Digital vibration threshold testing and ergonomic stressors in automobile manufacturing workers: a cross-sectional assessment

Upper extremity musculoskeletal disorders (UEMSDs) comprise a large proportion of work-related illnesses in the USA. Physical risk factors including manual force and segmental vibration have been associated with UEMSDs. Reduced sensitivity to vibration in the fingertips (a function of nerve integrity) has been found in those exposed to segmental vibration, to hand force, and in office workers. The objective of this study was to determine whether an association exists between digital vibration thresholds (VTs) and exposure to ergonomic stressors in automobile manufacturing. Interviews and physical examinations were conducted in a cross-sectional survey of workers (n = 1174). In multivariable robust regression modelling, associations with workers' estimates of ergonomic stressors stratified on tool use were determined. VTs were separately associated with hand force, vibration as felt through the floor (whole body vibration), and with an index of multiple exposures in both tool users and non-tool users. Additional associations with contact stress and awkward upper extremity postures were found in tool users. Segmental vibration was not associated with VTs. Further epidemiologic and laboratory studies are needed to confirm the associations found. The association with self-reported whole body vibration exposure suggests a possible sympathetic nervous system effect, which remains to be explored.     

Occupational musculoskeletal disorders in the neck and upper limbs of forestry workers exposed to hand-arm vibration.

An epidemiologic and clinical study of neck and upper limb musculoskeletal disorders was carried out on 65 vibration-exposed forestry operators using chain-saws and 31 comparable control subjects (maintenance workers) performing manual activity and not exposed to vibration. Upper limb function was evaluated by measuring finger and wrist circumference size, maximal hand grip strength and range of motion manoeuvres in both the controls and the exposed workers. Vibration from two chain-saws was measured, and vibration exposure for each forestry worker was assessed in terms of 4 h energy-equivalent frequency-weighted acceleration according to ISO 5349. Job analysis indicated a slight excess risk of upper extremity cumulative trauma disorders (CTDs) in the forestry operators compared with the control workers. After adjustment for age and body constitution, significantly higher prevalence rates of persistent upper limb pain, muscle-tendon syndromes and carpal tunnel syndrome were observed among the forestry workers than among the controls. In the forestry operators, the occurrence of upper limb musculoskeletal disorders increased with increasing vibration exposure. Upper limb function was found to be impaired in the forestry workers compared with the controls. Vibration exposure was significantly related to increased finger circumference size, diminished muscle force and reduced joint function. Even though it is difficult to establish the relative importance of vibration and ergonomic factors in the aetiology of CTDs, nevertheless the results of this study indicate that musculoskeletal impairment to the upper limbs was more severe in the forestry operators than in the controls who did solely manual work. This finding and the observed dose-effect relationships suggest that vibration stress is an important contributor to the development of musculoskeletal disorders in workers using hand-held vibrating tools.     

The effect of hand tools’ handle shape on upper extremity comfort and postural discomfort among hand-woven shoemaking workers

Hand tools are widely used in a large number of occupations. Many workers have to use hand tools to accomplish their duties. This may cause work-related Upper Extremities Musculoskeletal Disorders (UEMSDs). The present study was conducted in Iranian hand-woven shoe industry to (a) investigate the design of hand tools currently used in hand-woven shoemaking operation and (b) design/redesign the tools' handles based on anthropometric tables and ergonomic principles. Based on Iranian workers' anthropometric tables, new handles with different shapes were designed and made for hand tools currently used in hand-woven shoemaking operation (e.g., awl and cloth cutting tool). Hand postures and postural comfort and discomfort were investigated via rating technique using Comfort Questionnaire for Hand Tools (CQH) and upper extremities body map. The results of CQH showed that the handle shape had a significant influence on the hand posture and perceived postural discomfort in the upper extremities. The new ergonomically designed handles were perceived to be more comfortable compared to the traditional ones. Additionally, the new handles improved the hand posture during the operation and reduced the severity of discomfort in the upper extremities compared to the tools with conventional handles. The findings of this study revealed that designing the hand tools’ handles based on ergonomic principles and using anthropometric tables could improve the hand posture, increase comfort, and decrease discomfort in the upper extremities. By this means, reduction in work-related UEMSDs is expected.     

Musculoskeletal disorders among female carpet weavers in Iran

The aim of this study was to determine factors associated with self-reported upper extremity musculoskeletal disorders (UEMSDs) among female carpet weavers. Data on demographic characteristics and workplace factors were collected from 626 female carpet weavers. Type of carpet weaving looms, weaving style (Persian vs. Turkish), daily working hours and work experience as well as personal factors including age and marital status were significantly and independently associated with self-reported UEMSDs (p < 0.05), while education, handedness and weight of weaving comb were not. A major finding of this study was the significant association between weaving style and UEMSDs. Better measures of the biomechanical requirements of carpet weaving tasks in Persian and Turkish weaving types are required to understand better their influences on the health of weavers and on UEMSDs in particular. Poor workstation design, in particular, design inappropriate for the anthropometric dimensions of weavers, was a major risk factor for musculoskeletal symptoms in carpet weaving. Therefore, this industry should develop equipment adapted to women's sizes and shapes. PRACTITIONER SUMMARY: This article provides an insight into the risk factors associated with self-reported UEMSDs among female carpet weavers, identifying major factors associated with upper extremity musculoskeletal symptoms and exploring guidelines for designing weaving workstations.     

Manufacturing and the new ANSI S2.70‐2006 hand–arm vibration exposure standard

Since 1918, hand–arm vibration (HAV) exposure, principally from but not limited to vibrating power tools and processes, affects some 1.5 to 2 million regularly exposed U.S. workers and many more worldwide. These HAV exposures usually lead to an irreversible disease of the fingers/hands called hand–arm vibration syndrome whose prevalence is as high as 50% in exposed worker populations. HAVS results not only in hand–arm deterioration, but invariably job loss. To help combat the mounting HAV problem, domestic and international consensus HAV exposure standards were developed and promulgated in the early 1980s; but for the first time, the European Union in 2005 passed into law exposure standards for both HAV and whole‐body vibration. In response, in 2006 in the United States, the American National Standards Institute (ANSI) developed, replaced, and promulgated its 1986 HAV exposure standard S3.34 with a completely revised HAV standard—S2.70‐2006—thus ushering in new profound implications for power tool users and tool manufacturers and countless related manufacturing operations throughout the United States. The background, salient aspects, safety and health, and manufacturing implications of this new ANSI S2.70 HAV standard are discussed. © 2008 Wiley Periodicals, Inc.     

Correlation between Different Hand Force Assessment Methods from an Epidemiological Study

This article presents the outcome of correlation analyses of data results obtained from using different methods for objectively and subjectively assessing hand force from a prospective study of 450 blue‐collar workers from several companies and industries, followed for up to 3 years. The study collected detailed ergonomic exposure data at baseline and upper extremity health outcome data at baseline and every 4 months during the study. Ultimately, the study was intended to evaluate dose‐response relationships of specific upper extremity disorders with detailed physical and psychosocial exposure data at the workplace while controlling for important individual factors. This article presents the methods used to collect data, as well as the hand force results of the epidemiological study in aggregate correlated form, as a means of exploring the degree of independence between the variables considered. These insights are useful in identifying musculoskeletal disorder (MSD) causation and predicting MSD risk based on work exposures. An enhanced understanding of the independence of MSD causal factors is instrumental in establishing more accurate multivariable models of MSD causation that will play an important role in extrapolating from the understanding of mechanisms of causation to establishing effective recommendations and programs to prevent the occurrence of MSDs. © 2011 Wiley Periodicals, Inc.     

Design of assembly lines with the concurrent consideration of productivity and upper extremity musculoskeletal disorders using linear models

Work-related musculoskeletal disorders (WMSDs) are common occupational diseases among assembly workers due to repetitive motions or heavy workloads. The conventional approaches to decreasing WMSDs in assembly workers usually focus on individual assembly work at the station level. These approaches, however, do not pay enough attention to work allocation at the whole assembly line level such as balancing ergonomic burdens among workers by proper work assignment. This paper presents a methodology that can be used to integrate ergonomic measures of upper extremities into assembly line design problems. Linear models are developed to link work-worker assignment to the upper extremity ergonomic measures based on a guideline from American Conference of Governmental Industrial Hygienists. These linear models allow ergonomic and productivity measures to be integrated as a mixed-integer programming model. The case studies of this paper show the new model can effectively balance and control exposure levels in the upper extremity while not significantly decreasing line efficiency. This research shows the potential to reduce the need of numerous task adjustments for ergonomic improvement after initial assembly line design in conventional trial-and-error based assembly task adjustment. Furthermore, these linearization methods can be generalized in order to incorporate other ergonomic measures in tabulated forms into assembly line design problems.     

Predicting subjective perceptions of powered tool torque reactions

Powered hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders. In this study, subjective ratings of discomfort and acceptability of reaction forces were collected in an attempt to identify their associations with factors such as work location, and response covariates such as grip force and tool handle displacement. Three work configurations using pistol grip and right angle pneumatic nutrunners on horizontal and vertical surfaces were set up in the laboratory. Twenty healthy right-handed male participants operated four tools at nine locations and the corresponding subjective responses were collected. The results indicate that normalized grip force during the torque buildup period was a significant factor for both subjective ratings. For the unacceptable torque reactions across the three tool configurations, the ratio of hand moment impulse over tool torque impulse was significantly greater than for the acceptable reactions. For pistol grip tools used on the vertical surface, as the working height increased 30 cm, the odds of an unacceptable rating over an acceptable rating increased 1.6 times. Prediction models for subjective ratings of discomfort and acceptability provide insight regarding either workstation design or exposure control. These models can further be used to establish exposure limits based on handle displacement and grip force.     

Ergonomic stress levels, personal characteristics, accident occurrence and sickness absence among factory workers

This study was designed to evaluate the association of a single, integrated measure of simultaneous exposure to a number of adverse work and environmental conditions, termed the Ergonomic Stress Level (E-S-L), on workers' accident and sickness absence rates. The factors determining the E-S-L were body motion and posture, physical effort, active hazards and environmental stressors. E-S-L evaluation was based on 'walk-through' hazard inventories, direct observations, measurements and interviews. Workers were assigned to one of four stress levels ranging from low (A) to high (D). Subjects were 729 males, aged 20-67 years, employed in five factories in Israel. A linear relationship between E-S-L AND accident incidence was found, increasing from the lowest to the highest E-S-L. Moreover, workers more sensitive to environmental stressors, as indicated by their reported subjective annoyance, showed higher accident rates across all the ergonomic stress levels, a tendency which was statistically significant at levels C and D. On the other hand, sickness absence was significantly related to the overall subjective stress experienced, as manifested by reported job dissatisfaction and somatic complaints, and not directly to E-S-L. These findings highlight the role of aggregate work stress, coupled with individual sensitivity to environmental stressors, in increasing the risk of accidents.     

Ergonomic stress levels,personal characteristics,accident occurrence and sickness absence among factory workers

This study was designed to evaluate the association of a single, integrated measure of simultaneous exposure to a number of adverse work and environmental conditions, termed the Ergonomic Stress Level (E-S-L), on workers' accident and sickness absence rates. The factors determining the E-S-L were body motion and posture, physical effort, active hazards and environmental stressors. E-S-L evaluation was based on ‘walk-through’ hazard inventories, direct observations, measurements and interviews. Workers were assigned to one of four stress levels ranging from low (A) to high (D). Subjects were 729 males, aged 20-67 years, employed in five factories in Israel. A linear relationship between E-S-L and accident incidence was found, increasing from the lowest to the highest E-S-L. Moreover, workers more sensitive to environmental stressors, as indicated by their reported subjective annoyance, showed higher accident rates across all the ergonomic stress levels, a tendency which was statistically significant at levels C and D. On the other hand, sickness absence was significantly related to the overall subjective stress experienced, as manifested by reported job dissatisfaction and somatic complaints, and not directly to E-S-L. These findings highlight the role of aggregate work stress, coupled with individual sensitivity to environmental stressors, in increasing the risk of accidents.     

Assessing exposure to risk factors for work-related musculoskeletal disorders using Quick Exposure Check (QEC) in taxi drivers

Work-related musculoskeletal disorders (WMSDs) are a common health problem throughout the world. This study aimed to examine the risk factors that are involved in the development of WMSDs in taxi drivers. In total 382 taxi drivers were observed using Quick Exposure Check (QEC) observational tool, which allows practitioners and workers to assess four key areas of the body. Results of the QEC scores were found to be very high for the shoulder/arm, wrist/hand and neck, whereas the scores for the back were found to be high for static use and moderate for moving. The results also showed that the occupational risk factors for WMSDs were associated with restricted postures, repetitive movements, vibration, work related stress. Essential ergonomic interventions are needed to eliminate risk of exposures to WMSDs in taxi drivers.Relevance to industryThe study results have relevance for ergonomists, health and safety practitioners as well as the drivers themselves, and helpful for estimating the main physical risk factors for WMDSs before choosing a method prior to an ergonomic intervention in industry.     

Effects of user experience,working posture and joint hardness on powered nutrunner torque reactions

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force and upper limb muscle activity (electromyography (EMG)) due to the effects of operator experience, working height and distance, type of tool and fastener joint hardness were measured in this study with 15 experienced and 15 novice nutrunner users. The results show that when pistol grip handles were used to work on a horizontal surface, experienced users allowed an average handle displacement of 7.9°, while novice users allowed 11.5°. Average EMG scaled by reference voluntary contraction (RVC) at forearm flexors, forearm extensors and biceps were greater for experienced users (318% RVC, 285% RVC, 143% RVC, respectively) than for novice users (246% RVC, 219% RVC, 113% RVC, respectively). Experienced users exerted more grip force than novice users when using right angle handles, but less force when using pistol grip handles. The results suggest that it is possible to minimize tool handle displacement by adapting the workplace layout to permit different working postures for each user group.     

Effects of user experience, working posture and joint hardness on powered nutrunner torque reactions

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force and upper limb muscle activity (electromyography (EMG)) due to the effects of operator experience, working height and distance, type of tool and fastener joint hardness were measured in this study with 15 experienced and 15 novice nutrunner users. The results show that when pistol grip handles were used to work on a horizontal surface, experienced users allowed an average handle displacement of 7.9 degrees, while novice users allowed 11.5 degrees. Average EMG scaled by reference voluntary contraction (RVC) at forearm flexors, forearm extensors and biceps were greater for experienced users (318% RVC, 285% RVC, 143% RVC, respectively) than for novice users (246% RVC, 219% RVC, 113% RVC, respectively). Experienced users exerted more grip force than novice users when using right angle handles, but less force when using pistol grip handles. The results suggest that it is possible to minimize tool handle displacement by adapting the workplace layout to permit different working postures for each user group.     

R2: Drilling into concrete: Effect of feed force on handle vibration and productivity

Approximately 1.6 million commercial construction workers in the US use rotary hammer drills for drilling into concrete to insert anchor bolts or rebar. The exposure to vibration may lead to hand-arm vibration syndrome and other musculoskeletal disorders depending on handle vibration acceleration level, hand grip force, and duration of exposure. There is little information on the relationship between feed force (FF), e.g., the push force applied by the worker, and handle vibration. A robotic test bench for rotary hammer drills was used to evaluate the effects of different FF on handle vibration and productivity (e.g., penetration rate and holes drilled). Increasing FF from 95 to 163 N was associated with an increase in total weighted handle vibration (a_hv) of 7.2–8.5 m/s² (slope, p < 0.001) but from 163 to 211 N there was no change in vibration level (slope, p = 0.17). Increasing FF from 95 to 185 N was associated with an increase in penetration rate of 7.2–8.5 m/s² (slope, p < 0.001) but from 185 to 211 N there was no change in penetration rate (slope, p = 0.49). Based on the maximum allowable duration of exposure to hand vibration, specified by the ISO and ACGIH Action Limits, and the penetration rate, the drilling productivity, in m drilled per day, is greatest for the lowest FF tested. Contractors and construction workers should be informed that when drilling into concrete, the lowest exposure to harmful hand vibration and the best overall productivity occurs when the lowest operational FF is applied during hammer drilling.     

Dutch Musculoskeletal Questionnaire: description and basic qualities.

A questionnaire ('Dutch Musculoskeletal Questionnaire', DMQ) for the analysis of musculoskeletal workload and associated potential hazardous working conditions as well as musculoskeletal symptoms in worker populations is described and its qualities are explored using a database of 1575 workers in various occupations who completed the questionnaire. The 63 questions on musculoskeletal workload and associated potentially hazardous working conditions can be categorized into seven indices (force, dynamic and static load, repetitive load, climatic factors, vibration and ergonomic environmental factors). Together with four separate questions on standing, sitting, walking and uncomfortable postures, the indices constitute a brief overview of the main findings on musculoskeletal workload and associated potentially hazardous working conditions. Homogeneity of the indices is satisfactory. The divergent validity of the indices is fair when compared with an index of psychosocial working conditions and discomfort during exposure to physical loads. Worker groups with contrasting musculoskeletal loads can be differentiated on the basis of the indices and other factors. With respect to the concurrent validity, it appears that most indices and factors show significant associations with low back and/or neck-shoulder symptoms. This questionnaire can be used as a simple and quick inventory for occupational health services to identify worker groups in which a more thorough ergonomic analysis is indicated.     

Musculoskeletal symptoms among commercial fishers in North Carolina

Musculoskeletal symptoms were reported by 215 fishermen followed at 6-month intervals over 18 months. Exposure information was collected through field observation and in-depth ethnographic interviews allowing potential ergonomic stressors to be identified and catalogued by task and stage of work. Symptoms causing work interference in the last 12 months were reported by 38.5% of the cohort at baseline. Low back symptoms were the most common cause of work impairment (17.7%), followed equally by pain in the hands or wrists and shoulders (7%). Symptoms in any body region were more likely to have been reported among individuals who did not fish full-time and those who worked other jobs part or all year had significantly lower symptom prevalence; both likely reflect a healthy worker effect. A number of ergonomic stressors were identified in all stages of fishing with exposure variability dictated by some unpredictable factors such as weather; but also by type of boat, gear, crew size, and level of experience. Reducing ergonomic exposures associated with work among these traditional workers is important, regardless of whether they directly cause or contribute to their musculoskeletal symptoms, or aggravate existing pathology.     

The influence of wood hardness and logging operation on coupling forces exerted by lumberjacks during wood harvesting

Petrol chain saws commonly used in forestry cause mechanical vibration, which may lead to the development of non-specific disorders in upper extremities of the chain saw operator, referred to as hand-arm vibration syndrome (HAVS). Progress of HAVS depends on the intensity of mechanical vibration transmitted throughout the body, which is directly proportional to coupling forces applied to the vibration tool. The aim of the study was to measure coupling forces exerted by lumberjacks on chain saws and find correlation between force magnitude, hardness of cut wood and kind of logging operation.Coupling forces exerted by workers with right and left hands were measured by means of hydro-electronic force meter. All measurements were done during harvesting wood in real work conditions.Maximal temporary forces exerted by woodcutters reached 275 N. The smallest average forces of 27 N were registered while limbing. During felling and cross-cutting chain saw operators exerted larger forces, reaching 50 N.The findings of this study suggest that coupling forces used by woodcutters during logging depend on wood hardness and kind of logging operation.

Relevance to industry

This study shows the relationship between coupling forces, wood hardness and technique of cut which are further expected to enhance our knowledge on the assessment of vibration exposure. Nowadays, understanding how changes in harvesting technique affect the magnitude of coupling force, should lead to improvements in ergonomic design of the tool and the workplace.     

An investigation on the relationship between grip, push and contact forces applied to a tool handle

Owing to the strong dependence of the health risks associated with vibration exposure of the human hand and arm on hand force, a laboratory study was conducted to develop a methodology for measurement of the contact force at the tool handle–hand interface, and to identify the relationship between the contact force and the hand grip and push forces. A simulated tool handle fixture was realized in the laboratory to measure the grip and push forces using compression/extension force sensors integrated within the handle and a force plate, respectively. The contact force was derived through integration of the interface pressure over the contact area. These were measured using a capacitive pressure-sensing grid. The measurements were performed with 10 male subjects and three circular cross-section handles of different sizes under different combinations of grip and push forces. The hand–handle interface pressure data were analyzed to derive the contact force, as functions of the constant magnitudes of the grip and push forces, and the handle size. The results suggest that the hand–handle contact force is strongly dependent upon not only the grip and push forces but also the handle diameter. The contact force for a given handle size can be expressed as a linear combination of grip and push forces, where the contribution of the grip force is considerably larger than that of the push force. The results further suggest that a linear relation can characterize the dependence of the contact force on the handle diameter. The validity of the proposed relationship is demonstrated by evaluating the magnitudes of errors between the estimated contact forces with the measured data for the range of handle diameters, and grip and push forces considered in the study.

Relevance to industry

The methodology proposed in this study can be applied to measure the effective hand–handle contact force at workplaces for assessing the health risks associated with exposure to hand-transmitted vibration exposure and hand–wrist cumulative trauma. The relationship proposed in the study could be effectively applied for estimating the hand–handle contact force from known grip and push forces that are conveniently and directly measurable in laboratory studies involving vibration analyses of the human hand, power tools and relevant vibration attenuation devices. It is expected to be most useful in field applications, where it could provide an estimate of the range of magnitudes of the hand-grip force applied to the handle of an actual tool, which is quite difficult and expensive to measure. The relationship is also expected to contribute to the on-going standardization efforts for defining a correction factor to account for the effects of hand force on the vibration transmission and hand injuries.     

Gender differences in prevalence of upper extremity musculoskeletal disorders

A literature review was conducted on the current literature base to determine the strength of support for the hypothesis that women experience higher prevalences of upper extremity musculoskeletal disorders (UEMSDs) than men. Fifty-six articles were reviewed for data on gender differences in frequency, incidence or prevalence rates for musculoskeletal disorders specific to the upper extremities. These articles included both general and working populations. The majority of the studies showed that women had significantly higher incidences of various types of UEMSDs than men. This trend was consistently observed in studies based on self-report or plant/workers compensation records, with and without physical examination, and after adjusting for potential confounders such as age and physical work factors. With men as the referent, the odds ratio (OR) or prevalence ratio (PR) for UEMSDs ranged from 0.85 to 10.05 for self report. For self report combined with physical examination, the OR/PR ranged from 0.66 to 11.4. The OR/PR for carpal tunnel syndrome (CTS) ranged from 0.6 to 2.87 with confounder adjustment. These findings suggest that women do have significantly higher prevalences than men for many types of UEMSDs, even after controlling for the type of data source and confounders such as age or work factors.     

Gender differences in prevalence of upper extremity musculoskeletal disorders

A literature review was conducted on the current literature base to determine the strength of support for the hypothesis that women experience higher prevalences of upper extremity musculoskeletal disorders (UEMSDs) than men. Fifty-six articles were reviewed for data on gender differences in frequency, incidence or prevalence rates for musculoskeletal disorders specific to the upper extremities. These articles included both general and working populations. The majority of the studies showed that women had significantly higher incidences of various types of UEMSDs than men. This trend was consistently observed in studies based on self-report or plant/workers compensation records, with and without physical examination, and after adjusting for potential confounders such as age and physical work factors. With men as the referent, the odds ratio (OR) or prevalence ratio (PR) for UEMSDs ranged from 0.85 to 10.05 for self report. For self report combined with physical examination, the OR/PR ranged from 0.66 to 11.4. The OR/PR for carpal tunnel syndrome (CTS) ranged from 0.6 to 2.87 with confounder adjustment. These findings suggest that women do have significantly higher prevalences than men for many types of UEMSDs, even after controlling for the type of data source and confounders such as age or work factors.