A novel rat-tail model for studying human finger vibration health effects

It has been hypothesized that the biodynamic responses of the human finger tissues to vibration are among the major stimuli that cause vibration health effects. Furthermore, the finger contact pressure can alter these effects. It is difficult to test these hypotheses using human subjects or existing animal models. The objective of this study was to develop a new rat-tail vibration model to investigate the combined effects of vibration and contact pressure and to identify their relationships with the biodynamic responses. Physically, the new exposure system was developed by adding a loading device to an existing rat-tail model. An analytical model of the rat-tail exposure system was proposed and used to formulate the methods for quantifying the biodynamic responses. A series of tests with six tails dissected from rat cadavers were conducted to test and evaluate the new model. The experimental and modeling results demonstrate that the new model behaves as predicted. Unlike the previous model, the vibration strain and stress of the rat tail does not depend primarily on the vibration response of the tail itself but on that of the loading device. This makes it possible to quantify and control the biodynamic responses conveniently and reliably by measuring the loading device response. This study also identified the basic characteristics of the tail biodynamic responses in the exposure system, which can be used to help design the experiments for studying vibration biological effects.

Effects of whole-body vibration on reproductive physiology in a rat model of whole-body vibration

Findings from epidemiological studies suggest that occupational exposure to whole-body vibration (WBV) may increase the risk of miscarriage and contribute to a reduction in fertility rates in both men and women. However, workers exposed to WBV may also be exposed to other risk factors that contribute to reproductive dysfunction. The goal of this experiment was to examine the effects of WBV on reproductive physiology in a rat model. Male and female rats were exposed to WBV at the resonant frequency of the torso (31.5 Hz, 0.3 g amplitude) for 4 hr/day for 10 days. WBV exposure resulted in a significant reduction in number of developing follicles, and decrease in circulating estradiol concentrations, ovarian luteinizing hormone receptor protein levels, and marked changes in transcript levels for several factors involved in follicular development, cell cycle, and steroidogenesis. In males, WBV resulted in a significant reduction in spermatids and circulating prolactin levels, elevation in number of males having higher circulating testosterone concentrations, and marked alterations in levels of transcripts associated with oxidative stress, inflammation, and factors involved in regulating the cell cycle. Based upon these findings data indicate that occupational exposure to WBV contributes to adverse alterations in reproductive physiology in both genders that may lead to reduction in fertility.

An investigation of the effectiveness of vibration-reducing gloves for controlling vibration exposures during grinding handheld workpieces

Prolonged and intensive vibration exposures during the grinding of handheld workpieces may cause hand-arm vibration syndrome. The objectives of this study are to develop an on-the-hand method for evaluating vibration-reducing (VR) gloves, and to determine whether VR gloves can significantly reduce the vibration exposures. A worker holding and pressing a typical workpiece (golf club head) against a grinding wheel or belt in order to shape the workpiece was simulated, and the input vibration and those on the workpiece and hand-arm system were measured. Ten human subjects participated in the experiment. The results demonstrate that VR gloves significantly reduced the vibrations at the palm, hand dorsum, and wrist. The grinding interface condition and hand feed force did not substantially affect glove effectiveness. The use of gloves slightly increased the workpiece resonant response, but the resonant response did not significantly affect glove effectiveness. This study concluded that the use of VR gloves can help control vibration exposures of workers performing grinding of handheld workpieces.

A Review of Hand-Arm Vibration Studies Conducted by US NIOSH since 2000

Studies on hand-transmitted vibration exposure, biodynamic responses, and biological effects were conducted by researchers at the Health Effects Laboratory Division (HELD) of the National Institute for Occupational Safety and Health (NIOSH) during the last 20 years. These studies are systematically reviewed in this report, along with the identification of areas where additional research is needed. The majority of the studies cover the following aspects: (i) the methods and techniques for measuring hand-transmitted vibration exposure; (ii) vibration biodynamics of the hand-arm system and the quantification of vibration exposure; (iii) biological effects of hand-transmitted vibration exposure; (iv) measurements of vibration-induced health effects; (iv) quantification of influencing biomechanical effects; and (v) intervention methods and technologies for controlling hand-transmitted vibration exposure. The major findings of the studies are summarized and discussed.

An alternative method for analyzing the slip potential of workers on sloped surfaces

Slips and falls on sloped roof surfaces remain an important safety issue among construction workers. The slip potential has been conventionally analyzed and assessed primarily based on ground reaction forces, which cannot differentiate the specific roles of each of the force factors (e.g., workers' motions-induced dynamic forces and slope-induced static forces) contributing to the slip potential. Their differentiation may enhance the understanding of the slip mechanisms on the sloped roof surfaces and help develop effective walking and working strategies/tactics to minimize the dangerous slips on the elevated roofs. Hence, the objective of this study is to develop a biodynamic method as an additional tool for analyzing the slip potential of a worker walking or working on sloped roof surfaces. A whole-body biodynamic model is proposed and used to develop the alternative method, in which the slip potential is expressed as an analytical function of its major controlling factors including coefficient of friction, slope angle, and biodynamic forces. Some experimental data available in the literature are used to demonstrate the application of the proposed method. The results suggest that the slope may not change the basic trends of the biodynamic forces, but the slope may affect their magnitudes, which can be explained using the system's energy equation also derived from the whole-body biodynamic model. The analytical results suggest that reducing the body acceleration in uphill direction or the deceleration in downhill direction can reduce the slip potential. 'Zigging' and 'zagging' walking on a sloped surface may also reduce the slip potential, as it reduces the effective slope angle. The proposed biodynamic theory can be used to enhance the safety guidelines not only for roofers but also for people walking on ramps, inclined walkways, and mountain terrains.

Identification of effective engineering methods for controlling handheld workpiece vibration in grinding processes

The objective of this study is to identify effective engineering methods for controlling handheld workpiece vibration during grinding processes. Prolonged and intensive exposures to such vibration can cause hand-arm vibration syndrome among workers performing workpiece grinding, but how to effectively control these exposures remains an important issue. This study developed a methodology for performing their analyses and evaluations based on a model of the entire grinding machine-workpiece-hand-arm system. The model can simulate the vibration responses of a workpiece held in the worker's hands and pressed against a grinding wheel in order to shape the workpiece in the major frequency range of concern (6.3-1600 Hz). The methodology was evaluated using available experimental data. The results suggest that the methodology is acceptable for these analyses and evaluations. The results also suggest that the workpiece vibration resulting from the machine vibration generally depends on two mechanisms or pathways: (1) the direct vibration transmission from the grinding machine; and (2) the indirect transmission that depends on both the machine vibration transmission to the workpiece and the interface excitation transformation to the workpiece vibration. The methodology was applied to explore and/or analyze various engineering methods for controlling workpiece vibrations. The modeling results suggest that while these intervention methods have different advantages and limitations, some of their combinations can effectively reduce the vibration exposures of grinding workers. These findings can be used as guidance for selecting and developing more effective technologies to control handheld workpiece vibration exposures.

Development of a finger adapter method for testing and evaluating vibration-reducing gloves and materials

The objective of this study was to develop a convenient and reliable adapter method for testing and evaluating vibration-reducing (VR) gloves and VR materials at the fingers. The general requirements and technical specifications for the design of the new adapter were based on our previous studies of hand-held adapters for vibration measurement and a conceptual model of the fingers-adapter-glove-handle system developed in this study. Two thicknesses (2 mm and 3 mm) of the adapter beam were fabricated using a 3-D printer. Each adapter is a thin beam equipped with a miniature tri-axial accelerometer (1.1 g) mounted at its center, with a total weight ≤ 2.2 g. To measure glove vibration transmissibility, the adapter is held with two gloved fingers; a finger is positioned on each side of the accelerometer. Each end of the adapter beam is slotted between the glove material and the finger. A series of experiments was conducted to evaluate this two-fingers-held adapter method by measuring the transmissibility of typical VR gloves and a sample VR material. The experimental results indicate that the major resonant frequency of the lightweight adapter on the VR material (≥800 Hz) is much higher than the resonant frequencies of the gloved fingers grasping a cylindrical handle (≤300 Hz). The experimental results were repeatable across the test treatments. The basic characteristics of the measured glove vibration transmissibility are consistent with the theoretical predictions based on the biodynamics of the gloved fingers-hand-arm system. The results suggest that VR glove fingers can effectively reduce only high-frequency vibration, and VR effectiveness can be increased by reducing the finger contact force. This study also demonstrated that the finger adapter method can be combined with the palm adapter method prescribed in the standardized glove test, which can double the test efficiency without substantially increasing the expense of the test.

Work-related upper extremity musculoskeletal disorders in the United States: 2006, 2009, and 2014 National Health Interview Survey

BACKGROUND

The annual incidence rate of work-related upper extremity musculoskeletal disorders (WUEMSDs) is increasing in US workers according to the United States Bureau of Labor Statistics (BLS). However, the prevalence of WUEMSDs among US total workers has not been estimated.

OBJECTIVE

We aimed to estimate the prevalence of WUEMSDs among US total workers and among each of major occupations and industries.

METHODS

We analyzed data from the National Health Interview Survey Arthritis supplements (2006, 2009, and 2014) among 50,218 current workers (age ≥18 years) to estimate the 30-day prevalence of WUEMSDs and of WUEMSDs affecting work using the SAS-callable SUDAAN software.

RESULTS

About 11.2 million workers reported WUEMSDs based on three surveys (2006, 2009, and 2014). The 30-day prevalence of WUEMSDs was 8.23% the prevalence of WUEMSDs affecting work was 1.24%. The Construction occupation and industry had the highest age- and sex-adjusted 30-day prevalence of WUEMSDs (10.98% for Construction occupation; 9.94% for Construction industry) and WUEMSDs affecting work (3.32% for Construction occupation; 2.31% Construction industry).

CONCLUSIONS

Our results show that construction workers had the highest prevalence of both WUEMSDs and WUEMSDs affecting work. They may be a priority group for interventions to reduce upper extremity musculoskeletal disorders.

The relationships between hand coupling force and vibration biodynamic responses of the hand-arm system

This study conducted two series of experiments to investigate the relationships between hand coupling force and biodynamic responses of the hand-arm system. In the first experiment, the vibration transmissibility on the system was measured as a continuous function of grip force while the hand was subjected to discrete sinusoidal excitations. In the second experiment, the biodynamic responses of the system subjected to a broadband random vibration were measured under five levels of grip forces and a combination of grip and push forces. This study found that the transmissibility at each given frequency increased with the increase in the grip force before reaching a maximum level. The transmissibility then tended to plateau or decrease when the grip force was further increased. This threshold force increased with an increase in the vibration frequency. These relationships remained the same for both types of vibrations. The implications of the experimental results are discussed. Practitioner Summary: Shocks and vibrations transmitted to the hand-arm system may cause injuries and disorders of the system. How to take hand coupling force into account in the risk assessment of vibration exposure remains an important issue for further studies. This study is designed and conducted to help resolve this issue.

Vibrations transmitted from human hands to upper arm, shoulder, back, neck, and head

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7-12 Hz, the shoulder resonance was 7-9 Hz, and the back and neck resonances were 6-7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed.

RELEVANCE TO INDUSTRY

Musculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.

Vibration characteristics of golf club heads in their handheld grinding process and potential approaches for reducing the vibration exposure

To control vibration-induced white finger among workers performing the fine grinding of golf club heads, the aims of this study are to clarify the major vibration sources in the grinding process, to identify and understand the basic characteristics of the club head vibration, and to propose potential approaches for reducing the vibration exposure. The vibrations on two typical club heads and two belt grinding machines were measured at a workplace. A simulated test station was also constructed and used to help examine some influencing factors of the club head vibration. This study found that the club head vibration was the combination of the vibration transmitted from the grinding machines and that generated in the grinding process. As a result, any factor that affects the machine vibration, the grinding vibration, and/or the dynamic response of the club head can influence the vibration exposure of the fingers or hands holding the club head in the grinding process. The significant influencing factors identified in the study include testing subject, grinding machine, machine operation speed, drive wheel condition, club head model, mechanical constraints imposed on the club head during the grinding, and machine foot pad. These findings suggest that the vibration exposure can be controlled by reducing the grinding machine vibration, changing the workpiece dynamic properties, and mitigating the vibration transmission in its pathway. Many potential methods for the control are proposed and discussed.

RELEVANCE TO INDUSTRY

Vibrations on handheld workpieces can be effectively transmitted to the hands, especially the fingers. As a result, a major component of the hand-arm vibration syndrome - vibration-induced white finger - has been observed among some workers performing the grinding and/or polishing tasks of the handheld workpieces such as golf club heads. The results of this study can be used to develop more effective methods and technologies to control the vibration exposure of these workers. This may help effectively control this occupational disease.

Modeling of the interaction between grip force and vibration transmissibility of a finger

It is known that the vibration characteristics of the fingers and hand and the level of grip action interacts when operating a power tool. In the current study, we developed a hybrid finger model to simulate the vibrations of the hand-finger system when gripping a vibrating handle covered with soft materials. The hybrid finger model combines the characteristics of conventional finite element (FE) models, multi-body musculoskeletal models, and lumped mass models. The distal, middle, and proximal finger segments were constructed using FE models, the finger segments were connected via three flexible joint linkages (i.e., distal interphalangeal joint (DIP), proximal interphalangeal joint (PIP), and metacarpophalangeal (MCP) joint), and the MCP joint was connected to the ground and handle via lumped parameter elements. The effects of the active muscle forces were accounted for via the joint moments. The bone, nail, and hard connective tissues were assumed to be linearly elastic whereas the soft tissues, which include the skin and subcutaneous tissues, were considered as hyperelastic and viscoelastic. The general trends of the model predictions agree well with the previous experimental measurements in that the resonant frequency increased from proximal to the middle and to the distal finger segments for the same grip force, that the resonant frequency tends to increase with increasing grip force for the same finger segment, especially for the distal segment, and that the magnitude of vibration transmissibility tends to increase with increasing grip force, especially for the proximal segment. The advantage of the proposed model over the traditional vibration models is that it can predict the local vibration behavior of the finger to a tissue level, while taking into account the effects of the active musculoskeletal force, the effects of the contact conditions on vibrations, the global vibration characteristics.

Tool-specific performance of vibration-reducing gloves for attenuating fingers-transmitted vibration

BACKGROUND

Fingers-transmitted vibration can cause vibration-induced white finger. The effectiveness of vibration-reducing (VR) gloves for reducing hand transmitted vibration to the fingers has not been sufficiently examined.

OBJECTIVE

The objective of this study is to examine tool-specific performance of VR gloves for reducing finger-transmitted vibrations in three orthogonal directions (3D) from powered hand tools.

METHODS

A transfer function method was used to estimate the tool-specific effectiveness of four typical VR gloves. The transfer functions of the VR glove fingers in three directions were either measured in this study or during a previous study using a 3D laser vibrometer. More than seventy vibration spectra of various tools or machines were used in the estimations.

RESULTS

When assessed based on frequency-weighted acceleration, the gloves provided little vibration reduction. In some cases, the gloves amplified the vibration by more than 10%, especially the neoprene glove. However, the neoprene glove did the best when the assessment was based on unweighted acceleration. The neoprene glove was able to reduce the vibration by 10% or more of the unweighted vibration for 27 out of the 79 tools. If the dominant vibration of a tool handle or workpiece was in the shear direction relative to the fingers, as observed in the operation of needle scalers, hammer chisels, and bucking bars, the gloves did not reduce the vibration but increased it.

CONCLUSIONS

This study confirmed that the effectiveness for reducing vibration varied with the gloves and the vibration reduction of each glove depended on tool, vibration direction to the fingers, and finger location. VR gloves, including certified anti-vibration gloves do not provide much vibration reduction when judged based on frequency-weighted acceleration. However, some of the VR gloves can provide more than 10% reduction of the unweighted vibration for some tools or workpieces. Tools and gloves can be matched for better effectiveness for protecting the fingers.

Review and Evaluation of Hand-Arm Coordinate Systems for Measuring Vibration Exposure, Biodynamic Responses, and Hand Forces

The hand coordinate systems for measuring vibration exposures and biodynamic responses have been standardized, but they are not actually used in many studies. This contradicts the purpose of the standardization. The objectives of this study were to identify the major sources of this problem, and to help define or identify better coordinate systems for the standardization. This study systematically reviewed the principles and definition methods, and evaluated typical hand coordinate systems. This study confirms that, as accelerometers remain the major technology for vibration measurement, it is reasonable to standardize two types of coordinate systems: a tool-based basicentric (BC) system and an anatomically based biodynamic (BD) system. However, these coordinate systems are not well defined in the current standard. Definition of the standard BC system is confusing, and it can be interpreted differently; as a result, it has been inconsistently applied in various standards and studies. The standard hand BD system is defined using the orientation of the third metacarpal bone. It is neither convenient nor defined based on important biological or biodynamic features. This explains why it is rarely used in practice. To resolve these inconsistencies and deficiencies, we proposed a revised method for defining the realistic handle BC system and an alternative method for defining the hand BD system. A fingertip-based BD system for measuring the principal grip force is also proposed based on an important feature of the grip force confirmed in this study.

The Effect of a Mechanical Arm System on Portable Grinder Vibration Emissions

Mechanical arm systems are commonly used to support powered hand tools to alleviate ergonomic stressors related to the development of workplace musculoskeletal disorders. However, the use of these systems can increase exposure times to other potentially harmful agents such as hand-transmitted vibration. To examine how these tool support systems affect tool vibration, the primary objectives of this study were to characterize the vibration emissions of typical portable pneumatic grinders used for surface grinding with and without a mechanical arm support system at a workplace and to estimate the potential risk of the increased vibration exposure time afforded by the use of these mechanical arm systems. This study also developed a laboratory-based simulated grinding task based on the ISO 28927-1 (2009) standard for assessing grinder vibrations; the simulated grinding vibrations were compared with those measured during actual workplace grinder operations. The results of this study demonstrate that use of the mechanical arm may provide a health benefit by reducing the forces required to lift and maneuver the tools and by decreasing hand-transmitted vibration exposure. However, the arm does not substantially change the basic characteristics of grinder vibration spectra. The mechanical arm reduced the average frequency-weighted acceleration by about 24% in the workplace and by about 7% in the laboratory. Because use of the mechanical arm system can increase daily time-on-task by 50% or more, the use of such systems may actually increase daily time-weighted hand-transmitted vibration exposures in some cases. The laboratory acceleration measurements were substantially lower than the workplace measurements, and the laboratory tool rankings based on acceleration were considerably different than those from the workplace. Thus, it is doubtful that ISO 28927-1 is useful for estimating workplace grinder vibration exposures or for predicting workplace grinder acceleration rank orders.

Theoretical foundation, methods, and criteria for calibrating human vibration models using frequency response functions

While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data.

An examination of an adapter method for measuring the vibration transmitted to the human arms

The objective of this study is to evaluate an adapter method for measuring the vibration on the human arms. Four instrumented adapters with different weights were used to measure the vibration transmitted to the wrist, forearm, and upper arm of each subject. Each adapter was attached at each location on the subjects using an elastic cloth wrap. Two laser vibrometers were also used to measure the transmitted vibration at each location to evaluate the validity of the adapter method. The apparent mass at the palm of the hand along the forearm direction was also measured to enhance the evaluation. This study found that the adapter and laser-measured transmissibility spectra were comparable with some systematic differences. While increasing the adapter mass reduced the resonant frequency at the measurement location, increasing the tightness of the adapter attachment increased the resonant frequency. However, the use of lightweight (≤15 g) adapters under medium attachment tightness did not change the basic trends of the transmissibility spectrum. The resonant features observed in the transmissibility spectra were also correlated with those observed in the apparent mass spectra. Because the local coordinate systems of the adapters may be significantly misaligned relative to the global coordinates of the vibration test systems, large errors were observed for the adapter-measured transmissibility in some individual orthogonal directions. This study, however, also demonstrated that the misalignment issue can be resolved by either using the total vibration transmissibility or by measuring the misalignment angles to correct the errors. Therefore, the adapter method is acceptable for understanding the basic characteristics of the vibration transmission in the human arms, and the adapter-measured data are acceptable for approximately modeling the system.

An examination of the vibration transmissibility of the hand-arm system in three orthogonal directions

The objective of this study is to enhance the understanding of the vibration transmission in the hand-arm system in three orthogonal directions (X, Y, and Z). For the first time, the transmitted vibrations distributed on the entire hand-arm system exposed in the three orthogonal directions via a 3-D vibration test system were measured using a 3-D laser vibrometer. Seven adult male subjects participated in the experiment. This study confirms that the vibration transmissibility generally decreased with the increase in distance from the hand and it varied with the vibration direction. Specifically, to the upper arm and shoulder, only moderate vibration transmission was measured in the test frequency range (16 to 500 Hz), and virtually no transmission was measured in the frequency range higher than 50 Hz. The resonance vibration on the forearm was primarily in the range of 16-30 Hz with the peak amplitude of approximately 1.5 times of the input vibration amplitude. The major resonance on the dorsal surfaces of the hand and wrist occurred at around 30-40 Hz and, in the Y direction, with peak amplitude of more than 2.5 times of the input amplitude. At higher than 50 Hz, vibration transmission was effectively limited to the hand and fingers. A major finger resonance was observed at around 100 Hz in the X and Y directions and around 200 Hz in the Z direction. In the fingers, the resonance magnitude in the Z direction was generally the lowest, and the resonance magnitude in the Y direction was generally the highest with the resonance amplitude of 3 times the input vibration, which was similar to the transmissibility at the wrist and hand dorsum. The implications of the results are discussed.

RELEVANCE TO INDUSTRY

Prolonged, intensive exposure to hand-transmitted vibration could result in hand-arm vibration syndrome. While the syndrome's precise mechanisms remain unclear, the characterization of the vibration transmissibility of the system in the three orthogonal dimensions performed in this study can help understand the syndrome and help develop improved frequency weightings for assessing the risk of the exposure for developing various components of the syndrome.

Antivibration gloves: effects on vascular and sensorineural function, an animal model

Anti-vibration gloves have been used to block the transmission of vibration from powered hand tools to the user, and to protect users from the negative health consequences associated with exposure to vibration. However, there are conflicting reports as to the efficacy of gloves in protecting workers. The goal of this study was to use a characterized animal model of vibration-induced peripheral vascular and nerve injury to determine whether antivibration materials reduced or inhibited the effects of vibration on these physiological symptoms. Rats were exposed to 4 h of tail vibration at 125 Hz with an acceleration 49 m/s(2). The platform was either bare or covered with antivibrating glove material. Rats were tested for tactile sensitivity to applied pressure before and after vibration exposure. One day following the exposure, ventral tail arteries were assessed for sensitivity to vasodilating and vasoconstricting factors and nerves were examined histologically for early indicators of edema and inflammation. Ventral tail artery responses to an α2C-adrenoreceptor agonist were enhanced in arteries from vibration-exposed rats compared to controls, regardless of whether antivibration materials were used or not. Rats exposed to vibration were also less sensitive to pressure after exposure. These findings are consistent with experimental findings in humans suggesting that antivibration gloves may not provide protection against the adverse health consequences of vibration exposure in all conditions. Additional studies need to be done examining newer antivibration materials.

Laboratory and workplace assessments of rivet bucking bar vibration emissions

Sheet metal workers operating rivet bucking bars are at risk of developing hand and wrist musculoskeletal disorders associated with exposures to hand-transmitted vibrations and forceful exertions required to operate these hand tools. New bucking bar technologies have been introduced in efforts to reduce workplace vibration exposures to these workers. However, the efficacy of these new bucking bar designs has not been well documented. While there are standardized laboratory-based methodologies for assessing the vibration emissions of many types of powered hand tools, no such standard exists for rivet bucking bars. Therefore, this study included the development of a laboratory-based method for assessing bucking bar vibrations which utilizes a simulated riveting task. With this method, this study evaluated three traditional steel bucking bars, three similarly shaped tungsten alloy bars, and three bars featuring spring-dampeners. For comparison the bucking bar vibrations were also assessed during three typical riveting tasks at a large aircraft maintenance facility. The bucking bars were rank-ordered in terms of unweighted and frequency-weighted acceleration measured at the hand-tool interface. The results suggest that the developed laboratory method is a reasonable technique for ranking bucking bar vibration emissions; the lab-based riveting simulations produced similar rankings to the workplace rankings. However, the laboratory-based acceleration averages were considerably lower than the workplace measurements. These observations suggest that the laboratory test results are acceptable for comparing and screening bucking bars, but the laboratory measurements should not be directly used for assessing the risk of workplace bucking bar vibration exposures. The newer bucking bar technologies exhibited significantly reduced vibrations compared to the traditional steel bars. The results of this study, together with other information such as rivet quality, productivity, tool weight, comfort, worker acceptance, and initial cost can be used to make informed bucking bar selections.

Anti-vibration gloves?

For exposure to hand-transmitted vibration (HTV), personal protective equipment is sold in the form of anti-vibration (AV) gloves, but it remains unclear how much these gloves actually reduce vibration exposure or prevent the development of hand-arm vibration syndrome in the workplace. This commentary describes some of the issues that surround the classification of AV gloves, the assessment of their effectiveness and their applicability in the workplace. The available information shows that AV gloves are unreliable as devices for controlling HTV exposures. Other means of vibration control, such as using alternative production techniques, low-vibration machinery, routine preventative maintenance regimes, and controlling exposure durations are far more likely to deliver effective vibration reductions and should be implemented. Furthermore, AV gloves may introduce some adverse effects such as increasing grip force and reducing manual dexterity. Therefore, one should balance the benefits of AV gloves and their potential adverse effects if their use is considered.

Tool-specific performance of vibration-reducing gloves for attenuating palm-transmitted vibrations in three orthogonal directions

Vibration-reducing (VR) gloves have been increasingly used to help reduce vibration exposure, but it remains unclear how effective these gloves are. The purpose of this study was to estimate tool-specific performances of VR gloves for reducing the vibrations transmitted to the palm of the hand in three orthogonal directions (3-D) in an attempt to assess glove effectiveness and aid in the appropriate selection of these gloves. Four typical VR gloves were considered in this study, two of which can be classified as anti-vibration (AV) gloves according to the current AV glove test standard. The average transmissibility spectrum of each glove in each direction was synthesized based on spectra measured in this study and other spectra collected from reported studies. More than seventy vibration spectra of various tools or machines were considered in the estimations, which were also measured in this study or collected from reported studies. The glove performance assessments were based on the percent reduction of frequency-weighted acceleration as is required in the current standard for assessing the risk of vibration exposures. The estimated tool-specific vibration reductions of the gloves indicate that the VR gloves could slightly reduce (<5%) or marginally amplify (<10%) the vibrations generated from low-frequency (<25 Hz) tools or those vibrating primarily along the axis of the tool handle. With other tools, the VR gloves could reduce palm-transmitted vibrations in the range of 5%-58%, primarily depending on the specific tool and its vibration spectra in the three directions. The two AV gloves were not more effective than the other gloves with some of the tools considered in this study. The implications of the results are discussed.

RELEVANCE TO INDUSTRY

Hand-transmitted vibration exposure may cause hand-arm vibration syndrome. Vibration-reducing gloves are considered as an alternative approach to reduce the vibration exposure. This study provides useful information on the effectiveness of the gloves when used with many tools for reducing the vibration transmitted to the palm in three directions. The results can aid in the appropriate selection and use of these gloves.

Analysis of the effects of surface stiffness on the contact interaction between a finger and a cylindrical handle using a three-dimensional hybrid model

Contact interactions between the hand and handle, such as the contact surface softness and contact surface curvature, will affect both physical effort and musculoskeletal fatigue, thereby the comfort and safety of power tool operations. Previous models of hand gripping can be categorized into two groups: multi-body dynamic models and finite element (FE) models. The goal of the current study is to develop a hybrid FE hand gripping model, which combines the features of conventional FE models and multi-body dynamic models. The proposed model is applied to simulate hand-gripping on a cylindrical handle with covering materials of different softness levels. The model included three finger segments (distal, middle, and proximal phalanxes), three finger joints (the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joint), and major anatomical substructures. The model was driven by joint moments, which are the net effects of all passive and active muscular forces acting about the joints. The finger model was first calibrated by using experimental data of human subject tests, and then applied to investigate the effects of surface softness on contact interactions between a finger and a cylindrical handle. Our results show that the maximal compressive stress and strain in the soft tissues of the fingers can be effectively reduced by reducing the stiffness of the covering material.

The effects of vibration-reducing gloves on finger vibration

Vibration-reducing (VR) gloves have been used to reduce the hand-transmitted vibration exposures from machines and powered hand tools but their effectiveness remains unclear, especially for finger protection. The objectives of this study are to determine whether VR gloves can attenuate the vibration transmitted to the fingers and to enhance the understanding of the mechanisms of how these gloves work. Seven adult male subjects participated in the experiment. The fixed factors evaluated include hand force (four levels), glove condition (gel-filled, air bladder, no gloves), and location of the finger vibration measurement. A 3-D laser vibrometer was used to measure the vibrations on the fingers with and without wearing a glove on a 3-D hand-arm vibration test system. This study finds that the effect of VR gloves on the finger vibration depends on not only the gloves but also their influence on the distribution of the finger contact stiffness and the grip effort. As a result, the gloves increase the vibration in the fingertip area but marginally reduce the vibration in the proximal area at some frequencies below 100 Hz. On average, the gloves reduce the vibration of the entire fingers by less than 3% at frequencies below 80 Hz but increase at frequencies from 80 to 400 Hz. At higher frequencies, the gel-filled glove is more effective at reducing the finger vibration than the air bladder-filled glove. The implications of these findings are discussed.

RELEVANCE TO INDUSTRY

Prolonged, intensive exposure to hand-transmitted vibration can cause hand-arm vibration syndrome. Vibration-reducing gloves have been used as an alternative approach to reduce the vibration exposure. However, their effectiveness for reducing finger-transmitted vibrations remains unclear. This study enhanced the understanding of the glove effects on finger vibration and provided useful information on the effectiveness of typical VR gloves at reducing the vibration transmitted to the fingers. The new results and knowledge can be used to help select appropriate gloves for the operations of powered hand tools, to help perform risk assessment of the vibration exposure, and to help design better VR gloves.

An examination of the handheld adapter approach for measuring hand-transmitted vibration exposure

The use of a handheld adapter equipped with a tri-axial accelerometer is the most convenient and efficient approach for measuring vibration exposure at the hand-tool interface, especially when the adapter is incorporated into a miniature handheld or wrist-strapped dosimeter. To help optimize the adapter approach, the specific aims of this study are to identify and understand the major sources and mechanisms of measurement errors and uncertainties associated with using these adapters, and to explore their improvements. Five representative adapter models were selected and used in the experiment. Five human subjects served as operators in the experiment on a hand-arm vibration test system. The results of this study confirm that many of the handheld adapters can produce substantial overestimations of vibration exposure, and measurement errors can significantly vary with tool, adapter model, mounting position, mounting orientation, and subject. Major problems with this approach include unavoidable influence of the hand dynamic motion on the adapter, unstable attachment, insufficient attachment contact force, and inappropriate adapter structure. However, the results of this study also suggest that measurement errors can be substantially reduced if the design and use of an adapter can be systematically optimized toward minimizing the combined effects of the identified factors. Some potential methods for improving the design and use of the adapters are also proposed and discussed.

Theoretical relationship between vibration transmissibility and driving-point response functions of the human body

The relationship between the vibration transmissibility and driving-point response functions (DPRFs) of the human body is important for understanding vibration exposures of the system and for developing valid models. This study identified their theoretical relationship and demonstrated that the sum of the DPRFs can be expressed as a linear combination of the transmissibility functions of the individual mass elements distributed throughout the system. The relationship is verified using several human vibration models. This study also clarified the requirements for reliably quantifying transmissibility values used as references for calibrating the system models. As an example application, this study used the developed theory to perform a preliminary analysis of the method for calibrating models using both vibration transmissibility and DPRFs. The results of the analysis show that the combined method can theoretically result in a unique and valid solution of the model parameters, at least for linear systems. However, the validation of the method itself does not guarantee the validation of the calibrated model, because the validation of the calibration also depends on the model structure and the reliability and appropriate representation of the reference functions. The basic theory developed in this study is also applicable to the vibration analyses of other structures.

Modeling of the biodynamic responses distributed at the fingers and palm of the hand in three orthogonal directions

The objectives of this study were to develop models of the hand-arm system in the three orthogonal directions (x_h, y_h , and z_h ) and to enhance the understanding of the hand vibration dynamics. A four-degrees-of-freedom (DOF) model and 5-DOF model were used in the simulation for each direction. The driving-point mechanical impedances distributed at the fingers and palm of the hand reported in a previous study were used to determine the parameters of the models. The 5-DOF models were generally superior to the 4-DOF models for the simulation. Hence, as examples of applications, the 5-DOF models were used to predict the transmissibility of a vibration-reducing glove and the vibration transmissibility on the major substructures of the hand-arm system. The model-predicted results were also compared with the experimental data reported in two other recent studies. Some reasonable agreements were observed in the comparisons, which provided some validation of the developed models. This study concluded that the 5-DOF models are acceptable for helping to design and analyze vibrating tools and anti-vibration devices. This study also confirmed that the 5-DOF model in the z_h direction is acceptable for a coarse estimation of the biodynamic responses distributed throughout the major substructures of the hand-arm system. Some interesting phenomena observed in the experimental study of the biodynamic responses in the three directions were also explained in this study.

Vibration-reducing gloves: transmissibility at the palm of the hand in three orthogonal directions

Vibration-reducing (VR) gloves are commonly used as a means to help control exposures to hand-transmitted vibrations generated by powered hand tools. The objective of this study was to characterise the vibration transmissibility spectra and frequency-weighted vibration transmissibility of VR gloves at the palm of the hand in three orthogonal directions. Seven adult males participated in the evaluation of seven glove models using a three-dimensional hand-arm vibration test system. Three levels of hand coupling force were applied in the experiment. This study found that, in general, VR gloves are most effective at reducing vibrations transmitted to the palm along the forearm direction. Gloves that are found to be superior at reducing vibrations in the forearm direction may not be more effective in the other directions when compared with other VR gloves. This casts doubts on the validity of the standardised glove screening test. Practitioner Summary: This study used human subjects to measure three-dimensional vibration transmissibility of vibration-reducing gloves at the palm and identified their vibration attenuation characteristics. This study found the gloves to be most effective at reducing vibrations along the forearm direction. These gloves did not effectively attenuate vibration along the handle axial direction.

Laboratory and field measurements and evaluations of vibration at the handles of riveting hammers

The use of riveting hammers can expose workers to harmful levels of hand-transmitted vibration (HTV). As a part of efforts to reduce HTV exposures through tool selection, the primary objective of this study was to evaluate the applicability of a standardized laboratory-based riveting hammer assessment protocol for screening riveting hammers. The second objective was to characterize the vibration emissions of reduced vibration riveting hammers and to make approximations of the HTV exposures of workers operating these tools in actual work tasks. Eight pneumatic riveting hammers were selected for the study. They were first assessed in a laboratory using the standardized method for measuring vibration emissions at the tool handle. The tools were then further assessed under actual working conditions during three aircraft sheet metal riveting tasks. Although the average vibration magnitudes of the riveting hammers measured in the laboratory test were considerably different from those measured in the field study, the rank orders of the tools determined via these tests were fairly consistent, especially for the lower vibration tools. This study identified four tools that consistently exhibited lower frequency-weighted and unweighted accelerations in both the laboratory and workplace evaluations. These observations suggest that the standardized riveting hammer test is acceptable for identifying tools that could be expected to exhibit lower vibrations in workplace environments. However, the large differences between the accelerations measured in the laboratory and field suggest that the standardized laboratory-based tool assessment is not suitable for estimating workplace riveting hammer HTV exposures. Based on the frequency-weighted accelerations measured at the tool handles during the three work tasks, the sheet metal mechanics assigned to these tasks at the studied workplace are unlikely to exceed the daily vibration exposure action value (2.5 m s(-2)) using any of the evaluated riveting hammers.

Assessment of hand-transmitted vibration exposure from motorized forks used for beach-cleaning operations

Motorized vibrating manure forks were used in beach-cleaning operations following the massive Deepwater Horizon oil spill in the Gulf of Mexico during the summer of 2010.

OBJECTIVES

The objectives of this study were to characterize the vibration emissions of these motorized forks and to provide a first approximation of hand-transmitted vibration exposures to workers using these forks for beach cleaning.

METHODS

Eight operators were recruited to operate the motorized forks during this laboratory study. Four fork configurations were used in the study; two motor speeds and two fork basket options were evaluated. Accelerations were measured near each hand as the operators completed the simulated beach-cleaning task.

RESULTS

The dominant vibration frequency for these tools was identified to be around 20 Hz. Because acceleration was found to increase with motor speed, workers should consider operating these tools with just enough speed to get the job done. These forks exhibited considerable acceleration magnitudes when unloaded.

CONCLUSIONS

The study results suggest that the motor should not be operated with the fork in the unloaded state. Anti-vibration gloves are not effective at attenuating the vibration frequencies produced by these forks, and they may even amplify the transmitted vibration and increase hand/arm fatigue. While regular work gloves are suitable, vibration-reducing gloves may not be appropriate for use with these tools. These considerations may also be generally applicable for the use of motorized forks in other workplace environments.

Frequency-dependent effects of vibration on physiological systems: experiments with animals and other human surrogates

Occupational exposure to vibration through the use of power- and pneumatic hand-tools results in cold-induced vasospasms, finger blanching, and alterations in sensorineural function. Collectively, these symptoms are referred to as hand-arm vibration syndrome (HAVS). Currently the International Standards Organization (ISO) standard ISO 5349-1 contains a frequency-weighting curve to help workers and employers predict the risk of developing HAVS with exposure to vibration of different frequencies. However, recent epidemiological and experimental evidence suggests that this curve under-represents the risk of injuries to the hands and fingers induced by exposure to vibration at higher frequencies (>100 Hz). To improve the curve, better exposure-response data need to be collected. The goal of this review is to summarize the results of animal and computational modeling studies that have examined the frequency-dependent effects of vibration, and discuss where additional research would be beneficial to fill these research gaps.

An analysis of contact stiffness between a finger and an object when wearing an air-cushioned glove: the effects of the air pressure

Air-cushioned gloves have the advantages of lighter weight, lower cost, and unique mechanical performance, compared to gloves made of conventional engineering materials. The goal of this study is to analyze the contact interaction between fingers and object when wearing an air-cushioned glove. The contact interactions between the the fingertip and air bubbles, which is considered as a cell of a typical air-cushioned glove, has been analyzed theoretically. Two-dimensional finite element models were developed for the analysis. The fingertip model was assumed to be composed of skin layers, subcutaneous tissue, bone, and nail. The air bubbles were modeled as air sealed in the container of nonelastic membrane. We simulated two common scenarios: a fingertip in contact with one single air bubble and with two air cushion bubbles simultaneously. Our simulation results indicated that the internal air pressure can modulate the fingertip-object contact characteristics. The contact stiffness reaches a minimum when the initial air pressure is equal to 1.3 and 1.05 times of the atmosphere pressure for the single air bubble and the double air bubble contact, respectively. Furthermore, the simulation results indicate that the double air bubble contact will result in smaller volumetric tissue strain than the single air bubble contact for the same force.

A practical biomechanical model of the index finger simulating the kinematics of the muscle/tendon excursions

Biomechanical models of the hand and fingers are useful tools for hand surgeons to improve surgical procedures and for biomedical researchers to explore the mechanical loading in the musculoskeletal system that cannot be easily measured in vivo. The purpose of the present study was to develop a realistic index finger model for solving practical problems. The model includes the meshes of four bony sections (distal, middle, proximal and metacarpal bones) obtained via micro-CT scans. The tendon attachment sites are adopted from the normative finger model. A total of seven tendon/muscles are included in the model. The predicted tendon excursions and moment arms were compared with published experimental data. One of the advantages of the current approach over previous studies is that the current model has been developed on a platform of a commercial software package, such that researchers can apply it as a universal tool for practical problems.

An evaluation of the methods for deriving representative frequency response functions of the human whole-body system

The biodynamic response functions of the human whole-body system measured with subjects participating in an experiment are commonly arithmetically averaged and used to represent their mean response functions in many studies. The reported means were further averaged to form the reference means for standardization and various applications. The objectives of this study are to clarify whether this response-based averaging process could significantly misrepresent the characteristics of the original functions, and to explore appropriate methods for deriving representative functions. A set of reported mechanical-equivalent models for 12 subjects was used to derive the vertical and fore-and-aft cross-axis response functions expressed in apparent mass. The response-based average was directly compared with the response derived from a property-based derivation method. This study found that the response-based average could differ from the property-based mean response by more than 30%, especially in the fore-and-aft cross-axis response functions. This study also theoretically demonstrated that the discrepancies result from the non-linear relationship between the apparent mass and the properties of a dynamic system. Therefore, the discrepancies depend on the variability of the subjects' dynamic properties. Practically, the discrepancies in the vertical response could be reduced to an acceptable level (e.g., <10%) if a sufficient number of subjects with similar body weights are selected or grouped in the measurement. However, it is very difficult to reduce the discrepancies in the fore-and-aft cross-axis to such a level. While more demanding than the response-based method, the property-based method is theoretically more reliable for deriving the representative response functions for each axis.

Comparing three methods for evaluating impact wrench vibration emissions

To provide a means for comparing impact wrenches and similar tools, the international standard ISO 8662-7 prescribes a method for measuring the vibrations at the handles of tools during their operations against a cotton-phenolic braking device. To improve the standard, alternative loading mechanisms have been proposed; one device comprises aluminum blocks with friction brake linings, while another features plate-mounted bolts to provide the tool load. The objective of this study was to evaluate these three loading methods so that tool evaluators can select appropriate loading devices in order to obtain results that can be applied to their specific workplace operations. Six experienced tool operators used five tool models to evaluate the loading mechanisms. The results of this study indicate that different loads can yield different tool comparison results. However, any of the three devices appears to be adequate for initial tool screenings. On the other hand, vibration emissions measured in the laboratory are unlikely to be fully representative of those in the workplace. Therefore, for final tool selections and for reliably assessing workplace vibration exposures, vibration measurements should be collected under actual working conditions. Evaluators need to use appropriate numbers of tools and tool operators in their assessments; recommendations are provided.

Modeling of the muscle/tendon excursions and moment arms in the thumb using the commercial software anybody

A biomechanical model of a thumb would be useful for exploring the mechanical loadings in the musculoskeletal system, which cannot be measured in vivo. The purpose of the current study is to develop a practical kinematic thumb model using the commercial software Anybody (Anybody Technology, Aalborg, Denmark), which includes real CT-scans of the bony sections and realistic tendon/muscle attachments on the bones. The thumb model consists of a trapezium, a metacarpal bone, a proximal and a distal phalanx. These four bony sections are linked via three joints, i.e., IP (interphalangeal), MP (metacarpophalangeal) and CMC (carpometacarpal) joints. Nine muscles were included in the proposed model. The theoretically calculated moment arms of the tendons are compared with the corresponding experimental data by Smutz et al. [1998. Mechanical advantage of the thumb muscles. J. Biomech. 31(6), 565-570]. The predicted muscle moment arms of the majority of the muscle/tendon units agree well with the experimental data in the entire range of motion. Close to the end of the motion range, the predicted moment arms of several muscles (i.e., ADPt and ADPo (transverse and oblique heads of the adductor pollicis, respectively) muscles for CMC abduction/adduction and ADPt and FPB (flexor pollicis brevis) muscle for MP extension/flexion) deviate from the experimental data. The predicted moment potentials for all muscles are consistent with the experimental data. The findings thus suggest that, in a biomechanical model of the thumb, the mechanical functions of muscle-tendon units with small physiological cross-sectional areas (PCSAs) can be well represented using single strings, while those with large PCSAs (flat-wide attachments, e.g., ADPt and ADPo) can be represented by the averaged excursions of two strings. Our results show that the tendons with large PCSAs can be well represented biomechanically using the proposed approach in the major range of motion.

An investigation on the biodynamic foundation of a rat tail vibration model

The objectives of this study are to examine the fundamental characteristics of the biodynamic responses of a rat tail to vibration and to compare them with those of human fingers. Vibration transmission through tails exposed to three vibration magnitudes (1 g, 5 g, and 10 g r.m.s.) at six frequencies (32 Hz, 63 Hz, 125 Hz, 160 Hz, 250 Hz, and 500 Hz) was measured using a laser vibrometer. A mechanical-equivalent model of the tail was established on the basis of the transmissibility data, which was used to estimate the biodynamic deformation and vibration power absorption at several representative locations on the tail. They were compared with those derived from a mechanical-equivalent model of human fingers reported in the literature. This study found that, similar to human fingers, the biodynamic responses of the rat tail depends on the vibration magnitude, frequency, and measurement location. With the restraint method used in this study, the natural frequency of the rat tail is in the range 161-368 Hz, which is mostly within the general range of human finger resonant frequencies (100-350 Hz). However, the damping ratios of the rat tail at the unconstrained locations are from 0.094 to 0.394, which are lower than those of human fingers (0.708-0.725). Whereas the biodynamic responses of human fingers at frequencies lower than 100 Hz could be significantly influenced by the biodynamics of the entire hand-arm system, the rat tail biodynamic responses can be considered independent of the rat body in the frequency range used in this study. Based on these findings it is concluded that, although there are some differences between the frequency dependences of the biodynamic responses of the rat tail and human fingers, the rat tail model can provide a practical and reasonable approach to examine the relationships between the biodynamic and biological responses at midrange to high frequencies, and to understand the mechanisms underlying vibration-induced finger disorders.

Energy absorption of seated occupants exposed to horizontal vibration and role of back support condition

Absorbed power characteristics of seated human subjects under fore-aft (x-axis) and lateral (y-axis) vibration are investigated through measurements of dynamic interactions at the two driving-points formed by the body and the seat pan, and upper body and the backrest. The experiments involved: (i) three back support conditions (no back support, and back supported against a vertical and an inclined backrest); (ii) three seat pan heights (425, 390 and 350 mm); and three magnitudes (0.25, 0.5 and 1.0 m/s2 rms acceleration) of band limited random excitations in 0.5-10 Hz frequency range, applied independently along the x- and y- axes. The force responses, measured at the seat pan and the backrest are applied to characterize total energy transfer reflected on the seat pan and the backrest. The mean responses suggest strong contributions due to back support, and direction and magnitude of vibration. In the absence of a back support, the seat pan responses dominated in lower frequency bands centered at 0.63 and 1.25 Hz under both directions of motion. Most significant interactions of the upper body against the back support was observed under fore-aft vibration. The addition of back support caused the seat pan response to converge to a single primary peak near a higher frequency of 4 Hz under x- axis, with only little effect on the y-axis responses. The back support serves as an additional source of vibration to the occupant and an important constraint to limit the fore-aft movement of the upper body and thus relatively higher energy transfer under. The mean responses were further explored to examine the Wd frequency-weighting used for assessing exposure to horizontal vibration. The results show that the current weighting is suited for assessing the vibration exposure of human subjects seated only without a back support.

Three-Dimensional Finite Element Simulations of the Dynamic Response of a Fingertip to Vibration

Although excessive dynamic deformation of the soft tissues in the fingertip under vibration loading is thought to induce hand-arm vibration syndrome, the in vivo distributions of the dynamic stress/strain of the tissues in the fingertip under vibration conditions have not been studied because they cannot be measured experimentally. In the present study, we analyzed the dynamic responses of a fingertip to vibrations by extending our previously proposed three-dimensional finite element (FE) model. The FE model of the fingertip contains the essential anatomical structures of a finger, such as skin layers (dermis and epidermis), subcutaneous tissue, bone, and nail. Our analysis indicated that the fingertip has a major local resonance around 100Hz and that the vibration displacement in the soft tissues under the nail bed is less than 10% of those in the finger pad for all precompression levels and vibration range. The resonant frequency of the fingertip was found to increase from 88Hzto125Hz with the static precompression increasing from 0.5mmto2.0mm. These results suggest that structural and functional changes in vascular function will likely initiate from the fingerpad, the location that undergoes the greatest deformation during vibration exposure. The current predictions are qualitatively consistent with the physiological data collected from workers with vibration white finger.

An evaluation of impact wrench vibration emissions and test methods

In the interest of providing more effective evaluations of impact wrench vibration exposures and the development of improved methods for measuring vibration emissions produced by these tools, this study focused on three variables: acceleration measured at the tool surface, vibration exposure duration per test trial, and the amount of torque required to unseat the nuts following a test trial. For this evaluation, six experienced male impact wrench operators used three samples each of five impact wrench models (four pneumatic models and one battery-powered model) in a simulated work task. The test setup and procedures were based on those provided by an International Organization for Standardization (ISO) Technical Committee overseeing the revision of ISO 8662-7. The work task involved the seating of 10 nuts onto 10 bolts mounted on steel plates. The results indicate that acceleration magnitudes vary not only by tool type but also by individual tools within a type. Thus, evaluators are cautioned against drawing conclusions based on small numbers of tools and/or tool operators. Appropriate sample sizes are suggested. It was further noted that evaluators could draw different conclusions if tool assessments are based on ISO-weighted acceleration as opposed to unweighted acceleration. As expected, vibration exposure durations varied by tool type and by test subject; duration means varied more for study participants than they did for tool types. For the 12 pneumatic tools evaluated in this study, torque varied directly with tool handle acceleration. Therefore, in order to reduce vibration exposure, tools should be selected and adjusted so that they produce no more than the needed torque for the task at hand.

A new approach to characterize grip force applied to a cylindrical handle

The grip force applied to a cylindrical handle is a function of the measurement reference axis. So far, however, no attempt has been made to fully describe the exact form of this function. The objectives of this study were to examine some fundamental characteristics of grip forces and to explore the basic pattern of the grip force function. Twenty subjects (10 males and 10 females) participated in the experiment. The subjects alternately used their left and right hands to apply maximum grip forces and medium grip forces (about 40% of maximum) to a 30 mm handle. A flexible pressure sensor mat was used to measure the grip pressure. The pressure was integrated with respect to different measurement axes; this resulted in the grip force function. This study found that every gripping action produces maximum and minimum force axes; these axes are separated by about 90 degrees . The maximum force is correlated with the minimum force, but the former is generally about 1.42 times the latter. The principal grip direction is about 78 degrees from the z(h)-axis of the hand biodynamic coordinate system defined in ISO 8727 [ISO 8727. Mechanical vibration and shock - human exposure - biodynamic coordinate systems. Geneva, Switzerland: International Organization for Standardization; 1997]. More interestingly, each of the 160 sets of experimental data reasonably fit this study's proposed elliptical model. The implications of the findings are discussed.

A method to quantify hand-transmitted vibration exposure based on the biodynamic stress concept

This study generally hypothesized that the vibration-induced biodynamic stress and number of its cycles in a substructure of the hand-arm system play an important role in the development of vibration-induced disorders in the substructure. As the first step to test this hypothesis, the specific aims of this study were to develop a practical method to quantify the biodynamic stress-cycle measure, to compare it with ISO-weighted and unweighted accelerations, and to assess its potential for applications. A mechanical-equivalent model of the system was established using reported experimental data. The model was used to estimate the average stresses in the fingers and palm. The frequency weightings of the stresses in these substructures were derived using the proposed stress-cycle measure. This study found the frequency dependence of the average stress distributed in the fingers is different from that in the palm. Therefore, this study predicted that the frequency dependencies of finger disorders could also be different from those of the disorders in the palm, wrist, and arms. If vibration-induced white finger (VWF) is correlated better with unweighted acceleration than with ISO-weighted acceleration, the biodynamic stress distributed in the fingers is likely to play a more important role in the development of VWF than is th e biodynamic stressdistributed in the other substructures of the hand-arm system. The results of this study also suggest that the ISO weighting underestimates the high-frequency effect on the finger disorder development but it may provide a reasonable risk assessment of the disorders in the wrist and arm.

Analysis of musculoskeletal loading in an index finger during tapping

Since musculoskeletal disorders of the upper extremities are believed to be associated with repetitive excessive muscle force production in the hands, understanding the time-dependent muscle forces during key tapping is essential for exploring the mechanisms of disease initiation and development. In the current study, we have simulated the time-dependent dynamic loading in the muscle/tendons in an index finger during tapping. The index finger model is developed using a commercial software package AnyBody, and it contains seven muscle/tendons that connect the three phalangeal finger sections. Our simulations indicate that the ratios of the maximal forces in flexor digitorum superficialis (FS) and flexor digitorum profundus (FP) tendons to the maximal force at the fingertip are 0.95 and 2.9, respectively, which agree well with recently published experimental data. The time sequence of the finger muscle activation predicted in the current study is consistent with the EMG data in the literature. The proposed model will be useful for bioengineers and ergonomic designers to improve keyboard design minimizing musculoskeletal loadings in the fingers.

Finite element analysis of the penetrations of shear and normal vibrations into the soft tissues in a fingertip

It is well accepted that the effects of mechanical vibration on the finger-hand-arm system are strongly frequency-dependent: low frequency vibration can transmit from hand to arm, while high frequency vibration is absorbed in the local tissue of fingers. This assertion has not been validated directly. The purpose of the present study is to analyze the frequency- and deformation-dependent dynamic strains in the soft tissues in a fingertip that is subjected to vibration normal or tangential to the contact surface. The dynamic responses of the fingertip were analyzed using a multi-layered two-dimensional finite element model. The major anatomical substructures, i.e., skin, subcutaneous tissue, bone, and nail, are included in the model. The fingertip was found to have a major resonance around 100-125 Hz and a second resonance around 250 Hz. The resonances of the fingertip are found to be independent of the direction of exposure (in normal or shear direction). The simulations further indicated that the dynamic strains induced by the vibration at low frequencies will penetrate deeper into the tissue (> 3 mm) while that at high frequencies will be concentrated in the superficial skin layer (< 0.8 mm). The model predictions are consistent with the published experimental observations.