Methods for assessing the physical demands of manual lifting: a review and case study from warehousing.

Assessment of the physical demands of potentially hazardous manual material handling (MMH) activities is fundamental to the prevention of disabilities from occupationally related low back pain, a problem costing the nation billions of dollars annually. Although there is a variety of ergonomic assessment methods available for assessing MMH activities, there is a lack of practical information to assist users in choosing the most appropriate assessment methods of a particular job. This article reviews currently available assessment methods and presents case study results of a physically demanding repetitive manual lifting job in two grocery warehouses. The case study will provide a framework for a comparison of the methods and a discussion of relevant application issues designed to assist users in selecting appropriate methods for assessing MMH jobs. Based on the results of the study, it is concluded that all of the ergonomic methods were in agreement that the job of grocery selector has a high level of risk for low back pain. Differences between the methods were noted, however, that should be considered when choosing a specific method for a specific application.

Back pain among workers in the United States: national estimates and workers at high risk.

Back pain accounts for about one fourth of workers' compensation claims in the United States. The Occupational Health Supplement to the 1988 National Health Interview Survey provided an opportunity to assess the scope of this problem. The 30,074 respondents who worked in the 12 months before the interview were defined as "workers", and those with back pain every day for a week or more during that period were defined as "cases." A weighting factor was applied to the answers to derive national estimates. In 1988, about 22.4 million back pain cases (prevalence 17.6%) were responsible for 149.1 million lost workdays; 65% of cases were attributable to occupational activities. For back pain attributed to activities at work, the risk was highest for construction laborers among males (prevalence 22.6%) and nursing aides among females (18.8%). Our analyses show that back pain is a major cause of morbidity and lost production for U.S. workers and identifies previously unrecognized high risk occupations, such as carpenters, automobile mechanics, maids, janitors, and hairdressers, for future research and prevention.

Prevalence and work-relatedness of self-reported carpal tunnel syndrome among U.S. workers: analysis of the Occupational Health Supplement data of 1988 National Health Interview Survey.

To estimate the prevalence and work-relatedness of self-reported carpal tunnel syndrome (CTS) among U.S. workers, data from the Occupational Health Supplement of 1988 National Health Interview Survey (NHIS) were analyzed. Among 127 million "recent" workers" who worked during the 12 months prior to the survey, 1.47% (95% CI: 1.30; 1.65), or 1.87 million self-reported CTS, and 0.53% (95% CI: 0.42; 0.65), or 675,000, stated that their prolonged hand discomfort was called CTS by a medical person. Occupations with the highest prevalence of self-reported CTS were mail service, health care, construction, and assembly and fabrication. Industries with the highest prevalence were food products, repair services, transportation, and construction. The risk factor most strongly associated with medically called CTS was exposure to repetitive bending/twisting of the hands/wrists at work (OR = 5.2), followed by race (OR = 4.2; whites higher than nonwhites), gender (OR = 2.2; females higher than males), use of vibrating hand tools (OR = 1.8), and age (OR = 1.03; risk increasing per year). This result is consistent with previous reports in that repeated bending/twisting of the hands and wrists during manual work is etiologically related to occupational carpal tunnel syndrome.

The US prevalence of self-reported carpal tunnel syndrome: 1988 National Health Interview Survey data.

To estimate the prevalence of carpal tunnel syndrome among US adults, data from the Occupational Health Supplement of the 1988 National Health Interview Survey were analyzed. Based on a sample of 44,233 households (response rate, 91.5%), an estimated 1.55% (2.65 million) of 170 million adults self-reported carpal tunnel syndrome in 1988. Females and Whites had a higher prevalence of self-reporting carpal tunnel syndrome than males and non-Whites, respectively. Among 127 million adults who worked during the 12 months before the survey, 0.53% (0.68 million) reported that their "prolonged" hand discomfort was called carpal tunnel syndrome by a health care provider.

Musculoskeletal disorders among visual display terminal users in a telecommunications company.

The relationship between workplace factors and work-related upper extremity musculoskeletal disorders (UE disorders) was assessed in a cross-sectional study of 533 telecommunication employees utilizing video display terminals (VDTs). Cases of UE disorders were defined using symptom questionnaires and physical examinations. Data on demographics, individual factors (medical conditions and recreational activities), work organization and practices, and psychosocial aspects of work, including electronic performance monitoring (EPM), were obtained by questionnaire. Associations between workplace factors and UE disorders were assessed by multiple logistic models generated for each of the four UE areas (neck, shoulder, elbow, hand/wrists). One-hundred and eleven (22%) participants met our case definition for UE disorders. Probable tendon-related disorders were the most common (15% of participants). Probable nerve entrapment syndromes were found in 4% of participants. The hand/wrist was the area most affected, 12% of participants. The following variables had associations in the final models (p < 0.05) with at least one of the four UE disorders, although the strength of these associations were modest. Non-white race, a diagnosis of a thyroid condition (self-reported) use of bifocals at work, and seven psychosocial variables (fear of being replaced by computers, increasing work pressure, surges in workload, routine work lacking decision-making opportunities, high information processing demands, jobs which required a variety of tasks and lack of a production standard) were associated with UE disorders. This study indicates that work-related UE musculoskeletal disorders are relatively common among telecommunication workers who use VDTs, and adds to the evidence that the psychosocial work environment is related to the occurrence of these disorders.

Revised NIOSH equation for the design and evaluation of manual lifting tasks.

In 1985, the National Institute for Occupational Safety and Health (NIOSH) convened an ad hoc committee of experts who reviewed the current literature on lifting, recommend criteria for defining lifting capacity, and in 1991 developed a revised lifting equation. Subsequently, NIOSH developed the documentation for the equation and played a prominent role in recommending methods for interpreting the results of the equation. The 1991 equation reflects new findings and provides methods for evaluating asymmetrical lifting tasks, lifts of objects with less than optimal hand-container couplings, and also provides guidelines for a larger range of work durations and lifting frequencies than the 1981 equation. This paper provides the basis for selecting the three criteria (biomechanical, physiological, and psychophysical) that were used to define the 1991 equation, and describes the derivation of the individual components (Putz-Anderson and Waters 1991). The paper also describes the lifting index (LI), an index of relative physical stress, that can be used to identify hazardous lifting tasks. Although the 1991 equation has not been fully validated, the recommended weight limits derived from the revised equation are consistent with or lower than those generally reported in the literature. NIOSH believes that the revised 1991 lifting equation is more likely than the 1981 equation to protect most workers.

Understanding and evaluating manual handling injuries: NIOSH research studies.

This paper presents an overview of NIOSH research aimed at characterizing and identifying intervention strategies for reducing musculoskeletal injuries during manual handling activities. Surveillance and evaluative research projects are reviewed. Future research directions of the Institute are also discussed.

Ergonomic analysis to characterize task constraint and repetitiveness as risk factors for musculoskeletal disorders in telecommunication office work.

A modified activity analysis procedure was devised to quantify the presence of two task attributes identified in previous research as contributing to an increase in work demands and ergonomic hazards. The purpose of this study was to develop an exposure index based on the presence of two task attributes. The utility of this job activity analysis will, of course, be determined by the extent to which workers with varying degrees of muscular pain and discomfort correspond to the risk exposure group we have described. The results of both the medical and psychological assessments of the workers--contained in the final HETA report--will be used to assess the utility of our method and determine whether the task attributes of constraint and repetitiveness contribute to the onset of cumulative trauma disorders among clerical workers.

Vibration thresholds as a function of age and diagnosis of carpal tunnel syndrome: a preliminary report.

To determine if vibration thresholds vary independently with age and carpal tunnel syndrome (CTS), 61 subjects, including 27 diagnosed with carpal tunnel-induced neuropathy, and 34 non-CTS controls, ranging in age from 20 to 65 years, were tested using the Optacon, a device used to assess vibration thresholds. No statistically significant interaction was found between the age and diagnosis factors. Results did confirm the findings of previous studies that vibration thresholds increased with age and that thresholds were elevated within the CTS group, compared to the controls. These results indicate that age-adjusted norms for vibration threshold data need to be developed. Without age-adjusted norms, screening programs for CTS that rely on vibration threshold data are likely to generate high levels of false positives, particularly for workers over 40 years of age.

Traumatogenic factors affecting the knees of carpet installers.

An ergonomics analysis of carpet installation tasks was performed. The purpose was to identify and quality potential sources of biomechanical trauma that may be responsible for the high rates of knee morbidity found by previous researchers among carpet layers. Nine carpet layers were studied either at an apartment building worksite or at a training school. Results from a job analysis indicated that workers spent approximately 75% of their time in the kneeling position using a tool called a knee-kicker to stretch and install carpet. Awkward body postures were identified from films of workers installing carpets. At the moment of impact the knee is severely flexed, subtended angles were less than 60 degrees. To obtain measures of impact force on the knee, the kicker-tool was instrumented with a load cell. Workers who executed the hardest kicks with the tool produced impact peak forces that averaged 3019 newtons (N), which is equivalent to about four times body weight. Measures from an accelerometer attached to the worker's knee showed values in excess of 120 m/s(2), which are comparable to those found during vigorous running and jumping exercises. The results imply that repetitive impact of the knee joint from the use of the knee-kicker combined with knee flexion, kneeling and squatting may be responsible for the high level of occupational knee-morbidity found among carpet layers.

Effects of acute exposure of toluene and methyl ethyl ketone on psychomotor performance.

Organic solvents are used frequently in industry and workers are often exposed to various combinations of these chemicals. Several are CNS depressants, and the purpose of this experiment was to assess the behavioral effects of 4-hour inhalation exposures to two solvents, toluene and methyl ethyl ketone (MEK) alone and combined. Ethanol at 0.08% blood levels was used as a positive control. A total of 144 paid volunteers were randomly assigned to one of eight treatment combinations in a series of four two-group between subjects studies. Testing was carried out in an exposure chamber, and participants were tested before, during, and after the treatment or control condition on three performance tasks. The tasks measured alertness and psychomotor function and produced a total of 28 measures on each individual over the approximate 8 h of testing. Results indicated that toluene at 100 ppm produced a small but significant impairment on one measure of a visual-vigilance task by lowering the percentage of correct hits. MEK at 200 ppm produced no interpretable significant effects on any of these measures. Additivity was not evident when individuals were exposed to MEK (100 ppm) and toluene (50 ppm) in combination, as no significant performance differences were noted. Ethanol, at 0.08%, affected both the visual-vigilance and a choice-reaction time task at statistically significant levels on two measures, confirming the sensitivity of these two tasks to CNS depressants.

A behavioral examination of workers exposed to carbon disulfide.

The present study was conducted with a group of 298 textile workers. Of the workers studied 131 had worked at least one year in a rayon plant where there were CS2 exposures of varying degree, but generally below 20 ppm, which is the U.S. occupational exposure limit. The remaining 167, who worked in plants that manufactured other textiles where any CS2 exposure was considered inconsequential, comprised a comparison group. The 298 workers completed a checklist of symptoms characteristic of various neurobehavioral syndromes. Mood and excitability were measured by the Profile of Mood States, and by a mania scale from the Minnesota Multiphasic Personality Inventory, respectively. Cognitive and psychomotor performance was studied by application of four standard tasks: the Neisser letter search, the memory span test, the eye-hand coordination test, and a combined simple and complex reaction time test. The results indicated an absence of behavioral changes of any major significance, suggesting that effects here may only be marginal. The major finding related to the significant cluster of reported symptoms of neurobehavioral ailments.

Methyl chloride and diazepam effects on performance.

Human behavioral effects resulting from the ingestion of an average dose of diazepam and from 3 h of inhaling either 100 ppm or 200 ppm of methyl chloride (MeCl) were studied in the laboratory. Each of 56 volunteers was randomly assigned to one of six groups comprising the combinations of diazepam and placebo and one of the two levels of MeCl plus control. Each individual was tested in an environmental room on three tasks involving components of eye-hand coordination, mental alertness, and time discrimination. Both pretreatment and treatment data were obtained. Diazepam produced a significant 10% impairment in task performance, whereas the effect of 200 ppm of MeCl was marginally significant (average performance impairment of 4.5%). When the two agents were combined, total impairment was equal to the sum of the individually induced losses. Large interindividual differences in breath and blood levels were found for MeCl.