A new framework for evaluating potential risk of back disorders due to whole body vibration and repeated mechanical shock

A number of studies have examined the potential relationship between exposure to occupational vibration and low back pain associated with operation of vehicles. Only a handful of studies, however, have attempted to differentiate between the relative contributions of the steady state and transient mechanical shock components (the latter also being known as 'jarring and jolting', 'high acceleration event', 'multiple shocks' and 'impact') of the vibration exposure. The primary objective of this paper is to present a review of current studies that examine mechanical shock, present a case for the importance of evaluating both steady state and mechanical shock components and propose a new framework for evaluating the health effects due to occupational vibration exposure. A computerized bibliographical search of several databases was performed with special reference to the health effects of mechanical shock in relation to lower back disorders. Based on the analysis, eight experimental studies and nine epidemiological studies with relevance to exposure to 'mechanical shock' were identified. These studies suggested that rough vehicle rides are prevalent and that repeated exposure to mechanical shock may increase the risk of lower back pain. There is an urgent need for assessing the health effects of mechanical shocks in epidemiological studies. In particular, the new ISO 2631-5: International Organization for Standardization 2004 standard for shock exposure assessment should be evaluated with regard to musculoskeletal health effects.     

Frequency-dependence of discomfort caused by vibration and mechanical shocks

The frequency content of a mechanical shock is not confined to its fundamental frequency, so it was hypothesised that the frequency-dependence of discomfort caused by shocks with defined fundamental frequencies will differ from the frequency-dependence of sinusoidal vibration. Subjects experienced vertical vibration and vertical shocks with fundamental frequencies from 0.5 to 16 Hz and magnitudes from ±0.7 to ±9.5 ms^–2. The rate of growth of discomfort with increasing magnitude of motion decreased with increasing frequency of both motions, so the frequency-dependence of discomfort varied with the magnitudes of both motions and no single frequency weighting will be ideal for all magnitudes. At the frequencies of sinusoidal vibration producing greatest discomfort (4–16 Hz), shocks produced less discomfort than vibration with same peak acceleration or unweighted vibration dose value. Frequency-weighted vibration dose values provided the best predictions of the discomfort caused by different frequencies and magnitudes of vibration and shock.

Practitioner Summary: Human responses to vibration and shock vary according to the frequency content of the motion. The ideal frequency weighting depends on the magnitude of the motion. Standardised frequency-weighted vibration dose values estimate discomfort caused by vibration and shock but for motions containing very low frequencies the filtering is not optimum.     

Combined exposures of whole-body vibration and awkward posture: a cross sectional investigation among occupational drivers by means of simultaneous field measurements

Abstract

Objective: Multifactorial workloads such as whole-body vibration (WBV), awkward posture and heavy lifting are potential predictors for low back pain (LBP). In this study, we investigate the association between LBP and these exposures among 102 professional drivers. Methods: The combined exposures of WBV and posture are measured at different workplaces. Health and personal data as well as information about lifting tasks are collected by a questionnaire. Results: The daily vibration exposure value (odds ratio 1.69) and an index for awkward posture (odds ratio 1.63) show significant association with the occurence of LBP. Awkward posture and heavy lifting appear to be more strongly associated with sick leave than WBV exposure. Furthermore, a combination of the measurement results of WBV and awkward posture into one quantity also shows significant correlation to LBP. Conclusion: The combined exposure of WBV and awkward posture can be described in terms of the daily vibration exposure and the index for awkward posture. This facilitates work place assessments and future research in this area.

Practitioner Summary: For the first time, quantitative measures combining whole-body vibration and awkward posture exposures have shown to correlate with the occurrence of low back pain significantly. This validates the proposed quantities and measurement methods, which facilitate workplace assessments and assist in the design of further studies which are necessary to establish a causal exposure–response relationship.     

Effect of reclining a seat on the discomfort from vibration and shock on fast boats

Passengers and crew on fast boats can experience high magnitudes of whole-body vibration and mechanical shocks that may present risks to health and cause discomfort. This study investigated the influence of reclining a seat on the discomfort caused by fast-boat motion and whether discomfort can be predicted by overall ride values according to current standards. Subjects judged the discomfort of simulations of a recorded fast boat motion in a seat reclined by 0°, 15°, 30°, 45°, or 60°. Reclining the seat caused no significant change in overall discomfort, suggesting that if a reclined seat can be shown to reduce risks of injury it may be acceptable in respect of comfort. The findings are inconsistent with the predictions of standards and show that revised frequency weightings are required to account for seat pan or seat back inclination.     

Whole body vibration exposure patterns in Canadian prairie farmers

Abstract

Whole body vibration is a significant physical risk factor associated with low back pain. This study assessed farmers’ exposure to whole body vibration on the Canadian prairies according to ISO 2631-1. Eighty-seven vibration measurements were collected with a triaxial accelerometer embedded in a rubber seat pad at the operator-seat interface of agricultural machinery, including tractors, combines, pickup trucks, grain trucks, sprayers, swathers, all-terrain vehicles, and skid steers. Whole body vibration was highest in the vertical axis, with a mean (range) frequency-weighted root mean squared acceleration of 0.43 m/s² (0.19?1.06 m/s²). Mean crest factors exceeded 9 in all 3 axes, indicating high mechanical shock content. The vertical axis vibration dose value was 7.55 m/s^1.75 (2.18?37.59 m/s^1.75), with 41.4% of measurements within or above the health guidance caution zone. These high exposures in addition to an ageing agricultural workforce may increase health risks even further, particularly for the low back.

Practitioner Summary: Agricultural workers are frequently exposed to whole body vibration while operating farm equipment, presenting a substantial risk to musculoskeletal health including the low back. Assessing vibration exposure is critical in promoting a safe occupational environment, and may inform interventions to reduce farmer’s exposure to vibration.     

Ergonomic analysis of the effects of a telehandler's active suspended cab on whole body vibration level and operator comfort

IntroductionExposure to whole body vibration (WBV) is one of the most important risks for musculoskeletal disorders (MSDs). The objective of the study was to investigate whether an active cab suspension system fitted on a telehandler was effective in reducing WBV and in improving comfort.MethodSixteen male healthy professional operators drove a telehandler on a 100 m ISO 5008 smooth track at two different speeds (5 and 12 kph) with activated and deactivated cab suspension system. Adopting an ergonomic approach, different aspects of the human-machine interaction were analyzed: 1) vibration transmissibility, 2) subjective ratings of general comfort and local body discomfort, and 3) anthropometric characteristics of the users.ResultsA series of ANCOVAs showed that the suspension system was effective in reducing WBV at both speeds but did not affect the perception of comfort by the operators. Moreover, individuals with higher Body Mass Index (BMI) experienced more comfort. Some neck/shoulder and lumbar complaints and perceived hard jolts seemed to remain even when the system was activated. No correlations were found between objective and subjective measures.Practical applicationsResults suggest that the operators, given their wide range of physical variability, may need more adjustable or customizable WBV reduction systems.     

The vibration transmissibility and driving-point biodynamic response of the hand exposed to vibration normal to the palm

Prolonged, intensive exposure to vibrations from palm and orbital sanders could cause finger disorders. They are likely to be associated with the biodynamic responses of the fingers. Although the biodynamic responses of the hand-arm system have been studied by many researchers, the detailed biodynamic responses distributed in the hand substructures have not been sufficiently understood. To advance the knowledge in this aspect and to aid in the development of improved finite element models of the substructures, this study simultaneously measured the overall driving-point biodynamic response and the distribution of vibration transmissibility at the fingers and back of the hand exposed to a flat plate vibration (as an approximate simulation of the operations of the palm and orbital sanders) and examined the relationship between these two measures of biodynamic responses. Ten subjects (five males and five females) participated in the experiment. A scanning laser vibrometer was used to measure the distributed vibration. This study confirmed that the distributed hand responses generally varied with locations on each finger, vibration frequencies, and applied hand force. Two major resonances were observed in the vibration transmissibility. At the first resonance, the transmitted vibrations at different locations were more or less in phase; hence, this resonance was also observed in the driving-point biodynamic response that measures the overall biodynamic response of the system. The second resonance was observed at the fingers. Because this resonant frequency varied greatly among the fingers and the specific segments of each finger, it is difficult to identify this resonance in the driving-point biodynamic response. The implications of the findings for further model developments and applications are discussed.

Relevance to industry

This study enhanced the understanding of the biodynamic responses of the fingers and hand exposed to vibrations on a contact surface with a large effective radius such as that found on palm and orbital sanders. The results can also be used to develop and/or validate models of the substructures of the hand-arm system, which can be further used to help design and analyze these tools and associated anti-vibration devices. The results may also be applicable to help develop location-specific frequency weightings to assess the risks of the finger vibration exposure.     

基于MEMS技术的复合型智能传感器设计

把微机电系统(MEMS)技术的加速度敏感元件和微处理器有机结合,借助智能算法,设计了一种多功能的复合传感器,可同时测量运动物体的的振动、冲击和倾斜角度。试验表明:该传感器能够足够同时精确地检测运动物体的振动、冲击和倾斜角度信息,用于汽车中时,能够及时检测汽车的动态信息与车体的姿态。     

Hand-arm and whole-body vibrations induced in cross motorcycle and bicycle drivers

Generally, and particularly at sports, the human body is constantly exposed to physical requests and to tests in many different situations. Although the practice of sports is considered a healthy act, there are limits and, when these limits are reached, the benefits of sport can turn into problems. Thus, the biodynamic response method is increasingly being used to study the human injuries induced by external vibrations. Moreover, the European Directive 2002/44/EC on the minimum health and safety requirements, regarding worker exposure to risks from physical agents (e.g. vibration), limit the exposure to vibrations. The aim of this study is to analyze the exposure level of cross motorcycle and of cycling drivers to hand-arm vibration (HAV) and to whole-body vibration (WBV). For this research, vibration levels of a common 200 cc cross motorcycle were experimentally measured and the maximum driving time that could be safely used in a stone road was established. Moreover, bicycle vibration measurements were performed using two different bicycles: a road cycling bike; a bike for track cycling. The road bike was evaluated at three road scenarios: asphalt; paved; and stone road pavement. The track bike was evaluated in track cycling and rollers. In the case of cycling the results indicate that impacts and transient vibrations lead to a higher musculoskeletal request particularly in what concerns shoulders, arms, wrists, knees and spine.     

Effects of horizontal whole-body vibration and standing posture on activity interference

Standing people are exposed to whole-body vibration in many environments. This paper investigates the effects of horizontal whole-body vibration and standing posture on task performance. Sixteen participants were exposed to random vibration (up to 4 Hz) whilst performing a timed pegboard task in two standing postures. Objective and subjective indicators of performance were used. Time taken to complete the task increased progressively with increases in vibration magnitude. The fore-and-aft posture generally showed greater performance decrements and postural interruptions (>1.0 ms^?2 root mean square) than the lateral. For both postures, performance was better during y-axis vibration than during x-axis vibration. Subjective ratings showed similar trends to time data. Impairments due to dual axis exposure were well predicted using root sum of squares calculations based on single axis components. These results indicate that best performance for those standing in moving environments will be achieved if individuals adopt a lateral posture with the most severe vibration in the y-axis.

Statement of Relevance: People have a need to work during transportation, either working for the transport provider or as a passenger. All modes of transport result in travellers being exposed to horizontal motion. This study demonstrates that task disturbance is affected by the orientation of the standing person to the vibration and, therefore, vehicle layouts can be optimised.     

All-terrain vehicle use in agriculture: Exposure to whole body vibration and mechanical shock

Whole body vibration (WBV) and mechanical shock were measured in 12 New Zealand farmers during their daily use of all-terrain vehicles (ATVs). As per the International Organization for Standardization (ISO) guidelines for WBV exposure, frequencies between 0 and 100 Hz were recorded via a seat-pad tri-axial accelerometer during 20 min of ATV use. The farmers were also surveyed to estimate seasonal variation in daily ATV usage as well as 7-day and 12-month prevalence of spinal pain. Frequency-weighted vibration exposure and total riding time were calculated to determine the daily vibration dose value (VDV). The daily VDV of 16.6 m/s^1.75 was in excess of the 9.1 m/s^1.75 action limit set by ISO guidelines suggesting an increased risk of low back injury from such exposure. However, the mean shock factor R, representing cumulative adverse health effects, was 0.31 indicating that these farmers were not exposed to excessive doses of mechanical shock. Extrapolation of daily VDV data to estimated seasonal variations of farmers in ATV riding time demonstrated that all participants would exceed the ISO recommended maximum permissible limits during the spring lambing season, as compared to lower exposures calculated for summer, autumn and winter. Low back pain was the most commonly reported complaint for both 7 day (50%) and 12 month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%) respectively. The results demonstrate high levels of vibration exposure within New Zealand farmers and practical recommendations are needed to reduce their exposure to WBV.     

Occupational hazards survey among coal workers using hand-held vibrating tools in a northern China coal mine

ObjectiveProlonged exposure to hand-transmitted vibration (HTV) is associated with an increased risk of hand-arm vibration syndrome (HAVS). This study aimed to identify the signs and symptoms associated with coal workers using hand-held vibrating tools in a northern China coal mine, and to determine the risk factors for HAVS.MethodsA cross-sectional survey was conducted of 167 male workers with part-time exposure to HTV. A structured questionnaire was administered to the workers along with a series of function tests. The frequency-weighted vibration acceleration of hand-held tools was measured. The prevalence ratio and symptom correlation to HAVS among the different subgroups were evaluated.ResultsThe prevalence of hand numbness, carpal tunnel syndrome, hand ache, tinnitus, memory loss, dizziness and headache showed significant differences in the longer-exposure groups (working years > 3 years or the daily-exposure duration > 2 h), compared with the control group (P < 0.05). Function tests showed abnormal findings only in vibration sensation and the X-ray examination of the longer-exposure groups (P < 0.05). The logistic regression analysis showed that longer working years, higher daily exposure and alcohol consumption were risk factors, while wearing anti-vibration gloves showed protective effects for hand numbness.ConclusionsThis study has identified the main signs and symptoms of HAVS among coal workers exposed to HTV in China. More information related to occupational safety and health programs are required to reduce the risk of HAVS.     

Biomechanical response of the human foot when standing in a natural position while exposed to vertical vibration from 10–200 Hz

Exposure to foot-transmitted vibration (FTV) can lead to pain and numbness in the toes and feet, increased cold sensitivity, blanching in the toes, and joint pain. Prolonged exposure can result in a clinical diagnosis of vibration-induced white foot (VIWFt). Data on the biomechanical response of the feet to FTV is limited; therefore, this study seeks to identify resonant frequencies for different anatomical locations on the human foot, while standing in a natural position. A laser Doppler vibrometer was used to measure vertical (z-axis) vibration on 21 participants at 24 anatomical locations on the right foot during exposure to a sine sweep from 10–200?Hz with a peak vertical velocity of 30?mm/s. The most notable differences in the average peak frequency occur between the toes (range: 99–147?Hz), midfoot (range: 51–84?Hz) and ankle (range: 16–39?Hz).

Practitioner Summary: The biomechanical response of the human foot exposed to foot-transmitted vibration, when standing in a natural position, was measured for 21 participants. The foot does not respond uniformly; the toes, midfoot, and ankle regions need to be considered independently in future development of isolation strategies and protective measures.     

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 industryHand-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.     

Experimental analysis of occupational whole-body vibration exposure of agricultural tractor with large square baler

This study investigates longitudinal whole-body vibration in agricultural tractors powering a large square baler. The aim is to test the hypothesis that four-wheel drive has an influence on the longitudinal dynamic response. A number of experimental measurements are carried out on a specific vehicle combination driving uphill and downhill. The whole-body vibration exposure is measured at the operator seat under different conditions.The statistic results show a significant difference on the whole-body vibration exposure depending on operating conditions. Driving uphill and downhill with four-wheel drive activated showed the highest difference with increased vibration level at downhill driving.The results indicate that four-wheel drive influences the longitudinal dynamics and hence the whole-body vibration exposure on tractors with large square balers.Relevance to industryThe findings of this work are highly relevant to the manufacturers of agricultural tractors and machinery as well advisers within occupational health. The paper demonstrates potential in reducing damaging vibrations by simple manual or automatic control of four-wheel drive.     

Equivalent comfort contours for fore-and-aft,lateral, and vertical whole-body vibration in the frequency range 1.0 to 10 Hz

Abstract

Standards assume vibration discomfort depends on the frequency and direction of whole-body vibration, with the same weightings for frequency and direction at all magnitudes. This study determined equivalent comfort contours from 1.0 to 10?Hz in each of three directions (fore-and-aft, lateral, vertical) at magnitudes in the range 0.1 to 3.5?ms^?2?r.m.s. Twenty-four subjects sat on a rigid flat seat with and without a beanbag, altering the pressure distribution on the seat but not the transmission of vibration. The rate of growth of vibration discomfort with increasing magnitude of vibration differed between the directions of vibration and varied with the frequency of vibration. The frequency-dependence and direction-dependence of discomfort, therefore, depended on the magnitude of vibration. The beanbag did not affect the frequency-dependence or direction-dependence of vibration discomfort. It is concluded that different weightings for the frequency and direction of vibration are required for low and high magnitude vibration.

Practitioner summary: When evaluating whole-body vibration to predict vibration discomfort, the weightings appropriate to different frequencies and different directions of vibration should depend on the magnitude of vibration. This is overlooked in all current methods of evaluating the severity of whole-body vibration.     

City bus driving and low back pain: a study of the exposures to posture demands, manual materials handling and whole-body vibration

A cross-sectional study was conducted to investigate worker exposure to posture demands, manual materials handling (MMH) and whole body vibration as risks for low back pain (LBP). Using validated questionnaire, information about driving experience, driving (sitting) posture MMH, and health history was obtained from 80 city bus drivers. Twelve drivers were observed during their service route driving (at least one complete round trip) and vibration measurements were obtained at the seat and according to the recommendations of ISO 2631 (1997), for three models of bus (a mini-bus, a single-decker bus, a double-decker bus). The results showed that city bus drivers spend about 60% of the daily work time actually driving, often with the torso straight or unsupported, perform occasional and light MMH, and experience discomforting shock/jerking vibration events. Transient and mild LBP (not likely to interfere with work or customary levels of activity) was found to be prevalent among the drivers and a need for ergonomic evaluation of the drivers' seat was suggested.     

The influence of shock-type vibrations on the absorption of mechanical energy in the hand and arm

In recent years there has been a discussion as to whether shock-type vibration from hand tools has stronger effects on the hand-arm system in comparison with non-impulsive vibration. The purpose of the investigation is to compare the influence of these two types of vibration on the absorption of mechanical energy in the human hand and on the grip and feed forces applied by the subjects.

The energy absorption has been measured by use of a specially designed laboratory handle. The grip and feed forces applied by the subject to the handle were measured simultaneously. In the study two different frequency weighted acceleration levels were used.

The outcome showed that the vibration exposure levels made a significant contribution to the vibration absorption as well as to the strength of the grip and feed forces. Moreover, it was found that the hand forces decrease while the absorption of energy increases during the experiment. Furthermore, the influence of shock-type exposure gave a significantly higher hand forces and absorption of energy compared with the non-impulsive exposure. It was, therefore, concluded that the vibration response characteristics of the hand and arm differ, depending upon whether the exposure is of shock or non-impulsive type.

Relevance to industry

The paper discusses the dynamic response of the hand and arm during exposure to shock and non-impulsive vibration. Whenever possible, a tool that requires low grip and feed forces should be used as well as tools that not generate shock-type excitation. This can be helpful in choosing the proper tool for the job.     

Effects of agricultural quad bike driving on postural control during static,dynamic and functional tasks – A field study

BackgroundDriving a quad bike in a rural occupational setting is likely to expose the driver to various physical stimuli including whole-body vibration (WBV). These exposures may be linked to post-driving postural alterations which in turn could lead to an increased risk of spinal injury while undertaking manual material handling activities immediately following driving or falls while exiting from a vehicle.PurposeThe purpose of this study was to use a battery of postural tasks namely; bipedal and unipedal stance, limits of stability (LOS) and lifting task to assess how quad bike driving alters the postural control (PC) in a group of rural workers.MethodsThe PC, determined from centre of pressure (COP) displacements in a group of rural workers (n = 34), was evaluated at three time (T) periods, once (T-I) before the 30 min quad bike driving session on a typical New Zealand farm terrain and twice (T-II and T-III) immediately following driving, each time period lasted approximately 10 min later.ResultsThe results demonstrated a significant (p < 0.05) increase and decrease in the magnitude of the COP measures for the lifting task and unipedal stance respectively during both T-II and T-III periods. However significant (p < 0.05) increase in the magnitude COP measures of bipedal stance, and increase in the maximal stability limits (LOS) were demonstrated only in the T-III.ConclusionsThese results demonstrate both immediate and sustained alterations in the PC following a period of occupational vehicle driving. Also, the results demonstrate both a worsening and improvement in postural control during the performance of a battery of tasks. Observed adverse or facilitatory postural effects will require further laboratory based investigations in order to determine how such disparity can best be explained or challenged.Relevance to industryThe findings will inform ergonomists about the potential risk involved in carrying out physically demanding occupational tasks following vehicle driving. This putative situation could be prevented by adopting behavioural strategies by drivers, and engineered interventions designed to reduce WBV exposure.     

Mechanisms of vibration-induced interference with manual control performance

Abstract

An experiment is described in which eight subjects performed three simple tasks (A, B and C) in static conditions and during exposure to whole-body vertical (z-axis) vibration at 0-5 and 40 Hz, at an acceleration magnitude of 2-1 ms^-2 r.m.s. All subjects performed all conditions with and without an arm support. The objective was to explore the mechanisms that may cause disruption of manual control performance during vibration exposure. With task A subjects simply held a control with no visual feedback of activity at the control. With task B, subjects used the control to hold a controlled element stationary on a display. Task C was the same as task B, except that subjects had improved visual feedback of movement of the controlled element. Results showed that both 0-5 and 40 Hz vibration caused significant increases in control activity at frequencies of up to about 1 Hz compared with the condition without vibration. With visual feedback in task C, subjects were able to detect drifting of the controlled element on the display and introduced compensatory control activity at frequencies above about 0 2 Hz. The arm support reduced the magnitude of vibration transmitted to the control at 4-0 Hz, but did not otherwise change the results.