Non-neutral Postures Research Articles

Wrist and carpal tunnel size and shape measurements: Effects of posture

Background Wrist anthropometrics and posture have been implicated in the development of carpal tunnel syndrome, yet it remains unclear how external measurements relate to carpal tunnel parameters in neutral and non-neutral postures. The purposes of this study were (i) to evaluate the effect of slice orientation on several indices of carpal tunnel size and shape and (ii) to examine the relationship between carpal tunnel and external wrist dimensions. Methods Three-dimensional static models were generated to measure carpal tunnel and wrist parameters for six wrists in three wrist postures (30° flexion, neutral and 30° extension). A simulated imaging plane enabled measurement of four carpal tunnel dimensions and two shape indices throughout the tunnel length, using “axial” and “tunnel” slice orientations (perpendicular to forearm and tunnel, respectively). Findings Correction for tunnel orientation eliminated posture-related changes in tunnel size and shape noted at the distal end using “axial” alignment. “Tunnel” alignment reduced average carpal tunnel area and depth by nearly 15% in extension, but generally less than 5% in neutral and 2% in flexion. Subsequently, “tunnel” alignment also decreased carpal tunnel and non-circularity ratios to reveal a flatter, more elliptical shape throughout the tunnel in extension than neutral and flexion. Wrist dimensions correlated significantly with tunnel dimensions, but not tunnel shape, while wrist shape correlated significantly with tunnel shape, area and depth. Interpretations Slice alignment with the carpal tunnel may improve the consistency of findings within and between patient and control populations, and enhance the diagnostic utility of imaging in clinical settings.

Smaller external notebook mice have different effects on posture and muscle activity

Background. Extensive computer mouse use is an identified risk factor for computer work-related musculoskeletal disorders; however, notebook computer mouse designs of varying sizes have not been formally evaluated but may affect biomechanical risk factors. Methods. Thirty adults performed a set of mouse tasks with five notebook mice, ranging in length from 75 to 105 mm and in width from 35 to 65 mm, and a reference desktop mouse. An electro-magnetic motion analysis system measured index finger (metacarpophalangeal joint), wrist and forearm postures, and surface electromyography measured muscle activity of three extensor muscles in the forearm and the first dorsal interrosseus. Findings. The smallest notebook mice were found to promote less neutral postures (up to 3.2° higher metacarpophalangeal joint adduction; 6.5° higher metacarpophalangeal joint flexion, 2.3° higher wrist extension) and higher muscle activity (up to 4.1% of maximum voluntary contraction higher wrist extensor muscle activity). Participants with smaller hands had overall more non-neutral postures than participants with larger hands (up to 5.6° higher wrist extension and 5.9° higher pronation); while participants with larger hands were more influenced by the smallest notebook mice (up to 3.6° higher wrist extension and 5.5% of maximum voluntary contraction higher wrist extensor values). Self-reported ratings showed that while participants preferred smaller mice for portability; larger mice scored higher on comfort and usability. Interpretation. The smallest notebook mice increased the intensity of biomechanical exposures. Longer term mouse use could enhance these differences, having a potential impact on the prevention of work-related musculoskeletal disorders.

Test–retest reliability and concurrent validity of a web-based questionnaire measuring workstation and individual correlates of work postures during computer work

Introduction: “Ergonomic” questionnaires are widely used in epidemiological field studies to study the association between workstation characteristics, work posture and musculoskeletal disorders among office workers. Findings have been inconsistent regarding the putative adverse effect of work postures. Underestimation of the true association might be present in studies due to misclassification of subjects to risk (i.e. exposed to non-neutral working postures) and no-risk categories (i.e. not exposed to non-neutral working postures) based on questionnaire responses. The objective of this study was to estimate the amount of misclassification resulting from the use of questionnaires. Methods: Test–retest reliability and concurrent validity of a newly developed questionnaire was assessed. This questionnaire collects data on workstation characteristics and on individual characteristics during computer work (i.e. work postures, movements and habits). Pictures were added where possible to provide visual guidance. The study population consisted of 84 office workers of a research department. They filled out the questionnaire on the Internet twice, with an in-between period of 2 weeks. For a subgroup of workers ( n=38), additional on-site observations and multiple manual goniometer measurements were performed. Results: Percentage agreement ranged between 71% and 100% for the test–retest analysis, between 31% and 100% for the comparison between questionnaire and on-site observation, and between 26% and 71% for the comparison between questionnaire and manual goniometer measurements. For 9 out of 12 tested items, the percentage agreement between questionnaire and manual goniometer measurements was below 50%. Conclusions: The questionnaire collects reliable data on workstation characteristics and some individual characteristics during computer work (i.e. work movements and habits), but does not seem to be useful to collect data on work postures during computer work in epidemiological field studies among office workers.

Evaluating Ergonomic Stresses in North Carolina Commercial Crab Pot and Gill Net Fishermen

There are challenges in evaluating physical demands of commercial fishing, including identifying sources of exposure variability. Low back biomechanical stresses associated with crab pot and gill net fishing were estimated; the variability was partitioned between and within fishing type, crew size, job title, and worker to improve understanding of risk factors for low back injury. The authors observed 162 person-hours of work among 25 North Carolina commercial fishermen on 16 crews. Postures and forces during fishing tasks were measured through direct and indirect observation using two methods to determine the percentage of time fishermen were exposed to high levels of low back stress. A multilevel linear model estimated exposure variability for the dependent variables by four nesting variables: fishing type, crew size, job title, and worker. Fishermen set and pulled crab pots or gill nets for 80% of the workday. Twenty-five percent of that time was spent handling gear. For both fishing types, handling heavy loads produced high peak compression values (3586 N to 5315 N) and high NIOSH lifting index values (3.3 to 5.4), but these tasks represent a small percentage of the overall work time (0 to 14%). The majority of exposure variation in non-neutral trunk posture and/or force > 9 kg, handling materials, NIOSH Lifting Index > 1, and Lumbar Motion Monitor probability of high-risk group membership > 70% was accounted for by fishing type (range 60 to 91%). Crew size was not an important source of variability for these six variables when fishing type and job title were accounted for in the model; but in the model restricted to crab pot fishing, crew size accounted for 51 to 88% of the variability in low back stress. For both models, job title comprised the majority of exposure variability for NIOSH Lifting Index > 3.0 (46 and 65%) and worker comprised the majority of variability for spine compression > 3400 N (54 and 65%). The magnitude and duration of musculoskeletal loads experienced by fishermen vary by the type of fishing and the tasks performed by the worker. Understanding this variability may help researchers target ergonomic interventions for this work population.

Ergonomic Evaluation of the Ambulance Interior to Reduce Paramedic Discomfort and Posture Stress

This study aims to evaluate safety and accessibility of an advanced life support (ALS) ambulance interior. The standard ambulance's interior design is unsatisfactory based on perceived discomfort and postures that constrain paramedics and medical staff, resulting in unsafe treatment of patients, mainly when being transported. Two procedures were used to evaluate performance during a wide range of rescue tasks: a survey, based on questionnaires, interviews, and observation of paramedics performing routine tasks; and upper body and back posture analysis, based on postural considerations. Findings revealed that 74% of the paramedics stated that the location of the paramedic's seat is inefficient while they perform clinical procedures; 94% found the bench uncomfortable; 77% felt that the vertical distance between the bench and the stretcher is too far; and 86% needed to steady themselves when the vehicle was moving. Posture analysis showed that paramedics undergo several nonneutral back postures, including twisted back (>20 degrees) and sitting with back flexion between 20 degrees and 45 degrees. Because the interior of the ALS ambulance was found to be unsatisfactory both to paramedics and patients, alternative design issues are proposed. The suggested practical layout contains four main modifications: (a) replacing the bench with two adjustable paramedic seats, (b) redesigning the medical cabinet for easy access, (c) adding an adjustable folding seat opposite the two new seats, and (d) adding a swiveling base and lifting apparatus that will accommodate the stretcher and enable better accessibility to patients by the paramedic personnel.

Predictions of health risks associated with the operation of load-haul-dump mining vehicles: Part 2—Evaluation of operator driving postures and associated postural loading

Driving posture and whole-body vibration (WBV) (reported in Part 1) were measured during the operation of seven load-haul-dump (LHD) mining vehicles. Simultaneous exposure to WBV and non-neutral postures could increase an LHD operator's risk of developing a musculoskeletal injury. The percentage of work time spent in neutral, moderate and severe neck rotation, trunk rotation, trunk flexion and trunk lateral bend postures was determined via a 3DMatch analysis of 1 h of videotaped driving for each LHD operator. Peak and cumulative spinal loads at the L4/L5 level also were estimated using 3DMatch. Operators averaged 89% of the time with their necks rotated more than 40°, 3% of the time with the trunk rotated more than 30°, 24% of the time with the trunk in forward flexion between 20° and 45°, and 16% of the time with the trunk in lateral bend between 15° and 30°. The average maximal compressive force (based on static measure estimations associated with posture only) at the L4/L5 level of the spine was 2176 N, and the cumulative compressive load for an 8-h work shift was 34 MN. A total injury risk score, which considered vibration exposure, working postures and spinal loading, was correlated with LHD operator musculoskeletal injury reports. Therefore, exposure to vibration and non-neutral working postures appears to increase musculoskeletal injury risk amongst LHD operators. Relevance to industry Equipment operators have the potential to be exposed to several factors that can contribute to the onset of adverse health effects. This study illustrates the importance of considering the combined impact of vibration exposure and non-neutral working postures in order to reduce injury risk associated with LHD vehicle operation.

Evaluation of the carpal tunnel based on 3-D reconstruction from MRI

While deviated wrist postures have been linked to the development of carpal tunnel syndrome, the relative contributions of posture-related changes in size, shape and volume of the carpal tunnel contribute to median nerve compression are unclear. The purpose of this study was two-fold: (1) to reconstruct the carpal tunnel from MRI data in neutral and non-neutral (30° extension, 30° flexion) wrist postures, and (2) to evaluate errors associated with off-axis imaging. Three-dimensional reconstruction of the carpal tunnels of 8 volunteers from the university community revealed that the orientation of the carpal tunnel was not directly explained by external wrist angle. The average orientation of the carpal tunnel was extended in all postures, ranging from 25°±9° in extension, 13°±5° in neutral and 4°±4° in the flexed wrist. Changing the orientation of the imaging plane to be perpendicular to the reconstructed carpal tunnel revealed that axial images overestimated cross-sectional area by an average of nearly 10% in extension, 4% in neutral and less than 1% in flexion. Similarly, adjusting the imaging plane to be perpendicular to external wrist angle overestimated cross-sectional area by an average of 2% in extension, 4% in neutral and 24% in flexion. Distortion of the carpal tunnel shape also became evident with rotation of the imaging plane. The data suggest that correction for the orientation of the carpal tunnel itself to be more appropriate than relying on external wrist angle. Computerized reconstruction provided detailed anatomic visualization of the carpal tunnel, and has created the framework to develop a biomechanical model of the carpal tunnel. Similar reconstruction of the tissue structures passing through (median nerve and flexor tendons) and entering the carpal tunnel (muscle tissue) will enable evaluation and partitioning of median nerve injury mechanisms.

An evaluation of backpack harness systems in non-neutral torso postures

Much of the research on backpack design has been focused on spinal loading/biomechanics while the wearer is in a neutral/upright trunk posture, such as those employed by outdoor enthusiasts and schoolchildren. This research has led to some important harness design improvements that reduce trunk muscle exertions, fatigue and improve overall comfort. There are number of occupations, however, wherein workers wear back-mounted packs/devices (e.g. air tanks) while working in non-neutral trunk postures. The objective of the current study was to evaluate the effects of these non-neutral postures on biomechanical loading and then reconsider the backpack system design recommendations. Fifteen participants were asked to support a 18.2 kg load on their back while assuming static forward flexed postures of the torso (15°, 30°, 45°, and 60° of sagittal bend). The mass on the back was attached to the participant through two different harness mechanisms: a basic harness design (as seen on college student backpacks) and a more advanced design containing lateral stiffness rods and a weight-bearing hip belt (as seen on backpacks for hikers). While performing these static, posture maintenance tasks, the activation levels of the bilateral trapezius, erector spinae, and rectus abdominis were collected. Participants also provided subjective ratings of comfort. The results showed that there was a significant interaction between harness type and forward flexion angle for the trapezius and the erector spinae muscles. The normalized EMG for the trapezius muscles showed a 14% and 11% reduction in muscle activity at 15° and 30°, respectively, with the advanced design but these positive effects of the advanced design were not found at the greater flexion angles. Likewise the erector spinae muscles showed a 24% and 14% reduction in muscle activity at 15° and 30°, respectively, with the advanced design harness but these effects of the advanced design were not found at the greater forward flexion angles. The level of forward flexion angle affected the rectus abdominis muscle activity, but neither the harness type main effect nor the interaction of harness type and forward flexion angle was significant. The subjective survey results agreed with the EMG results and showed the advanced design harness was generally more comfortable with respect to the shoulder and low back areas. Collectively, the subjective and objective results show a significant improvement with the advanced harness system but also note an interesting interaction with degree of sagittal flexion, indicating a diminished effectiveness of the design improvements at forward flexed postures. Design criteria for harness systems in these forward flexed postures are discussed.

Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors

In order to determine differences in biomechanical risk factors across computer tasks, a repeated measures laboratory experiment was completed with 30 touch-typing adults (15 females and 15 males). The participants completed five different computer tasks: typing text, completing an html-based form with text fields, editing text within a document, sorting and resizing objects in a graphics task and browsing and navigating a series of intranet web pages. Electrogoniometers and inclinometers measured wrist and upper arm postures, surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles and a force platform under the keyboard and force-sensing computer mouse measured applied forces. Keyboard-intensive tasks were associated with less neutral wrist postures, larger wrist velocities and accelerations and larger dynamic forearm muscle activity. Mouse-intensive tasks (graphics and intranet web page browsing) were associated with less neutral shoulder postures and less variability in forearm muscle activity. Tasks containing a mixture of mouse and keyboard use (form completion and text editing) were associated with higher shoulder muscle activity, larger range of motion and larger velocities and accelerations of the upper arm. Comparing different types of computer work demonstrates that mouse use is prevalent in most computer tasks and is associated with more constrained and non-neutral postures of the wrist and shoulder compared to keyboarding.

Whole-Body Vibration Exposure and Non-neutral Neck Postures During Occupational Use of All-terrain Vehicles

The purpose of this study was to characterize whole-body vibration (WBV) exposure from various all-terrain vehicles (ATVs) like snowgroomers, snowmobiles and forwarders, and to investigate how frequently the drivers' cervical spine is positioned in a non-neutral rotational position during operation. Field measurements of WBV were measured according to the international standard ISO 2631-1 in 19 ATVs. Simultaneous recordings of frequency and duration of rotational neck movements exceeding 15 degrees were achieved through an observational method, PEOflex. The sum of the vectors of frequency-weighted r.m.s. acceleration varied between 0.5 and 3.5 m s(-2), which meant that for most vehicles they exceeded the action value stated by the European Union (0.5 m s(r.m.s.)(-2)). In general, snowmobiles achieved the highest vibration total value. The dominant vibration direction for the snowmobile was the x-axis but the z-axis also had relatively high vibration dose values and maximal transient vibration values. The z-axis was the dominant vibration direction for the snowgroomer and the y-axis for the forwarder. Frequency and duration of non-neutral rotational neck postures were relatively low for all driver categories. Vibration magnitudes in ATVs are considerably high than the EU's action value and the health guidance caution zones in ISO 2631-1. The dominant vibration direction varies depending on the machine type. Duration and frequency of non-neutral rotational positions do not seem to constitute single ergonomic risk factors for musculoskeletal symptoms in the neck among professional drivers of ATVs. However, synergistic effects with other factors are conceivable.

Relation between Whole-Body Postural Discomfort and Body-Part Postures for Working Postures of Automobile Assembly Tasks

Observational methods have been widely used for identifying posture-related risks in industry. In those methods, a single score of postural load for a working posture is required for evaluating the level of corrective actions, on the basis of each body-parts stressfulness evaluated. However, most existing methods have transformed stressfulness for several joints into a postural load based on subjective judgments of ergonomic experts, not on an objective basis. In this study, the relationship between body-part postural load and whole-body discomfort for working postures was investigated. A laboratory experiment was conducted to evaluate static postures frequently assumed during the automobile assembly tasks, based on perceived discomfort. The results showed that the postural load was strongly associated with the combination of discomfort for non-neutral joint postures. The more joints severely deviated from neutral position were involved in a working posture, the higher level of the whole-body postural discomfort was imposed. In a regression analysis, the relationship was quite well fitted with a linear model, in which shoulder motion was found to be the most affecting factor on the whole-body postural stresses. The linear relationship is expected to be useful for better understanding adverse effect of joint motions on a whole-body posture.

Task content and physical ergonomic risk factors in construction ironwork

Construction ironwork (CI) has been identified as a trade wherein the exposures to ergonomic risk factors are high. In this study, quantitative exposure assessments for seven specific ironwork tasks selected from the four main specialties of CI—machinery moving/rigging, ornamental, reinforcing, structural—were performed. A total of 13,821 observations were made using the work-sampling, specialty-task-activity-based analysis method called PATH (posture, activity, tools, and handling) and a taxonomy developed specifically for CI. The PATH data provided specialty-task-activity estimates of the percentage of time ironworkers spent in specified postures of the trunk, arms, and legs, and also gave estimated frequencies of manual materials handling activities as well as 11 other predefined activities. Depending on the specialty-task-activity performed, results showed that ironworkers spent anywhere from 13% to 48% of their work time in non-neutral trunk postures; worked with one or both arms at or above shoulder level 6–21% of the time; and stood on uneven/unstable work surfaces 3–53% of the time. The type of activity performed was consistently found to be a major predictor of the frequency of work time spent in non-neutral postures for the trunk, legs, and arms. Relevance to industry These results can be used to target hazardous activities in CI such as rebar and structural ironwork and confirms the need for specialty-task-activity-specific information within each construction trade on exposures and worker activities so that the most appropriate ergonomic interventions can be designed and implemented.

Work-related musculoskeletal disorders: the epidemiologic evidence and the debate

The debate about work-relatedness of musculoskeletal disorders (MSDs) reflects both confusion about epidemiologic principles and gaps in the scientific literature. The physical ergonomic features of work frequently cited as risk factors for MSDs include rapid work pace and repetitive motion, forceful exertions, non-neutral body postures, and vibration. However, some still dispute the importance of these factors, especially relative to non-occupational causes. This paper addresses the controversy with reference to a major report recently commissioned by the US Congress from the National Research Council (NRC) and Institute of Medicine (IOM) (2001). The available epidemiologic evidence is substantial, but will benefit from more longitudinal data to better evaluate gaps in knowledge concerning latency of effect, natural history, prognosis, and potential for selection bias in the form of the healthy worker effect. While objective measures may be especially useful in establishing a more secure diagnosis, subjective measures better capture patient impact. Examination techniques still do not exist that can serve as a “gold standard” for many of the symptoms that are commonly reported in workplace studies. Finally, exposure assessment has too often been limited to crude indicators, such as job title. Worker self-report, investigator observation, and direct measurement each add to understanding but the lack of standardized exposure metrics limits ability to compare findings among studies. Despite these challenges, the epidemiologic literature on work-related MSDs—in combination with extensive laboratory evidence of pathomechanisms related to work stressors—is convincing to most. The NRC/IOM report concluded, and other reviewers internationally have concurred, that the etiologic importance of occupational ergonomic stressors for the occurrence of MSDs of the low back and upper extremities has been demonstrated.

Physical and psychosocial risk factors for lateral epicondylitis: a population based case-referent study

Aims: To assess the importance of physical and psychosocial risk factors for lateral epicondylitis (tennis elbow). Methods: Case-referent study of 267 new cases of tennis elbow and 388 referents from...

Quantification of ergonomic hazards for ironworkers performing concrete reinforcement tasks during heavy highway construction.

A study was conducted to assess the ergonomic hazards of ironwork job tasks associated with concrete reinforcement work at a large highway construction site. PATH (posture, activity, tools, and handling) analysis, a work-sampling method, was used to provide task-based estimates of the percentage of time ironworkers spent in specified postures of the trunk, arms, and legs; performed activities; used tools; and handled loads. A total of 2128 PATH observations were made of 17 ironworkers performing 5 job tasks: (1) ground-level reinforcement bar (rebar) construction, (2) wall rebar construction, (3) ventilation rebar construction, (4) preparation work, and (5) supervising. Nonneutral trunk postures were observed frequently (exceeding 30%) and manual material handling (MMH) was the most commonly observed activity (exceeding 20%) for all job tasks except supervising. The percentage of time workers spent in specific postures, activities performed, tool use, and MMH activities differed significantly between the five main job tasks, even when supervising was excluded from the analysis. It was concluded that ironworkers are exposed to significant ergonomic hazards when performing concrete reinforcing tasks, and that opportunities exist for the implementation of ergonomic interventions. Further, the results of this study can be used to target specific hazardous tasks for ergonomic interventions and confirms the need to use a task-based exposure assessment strategy to properly assess ergonomic risk profiles for nonstructured jobs such as construction.

LOW BACK PAIN IN PORT MACHINERY OPERATORS

The occurrence of several types of low back pain (LBP) was investigated by a standardized questionnaire in a group of 219 port machinery operators exposed to whole-body vibration (WBV) and postural load and in a control group of 85 maintenance workers employed at the same transport company. The group of port machinery operators included 85 straddle carrier drivers, 88 fork-lift truck drivers, and 46 crane operators. The vector sum of the frequency-weighted r.m.s. acceleration of vibration measured on the seatpan of port vehicles and machines averaged 0·90 m/s2 for fork-lift trucks, 0·48 m/s2 for straddle carriers, 0·53 m/s2 for mobile cranes, and 0·22 m/s2 for overhead cranes. The 12-month prevalence of low back symptoms (LBP, sciatic pain, treated LBP, sick leave due to LBP) was significantly greater in the fork-lift truck drivers than in the controls and the other two groups of port machinery operators. After adjusting for potential confounders, the prevalence of low back symptoms was found to increase with the increase of WBV exposure expressed as duration of exposure (driving years), equivalent vibration magnitude (m/s2), or cumulative vibration exposure (yr m2/s4). An excess risk for lumbar disc herniation was observed in the port machinery operators with prolonged driving experience. In both the controls and the port machinery operators, low back complaints were strongly associated with perceived postural load assessed in terms of frequency and/or duration of awkward postures at work. Multivariate analysis showed that vibration exposure and postural load were independent predictors of LBP. Even though the cross-sectional design of the present study does not permit firm conclusions on the relationship between WBV exposure and low back disorders, the findings of this investigation provide additional epidemiological evidence that seated WBV exposure combined with non-neutral trunk postures, as while driving, is associated with an increased risk of long-term adverse health effects on the lower back.

Effects of notebook computer configuration and task on user biomechanics, productivity, and comfort

This study took a comprehensive approach to evaluating effects of using a notebook computer stand-alone or along with inexpensive peripheral input devices. The study examined effects on biomechanics, productivity, and discomfort, and considered the impact of both computer configuration and task performed. It was hypothesized that, in general, the stand-alone configuration would induce greater postural fixity and more non-neutral postures than configurations with peripheral input devices. Dependent measures included muscle activity, posture and posture variation/fixity, productivity, and subjective assessments of discomfort and preference. The data were generally consistent with the hypothesis, though some biomechanical advantages were identified for each configuration; specifics and exceptions are discussed, along with reasons for a general recommendation for the use of an external mouse, or mouse and keyboard (without number pad) when using a notebook computer for an extended period of time, as in a desktop replacement scenario. Relevance to industry Notebook computer use is rapidly increasing, in industry and schools. Yet the notebook form factor is inconsistent with a number of current design recommendations. Little research concerning physical ergonomics of notebook computer use has been conducted, so recommendations for use are currently limited and not strongly supported by objective evidence.

The diagnosis of disorders caused by hand-transmitted vibration: Southampton Workshop 2000.

To identify the current state of knowledge, current uncertainties and future needs related to the diagnosis of disorders associated with the use of vibratory hand-held tools. An international workshop was convened with invited experts, medical doctors, scientists and engineers familiar with hand-transmitted vibration and the diagnosis of vascular, neurological and musculoskeletal disorders. This paper records the general conclusions from four panel discussions. For the most common vascular disorder (vibration-induced white finger), the principal symptom and sign involves attacks of well-demarcated finger blanching (Raynaud's phenomenon); low finger systolic blood pressure following cooling is indicative of vibration-induced white finger and zero finger systolic blood pressure can confirm an attack of Raynaud's phenomenon. For neurological disorders, some symptoms can exist without detectable signs and some signs can exist without symptoms; numbness and tingling are commonly reported but neurological changes may be present without these symptoms. The pathogenesis of musculoskeletal disorders in users of vibratory tools is not clear; symptoms may include pain that may not be associated with abnormal results in objective tests. For both neurological and musculoskeletal disorders, a thorough neuromuscular and skeletal examination is required; diagnosis must consider the work history and medical history, the results of physical examination and any objective tests in addition to other factors (e.g. age, smoking, alcohol, systemic disorders, medication and neurotoxic agents) that might have contributed to symptoms, signs and test results. While vibration-induced white finger is caused by vibration, some neurological and musculoskeletal disorders are the result of work with vibratory tools where the separate roles of vibration, repetitive movements, grip and push forces, non-neutral postures and any other ergonomic stressors are often unclear. Such disorders may be more easily identified as being caused by the work rather than by exposure to hand-transmitted vibration per se. A person found to have developed disorders induced by either vibration or the work situation should not be returned to the same vibration exposure or work without any changes expected to lessen the risks.

Interobserver repeatability and validity of an observation method to assess physical loads imposed on the upper extremities

Interobserver repeatability and validity were assessed for a new semiquantitative, time-based observation method for the estimation of physical loads imposed on the upper extremities. Six risk factors of upper extremity disorders were included in the method: repetitive use of hand, use of hand force, pinch grip, non-neutral wrist posture, elevation of upper arm, local mechanical pressure. Two occupational health nurses were trained to use the method. They observed 127 work cycles at a food-processing plant and a paper mill. The method was validated against expert observations from the video, continuous recordings of myoelectric activity (EMG) of forearm muscles, and wrist posture measured with goniometers. Interobserver repeatability was good or moderate for repetitive use of hand, hand force, pinch grip (range κ = 0.58–0.71 on the right; 0.60–0.61 on the left side). Interobserver repeatability was moderate or poor for non-neutral wrist posture, elevation of the upper arm and local mechanical pressure. Validity ranged from moderate to good for repetitive use of hand, use of hand force, pinch grip and non-neutral wrist posture when expert observation was used as reference standard. When observations were validated against force estimations (EMG) and wrist goniometer data, validity was poor. In the absence of generally accepted reference values, arbitrarily chosen limits were used for the proportional duration of some physical load factors. Studies should be carried out to assess the limits that best diVerentiate between safe and hazardous jobs.

Part I: Participatory Ergonomics Approach to Waste Container Handling Utilizing a Multidisciplinary Team

This multidisciplinary team approach to waste container handling, developed within the Grassroots Ergonomics process, presents participatory ergonomic interpretations of quantitative and qualitative aspects of this process resulting in a peer developed training. The lower back, shoulders, and wrists were identified as frequently injured areas, so these working postures were a primary focus for the creation of the workers' training. Handling procedures were analyzed by the team to identify common cycles involving one 5 gallon (60 pounds), two 5 gallons (60 and 54 pounds), 30 gallon (216 pounds), and 55 gallon (482 pounds) containers: lowering from pallet, transporting to/from transport vehicles, loading/unloading on transport vehicles, and loading onto pallet. Eleven experienced waste container handlers participated in this field analysis. Ergonomic exposure assessment tools measuring these field activities included posture analysis, posture targeting, Lumbar Motion Monitor™(LMM), and surface electromyography (sEMG) for the erector spinae, infraspinatus, and upper trapezius muscles. Posture analysis indicates that waste container handlers maintained non-neutral lower back postures (flexion, lateral bending, and rotation) for a mean of 51.7% of the time across all activities. The right wrist was in non-neutral postures (radial, ulnar, extension, and flexion) a mean of 30.5% of the time and the left wrist 31.4%. Non-neutral shoulder postures (elevation) were the least common, occurring 17.6% and 14.0% of the time in the right and left shoulders respectively. For training applications, each cycle had its own synchronized posture analysis and posture target diagram. Visual interpretations relating to the peak force modifications of the posture target diagrams proved to be invaluable for the workers' understanding of LMM and sEMG results (refer to Part II). Results were reviewed by the team's field technicians and their interpretations were developed into ergonomic training that address the issues originally raised. This training includes intervention methods, ergonomic tools used, data acquired, and effects of waste container handling techniques on lower back, shoulder, and wrists and methods to help proactively reduce injuries associated with this profession.