Effect of a Rehabilitation Program Including Home-Based Vibration-Assisted Therapy on Gait Parameters in Children with Cerebral Palsy.

OBJECTIVES: The aim of the present study was to examine the effects of a rehabilitation program combined with a home-based vibration-assisted therapy on gait parameters in children with cerebral palsy (CP). METHODS: In a retrospective study, 180 children, 101 boys and 79 girls, (mean age 7.2 ± 3.3 years) with CP at Gross Motor Function Classification System (GMFCS) Level I and Level II were examined using gait analyses with the Leonardo Mechanograph® Gangway at three measurement points. The measurements were conducted before (M0) and after a six-month rehabilitation period (M6), as well as 12 months after the commencement of rehabilitation (M12). The difference between measurement points M6-M0 (treatment interval) and M12-M6 (follow-up interval) were compared, and significance was determined using the Wilcoxon test. RESULTS: Children with CP at GMFCS Level I and II demonstrated a significant improvement in gait efficiency (pathlength/distance M6-M0: -0.053 (SD 0.25) vs M12-M6: -0.008 (0.36), p=0.038). There were no significant difference in change of mean velocity and average step length between M6-M0 and M12-M6 (p=0.964 and p=0.611). CONCLUSIONS: The rehabilitation program seems to enhance gait efficiency in children with CP. German Clinical Trial Registry: DRKS0001131 at www.germanctr.de.

Acute effects of whole-body vibration on unilateral isometric knee extensors maximal torque and fatigability during an intermittent endurance task in adult males.

Whole-body vibration (WBV) has been employed for performance-enhancing purposes. WBV may positively affect muscular endurance and its underlying neural mechanisms due to an enhanced muscular blood circulation and oxygen uptake. However, the effects of WBV on endurance-related torque signal complexity have been understudied. This study aims to investigate the acute effects of WBV on i) maximal isometric torque production; ii) isometric knee extensors fatigability and iii) torque signal complexity during an isometric endurance task. Thirty adult males performed an isometric intermittent endurance protocol on their dominant lower limb after performing: static half squat with WBV (WBV), static half squat without WBV (HS), and no exercise protocol (CC). For each repetition the maximal torque was identified. The maximal torque of the first repetition was identified as the PeakT. The Mean torque (MTorque) and fatigue index (pFatigue) were calculated as the mean and the percentage decay in torque across the entire set of eighteen repetitions (MTorque0-100 %, pFatigue0-100 %), and across shorter blocks of six repetitions (MTorque0-33 %, pFatigue0-33 %; MTorque34-66 %, pFatigue34-66 %, and MTorque67-100 %, pFatigue67-100 %). Torque fluctuations were analysed computing Sample Entropy (SampEn) and the coefficient of variation (CV). PeakT was significantly higher in CC than in WBV (p < 0.01) and in HS (p < 0.01). PeakT was significantly higher in HS than in WB (p < 0.05). MTorque0-100 %, MTorque0-33 %, MTorque34-66 %, and MTorque67-100 % were significantly higher in CC than in WBV (all p-values <0.01) and in HS (p < 0.01). MTorque67-100 % was significantly higher in HS than in WB (p = 0.049). pFatigue34-66 % was significantly higher in WBV than in CC (p < 0.05) whereas pFatigue67-100 % was significantly higher in CC than in WB (p < 0.01) and in HS (p < 0.01). No effect of condition was observed for SampEn and CV. Acute WBV does not lead to beneficial effects on maximal torque production and isometric knee extensors fatigability. These acute detrimental effects may be related to long-term WBV-related adaptations.

ResNet diagnosis of rotor faults in oil transfer pumps.

To address rotor imbalance and misalignment in oil transfer pumps, an innovative diagnostic framework using Residual Network (ResNet) is proposed. The model incorporates advanced signal processing algorithms and strategic sensor placement to enhance diagnostic efficacy. A fault simulation test rig captured vibration signals from eight key measurement points on the pump. One-dimensional and multi-dimensional signal processing techniques generated comprehensive datasets for training and validating the model. Sensor placement optimization, focusing on the bearing seat's axial direction, inlet flange's vertical direction, and outlet flange's axial direction, increased rotor fault sensitivity. Time-frequency data processed via Short-Time Fourier Transform (STFT) achieved the highest diagnostic accuracy, surpassing 98 %. This study highlights the importance of optimal signal processing and precise sensor placement in improving the accuracy of diagnosing rotor faults in oil transfer pumps, thus enhancing the operational reliability and efficiency of energy transportation systems.

Label-free spatiotemporal decoding of single-cell fate via acoustic driven 3D tomography.

Label-free three-dimensional imaging plays a crucial role in unraveling the complexities of cellular functions and interactions in biomedical research. Conventional single-cell optical tomography techniques offer affordability and the convenience of bypassing laborious cell labelling protocols. However, these methods are encumbered by restricted illumination scanning ranges on abaxial plane, resulting in the loss of intricate cellular imaging details. The ability to fully control cellular rotation across all angles has emerged as an optimal solution for capturing comprehensive structural details of cells. Here, we introduce a label-free, cost-effective, and readily fabricated contactless acoustic-induced vibration system, specifically designed to enable multi-degree-of-freedom rotation of cells, ultimately attaining stable in-situ rotation. Furthermore, by integrating this system with advanced deep learning technologies, we perform 3D reconstruction and morphological analysis on diverse cell types, thus validating groups of high-precision cell identification. Notably, long-term observation of cells reveals distinct features associated with drug-induced apoptosis in both cancerous and normal cells populations. This methodology, based on deep learning-enabled cell 3D reconstruction, charts a novel trajectory for groups of real-time cellular visualization, offering promising advancements in the realms of drug screening and post-single-cell analysis, thereby addressing potential clinical requisites.

Physical realizations of inerter and inerter-based vibration control.

Vibration control is extremely important for countless mechanical systems. Inerter is a two-terminal dynamic element proposed in 2002, based on analogy between mechanical system and electric system. Dynamic characteristic of an ideal inerter is pure inertia. Force applied on each terminal of an inerter is directly proportional to relative acceleration of two terminals. Since inerter was put forward, it has made significant progress in vibration control systems. The paper is a review about physical realizations of inerter as well as inerter-based vibration control. Physical realizations and applications in vibration control of inerter are focused. First, the develop of inerter and typical physical realizations of inerter are introduced. The normative derivation processes based on Lagrange equation method of the dynamic relationships in the different inerters are summarized. And then, three categories of common inerter-based vibration control systems are explained. Finally, research trend of physical realizations of inerter are summarized, and the possible researches on inerter-based vibration control are discussed.

Client-based evaluation of the effects of localized vibration therapy on pain and mobility scores in dogs with radiographic bilateral hip dysplasia.

Introduction: This study evaluated the effects of localized vibration (LV) in 37 dogs with bilateral hip dysplasia (HD). HD is a common cause of lameness in dogs, and is a contributory factor to osteoarthritis, which can reduce the dog's overall quality of life. Materials and methods: This was a multi-center, prospective survey-based study of 37 dogs with bilateral HD and no prior history of surgical management. Dogs were given LV therapy daily for 14 consecutive days using the same commercially available handheld vibration device. Canine Brief Pain Index (CBPI) data was collected prior to the initiation of therapy, then for 14 days following daily LV therapy. The dogs' medications, supplements, additional rehabilitation modalities, and activity level were unchanged during the study period. Baseline CBPI pain severity and pain interference scores were compared to scores after 7 or 14 days of LV. Results: There were significant decreases in average pain severity and average pain interference CBPI scores in response to 7 and 14 days of therapy compared to baseline. When response to therapy was defined as a decrease in both pain severity score and pain interference score, 62% (23/37) of dogs responded to therapy at 7 days of treatment and 73% (27/37) responded at 14 days of treatment. Of the individuals that responded to treatment at 7 days, 91% (21/23) continued to respond at 14 days. Conclusion: Daily LV resulted in a significant reduction in CBPI scores in 73% of dogs with bilateral HD in this study. Randomized and blinded studies should be performed to further assess daily LV as a treatment modality for canine HD.

2D coordination polymers of cadmium(II) and zinc(II) derived from N,N'-bis(glycinyl)pyromellitic diimide: microwave-assisted synthesis, structures, spectroscopic properties and influence of metal-ion size.

Two new two-dimensional (2D) coordination polymers (CPs), namely, poly[diaqua[µ4-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato-κ4O:O':O'':O''']cadmium(II)], [Cd(C14H6N2O8)(H2O)2]n (1), and poly[[tetraaqua[µ4-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato-κ4O:O':O'':O'''][µ2-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato-κ2O:O']dizinc(II)] dihydrate], {[Zn(C14H6N2O8(H2O)2]·H2O}n (2), have been synthesized by the microwave-irradiated reaction of Cd(CH3COO)2·2H2O and Zn(CH3COO)2·2H2O, respectively, with N,N'-bis(glycinyl)pyromellitic diimide {BGPD, namely, 2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetic acid, H2L}. In the crystal structure of 1, the CdII ion is six-coordinated by four carboxylate O atoms from four symmetry-related L2- dianions and two coordinated water molecules, furnishing an octahedral coordination geometry. The bridging L2- dianion links four symmetry-related CdII cations into a 2D layer-like structure with a 3,4-connected bex topology. In the crystal structure of 2, the ZnII ion is five-coordinated by three carboxylate O atoms from three different L2- dianions and two coordination water molecules, furnishing a trigonal bipyramidal coordination geometry. Two crystallographically independent ligands serve as µ4- and µ2-bridges, respectively, to connect the ZnII ions, thereby forming a 2D layer with a 3,3-connected hcb topology. Crystal structure analysis reveals the presence of n→π* interactions between two carbonyl groups of the pyromellitic diimide moieties in 1 and 2. CP 1 exhibits an enhanced fluorescence emission compared with free H2L. The framework of 2 decomposes from 720 K, indicating its high thermal stability. A comparative analysis of a series of structures based on the BGPD ligand indicates that the metal-ion size has a great influence on the connection modes of the metal ions due to different steric effects, which, in turn, affects the structures of the SBUs (secondary building units) and frameworks.

Effects of lower limb vibration on hip pain and function after total hip arthroplasty: A randomized controlled trial.

BACKGROUND: A vibration roller is an effective tool for reducing muscle soreness and improving damaged muscle function. However, its efficacy in reducing hip pain and improving function after total hip arthroplasty is unclear. We investigated the effect of lower limb vibration using a vibration roller on postoperative hip pain and function after total hip arthroplasty in a randomized controlled clinical trial. METHODS: Thirty patients scheduled for total hip arthroplasty were randomly assigned to vibration and control groups. The patients in the vibration group performed lower limb vibration using a vibration roller. The patients in the control group performed sham therapy using a hot pack. Patients performed both interventions for 10 min daily on postoperative days 1-7, in addition to regular physical therapy. Primary outcome was hip pain intensity as measured using a visual analog scale. Secondary outcomes were pain-pressure threshold and serum creatine kinase and C-reactive protein levels. We also assessed physical functions, including the Harris Hip Score, range of motion of the hip joint, muscle strength, gait velocity, and timed up-and-go test. The effects of the interventions on outcome measurements in the groups were compared using a split-plot design variance analysis. RESULTS: After one week of the intervention and three weeks of follow-up, the vibration group showed statistically significant improvement in the exercise-induced hip pain, pain-pressure threshold of lateral thigh, and serum creatine kinase compared to the control group (p = 0.006, 0.003, and 0.012, respectively). No statistically significant differences were found between the groups regarding the physical functions. CONCLUSIONS: Lower limb vibration using a vibration roller after total hip arthroplasty was an effective intervention to reduce exercise-induced hip pain and improve serum creatine kinase, but there was no synergistic effect on the physical functions.

Optimising 4D imaging of fast-oscillating structures using X-ray microtomography with retrospective gating.

Imaging the internal architecture of fast-vibrating structures at micrometer scale and kilohertz frequencies poses great challenges for numerous applications, including the study of biological oscillators, mechanical testing of materials, and process engineering. Over the past decade, X-ray microtomography with retrospective gating has shown very promising advances in meeting these challenges. However, breakthroughs are still expected in acquisition and reconstruction procedures to keep improving the spatiotemporal resolution, and study the mechanics of fast-vibrating multiscale structures. Thereby, this works aims to improve this imaging technique by minimising streaking and motion blur artefacts through the optimisation of experimental parameters. For that purpose, we have coupled a numerical approach relying on tomography simulation with vibrating particles with known and ideal 3D geometry (micro-spheres or fibres) with experimental campaigns. These were carried out on soft composites, imaged in synchrotron X-ray beamlines while oscillating up to 400 Hz, thanks to a custom-developed vibromechanical device. This approach yields homogeneous angular sampling of projections and gives reliable predictions of image quality degradation due to motion blur. By overcoming several technical and scientific barriers limiting the feasibility and reproducibility of such investigations, we provide guidelines to enhance gated-CT 4D imaging for the analysis of heterogeneous, high-frequency oscillating materials.

Improved Liver Intravital Microscopic Imaging Using a Film-Assisted Stabilization Method.

Intravital microscopy (IVM) is a valuable method for biomedical characterization of dynamic processes, which has been applied to many fields such as neuroscience, oncology, and immunology. During IVM, vibration suppression is a major challenge due to the inevitable respiration and heartbeat from live animals. In this study, taking liver IVM as an example, we have unraveled the vibration inhibition effect of liquid bridges by studying the friction characteristics of a moist surface on the mouse liver. We confirmed the presence of liquid bridges on the liver through fluorescence imaging, which can provide microscale and nondestructive liquid connections between adjacent surfaces. Liquid bridges were constructed to sufficiently stabilize the liver after abdominal dissection by covering it with a polymer film, taking advantage of the high adhesion properties of liquid bridges. We further prototyped a microscope-integrated vibration-damping device with adjustable film tension to simplify the sample preparation procedure, which remarkably decreased the liver vibration. In practical application scenarios, we observed the process of liposome phagocytosis by liver Kupffer cells with significantly improved image and video quality. Collectively, our method not only provided a feasible solution to vibration suppression in the field of IVM, but also has the potential to be applied to vibration damping of precision instruments or other fields that require nondestructive ″soft″ vibration damping.

A comparison between the effects of vibration exercise and needle therapy on fibromyalgia symptoms and well-being in community-dwelling older adults: A randomized control study.

This randomized controlled pilot study compared the efficiency of exercise on a vibration machine combined with needle therapy versus needle therapy alone in managing fibromyalgia symptoms and well-being among older adults. Conducted at King Khalid Hospital in Alkharj, Saudi Arabia, the study involved eighty-six patients aged 60 to 67 years. Participants were randomly assigned to either the VENT (Vibration Exercise Device) group or the NT (Needle Therapy) group. The VENT group underwent 10-minute vibration training sessions twice a week, paired with 30-minute needle acupuncture sessions once a week, while the NT group received needle therapy alone. Both interventions were carried out over 12 weeks. Pre- and post-intervention assessments measured disability, pain, balance, and quality of life. Data analysis showed that 94.1% of participants completed the study, with significant improvements in disability observed in the VENT group. Both groups demonstrated significant improvements in pain, balance, and well-being. However, post-intervention comparisons favored the VENT group, showing significantly better outcomes. The findings suggest that combining vibratory exercise with needle therapy offers enhanced benefits for older adults with fibromyalgia.

Embedded periodically ABHs and distributed DVAs for passive low-frequency broadband vibration attenuation in thin-walled structures.

The acoustic black hole (ABH) structure exhibits remarkable energy focalization above a given cut-on frequency, offering potential for broadband vibration suppression in structures. However, its energy focusing properties diminish significantly below this cut-on frequency. Therefore, it is crucial to enhance the vibration attenuation capabilities of ABH structures within the low frequency range. This study presents a numerical investigation into the impact of thin-walled structures with embedded ABHs and distributed dynamic vibration absorbers (DVAs) on low frequency broadband vibration reduction. Initially, the focusing characteristics of the ABH thin-walled structure is analyzed, aiding in the attached position of DVAs. Furthermore, the influence of the design parameters and attached position of DVA on the broadband damping effect of the structure is explored. The findings indicate that DVAs designed for low frequencies can achieve significant vibration attenuation across the entire frequency spectrum, including low frequencies, when installed at specific focusing positions. When compared to the position with the maximum vibration response, while the attenuation of the low frequency common amplitude value is slightly reduced, greater vibration attenuation across the entire frequency band is achieved. This research offers valuable insights into optimizing the integration of DVAs with ABHs in thin-walled structures for enhanced broadband vibration attenuation.

Calibrating the Discrete Boundary Conditions of a Dynamic Simulation: A Combinatorial Approximate Bayesian Computation Sequential Monte Carlo (ABC-SMC) Approach.

This paper presents a novel adaptation of the conventional approximate Bayesian computation sequential Monte Carlo (ABC-SMC) sampling algorithm for parameter estimation in the presence of uncertainties, coined combinatorial ABC-SMC. Inference of this type is used in situations where there does not exist a closed form of the associated likelihood function, which is replaced by a simulating model capable of producing artificial data. In the literature, conventional ABC-SMC is utilised to perform inference on continuous parameters. The novel scheme presented here has been developed to perform inference on parameters that are high-dimensional binary, rather than continuous. By altering the form of the proposal distribution from which to sample candidates in subsequent iterations (referred to as waves), high-dimensional binary variables may be targeted and inferred by the scheme. The efficacy of the proposed scheme is demonstrated through application to vibration data obtained in a structural dynamics experiment on a fibre-optic sensor simulated as a finite plate with uncertain boundary conditions at its edges. Results indicate that the method provides sound inference on the plate boundary conditions, which is validated through subsequent application of the method to multiple vibration datasets. Comparisons between appropriate forms of the metric function used in the scheme are also developed to highlight the effect of this element in the schemes convergence.

Robotic-Enhanced Prosthetic Liners for Vibration Therapy: Reducing Phantom Limb Pain in Transfemoral Amputees.

Phantom limb pain, a common challenge for amputees, lacks effective treatment options. Vibration therapy is a promising non-pharmacologic intervention for reducing pain intensity, but its efficacy in alleviating phantom limb pain requires further investigation. This study focused on developing prosthesis liners with integrated vibration motors to administer vibration therapy for phantom limb pain. The prototypes developed for this study addressed previous issues with wiring the electronic components. Two transfemoral amputees participated in a four-week at-home trial, during which they used the vibration liner and rated their initial and final pain intensity on a numeric rating scale each time they had phantom pain. Semi-structured interviews were conducted to gather feedback following the at-home trial. Both participants described relaxing and soothing sensations in their residual limb and phantom limb while using vibration therapy. One participant reported a relaxation of his phantom limb sensations, while both participants noted a decrease in the intensity of their phantom limb pain. Participants said the vibration liners were comfortable but suggested that the vibration could be stronger and that aligning the contacts could be easier. The results of this study highlight the potential effectiveness of using vibration therapy to reduce the intensity of phantom limb pain and suggest a vibration liner may be a feasible mode of administering the therapy. Future research should address optimizing the performance of the vibration liners to maximize their therapeutic benefits.

Effect of Local Vibration Therapy on Pain, Joint Position Sense, Kinesiophobia, and Disability in Cervical Disc Herniation: A Randomized Controlled Trial.

Background/Objectives: Vibration therapy approaches are an effective and safe treatment option for musculoskeletal disorders. This study examines the effects of vibration therapy using a percussion massage gun (PMG) on joint position sense, range of motion, pain, functionality, and kinesiophobia in individuals with cervical disc herniation (CDH). Methods: This single-blind randomized controlled trial involved 44 CDH patients divided into a Vibration Group (VG) and a Conventional Group (CG). The CG underwent a standard physiotherapy treatment heat application, Transcutaneous Electrical Nerve Stimulation (TENS), and exercises for range of motion and strengthening. VG received conventional therapy augmented with vibration therapy (VT) via a PMG. Joint position sense (JPS) using the Laser Pointer Assisted Angle Repetition Test; pain intensity with the Visual Analog Scale, kinesiophobia with the Tampa Scale for Kinesiophobia, and cervical dysfunction with the Neck Disability Index were assessed. Results: Both groups showed statistically significant improvements in pain, kinesiophobia, disability, and proprioception after treatment (p < 0.05). When comparing the difference values between groups, the VG was found to be more effective than the CG in the parameters of VAS activity (p = 0.013). The CG had more improvement in JPS neck left rotation than the VG (p = 0.000). Conclusions: VT, when combined with conventional physiotherapy, is effective in improving pain, proprioception, and functionality in individuals with CDH. These findings support the inclusion of VT as a beneficial adjunct therapy. Further research with larger sample sizes and longer follow-ups is recommended to validate these results and explore the long-term effects of VT on CDH.

An Analysis of the Displacements in 3D-Printed PLA Acoustic Guitars.

This study focuses on the analysis of the displacements generated in 3D-printed acoustic guitar tops. Specifically, the influence of 3D printing direction parameters on the vibrational behavior of a guitar top designed for polylactic acid (PLA) by analyzing five points of the top surface at a reduced scale. For this purpose, finite element tests and laboratory experiments have been carried out to support the study. After analyzing the results, it can be affirmed that the vibrational response in reduced-scale top plates can be modified and controlled by varying the printing direction angle in additive manufacturing, providing relevant information about the displacement in the vibrational response of PLA acoustic guitars. Furthermore, this work shows that the behavior of a specific acoustic guitar design can be characterized according to a specific need.

Frequency-Dependent Fatigue Properties of Additively Manufactured PLA.

Vibration-fatigue failure occurs when a structure is dynamically excited within its natural frequency range. Unlike metals, which have constant fatigue parameters, polymers can exhibit frequency-dependent fatigue parameters, significantly affecting the vibration resilience of 3D-printed polymer structures. This manuscript presents a study utilizing a novel vibration-fatigue testing methodology to characterize the frequency dependence of polymer material fatigue parameters under constant temperature conditions. In this investigation, 3D-printed PLA samples with frequency-tunable geometry were experimentally tested on an electro-dynamical shaker with a random vibration profile. Using the validated numerical models, the estimation of vibration-fatigue life was obtained and compared to the experimental results. Performing the numerical minimization of estimated and actual fatigue lives, the frequency-dependent fatigue parameters were assessed. In particular, the results indicate that the tested samples exhibit varying fatigue parameters within the loading frequency range of 250-750 Hz. Specifically, as the loading frequency increases, the fatigue exponent increases and fatigue strength decreases. These findings confirm the frequency dependence of fatigue parameters for 3D-printed polymer structures, underscoring the necessity of experimental characterization to reliably estimate the vibration-fatigue life of 3D-printed polymer structures. The utilization of the introduced approach therefore enhances the vibration resilience of the 3D-printed polymer mechanical component.

Reusability of Scrap Rubber, Tire Shredding, Recycled PVC and Fly Ash for Development of Composites with Vibration Damping Ability.

The study focuses on harnessing recycled materials to create sustainable and efficient composites, addressing both environmental issues related to waste management and industrial requirements for materials with improved vibration damping properties. The research involves the analysis of the physico-mechanical properties of the obtained composites and the evaluation of their performance in practical applications. Composite materials were tested in terms of their tensile strength and vibration damping capabilities, considering stress-strain diagrams, vibration amplitudes, frequency response functions (FRFs) and vibration modes. The research results have shown that by adding PVC and FA to the rubber-based matrix composition, the stiffness decreases and elasticity increases. The use of FA in the structure of composite materials causes an increase in the vibration damping possibilities due to the fact that it contributes to the chemical properties of the analyzed composite materials. Additionally, the use of PVC results in increased material elasticity, as evidenced by the higher damping factor compared to materials containing only rubber. Simultaneously, the addition of FA and PVC in specific proportions (60 phr) can lead to a decrease in stiffness and a greater increase in the damping factor. The incorporation of PVC and fly ash (FA) particles into rubber-based matrix composites reduces their stiffness and increases their elasticity. These effects are due to the fact that FA particles behave as extensions of chemical bonds during traction, which contributes to the increase in yield elongation. In addition, the use of flexible PVC increases the elasticity of the material, which is evidenced by the increase in the damping factor.

Effect of anteroposterior vibration frequency on the risk of lumbar injury in seated individuals.

Few studies investigate the impact of anterior-posterior excitation frequency on the time-domain vibrational response and injury risk of the lumbar spine in seated individuals. Firstly, this study utilised a previously developed finite element model of an upright seated human body on a rigid chair without a backrest to investigate the modes that affect the anterior-posterior vibrations of the seated body. Subsequently, transient dynamic analysis was employed to calculate the lumbar spine's time-domain responses (displacement, stress, and pressure) and risk factors under anteroposterior sinusoidal excitation at varying frequencies (1-8 Hz). Modal analysis suggested the frequencies significantly affecting the lumbar spine's vibration were notably at 4.7 Hz and 5.5 Hz. The transient analysis results and risk factor assessment indicated that the lumbar responses were most pronounced at 5 Hz. In addition, risk factor assessment showed that long-term exposure to 8 Hz vibration was associated with a greater risk of lumbar injury.

Although the anterior-posterior resonance frequency of the sitting body is around 1 Hz, the anterior-posterior vibrations approaching 5 Hz and at 8 Hz inflict more significant harm upon the lumbar spine than other frequencies, thereby elevating the risk of lumbar injury and back disorders.

Acute effects of local vibration inducing tonic vibration reflex or illusion of movement on maximal wrist force production.

Local vibration (LV) mainly stimulates primary afferents (Ia) and can induce a tonic vibration reflex (TVR) and an illusion of movement. This study aimed to evaluate the effect of these two phenomena on maximal voluntary isometric contraction (MVIC) capacity. LV (80 Hz) was applied to the wrist flexor muscles in two randomized experiments for 6 minutes. LV conditions were adjusted to promote either TVR (visual focus on the vibrated wrist) or ILLUSION (hand hidden, visual focus on electromyographic activity of the flexor carpi radialis muscle (FCR)). Mechanical and electromyographic (EMG) responses of the FCR and extensor carpi radialis muscles were recorded during MVIC in flexion and extension and during electrically evoked contractions at supramaximal intensity. Measurements were performed before (10 minutes and just before) and after (0 and 30 minutes) LV protocol. An increase in FCR EMG was observed during LV in the TVR condition (+340%) compared to the illusion condition (P=0.003). In contrast, the movement illusion was greater in the ILLUSION condition (assessed through subjective scales) (P=0.004). MVIC was reduced in flexion only after the TVR condition (≈ -7%, all P<0.034). Moreover, the decrease in force was correlated with the amount of TVR recorded on the FCR muscle (r=-0.64, P=0.005). Although potentiated doublets of each muscle did not evolve differently between conditions, a decrease was observed between the first and the last measure. In conclusion, when conducting research to assess maximal strength, it is necessary to have better control and reporting of the phenomena induced during LV.