Musculoskeletal Disorders: Work-related Risk Factors ...

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INTERNATIONAL COMMISSION ON OCCUPATIONAL HEALTH (ICOH)*. Work-related musculoskeletal disorders cause chronic pain and functional impairment ...
Reprinted from INTERNATIONAL JOURNAL O F OCCUPATIONAL AND ENVIRONMENTAL HEALTH, © 1996 by HANLEY &. BELFUS , INC. , Philadelphia, PA

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Position Paper on Work-related Musculoskeletal Disorders

Musculoskeletal Disorde rs: Work-related Risk Factors and Prevention SCIENTIFIC COMMITTEE FOR MUSCULOSKELETAL DISORDERS OF THE INTERNATIONAL COMMISSION ON OCCUPATIONAL HEALTH (ICOH)*

Work-related musculoskeletal disorders cause chronic pain and functional impairment, impose heavy costs on society, and reduce productivity. In this position paper from the Scientific Committee for Musculoskeletal Disorders of the ICOH, the most important risk factors at work are described. Workrelated musculoskeletal disorders have high incidences and prevalences among workers who are exposed to manual handling, repetitive and static work, vibrations, and poor psychological and social conditions. The application of ergonomic principles in the workplace is the best method for prevention. International organizations should develop standards, common classifications, and terminologies. Surveillance systems should be further developed nationally and in workplaces, and more effort should be directed to information dissemination, education, and training. Key words: musculoskeletal disorders; ergonomics; prevention.

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ork-related musculoskeletal disorders cause chronic pain and functional impairment for millions of people, impose heavy costs on society for treatment, sick-leave, and retirement, and reduce productivity in working life. The aim of this article is to summarize available knowledge about the workrelatedness of musculoskeletal disorders, and to identify and describe the most important risk factors, especially at work. Effective prevention requires distribution of this information to decision makers, health authorities



Address correspondence and requests for reprints to Asa Kilborn , National Institute for Working Life, 171 84 Solna, Sweden. *The following members of the committee co-authored this article: Asa Kilborn, MD, Thomas Armstrong, PhD, Peter Buckle, PhD, Larry Fine, MD, Mats Hagberg, MD, Marie Haring-Sweeney, PhD, Bernard Martin, PhD, Laura Punnett, PhD, Barbara Silverstein, PhD, Gisela Sj0gaard, DrMedSc, Tores Theorell, MD, and Eira ViikariJuntura, DrMedSc.

and researchers who can affect conditions in the workplace.

CLINICAL FEATURES OF WORK-RELATED MUSCULOSKELETAL DISORDERS Work-related musculoskeletal disorders cover a wide range of inflammatory and degenerative diseases and also include some less well-known states of pain and functional impairment. Inflammations of tendons (tendinitis and tenosynovitis), especially in the forearm-wrist, elbow, and shoulder, have high prevalences and incidences in occupations involving prolonged periods of repetitive and static work. The onset of a tendon disorder may be acute or insidious. Workers usually recover, but they may in some cases develop chronic disorders. Myalgias, i.e., pain and functional impairments of muscles, occur predominantly in the shoulder-neck region in occupations with large static-work demands, e .g., those involving precision work with the hands. Myalgias usually have a longlasting course, and many cases of chronic impairment with inability to resume work have been reported. Compression of nerves--entrapment syndromes--occurs especially in the wrist and forearm, causing pain and loss of sensibility and strength. With continued exposure, functional impairment may remain for life. Degenerative disorders occur in the spine, usually in the neck and low back regions, as well as in the hip and knee joints. Such disorders are common in the general population at advanced ages. However, several factors at work, especially heavy physical work and manual handling, interact with aging and accelerate joint degeneration. These disorders are chronic, and symptoms usually occur only after exposure to work-related risk factors for many years. The disorders described above are most accurately described as work-related disorders. A work-related disorder is, according to the World Health Organization (WHO) definition, multifactorial, and the work envi-



TABLE 1 Prevalences (age-adjusted) of low-back, neck, and shoulder pain and clinically verified syndromes In the Finnish papulation over 30 years of age·

Lifetime prevalence of low back pain Lifetime prevalence of sciatic pain One-month prevalence of low back or sciatic pain Point prevalence of low back pain syndrome Point prevalence of sciatica or prolapsed disc Lifetime prevalence of neck pain One-month prevalence of neck pain Point prevalence of chronic neck syndrome Lifetime prevalence of shoulder pain One-month prevalence of shoulder pain

Men

Women

76.3 34.6

73.3 38.8

19.4 17.5 5.1

23.3 16.3 3.7

not

41.1 t 9.5 13.5 46.0 52.7 25.1 31 .8

"Adapted from Heli0vaara.4 tMen and women .

ronment and the performance of work contribute significantly, but in varying magnitude, to the causation of the disease . A work-related risk factor is one among several factors (although not necessarily a sufficient factor) that cause, provoke, or aggravate a latent disorder (WHO, 1985) . Work-related disorders must therefore be separated from occupational disorders, where one factor is sufficient to cause the disease. A large number of studies, reviewed below, indicate a close relationship between certain risk factors at work and musculoskeletal disorders. These findings, together with poor results of medical treatment, imply that early prevention through elimination of risk factors in the workplace is the most effective way to influence the onset and course of many musculoskeletal disorders. The application of ergonomics (boxed text) to work-system design is essential to reduce work-related musculoskeletal disorders and improve workers' satisfaction and productivity.

SIZE OF THE PROBLEM



Musculoskeletal diseases constitute a major part of all registered occupational diseases in many countries. 1·2· 3 Criteria for considering a musculoskeletal disease an occupational disease vary between different countries, making comparison of disease figures difficult. Even in countries that have relatively strict criteria, musculoskeletal diseases are the largest group of occupational diseases, representing a third of all registered cases. 1 Disorders of the low back, neck, shoulder, and upper extremity are prevalent among working populations, although they vary in incidence and severity according to different sources. Table 1 shows the prevalence figures for low-back, neck, and shoulder pain, as well as for some clinically verified neck and low-back disorders, obtained in a population health survey in Finland.4 The liftetime prevalence of regional musculoskeletal pain is much higher than the one-month prevalence, reflecting the episodic nature of many of the disorders. Con-

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ditions fulfilling specific diagnostic criteria, such as sciatica or prolapsed disc, are less prevalent than the nonspecific conditions . Musculoskeletal disorders accounted for 33% of all days of national sickness allowance payment in Finland in 1992, 5 and back pain alone constituted 12.5% of the total sick days in the United Kingdom in 1988-89.6 In an industrial working population, the prevalences of clinically verified cumulative trauma disorders of the wrist and hand, consisting primarily of tendon disorders, ranged from 1% to 25% according to the force demands and repetitiveness of work task.7 In the food-processing industry, the incidence density of tenosynovitis or peritendinitis was 1 per 100 person-years in nonstrenuous jobs, but it was 13 to 25 in various hand-intensive jobs.8 The corresponding figures for humeral epicondylitis were 1 and 6 to 11, respectively. The costs of musculoskeletal disorders were estimated to have ranged from 2.7% to 5.2 % of the gross national product (GNP) in the Nordic countries in 1991, at a time when all costs due to illness were estimated to range from 15.8% to 22.2% of the GNP.9 An attempt to evaluate the etiologic fraction of musculoskeletal disorders due to work resulted in an estimate ranging from 15% to 49%. Using an assumption of an etiologic fraction of 32%, the costs of work-related musculoskeletal disorders can be estimated to be approximately 1% of the GNP in the Nordic countries.

ERGONOMICS is the science of human capacity in relation to demands, and the application of this knowledge to improve work. "Ergonomics" is composed of two Greek words: "ergo"= work "nomos" = law Ergonomics is a multidisciplinary science consisting of three main areas: • Human biology (anatomy, physiology, medicine): body size, sensory function , physical working capacity as well as symptoms/ signs of disorders caused by excessive demands • Psychology: human perception, information processing and cognitive function, and psychological responses to varying demands • Technology: the design of work stations and work systems to optimize output

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CAUSES







Exposure

(Wor1c Requirements)

A Conceptual Model EXTERNAL

Primary prevention of work-related musculoskeletal dis·orders calls for reducing exposure to risk factors. The impacts of risk factors are also modified by individual capacity. Armstrong et al. 10 presented a conceptual model (Figure 1) that helps to explain the complex interrelationships between multiple risk factors at work, individual factors, and musculoskeletal disorders. The model suggests that repetitive or sustained microtrauma (mechanical or physiologic) occurring over time compromises the integrity or functioning of specific tissues and structures of the musculoskeletal system. Exposure refers to the external factors of work that produce internal doses (e.g., metabolic demands or tissue loads). These doses disturb the internal state of the individual (tissue deformation, production of metabolites, pain, anxiety), resulting in internal responses that may be mediated by individual capacity. The model characterized this dynamic relationship as a series of cascades where the response may in turn be viewed as another dose, which may improve or decrease individual capacity. The level, duration, and frequency of the loads imposed on tissues, as well as the adequacy of recovery time, are critical factors in determining whether dose tolerance increases (training effect) or capacity is reduced and a musculoskeletal disorder occurs . The cascade model thus describes mechanisms of musculoskeletal disorders. Ideally, from existing scientific knowledge, this model could be used to estimate the likelihood that any specific set of working conditions would cause a specific musculoskeletal disorder. However, while many of the major work-related factors have been identified, there is considerable scientific debate about the levels of risk associated with most common exposures. In general, for the most common work exposures such as repetitive work or manual handling, there are few if any widely accepted international guidelines or standards equivalent to threshold limit values. The discussions of the risk factors below, include brief comments concerning suggested guidelines for major exposures. In addition to the scientific uncertainty that surrounds these guidelines, the technologic or eaonomic feasibility of their wide-scale implementation is unknown. Nevertheless, there is substantial evidence that the major work-related risk factors that should be eliminated or at least minimized are those related to the manual handling of materials, repetitive work, static work, segmental vibration, and poor psychosocial work environments.

Manual Handling Manual handling includes carrying, holding, and pushing and pulling objects. In many epidemiologic studies,

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Capadty

-4-----'---.1

~e~r--R-~-----1-----L----------~ -

-

Response2

- - Response n

INTERNAL Figure /-Proposed conceptual model for work-related musculoskeletal disorders.

manual handling has been identified as a risk factor for low back pain, and also for shoulder disorders. II Typically, a two-to-threefold increase in risk of low back disorders has been found in occupations that involve manual lifting of heavy objects. Lifting away from the occupational setting, e .g., the lifting of objects or children weighing 25 pounds or more, frequent lifting with extended arms, and twisting while lifting, is associated with an increase in risk. 12 It would seem, therefore, that evidence collected away from the workplace identifies manual handling activities as increasing the risk for the development of a back disorder or injury. Manual handling also includes exposures to risk factors other than the exertion of forces. In a large number of studies, it is obvious that manual handling frequently induces static loads due to awkward postures, and sometimes whole-body vibration while driving vehicles. In a review by Riihimaki, 12 the following workrelated risk factors for low back disorders were identified: heavy physical work, lifting, carrying, pulling, pushing, twisting, bending, other non-neutral trunk postures, motor vehicle driving, sitting, monotonous work, job dissatisfaction, and trauma. In addition, individual factors influencing the risk were identified. Although risk factors for low back disorders also include other types of exposures, the importance of manual handling is widely recognized. The response of government and national agencies has been to prepare guidelines on hazard and risk reduction. Within the European community, the Directive on Manual Handling was passed and put into effect in the member states at the beginning of 1993. In the United States, NIOSH has prepared standards that help to set limits for load lifting, considering such factors as asymmetry, work duration, and frequency of the lifting task. 13 The full impact of such directives has yet to be evaluated. Buckle et aJ.l4 have expressed concern about how few of the many im-

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portant factors in manual handling systems are addressed by these directives. Despite such limitations, these guidelines are evidence that most authorities now consider that manual handling is a significant factor in the development of back problems and back injuries.

Repetitive Work



In repetitive work, the same tasks are repeated for long periods of time. Typically, the work pace is rapid and the work requires frequent movements or exertions of the same body part. Repetitive work of the hand is a common problem at work, but other parts of the body also may be affected. 15 Repetitiveness of work is characterized conceptually in terms of the number of exertions ·p er unit time and the ratio of work to rest. When the frequency of exertion is too high or the recovery time is too short, workers may experience discomfort and impairment in performing their jobs. If the exposure to overexertion continues, tissue viability may be impaired, leading to further symptoms and reducing capacity (see boxed test). In extreme cases, activities at work and in daily living may be impaired. Gradual increase in physical exertion has a training effect on the musculoskeletal system. In some cases, this adaptation can cause undesired secondary effects. As an example, thickening of the tendon sheaths inside the wrist can in some cases lead to compression of the median nerve and impairment of nerve function in the hand. Epidemiologic studies have generally found that carpal tunnel syndrome (compression of the median nerve in the wrist) 16 and tendon disorders in the wrist and forearm are related to repetitive manual work, whereas there is less evidence regarding epicondylitis (tennis elbow). Frequent twisting and bending of the trunk and frequent lifting are associated winh an increased risk oflow back pain. While there are no widely accepted recommendations about the acceptable levels of repetition, either alone or in combination with other factors, some researchers have suggested tentative guidelines. 17 The means to redesign work and reduce n~petitive­ ness include increased rest allowances, improved motion economy, work enlargement, worker rotation, and changes in process. One approach that can be taken with repetitive work or other potentially hazardous exposures is to reduce the magnitude or duration of the exposure and then reassess whether the incidence of severity of musculoskeletal disorders has been reduced.

Static Work



Static or sustained work implies that one or several body regions are elevated, twisted, bent, or extended for prolonged periods. Thereby muscles, tendons, and joints are exposed to long-lasting loads without rest for recov-

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ery. Static postures of the neck, arms, and trunk are common in many jobs, e.g., among assembly and cash register workers, seamstresses, welders, and building workers. Several epidemiologic studies have demonstrated high prevalences of myalgia and tendon disorders associated with static postures.18-20 Myalgias are especially likely to occur in the shoulder and neck muscles that stabilize the head and elevate the arms. Static postures are characterized in terms of the duration of exertions in a given position and the percentage of maximum strength used. Static exertions can· be assessed using observations, time studies, video analysis, and electromyography (EMG). The mechanism of muscle and tendon iqjuries in static postures is likely to be insufficient supply of energy. 21 Mechanical compression due to increased intramuscular pressure may further impede the circulation and an inflammatory reaction may develop, eventually leading to degeneration and reduced strength. Muscle fibers with marked degenerative changes have been found more frequently in muscle biopsies from patients with work-related chronic myalgia.22 Additionally, mental load and visual demands can generate non-postural muscle tension that adds to the postural load. Postures can be improved by redesigning workstations and tools so that postures closer to neutral can be maintained. In addition, workstations and work tasks should be designed to encourage changes of posture. There are no widely accepted recommendations about the acceptable levels of static work, either alone or in combination with other risk factors. However, some researchers have suggested tentative guidelines.2 3

Vibration Exposure of the human body to vibration is known to produce a large variety of subjective sensations and disorders affecting the musculoskeletal, vascular, nervous, and motor systems.2 4 It is reasonable to hypothesize that vibration-induced disturbances in these systems act in combination to affect the tissues and the development of musculoskeletal symptoms. The relative motions of _muscular masses and bones, amplified by resonance at low and medium frequencies, cause tissue stress and damage cartilage and bone. Power tools expose their operators to hand-arm vibration. The hand-arm vibration syndrome (HAVS) mainly consists of three phenomena; vibration-induced white fingers, sensory disturbance in the hand, and musculoskeletal disorders of the arm such as tendinitis and degenerative joint disorders. 25,26 Vehicles such as trucks and tractors are common sources for whole-body vibration exposure. Whole-body vibrations have been associated with back pain, and pain in the shoulder and neck may also be related. 27 In spite of improvements in the designs of hand-held machines and vehicles, high levels of exposure to vi bra-

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tions still exist. The injurious effects of local vibrations have been known for many years, and an international standard (ISO 5349) specifies acceptable exposure times. Similarly, recommendations for exposures to whole-body vibrations (ISO 2631) have been issued.

chological states at the work site. The psychological states may in turn influence symptoms from .and disorders in the musculoskeletal system. It is acknowledged that psychosocial factors outside work may also be important.34

Psychological and Social Job Factors

INDIVIDUAL FACTORS-IMPORTANT RISK FACTORS IN WORK-RELATED MUSCULOSKELETAL DISORDERS?

According to the demand-control-support model, psychological demands of the job have adverse consequences if they occur jointly with the lack of possibility to influence decisions regarding the job (low decision latitude). 28 Poor support from workmates and superiors further increases the strain experienced by an individual. The global concepts of demands, decision latitude and social support at work have been used in many studies. 29 The designs of these studies have varied considerably. Few have simultaneously included physical loads and psychosocial factors. Psychological demands, low decision latitude, and lack of social support at work are established risk factors for musculoskeletal disorders. Differences between the results of studies of these factors seem to be related to variances of the individual factors in the study gnmps. There may also be differences between the psychosocial risk patterns associated with low back pain versus neck-shoulder pain. Three kinds of mechanisms may relate psychosocial factors to symptoms in the musculoskeletal system: • Physiologic mechanisms that lead to bodily changes. Long-lasting psychological arousal may inhibit repair and restoration of body tissues. This may lead to deconditioning of the muscles and hence increased vulnerability to mechanical stress. Thus, a relatively small mechanical load that does not cause injury under normal conditions may do so during such a period. Chronic pain syndromes may then arise if the psychosocial conditions for rehabilitation are unfavorable.30 • Physiologic mechanisms that influence pain perception. In chronic pain syndromes there is a strong element of psychological depression, which may influence hormonal activity and thereby increase the sensitivity to pain stimuli. The release and breakdown of endorphins (pain depressants produced within the body) may also be influenced. Feelings of lack of control in general life may increase pain sensitivity. 31-33 • Sociopsychological conditions that affect the capacity to cope with the illness. Such conditions are of central importance in the rehabilitation of those subjects who suffer from pain in the musculoskeletal system. Social organizational factors that affect psychological demands and decision latitude may influence the psy-

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In the context of musculoskeletal disorders, individual factors can be regarded as factors that influence individual susceptibility. This is defined as an increased vulnerability in a person, due to an impairment in capacity caused by disease, genetic code, or lack of fitness .35 Increased susceptibility may result in a lower-than-normal threshold for an exposure to cause an effect, resulting in a work-related musculoskeletal disorder. Furthermore, exposure may trigger symptoms early and at an unusual location under local strain in an individual who has a preclinical systemic disease .36 The risk for most musculoskeletal disorders increases with age . Gender may be an important individual factor for musculoskeletal disorders. Females have a higher reported incidence of carpal tunnel syndrome, 37 and neck-shoulder muscular pain is more common in females than in males both in the general population and among industrial workers. 38 Whether this skewed distribution of neck-shoulder pain by gender is due to genetic differences between males and females or gender differences in exposures both at work and at home is not clear. While women appear to be at greater risk of musculoskeletal disorders in clinical studies, the risk is much smaller in work populations in which work factors are controlled. In addition, it has been suggested that a rise in compensation claims for carpal tunnel syndrome may reflect either a self-selection or a movement of women into jobs with greater risk. 39 Anatomic variations or malformations in some individuals may cause symptoms, often triggered by ergonomic factors. Examples of disorders where anatomic variations may be important are thoracic outlet syndrome (TOS = compression of nerves leaving the chest), biceps tendinitis, and spinal stenosis. Smoking is a risk factor for low back pain,40 probably through accelerated degeneration due to nicotinereduced blood flow and smoke-induced coughing causing mechanical strain. Local musculoskeletal symptoms may be the first sign of a systemic inflammatory disorder. 41 One common disorder of this nature is rheumatoid arthritis. A positive rheumatoid factor without manifest rheumatoid arthritis was found in a third of workers with hand-intensive tasks presenting with repeated tenosynovitis or peritendinities of the wrist-forearm region .42 In epidemiologic studies of work-related musculoskeletal disorders, the risks associated with these indi-

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vidual fac tors are usually low compared with the workrelated risk factors.35

STRATEGIES FOR PREVENTION Available data, reviewed above, can be used • to follow trends in the occurrences of symptoms or disorders • to mon itor the levels of risk factors It can be argued that our knowledge is insufficient to instigate wide-ranging actions. It is true that knowledge about the exact mechanisms of musculoskeletal inj uries and quantitative exposure-effect relationships is still incomplete. These areas need further research and will provide even better tools for prevention, especially as a basis for gu idelines, directives, and standards. Nevertheless, available research on the relationships between work-related risk factors and many musculoskeletal disorders is uncontroversial, and certain actions need to be taken now. To address the ever-increasing problem of workrelated musculoskeletal disorders, prevention strategies should be d eveloped at all levels of society: internationally, nationally, and locally.43 Here, we focus on th e international and national levels.



International Level International organizations such as the World H ealth . Organisation (WHO), the International Labor Organization (ILO), the International Commission on O ccupational Health (ICOH), and the International Ergonomic Association (lEA) play important roles in supporting research, disseminating information, standardizing methods, and issuing guidelines. In the development of prevention strategies, the international groups should work to develop standard international terminology and uniform criteria for d efining work-relatedness. Additionally, the groups should strive to develop, validate, and implement a common classification of work-related disorders. Furthermore, the development of international ergonomic standards and guidelin es for the design of work systems should be continued. Standards should protect all workers regardless of gender or age.

National Level



Vital components of successful prevention strategies include information dissemination, education, and training at all levels of the government and population; effective use of current technologies; surveillance and medical man agement; and enforcement. Every country should develop prevention strategies based on national social and economic conditions.

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Economic benefits and incentives. Work environments that incorporate ergonomic principles are beneficial for health and for the economy. Development of preventive ergonomic activities often leads to economic benefits such as increased productivity, decreased absenteeism, and improved work satisfaction. Information about the economic benefits of ergonomically sound working conditions should be disseminated. Management commitment to prevention is essential for success, as is the participation of employees in the process. National programs should encourage and promote such commitments and participation. Technologies. Tools, equipment, and workplaces must be designed to accommodate the human body and its limitations. Installation of ergonomically designed equipment and work systems at the time the workstation is built is better and more cost-effective than later adaptation. Present scientific knowledge is sufficient to create better designed tools and equipment, which can be more effectively introduced into the workplace if designers are better trained in fundamental ergonomic principles. The pace and organization of work should b~ adjusted to the psychosocial demands placed on the worker. When introducing new technology, attention must be paid both to good workstation design and to the human need to influence the work process. Scientists and manufacturers must cooperate in creating better tools and equipment. In some countries, such cooperation has begun. The most common tools and machinery should be tested and redesigned when necessary. Ergonomics should also be applied to the design and evaluation of machinery. Surveillance and health care. Because we cannot precisely predict risks, we need surveillance

• to identify affected workers • to evaluate interventions Statistics about work-related musculoskeletal disorders should be used as an incentive to improve workplaces. Through national surveillance systems, the rates and possible causes of musculoskeletal disorders among the working population can be ascertained. These systems can be used to track work-related musculoskeletal disorders by industry and occupation and provide feedback to enterprises for identifying and controlling disorders internally. The system must not violate the rights of each worker to confidentiality of personal medical data. Also, the system must protect the worker from possible loss of employment or discrimination. To effectively use national surveillance data about work-related mu sculoskeletal disorders, labor inspectorates, occupational health care services, and health care personnel must have sufficient training about the characteristics of work-related musculoskeletal disorders and their relationships to the work environment.

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Occupational health care services can provide surveillance of workplaces and gather more data than is possible in a national surveillance system. Such services, or, in some countries, the health care system, can monitor workload factors, identify the problems individual . workers have, arrange rehabilitation, and cooperate with management, designers, and workers in redesigning workplaces and in reorganizing the work. The occupational health care services have an opportunity to monitor the introduction of new technologies. Information, education, and training. Education and training about work-related musculoskeletal disorders and solutions play a vital role in the prevention of musculoskeletal disorders. Knowledge of work-related risk factors as well as work and equipment technologies is essential for everyone--designers, administrators, foremen, production engineers, workers, and occupational health professionals-involved in the technical and administrative organization of individual workplaces. Courses in ergonomics should be included in the requirements for academic degrees in engineering, medicine, psychology, public health, and administration. Employer associations and trade unions have an important role. Employer associations can, for example, organize local and nationwide managers' groups to exchange knowledge and provide education. Trade unions can arrange education and encourage workers to take an active interest in improving workplace conditions. Legislation. Laws and rules regulating work environments differ from country to country, depending on present legislative and social security systems. It is, therefore, not possible for us to outline in detail suggestions for new legislation to prevent musculoskeletal disorders. However, we suggest some principles: When ergonomic standards are formulated, it is important that they be treated as minimum requirements and that they reflect the latest scientific knowledge. Standards should be gradually revised to incorporate new knowledge and to ensure that preventive ergonomic activities continue. Labor inspectorates can act in the preventive work. They can advise and counsel enterprises about possible improvements and penalize them if risk factors for musculoskeletal disorders are frequent among their workforces or rates of work-related musculoskeletal disorders are high. In many countries, environmental-impact studies are required before starting or changing an industrial process or introducing a new technologic process. In the same spirit, ergonomic-impact studies could be a requirement for the introduction of new technologies, in order to protect health and safety.

CONCLUSIONS Work-related musculoskeletal disorders have high incidences and prevalences among workers exposed to

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manual handling, repetitive and static work, vibrations, and poor psychological and social conditions. Application of ergonomic principles at the workplace is the best method for primary and secondary prevention. Furthermore, international organizations should work to develop standards, common classifications, and uniform terminologies. Surveillance systems should be further developed nationally and at the workplaces, and more effort needs to be put into information dissemination, education, and training. The authors thank Choon-Nam Ong and Hilkka Riihimaki for valuable comments about the manuscript.

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