (DM2). Methods and analyses: This is a protocol (1st version) for Pa single-blind, randomized, controlled clinical trial guided by the SPIRIT guidelines. Our sample will consist of 51 older adults with DM2 randomly allocated to three groups: low frequency WBV (16–26 Hz) associated to ST (G1), WBV sham (G2) and nonintervention control (G3). The study protocol is set for a 12-week (three times per week) schedule. Primary outcomes: skin temperature using infrared thermographic imaging (ITI); mean peripheral arterial blood flow velocity (MBF) by a handheld Doppler ultrasound (DU), and functional mobility by Timed Up and Go (TUG) test. Secondary outcomes: quasi-static posture using the DX100 BTS Smart optoelectronic system, and plantar pressure and body balance using the MPS stabilometric platform. Data will be collected and analyzed at baseline and post-intervention, considering p-value < 0.05 level of significance. The analyses will also be conducted with an intention-to-treat method and effect size. Dissemination: All results will be published in peer-reviewed journals as well as presented in conferences.

Association Between High Risk of Obstructive Sleep Apnea and Excessive Daytime Sleepiness in Elderly People Based on Epworth Sleepiness Scale and Karolinska Sleepiness Scale after Exposure to Low Frequency Whole Body Vibration

Background: The most common symptom of obstructive sleep apnea (OSA) is excessive daytime sleepiness (EDS). Aim: To look for the high risk of OSA in the elderly population and its association with increased Epworth sleepiness scale (ESS) and Karolinska sleepiness scale (KSS) scores after exposure with low-frequency whole body vibration (LFWBV). Method: This study used a one group pretest-post test design. Subjects examined for Snoring Score (SS), ESS and KSS scores, after which subjects were given exposure to LFWBV and examined for post-exposure KSS scores. Results: There were more elderly people who have a high risk of OSA. The ESS score showed a non-significant relationship between high risk of OSA and the incidence of EDS based on an increase in ESS score (r 0.401; p value 0.064) and the degree of sleepiness based on the KSS score after LFWBV exposure (r 0.296; p value 0.181), although ESS scores were higher in the group with high risk of OSA (mean score 4.85; p value 0.003). Discussion: The results of this study are consistent with several other studies which show no significant correlation between high risk of OSA and increased ESS scores. LFWBV does provide comfort and increases the degree of sleepiness in subjects with or without a high risk of OSA. Conclusion: Older age increases the risk of OSA, but does not cause EDS. LFWBV caused an increase in the degree of sleepiness, both the high-risk and non-high-risk OSA groups. Keywords: Obstructive sleep apnea, Epworth sleepiness scale, whole body vibration, Karolinska sleepiness scale.

Abstract TP231: Irisin, Elicited By Low Frequency Whole Body Vibration Or Exogenously, Improves Post-Stroke Cognition And Reduces Infarct Volume In Middle-Aged Rats

Significance: Low frequency whole body vibration (LFV) at 40 Hz, a low impact form of exercise, for a month following mild transient middle-cerebral artery occlusion (tMCAO) reduces infarct volume and improves motor function in reproductively senescent, middle-aged female rats (1). In humans, LFV was shown to increase circulating levels of irisin, a skeletal muscle-derived hormone. Irisin has also been shown to play a crucial role in preserving mitochondrial function, preventing oxidative stress, and elevating expression of BDNF, among other neuroprotective measures. The current study aims to investigate the efficacy of LFV in ameliorating post-tMCAO cognitive deficits and to determine the putative role of irisin in conferring the benefits of LFV in middle-aged rats. Methods: Middle-aged rats of both sexes (5-8) were randomly assigned to tMCAO (90 min), or sham surgery followed by exposure to either LFV (twice a day for 15 min each for 5 days a week over a month) or no LFV treatment groups. Following the last LFV treatment, rats were tested for hippocampus-dependent learning and memory using a water maze followed harvesting brain and blood samples for histopathological and inflammatory marker analyses, respectively. In a parallel experiment in the absence of LFV, middle-aged female rats were randomly assigned to either saline or irisin treatment following tMCAO. Recombinant irisin was purchased from PeproTech (Rocky Hill, NJ). Rats were treated with irisin (0.2 μg/g BW; IP) or saline for a month followed by their brains were assessed by histopathology. Results: Post-tMCAO LFV significantly lessens cognitive deficits in rats of both sexes. It also significantly decreased circulating pro-inflammatory cytokines and increased serum levels of native irisin. Quantification of infarct volume irisin-treated rats demonstrated that, compared to saline, infarct volume was significantly reduced. Saline treatment resulted in 234 ± 30 mm 3 , while irisin treatment yielded 128 ± 34 mm 3 (p&lt;0.05) of infarct volume. Conclusion: Irisin, either as elicited by LFV or administered exogenously without LFV, regulates brain metabolism and inflammation and its beneficial effects can be stimulated by LFV.Reference: 1. Raval, A.P., et al., Int J Mol Sci, 2018. 19 (9).

Irisin-Associated Neuroprotective and Rehabilitative Strategies for Stroke.

Irisin, a newly discovered protein hormone that is secreted in response to low frequency whole body vibration (LFV), could be a promising post-stroke rehabilitation therapy for patients who are frail and cannot comply with regular rehabilitation therapy. Irisin is generated from a membrane-bound precursor protein fibronectin type III domain-containing protein 5 (FNDC5). Aside from being highly expressed in muscle, FNDC5 is highly expressed in the brain. The cleaved form of FNDC5 was found in the cerebrospinal fluid as well as in various regions of the brain. Numerous studies suggest that irisin plays a key role in brain metabolism and inflammation regulation. Both the metabolism and inflammation govern stroke outcome, and in a published study, we demonstrated that LFV therapy following middle cerebral artery occlusion significantly reduced innate immune response, improved motor function and infarct volume in reproductively senescent female rats. The observed effect of LFV therapy could be working via irisin, therefore, the current review focuses to understand various aspects of irisin including its mechanism of action on the brain.

The Effects of Whole Body Vibration on the Limits of Stability in Adults With Subacute Ankle Injury.

BackgroundLimited research exists on the effects of both high and low frequency whole body vibration (WBV) on individuals with subacute lateral ankle sprains.Hypothesis/PurposeTo examine the difference in the effects of high and low frequency WBV on limits of stability (LOS) in adults with a subacute ankle sprain. It was hypothesized that WBV would improve effects on outcome variables for LOS as a component of dynamic balance.Study DesignQuasi-experimental, pretest-posttest design.MethodsFifteen participants ages 19-27 years (Mean age 22±2.36) with either a Grade I or Grade II lateral ankle sprain received WBV in bilateral stance under three randomized conditions (high frequency-25 Hz, low frequency-6 Hz, and control, which consisted of bilateral stance with machine off) for six minutes over three sessions (one time per week). The LOS test, consisting of 5 variables, were assessed using the NeuroCom® Balance Manager-SMART EquiTest® (Natus Medical Incorporated, Pleasanton, CA) at baseline and after the intervention period. The participants completed a practice LOS test and then had a six-minute standing rest break. After the rest break, they completed the pre-LOS (baseline) test. Intervention was administered using the Galileo® Med L Chip Research (Novotec Medical GmbH, Pforzheim, Germany) for six minutes for the appropriate condition of either high or low frequency WBV or control. Data analysis was performed using 2-Way (2x3) Repeated Measures ANOVAs with additional post hoc testing as needed.ResultsSignificant interactions were found for reaction time (RT), movement velocity (MVL), and maximal excursion (MXE) composite scores with a decrease in RT of 0.117 seconds (p=0.022) between control and high frequency conditions during the post LOS. For composite MVL, an increase of 0.547 degrees/second (p=0.002) between pre- and post-high frequency WBV occurred. For composite MXE, an increase of 2.13% p=0.031 (when comparing pre- and post-high frequency WBV.ConclusionFindings suggest that a single session of high frequency WBV in individuals with a subacute lateral ankle sprain may result in improvement in several components of postural stability. WBV is a quick intervention that could be implemented in physical therapy clinics, athletic training rooms, and workout facilities to improve an individual’s LOS as a component of dynamic balance one to eight weeks post lateral ankle sprain.Level of Evidence2b

The effect of exercise load deviations in whole body vibration on improving muscle strength imbalance in the lower limb

BACKGROUND: The amount of patients with muscle imbalance of the left and right side increases rapidly due to an incorrect lifestyle.OBJECTIVE: We investigated the optimal exercise load required to improve muscle imbalance.METHODS: Thirty participants were enrolled in the study. They performed squat exercises according to a whole body vibration (WBV) frequency protocol over a period of eight weeks. The exercises were performed three days a week and comprised five sets of fifteen trials per set per day. We validated muscle imbalance improvement using WBV by comparing and analyzing the results at different vibration frequencies. The participants were divided into three WBV protocol groups: no WBV, low-frequency WBV (25 Hz and 5 mm amplitude), and high-frequency WBV (50 Hz and 5 mm amplitude). We estimated the isokinetic muscle functions of the hip, knee, and ankle joints using BIODEX system 3. Ultimately, low-frequency WBV improved balance 10.2 26.5% more than high-frequency WBV.RESULTS: Continuous load-deviation motions during low-frequency WBV were more effective at improving muscle imbalance than high-frequency WBV. WBV load variation methods improved muscle function and contractility more than external weights or loads by directly transferring kinetic energy into the body.CONCLUSION: In this clinical study, we demonstrated that low-frequency WBV was more effective at improving muscle imbalance. The WBV protocol can be used in rehabilitation programs to improve imbalance without requiring elderly or physically decompensated patients to participate in excessive exercise.

Effects of Different Frequencies of Whole Body Vibration on Repositioning Error in Patients With Chronic Low Back Pain in Different Angles of Lumbar Flexion

ObjectiveThis study aimed to evaluate the effect of high and low frequency of whole body vibration (WBV) on repositioning error in 3 different angles of lumbar flexion in patients with chronic low back pain. MethodsTwenty-four participants with chronic low back pain, aged between 20 and 35 years, were included in this randomized crossover trial study. Participants were randomly assigned into 2 groups as follows: (1) low frequency/high frequency, and (2) high frequency/low frequency. Participants received high-frequency (50 Hz) and low-frequency (30 Hz) WBV in a semi-squat position for 5 minutes in 2 sessions, with 2 weeks of rest. Before and after the WBV, lumbar repositioning error in 30% and 60% of lumbar full flexion and neutral position with eyes closed when standing was evaluated using an electrogoniometer. ResultsThe repositioning error was decreased in neutral, 30%, and 60% of lumbar flexion after the low-frequency and high-frequency WBV. Post hoc testing revealed that the effect of angle was not significant in repositioning error changes between high-frequency and low-frequency WBV (P > .05). However, the effect of low-frequency WBV on the repositioning error was significantly higher compared with high-frequency WBV (P < .05). ConclusionLow-frequency WBV might induce more improvement in the accuracy of lumbopelvic repositioning compared with high-frequency WBV with the method of WBV used in this study.

The macroscopic and microscopic effect of low-frequency whole body vibration after cerebral ischemia in rats

Whole body vibration (WBV) has been applied in stroke patients with uncertain effects on motor and sensory dysfunction, and its effects on neurogenesis have not been studied yet. In total, 144 rats were used for experiments with 29 rats excluded due to early attrition, exclusion by rCBF criterion or death of ischemia in acute phase. Rats included were divided into 3 groups: WBV group ( n = 50), control group ( n = 50) group, and sham group ( n = 15). To explore the effects of daily WBV on neurological behavior, brain structure, and neurogenesis after cerebral ischemia in rats for 4 weeks. Improvements in weight or comprehensive neurological deficits were not significantly different under WBV or control treatment, and the degrees of brain damage and the numbers of necrotic neurons in the ischemic cortex were similar in two groups. However, WBV markedly improved animals’ coordination from 14d to 28d ( P < 0.05) and muscle strength of the upper limbs at 21d and 28d ( P < 0.05 & P < 0.001) compared with the control group. WBV promoted the increase in the number of bromodeoxyuridine-positive (BrdU + ) cells at 3d ( P < 0.05) and 14d ( P < 0.001) and the number of BrdU+/nestin + cells at 14d ( P < 0.01) after ischemia when compared to the control group. The numbers of BrdU+/NeuN + cells at 21d and 28d ( P < 0.001) were enhanced by WBV treatment. WBV significantly promoted the proliferation of astrocytes and their neural processes thickening after 14d. The expression levels of neural markers, such as double cortin, microtubule-associated protein 2, and glial fibrillary acidic protein, were upregulated in the ipsilateral cortex at different time points. Low-frequency WBV showed inconspicuous improvements in behavioral performance and brain damage after cerebral ischemia, but showed the potential in improving coordination and muscle strength and promoted neurogenesis after long-term exposure.

Multibody Biomechanical Modelling of Human Body Response to Direct and Cross Axis Vibration

Operators of the vehicles and heavy earth moving machinery are continuously exposed to low frequency whole-body vibration (WBV) of comprehensive magnitudes arising from tire/track-terrain interactions. Research studies shown a high presence of back disorders such as disc degeneration, muscular pain, among the occupational vehicle drivers subjected to whole-body vibration. The modelling and measurement of the biodynamic response of human body is major research topic, with applications to ergonomics, paasive or active suspension control system technologies, adverse effects on the human body that causes discomfort and some health issues. The risk of the vibration exposure depends on three different factors: the time span, the amplitude and the frequency of the transmitted vibration. In the field of automotive engineering, manufacturers and designers require to understand how the acceleration signals are amplified or damped by the human-seat interface in order to increase human comfort.Most of human body models reported in literature are lumped parameter. The limitation with lumped parameter model is that they can be analysed in one direction only. Human body is having complex motion so minimum two dimensional (2D) model need for analysing human body response. The models considered two objective functions with considering vertical or fore and aft vibrations. Multibody human body models of 20 degree of freedom (DOF) developed for seated human, and model parameters are optimized using genetic algorithm (GA) for published experimental data from literature. Model is able to match the published experimental data for Seat to Head Transmissibility (STHT) and Apparent Mass (AM).

The macroscopic and microscopic effect of low-frequency whole-body vibration after cerebral ischemia in rats.

Whole body vibration (WBV) has been applied in stroke patients with uncertain effects on motor and sensory dysfunction, and its effects on neurogenesis have not been studied yet. Here, we intended to explore the effects of daily WBV on neurological behavior, brain structure, and neurogenesis after cerebral ischemia in rats for 4weeks. Results showed that improvements in weight or comprehensive neurological deficits were not significantly different under WBV or control treatment, and the degrees of brain damage and the numbers of necrotic neurons in the ischemic cortex were similar in two groups. However, WBV markedly improved animals' coordination from 14d to 28d (P<0.05) and muscle strength of the upper limbs at 21d and 28d (P<0.05 & P<0.001) compared with the control group. WBV promoted the increase in the number of bromodeoxyuridine-positive (BrdU+) cells at 3d (P<0.05) and 14d (P<0.001) and the number of BrdU+/nestin+ cells at 14d (P<0.01) after ischemia when compared to the control group. The numbers of BrdU+/NeuN+ cells at 21d and 28d (P<0.001) were enhanced by WBV treatment. In addition, WBV significantly promoted the proliferation of astrocytes and their neural processes thickening after 14d. The expression levels of neural markers, such as doublecortin, microtubule-associated protein 2, and glial fibrillary acidic protein, were upregulated in the ipsilateral cortex at different time points. Low-frequency WBV showed inconspicuous improvements in behavioral performance and brain damage after cerebral ischemia, but showed the potential in improving coordination and muscle strength and promoted neurogenesis after long-term exposure.

International Clinical Protocol on Vestibular Disorders (Dizziness).

26-28 May at 43 Congress of Neurootological and Equilibriometric Society (Budapest, Hungary) International Clinical Protocol on Vestibular Disorders (Dizziness) being discussed and accepted as Consensus Document. Cochrane reports estimates that dizziness has prevalence of 22.9% in the last 12 months and an incidence of 3.1%. Only 1.8% of adults consulted a physician in the last 12 months. Cochrane reviews suggest that the evidence base for dizziness evaluation is weak, thus necessitates the creation of evidence-based document. Protocol is based at the new concept of vestibular system, which involves the vestibular peripheral sensors, space orientation tetrad, vestibular presentations in the brain cortex and vestibular effectory projections in the brain. Labyrinth consists of sensors, for which six modalities are adequate: 1. acceleration, 2. gravitation, 3. low frequency whole-body vibration, 4. Infrasound, 5. magnetic impulse, 6. metabolic changes. Vestibular system from rhomboid fosse gets the inputs from visual, acoustic, somatosensory organs, integrating them and forming space perception and orientation. Interaction with space is realized through sensory, motor, vegetative and limbic projections. So, vestibular disturbances may manifest as paropsia, tinnitus, numbness. Vestibular evoked potentials (not VEMP) and craniocorpography have highest sensitivity (90% and more). As vestibular dysfunction has recurrent character patients need monitoring.

2E2-4 低周波数領域の振動感覚に及ぼす音の影響について

2E2-4 低周波数領域の振動感覚に及ぼす音の影響について

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.

Time-domain analysis of passenger comfort on cruise ships under motion responses in waves

The assessment of passenger comfort in modern cruise ships is considered from a hydrodynamic point of view, in addition to improvement using stabilizing fins. Passenger comfort is evaluated in this study based on the symptoms of motion sickness on ships provoked by low-frequency whole-body vibration. Motion sickness dose value is an index used to quantify seasickness and is chosen as a primary index to evaluate passenger comfort. To calculate motion sickness dose value in the time domain, a time series of vertical accelerations should be processed using frequency filters, which are defined in the international standards and guidelines provided by classification societies as forms of transfer functions in the frequency domain. Digital frequency band–limiting and weighting filters are formulated as a form of infinite impulse response filter and then applied to the present case. Two pairs of stabilizing fins are equipped to reduce the roll and pitch motions and to improve the passenger comfort on a model cruise ship. A linear optimal control algorithm, linear quadratic Gaussian, is considered to actuate each stabilizing fin. Numerical computations are carried out based on practical operating conditions for the cruise ship model using a time-domain ship motion program, which integrates the motion control algorithm and the passenger comfort analysis. The results of computations show that passenger comfort on a cruise ship can be evaluated appropriately by computing the index motion sickness dose value in the time domain. The motion stabilization by the stabilizing fins can be considered as a good method to reduce the motion of the present cruise ship model and eventually contribute to improve passenger comfort.

Changes in joint angle, muscle‐tendon complex length, muscle contractile tissue displacement, and modulation of EMG activity during acute whole‐body vibration

It has been suggested that vibration causes small changes in muscle length, but to the best of our knowledge, these have yet to be demonstrated during whole-body vibration (WBV). This was an observational study to determine whether acute WBV would result in muscle lengthening. We hypothesized that acute WBV would increase electromyography (EMG) activity concurrently with measurable changes in muscle contractile length. Nine healthy males performed two conditions on a Galileo vibration machine for 15 s at 0 HZ (resting) and 6 HZ at a set knee angle of 18 degrees. Muscle tendon complex length, contractile tissue displacement of the medial gastrocnemius muscle, and EMG of soleus, tibialis anterior, and vastus lateralis muscles were measured. At 6 HZ the medial gastrocnemius (MG) muscle tendon complex (MTC) amplitude (375 microm) was significantly greater (P < 0.05) compared to 0 HZ (35 microm). The MG contractile length (CD) amplitude at 6 HZ (176 microm) was significantly greater (P < 0.01) compared to 0 HZ (4 microm). Significant increases (P < 0.05) in EMG modulation were found for all muscles during the 6 HZ compared to the 0 HZ condition. The major finding was that approximately 50% of the elongation occurred within the muscle itself and was associated with preceding changes in EMG. This indicates muscle lengthening may be a prerequisite for eliciting stretch reflexes. In conclusion, there is a temporal association between EMG activity and muscle contractile tissue displacement where low-frequency WBV results in small muscle length changes and increases muscle activation.

Effects of low‐frequency whole‐body vibration on motor‐evoked potentials in healthy men

The aim of this study was to determine whether low-frequency whole-body vibration (WBV) modulates the excitability of the corticospinal and intracortical pathways related to tibialis anterior (TA) muscle activity, thus contributing to the observed changes in neuromuscular function during and after WBV exercise. Motor-evoked potentials (MEPs) elicited in response to transcranial magnetic stimulation (TMS) of the leg area of the motor cortex were recorded in TA and soleus (SOL) muscles of seven healthy male subjects whilst performing 330 s continuous static squat exercise. Each subject completed two conditions: control (no WBV) and WBV (30 Hz, 1.5 mm vibration applied from 111 to 220 s). Five single suprathreshold and five paired TMS were delivered during each squat period lasting 110 s (pre-, during and post-WBV). Two interstimulus intervals (ISIs) between the conditioning and the testing stimuli were employed in order to study the effects of WBV on short-interval intracortical inhibition (SICI, ISI = 3 ms) and intracortical facilitation (ICF, ISI = 13 ms). During vibration relative to squat exercise alone, single-pulse TMS provoked significantly higher TA MEP amplitude (56 +/- 14%, P = 0.003) and total area (71 +/- 19%, P = 0.04), and paired TMS with ISI = 13 ms provoked smaller MEP amplitude (-21 +/- 4%, P = 0.01) but not in SOL. Paired-pulse TMS with ISI = 3 ms elicited significantly lower MEP amplitude (TA, -19 +/- 4%, P = 0.009; and SOL, -13 +/- 4%, P = 0.03) and total area (SOL, -17 +/- 6%, P = 0.02) during vibration relative to squat exercise alone in both muscles. Tibialis anterior MEP facilitation in response to single-pulse TMS suggests that WBV increased corticospinal pathway excitability. Increased TA and SOL SICI and decreased TA ICF in response to paired-pulse TMS during WBV indicate vibration-induced alteration of the intracortical processes as well.