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Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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II
WORKSHOP SUMMARY

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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Introduction

In May 1998, the National Institutes of Health asked the National Academy of Sciences/National Research Council to assemble a group of experts for two tasks: to examine the scientific literature relevant to the issue of work-related musculoskeletal disorders of the lower back, neck, and upper extremities and to address seven questions posed by U.S. Representative Robert Livingston on this topic. The steering committee established to carry out these tasks was composed of experts in orthopedic surgery, occupational medicine, epidemiology, ergonomics, human factors, and risk analysis. It was responsible for designing and moderating a workshop, identifying and inviting participation by the leading researchers in relevant areas, and preparing two reports: one presenting the steering committee's conclusions and the other summarizing the workshop and providing the papers prepared for the workshop. The first report (National Research Council, 1998) was issued in September 1998. This is the second report.

The workshop was designed to focus on the current state of the scientific research base pertaining to work-related musculoskeletal disorders, including risk factors that can contribute to such disorders, and interventions that may alleviate or prevent such disorders. The steering committee invited approximately 90 leading scientists from the fields of orthopedic surgery, occupational medicine, public health, ergonomics, and human factors to participate in the workshop; 66 of the invitees attended. In selecting participants, the steering committee relied primarily on two criteria: experts who are

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

actively engaged in pertinent research and diversity of participants, representing a wide range of scientific disciplines, perspectives, beliefs, and approaches.

The workshop took place at the National Academy of Sciences on August 20-21, 1998. Several participants were commissioned to prepare and present papers; others provided written and oral responses to the papers. This report summarizes the papers and workshop discussions. (See Appendices A and B for the list of participants and the agenda.)

In designing the workshop and commissioning papers, the steering committee chose not to focus on specific parts of the body and associated musculoskeletal disorders. Instead, the steering committee sought to examine the many biological, biomechanical, non-biomechanical, and physical and psychological differences among individuals that might play a role in the development of musculoskeletal disorders. The steering committee believed this approach would provide a framework for reviewing the science base in each area, as well as the overlaps among them.

The steering committee organized the workshop around five major topics: (1) biological responses of tissues, specifically muscles, tendons, and nerves, to biomechanical stressors;1 (2) work factors, individual factors, and internal loads—that is, the biomechanics of work stressors; (3) the epidemiology of physical factors; (4) non-biomechanical factors that may affect musculoskeletal disorders; and (5) interventions to prevent or mitigate musculoskeletal disorders. For four of these topics, discussions at the workshop centered on a paper (or papers) commissioned for the workshop, followed by the comments of invited discussants. For the epidemiology of physical factors, the steering committee used a panel format to take advantage of a recent review of this literature (Bernard et al., 1997).

Organizing Framework

The steering committee developed a conceptual framework integrating the factors thought to be related to the occurrence of musculoskeletal disorders. This framework was used to organize the workshop topics and was presented to all participants at the outset of the workshop.

Figure 1 presents that framework. It diagrams the work-related and other factors most frequently involved in the development of musculoskeletal disorders. It is a useful framework for examining the diverse literatures associated with musculoskeletal disorders, each reflecting the roles that work-related biomechanical, psychosocial, organizational, and individual factors can play in the development of musculoskeletal disorders. The framework also suggests the pathways by which musculoskeletal disorders can occur and be avoided.

The central musculoskeletal disorder mechanism appears within the load-response box of Figure 1. It shows the load-response relationship that expresses the biomechanical

1  

Two papers were commissioned for this topic—one focusing on muscles and tendons and the other on nerves.

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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FIGURE 1

Conceptual framework of physiological pathways and factors that potentially contribute to musculoskeletal disorders.

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

component of musculoskeletal disorders. Loads of various magnitudes are imposed on bone or tissue in various ways. The impact of loads on tissues may change in the course of a day because of changes in fatigue, work pattern or style, coactivation of muscle structures, or other factors. The impact of loads on tissues can provoke several responses. If the load exceeds a mechanical tolerance or the ability of the tissue to withstand the load, tissue damage will occur. For example, damage to a vertebral end plate will occur if the load borne by the spine is heavy enough. Other tissue responses may include such reactions as inflammation, edema, and biochemical responses.

Systematic responses of the body to biomechanical loading may produce both symptomatic and asymptomatic reactions. Some of these reactions contain feedback mechanisms that can influence the tissue loading and response relationship, as illustrated in the gray box (physiological pathways) of Figure 1. For example, pain might cause an individual to use muscles in a different way, thus changing the associated loading pattern. Repetitive loading of a tissue might lead an individual to ignore discomfort signals and expose himself to greater loads, which he might or might not be able to bear. The symptom and adaptation portions in Figure 1 can interact with each other as well. For example, swelling might lead to a tissue adaptation, such as increased production of lubricant in a joint.

These symptoms, responses, and adaptive behaviors can lead to functional impairment. In the workplace, this might be reported as a work-related musculoskeletal disorder. If severe enough, the impairment could be considered a disability, and lost or restricted workdays could result.

In the box to the right, the framework recognizes the influence of individual factors, including physical and psychological factors, that might affect the musculoskeletal disorder sequence. For example, psychological factors can affect one's willingness to report a musculoskeletal disorder or claim that the impairment is a disability. Physical factors might involve reduced tissue tolerance due to age, gender, and overall physical condition. Disease states, such as arthritis, also can affect a person's biochemical response to tissue loading.

In the boxes to the left of the central physiological pathways, Figure 1 identifies environmental factors that might affect the development of musculoskeletal disorders, including physical work, organizational factors, and social context. For example, physical work factors (such as lifting heavy boxes or equipment) can affect the loading that is experienced by a worker's tissues and structures, and can also influence the symptoms and reported incidence of a musculoskeletal disorder. Organizational factors can also influence each component of the musculoskeletal disorder sequence. For example, time pressures to complete a task might frustrate a worker and provide an incentive or disincentive to report a musculoskeletal disorder or to claim that an impairment should be considered a disability. Although little studied, pathways exist between organizational influences and the biomechanical and body reaction (symptoms and response) components of the musculoskeletal disorder sequence.

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

Finally, social context is also a potential modifier of the musculoskeletal disorder sequence. For example, social factors, such as lack of support in dealing with psychological stress (e.g., no spousal support), might influence a worker's reporting behavior or even the worker's biomechanical responses.

The steering committee believes that this framework summarizes the diverse literatures regarding musculoskeletal disorders by characterizing the pathways that each literature addresses. For example, epidemiological investigations often explore the pathways between the physical work environment and the reporting of impairments or the pathway between organizational factors and the reporting of symptoms. Ergonomic studies often explore the pathways between physical work factors and biomechanical loads imposed on a tissue. The framework also provides a means to explain the interactions among factors. For example, the combination of a particular set of physical work and organizational factors might yield an increase in the reporting of symptoms that neither, considered alone, would yield.

Often the whole is greater than the sum of its parts. The steering committee deliberately sought to examine the evidence as a whole and not to restrict inquiry to one particular sector or field of inquiry. It also sought to place individual studies in context, by showing the factors that they do and do not address. The workshop was designed with these considerations in mind.

The next five sections provide summaries of each paper and the workshop discussions of them.

Biological Responses of Tissues to Stressors

Presentations

Soft Tissue Responses to Physical Stressors: Muscles, Tendons, and Ligaments

James Ashton-Miller

Reported soft tissue injuries can be the result of stresses (e.g., of posture, motion, or vibration) from a single, mechanical event or from repetitive events. The risk of such injury increases with acute or chronic changes in intrinsic factors (age, gender, inherited tissue anatomy, pain responses) related to an individual's physical capacity and extrinsic factors (work and life-style factors) related to the physical demands of the environment. Responses to soft tissue injuries include a complex cascade of events involving inflammatory responses, which mark the first phase of the healing process, followed by a remodeling phase in which tissues are restored. A smooth transition through these healing phases requires that physical loading of tissues be temporarily

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

reduced, in part because of pain and discomfort. This should be followed by a careful increase of physical loading during remodeling to avoid exacerbating symptoms.

Muscles

Muscles can suffer from a variety of injuries, including contraction induced injuries, single-event muscle strain injuries, and fatigue. There is considerable scientific exploration of these types of muscle injury. Three models of muscle injury promise the most return in understanding work-related muscle disorders. The first is an ''eccentric contraction model" in which muscles are subjected to a single, rapid stretch or a series of repetitive contractions. Research using this model has been conducted over the past 15 years in human and animal studies. The animal studies, in particular, have demonstrated that if a period of healing is allowed, the same forces can be later applied without reinjury. Age can affect the ability of the muscles to heal, and exercise, at any age, improves muscle strength and endurance, though it does not compensate for all the advantages of youth.

A second promising model has been developed to investigate muscle fatigue. This model is driven by theories that a muscle's ability to sustain power output is a function of its fiber composition and oxidative capacity. Recent in vivo laboratory studies of human muscle have used noninvasive spectroscopy to measure changes in tissue oxygenation in response to varying levels and duration of force. Decreased oxygen levels with increasing force were demonstrated (in nearly linear proportions) and also were associated with higher reports of discomfort by the study subjects.

The third model suggests that muscle stiffness, tenderness, and pain are associated with the release of substances, such as potassium chloride and lactic acid, during muscle contraction. Laboratory experiments testing this model involve either induced muscle fatigue or the injection of irritants into human muscle tissue. Both subjectively reported pain and myoelectric activity are monitored. The results of these studies also suggest that different muscle groups have different pain levels (jaw muscles, for example, are more sensitive than neck muscles).

Tendons and Ligaments

Tendons, ligaments, retinaculae, intervertebral discs, and the fasciae of muscles are all connective tissues between bone and muscles. The primary structural component of these tissues is collagen, which is demonstrably susceptible to external stresses. In the case of ligaments, theory suggests that strains can reduce the crimp or waviness of collagen fibrils in the ligaments and increase susceptibility to injury. Most studies of ligament injuries have focused on the knee; these studies show that ligaments are generally slow to heal and repair themselves (up to 2 years in animal studies). Aging also appears to affect the tensile strength and elasticity of the ligaments. Biomechanical, in vitro laboratory studies have shown that human hand tendons can be weakened under the friction generated by awkward hand or wrist postures when the hand is

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

gripping an object. Animal studies show that repetitive strains on tendons can cause degenerative changes—increased inflammation, more capillaries, edema and fibrosis. These study findings could be augmented by in vivo evidence of the link between cumulative strain and tendon and ligament injury.

The ability to study cause and effect in overuse-related injuries is hampered by difficulties in accurately estimating the relationships between force and human muscles and tendons throughout different parts and activities of the day—commuting, work, and home and leisure activities. A laudable goal would be to reduce work-related stress on tissues sufficiently so that whether injured "on" or "off" the job, tissues can heal and repair in a reasonable time without risk of becoming chronic conditions.

Soft Tissue Responses to Physical Stressors: Nerves

David Rempel, Lars Dahlin, and Göran Lundborg

We focus on the effects of compression on peripheral nerve functioning as demonstrated in human and animal studies. Peripheral nerve dysfunction associated with nerve compression typically occurs where nerves pass through a tight tunnel formed by stiff tissue boundaries. The resulting "confined space" limits tissue movement and can lead to sustained tissue pressure. Well-known examples are compression of the median nerve at the wrist, of the ulnar nerve at the wrist or elbow, and the spinal root nerves at the vertebral foramen. Clinical reports suggest that lesions that take up some of this confined space (tumors, cysts, and so forth) can cause nerve injury. So too can edema and extracellular matrix in the soft tissues (such as those associated with pregnancy and congestive heart failure). Other conditions, such as diabetes mellitus or an inflammatory reaction, can also increase the susceptibility of nerves to compression injuries.

The studies we examined to illustrate the effects of nerve compression on peripheral nerves included human and animal laboratory studies of the physiologic, pathophysiologic, biochemical, and histologic effects of "loading." Four of these studies demonstrate the state of the evidence on peripheral nerves as well as its limitations.

The first of these studies is an histological study on laboratory rats. In this study, varying levels of nerve compression were applied to the sciatic nerves. Endoneurial fluid pressure was measured at several time intervals up to 24 hours after the removal of compression. Greater levels of compression were associated with greater and longer lasting levels of endoneurial fluid pressure. Histologic examination of nerve tissue showed edema and degenerating nerve fibers after 8 hours even at the lowest levels of induced compression used in the study.

A second, similar study examined nerve compression over longer time periods—up to 4 weeks, under relatively high levels of nerve compression. The histologic results were edema, inflammatory reactions, and fibrosis within hours of compression. After 2 to 3 weeks, marked fibrosis, demyelination, and axonal degeneration were evident.

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

Related studies of animals exposed to vibration of the hind limbs for 4 hours over a period of 5 days suggest similar edema and structural nerve changes.

These two studies deal with sciatic nerves. Two other illustrative studies deal with nerves in the fingers and wrists. One study examined carpal tunnel nerve pressure in 20 people by asking them to press a load cell with their index fingers and then pinch the same cell between thumb and index finger. Both the pressing and pinching tasks led to increasing extraneural pressure in the carpal tunnel, but the pinching task was associated with pressures twice as high as the pressing task. The other study involved 10 men (ages 17-30) exposed to hand vibration in their work who were matched with 12 male cadavers of similar ages without such work exposures. Biopsies of the nerve just proximal to the wrist in both the living subjects and the control group (cadavers) showed pathological changes to the nerve in all 10 subjects and in one of the controls. Nerve changes included the breakdown of myelin and fibrosis.

These studies demonstrate a clear biological effect: that nerves are particularly sensitive to loading at relatively low levels of compression and exhibit changes that can persist. Humans exposed to hand vibrations or performing certain maneuvers can experience elevated extraneural pressures that in laboratory animals would result in nerve injury. All of these studies are limited in some ways: limited exposures to compression, lack of statistical comparisons, investigation of only one area of nerve dysfunction when multiple nerves are involved, and measurement difficulties that limit understanding of precise dose-response relationships. Further research could overcome some of the limits and usefully add to our understanding of these biological effects.

Discussion

The papers provide evidence for several conclusions about soft tissue response to physical stress. Although certain loads can be tolerated or adapted to, all soft tissues, including muscle, tendon, ligament, fascia, synovia, cartilage, intervertebral disc, and nerve, fail if subjected to sufficient force. Data from cadaver studies provide ranges within which such failures occur, as do animal models of some soft tissues tested in laboratory studies. Even at levels clearly below these failure ranges, however, there is scientific evidence from laboratory studies that soft tissue responses include inflammation, muscle fatigue, and ultrastructural degeneration that does not heal without cessation or restriction of the provoking force. As Figure 1 illustrates, intrinsic factors, such as age and conditioning, can influence soft tissue response and recovery, as can extrinsic factors, including the work environment and life-style characteristics.

The discussants of the Ashton-Miller and Rempel et al. papers did not generally dispute the conclusions presented, though many believe that greater attention to some aspects of the scientific evidence on soft tissue responses to stress could provide additional, important insights on tissues responsible for work-related musculoskeletal disorders. Suggested research areas included:

  • studies of the synovium (the tissue lining the tendons and joints);
Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×
  • recent biological work on cytokines and growth factors considered important in tissue inflammation, healing, and repair;
  • more scrutiny of studies using electromyography (EMG) to monitor muscle fatigue and pain (EMG measurement is noninvasive, objective, and can be used to establish biomarkers for muscle injury); and
  • studies of the effects of peripheral tissue inflammation on the central nervous system, especially in cases where muscle pain lasts much longer than expected.

Several other themes emerged from the discussions of these papers. The need for more research and more integrative research was a major theme. The long-term or chronic effects of soft tissue responses to stressors was one area in which discussants believed further research was critical. Steven Lehman, University of California at Berkeley, raised this issue in discussing the need to better understand the physiology of low-force, long-duration work and its effects on motor control, muscle fatigue, pain, and the recovery process. Carlo de Luca, Boston University, suggested the use of electromyography as a method for studying muscle fatigue.

The clinicians among the discussants stressed that, although most of the laboratory evidence presented in the papers corroborated their own case observations, that laboratory evidence deals primarily with acute stressors while they find the most difficult cases to be those involving chronic stressors. Susan Mackinnon, Washington University School of Medicine, noted that her experience indicates that an understanding of patient symptoms requires an understanding of chronic nerve compression. She described a model of chronic nerve compression in rats and primates that closely mimics the pathological changes seen in humans. These pathological changes (ranging from edema to degeneration) are paralleled by the symptoms of patients in clinical testing. Patient complaints typically begin with intermittent numbness brought on by specific postures, but not apparent when the patient is resting. As compression continues or increases, numbness becomes more persistent and, eventually, permanent. There are also neural and physiological symptoms which begin with complaints of aching and progress to weakness and finally, to muscle atrophy.

We need a good model of chronic nerve compression.

(Robert Szabo, University of California, Davis)

Robert Szabo, University of California, Davis, reinforced Mackinnon's comments, noting that the Rempel et al. paper's discussion of laboratory studies on nerve compression over time did not highlight the clinical relevance of the findings. The findings show a progressive degeneration of nerve health under sustained compression, which suggests that nerve compression effects can be viewed on a spectrum divided into early, intermediate, and late categories. In clinical terms, early stages respond most favorably to conservative treatment (such as steroid injections and splinting for carpal tunnel syndrome). For intermediate stages of nerve compression, involving numbness and parasthesia, patients

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

respond well to nerve decompression via the surgical release of the carpal tunnel. In late stages, patients often have permanent sensory loss with long-standing edema and fibrosis: these patients may benefit from carpal tunnel release, but this will not eliminate all their symptoms.

Putting these clinical views on chronic nerve compression in an even broader context, Thomas Mayer, PRIDE, Dallas, Texas, reported that even when all forms of acute nerve compression and musculotendinous sprains and strains are considered, they account for a small portion of medical care and medical costs (see box).

It has been known for 2 to 3 decades that 90 percent of the musculoskeletal claims comprise only 20 percent of the medical and indemnity expenditures . The 10 percent of cases extending beyond the acute phase of soft tissue healing account for 80 percent of the system costs for low back pain.

(Thomas Mayer, PRIDE, Dallas, Texas)

Another common "need for research" theme among the paper discussants was the need to generate links between specific anatomically distinct disorders (as they are clinically observed) and specific underlying patterns of pathology. J. Steven Moore, Texas A&M, summarized this view by noting that models that relate (1) specific patterns of musculoskeletal loading to (2) distinct internal stress in specific anatomical structures that (3) elicit tissue responses that (4) lead to observed tissue changes—are critical to diagnosis, treatment, and epidemiological tracking of musculoskeletal disorders and the circumstances under which people are exposed to such disorders. Echoing these remarks, Kai-Nan An, Mayo Clinic, noted that inconsistencies in the definitions and diagnosis of work-related repetitive stress injuries makes the true incidence of such injuries and the factors that provoke them difficult to identify.

Overall, the paper authors and discussants agreed that sound research shows that muscles, tendons, ligaments, and nerves can fail when subjected to sufficient force and that they can heal and repair themselves over time under the appropriate conditions (restriction or cessation of force and gradual reconditioning). However, there was also agreement that work remains to be done in establishing the links between impetus to injury to soft tissue response, on one side, and optimal conditions (either physical or environmental) for healing and repair of injury, on the other.

We now have the biomechanical and mechanobiological concepts and techniques to begin rigorous study that could lead to progress in prevention and treatment of these [musculoskeletal] disorders. The challenge is to bring first-rate mechanics, biology, and clinical perspectives together in order to approach the [research] problems in a unified, consistent manner.

(Dennis Carter, Stanford)

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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Work Factors, Individual Host Factors, and Internal Loads: Biomechanics of Work Stressors

Presentation

Work Factors and Biomechanics

Robert Radwin and Steven Lavender

The key tissues involved in the development of work-related musculoskeletal disorders (bone, ligament, tendon, muscle, disc, and nerve tissues) are stressed or loaded during the performance of work tasks in ways that can be predicted by theory and observed using diverse measurement methods. Tissue stress may be influenced by exertion, posture, contact stress, vibration, and variations in temperature. There is a considerable body of empirical evidence and findings, using models, that support relationships between external loads and the associated internal loads that can damage key tissues. This evidence not only supports a relationship between external and internal loads, but also demonstrates that, because of the biomechanics of the musculoskeletal system, internal loads are generally several times higher than the external loads that generate them.

Typically, theoretical models used to predict relationships between external and internal loads are mathematical representations of musculoskeletal mechanics that predict tissue reactions under external force. For example, Armstrong and Chaffin (1979) used a mathematical model of the mechanical relationships between belts and pulleys to describe the external forces, postures, and internal tendon positions that induce loads in the carpal tunnel of the wrist. If a tendon sliding over the surface of the wrist is considered analogous to a belt wrapped around a pulley, then the mathematical expression of this relationship predicts that the external force generated by the exertion of the hand is proportional to the compressive force of the internal tension developed in the tendons over the wrist and in the finger flexor muscles. This tension can affect adjacent anatomical structures such as ligaments and bones. The model also predicts that if the tissue lining the tendon (the synovia) becomes inflamed, internal tension increases. Repeated tension can further aggravate inflammation and induce swelling (Chaffin and Andersson, 1991).

Empirical observation of the relationship between external and internal loads requires a variety of measurement methods. External loads that impact internal tissues are rarely measured directly due to the obvious risks associated with subjecting people to potentially damaging levels of physical force and the invasiveness of direct measures of internal tissue responses. Direct measures are found in cadaver studies: they show the geometric and mechanical properties of tissues and their responses to external loads, including the order in which tissues respond. For example, Adams et al. (1980) found that severing ligaments in cadaver lumbar motion segments demonstrates that the supraspinous/interspinous ligament segments are the first ligament tissues to be-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

come stressed when there is forward bending of the lumbar spine. Other measures of external and internal stress relationships come from the use of force gauges and electromyography in studies of people engaged in physical activities that involve a range of exertion, posture, vibration, and temperature. These studies have been conducted both in laboratories and workplaces.

Physical stress factors in the workplace can be measured by observational surveys of the physical demands of jobs or tasks, by time and motion studies in which specific data are collected to assess physical stress, and by analytical examination of workplace layout and work processes (especially material flow and work scheduling). If hand tools are required, study of the exertion and the type of grip needed to use them can be made. These measures are considered less accurate and precise than more direct measures, partly because their ability to link external and internal stresses is limited and partly because they rely more on human observation. An example of an observational study measure is the comparison between a workplace designed so that workers must lift heavy objects from a low position and one in which the lift starts at a higher position. Biomechanical theory and laboratory studies show that the low-level lift results in greater spine and disc compression than the high-level lift. Observation and worker self-reports parallel findings from laboratory studies and from models.

Time and motion analyses indicate that the pace of work can also influence the duration and repetitiveness of exertion. These findings, coupled with laboratory results, suggest that faster pacing exacerbates the contraction of soft tissues, although it is known that their ability to perform static contraction decays rapidly over time. Planned job rotation can provide relief from potentially damaging lift, stretch, and repetition exposures. Workers can move from a task that requires shoulder abduction, for example, to one that requires low-level lifting, thus allowing both the shoulder muscles and the spine to recover.

Individuals vary in their internal tissue response to external loads or stresses. Anatomical and physiological differences—including muscle mass, tendon size, ligament range, and bone lengths, for example—can influence the impact of work tasks on individual tissues. Anatomical and physiological factors can also differ with age and gender. Moreover, exposure to physical stresses outside the workplace can influence tissue response.

There is a significant range of measurement, accuracy, precision, and reliability in studies of the relationships between external forces and their impact on internal tissue responses. Taken as a whole, these studies support the link between the physical stresses of work and their impact on the human musculoskeletal system.

Discussion

The relationships among external work factors, external and internal loads, and soft tissue responses (as shown in Figure 1) have been studied extensively, using models, human laboratory studies, and workplace analyses. Exertion, posture, contact stress, vibration, and varying temperatures are all types of external forces or loads that

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

are associated with physical activities. The studies described by the paper and discussants demonstrate that the physical activities of work, daily living, and recreation produce external loads that can be used to estimate internal loads on soft tissues. These estimates of internal loads often approach the mechanical limits of soft tissues, and, in some cases, for some individuals, exceed those limits. The studies also show that soft tissues vary in their responses to loading. Muscle tissue, for example, is better able than nerve tissue to adapt to the types of repetitive loading that can be observed in some workplace environments. In general, the findings of these biomechanical studies, especially when combined with the earlier findings from studies of soft tissue responses, strongly support a relationship between musculoskeletal disorders and external physical stress.

There was a general consensus among the workshop participants invited to discuss the Radwin and Lavender paper. Most clearly agreed that there is enough scientific evidence to confirm that strain on musculoskeletal tissue increases when humans perform physical activities that involve forceful manual exertions, awkward postures, repetitive or prolonged exertions, exposure to vibrations, and exposure to cold temperatures. Discussants differed in their views on the soundness of methodologies used to produce the evidence, in particular, several were skeptical about the reliability of at least some of the observational and analytical methods used in workplace studies.

In some areas, problematic loading conditions have been clearly delineated. For example, epidemiological studies have repeatedly linked adverse health outcomes with repeated lifting and working of the trunk bent forward, to the side, or twisted.

(Carolyn Sommerich, North Carolina State University)

Several themes emerged in the workshop discussions. Some discussants reinforced and expanded on ideas addressed in the Radwin and Lavender paper; others noted omissions from the paper that, if filled in, could strengthen its conclusions. On the omissions side, several discussants noted the lack of treatment of epidemiological studies that discuss musculoskeletal injury rates in relation to biomechanics. They believe that these links help to establish dose response relationships between external factors and tissue damage, although the relationships are often only at "high/low" level of detail.

Richard Wells, University of Waterloo, noted that the paper does not clearly delineate the fact that different histories of external loading may produce different injuries or disorders. As an example, he noted that a single high load on a spinal motion unit may produce an end plate fracture, while low continuous loading, especially in a flexed spinal position, may lead to disc herniation. Thus, sitting in a "low demand" situation may produce injury. Similarly, in muscles, a single, high-force contraction and low-force, long-duration contractions produce different outcomes. These aspects of soft tissue responses help explain apparently paradoxical findings that both high loads and

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

low loads (as in sitting) may be associated with low back pain and that high demand manual tasks and low demand manual tasks (such as keyboard work) may lead to upper limb disorders.

The carpal tunnel syndrome (CTS) may de-serve more detailed [scrutiny ] since there is much controversy over CTS and its biomechanical causation.

(Mark Redfern, University of Pittsburgh)

Another omission noted by several discussants was the lack of representation of the range of views on the relationships between biomechanical measures and specific injuries. Mark Redfern, University of Pittsburgh, observed that there is controversy over the biomechanical causation of carpal tunnel syndrome. He also noted that there are differing opinions about how biomechanical measures are related to musculoskeletal disorders and about how such measures are used.

Discussant themes that reinforced and expanded on the points made by Radwin and Lavender include Robert Norman's and W. Monroe Keyserling's comments about the strengths and weaknesses of contemporary methods of workplace analysis. Robert Norman, University of Waterloo, observed that many of the workplace methods that have been used to estimate physical loads are not believed to be highly reliable. These include worker self-reports, checklists, and the use of job titles. W. Monroe Keyserling, University of Michigan, observed that many of the methods discussed in the paper (trained observations, video analysis, electromyography, and goniometry) can produce reliable risk exposure information for jobs that have relatively short cycle times (such as assembly line jobs) or for non-cyclical jobs performed primarily at a single workstation (such as those of telephone operators for an airline). However, numerous jobs remain very difficult to analyze because they involve variability in work activities, locations, and exposures to musculoskeletal stressors. Improvements in workplace analysis methods could better capture the complexities of many jobs.

Many researchers. . . in this area [biomechanics of work and musculoskeletal disorders] still focus on physical or nonphysical factors. . .[This ] may influence their conclusions ... about the relative importance of these factors. The science base. . .[is] enhanced when researchers form interdisciplinary teams. . .[make] assessments across the range of. . . influential factors.

(Carolyn Sommerich, North Carolina State University)

Finally, all discussants agreed with the paper authors that the difficulties of directly measuring the relationships between external force and internal injury makes refinement of knowledge a challenge in this area of research. The need to more clearly isolate external work forces from those of workers' characteristics (anatomy, strength) and life-styles in their impact on musculoskeletal disorders adds to the research challenges. Carolyn Sommerich, North Carolina State University, Raleigh, called for in-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

terdisciplinary research teams to conduct joint investigations on the range of potential factors—workplaces, life-styles, workers' physical characteristics, and a variety of methodological measures.

Epidemiology: Physical Factors

The steering committee decided to use a recent review of the epidemiological studies of work-related musculoskeletal disorders by the National Institute for Occupational Safety and Health (NIOSH) (Bernard et al., 1997) as a starting point for its review of the research literature. The review examines the strengths and weaknesses of 600 selected studies investigating exposure to musculoskeletal disorders in the workplace. The steering committee invited a group of respected epidemiologists to discuss the NIOSH review and the epidemiological studies it covered. These six experts—from within and outside the field—submitted written comments and participated in a panel discussion at the workshop.

The panelists were asked by the steering committee to use four questions to organize their reviews and comments:

  1. Has NIOSH missed or overlooked any important body of epidemiological evidence it its review?
  2. Describe the methodologies of the studies that have been heavily weighted in the NIOSH assessment. What is the general quality of these studies?
  3. Would either the inclusion of any omitted studies or the reassessment of the quality of those reviewed substantially alter the interpretation of the epidemiological evidence that certain physical stressors in the workplace increase the risk of acquiring certain musculoskeletal disorders [MSDs]?
  4. What does the evidence [in the NIOSH review] tell us about the incidence [of MSDs] in the general population versus among specific groups of workers? In most cases, the panelists restricted their reviews to NIOSH coverage of studies involving exposure to work-related biomechanical stressors of the upper extremities, neck, and back. The panel discussion was moderated by Ronald Gray.
  5. Panel Discussion

    Bradley Evanoff, Alfred Franzblau, Fredric Gerr, Laura Punnett, Howard Sandler (with Richard Blume), and David Wegman

    The general consensus of the panelists was that there is strong evidence from many studies for a positive relationship between the conduct of work and the occurrence of musculoskeletal disorders of the upper extremities, neck, and back. This relationship is especially clear in studies involving high levels of exposure to workplace biomechanical

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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stressors. Examples include the excesses of musculoskeletal disorders of upper extremities among auto assembly workers and sawyers and the excesses of musculoskeletal disorders of the back among materials handlers and health care workers. It is also clear that in such high exposure cases the reduction of biomechanical stress also reduces the prevalence of musculoskeletal disorders. The evidence for the role of biomechanical stress in the occurrence of musculoskeletal disorders among work populations exposed to low levels of biomechanical stress is weaker, although several high quality studies suggest that further investigation is warranted.

In response to the first question—on the comprehensiveness of the NIOSH study—the panelists generally agreed in answering: No. However, some qualifications were noted. For example, NIOSH could have usefully included a listing of the studies not considered in its review but identified in its search; some specific additional studies were discussed by several panelists, but they agreed that no important body of evidence was omitted. Disagreements with the comprehensiveness of the NIOSH review also focused on the lack of assessment regarding the full range of musculoskeletal disorders, the neglect of specific dose relationships and threshold ''triggers" of exposure in specific disorders, and the focus on work related factors over non-work-related factors.

In answer to the steering committee's second question—on the weighting and quality of the studies—the panelists generally agreed that the study methods most heavily weighted in the NIOSH review resulted in examination of high-quality studies. Several panelists noted that study methodology was not the sole criterion that NIOSH used to select studies and that NIOSH's comprehensive approach used multiple criteria, including: high participation rates; appropriate "blinding" of investigators; health outcomes defined by symptoms, physical examinations, and independent exposure measures; and explicit criteria for causality that met standard epidemiological practices. Many panelists noted the lack of longitudinal studies in the review, but they emphasized the strengths of well-planned cross-sectional studies, as well as the difficulties and potentially confounding factors in conducting longitudinal studies in the workplace. They noted that the review included many study designs, including ones that were population based, case control, cross-sectional, and case series.

Several panelists suggested that the diagnostic definitions of carpal tunnel syndrome used in many of the studies were problematic since evidence for this diagnosis requires electrodiagnostic measures. Others suggested that some studies of questionable quality were included in the review and that the methods NIOSH used in selecting and weighting studies were not repeatable.

Although inconsistencies and problems in the NIOSH review were noted by many panelists, their answer to the third question posed by the steering committee—on the effects of omitted studies or reassessment of the quality of included studies—were nearly unanimous: No. Fredric Gerr noted that more rigorous elimination of studies failing to meet all NIOSH's outlined criteria would substantially reduce the number of studies available for review, but that this smaller body of literature would not substantively change the conclusions drawn by NIOSH regarding work and musculoskeletal disorders. In dissent, however, Howard Sandler said that the NIOSH approach to their

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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review of the evidence was sufficiently flawed to make the conclusions questionable. He stated that NIOSH failed to specify the methodology used to perform weighting, that many of the cited studies had serious deficiencies, and that the cross-sectional studies were particularly weak.

The steering committee's fourth question—on the disorders in the general population versus among specific groups of workers—was acknowledged by all the panelists to be difficult to answer. Although several panelists noted that studies show a higher than expected rate of the disorders among workers with high exposures to physical risk factors, they also agreed that there were very few studies of the incidence or prevalence of specific musculoskeletal disorders in the general population. Even the existing studies are old enough to be suspect, and virtually none are longitudinal. For example, the most recent study of carpal tunnel syndrome incidence in the general population is based on data collected from 1961 to 1980, and incidence may have greatly increased in recent years; in addition, the accuracy and completeness of the data in the study are open to question.

Workshop Discussion

Workshop participants offered both criticisms and support of the NIOSH review. For example, Robert Szabo, University of California, Davis, suggested that even though not one of the studies cited by NIOSH had implicated keyboarding as a cause of carpal tunnel syndrome, the report suggests that keyboarding is a cause. David Florence, American Academy of Orthopedic Surgeons, added that a problem that exists in practice is that workers fabricate musculoskeletal injuries, perhaps as a result of the widespread publicity such injuries have received. Thomas Mayer, PRIDE, Dallas, Texas, observed that there are also macroeconomic implications of concluding that exposure to risk factors at work is associated with higher rates of musculoskeletal disorders, making the review of any evidence in this area a political as well as a scientific discussion. Peter Nathan, Portland Hand Surgery Rehabilitation Center, Oregon, maintained that NIOSH had ignored studies examining the role of nonoccupational factors in the etiology of carpal tunnel syndrome.

I believe the NIOSH document is one of social and political interest . It is not a scientific document; it is a political statement, it is a social statement, and we should acknowledge that. For the most part, only articles suggesting a positive association between work exposure and neuromusculoskeletal symptoms are cited. If an article questioning the work-related hypothesis is presented, the discussion is highly critical. In general, the document does not discuss studies which examine nonoccupational causes of carpal tunnel syndrome.

(Peter Nathan, Portland Hand Surgery Rehabilitation Center)

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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In contrast, several workshop participants offered views supporting the general consensus of the panelists and the NIOSH review. For example, Paulien Bongers, TNO Prevention and Health, Netherlands, noted that the systematic reviews of the evidence that she had conducted, including both longitudinal and cross-sectional studies, supported the NIOSH conclusions. Margaret Seminario, AFL-CIO, emphasized that the question the NIOSH review, the panel, and the workshop must address is not whether the scientific evidence is perfect, but whether it is sufficient to justify interventions. She added that she finds the evidence is sufficient.

The world I come from is one more concerned with policy issues involving how to use the scientific research base in protecting workers. In the context of policy decisions, we do not need perfect information . We need to know that there is a scientific base showing there is risk in the workplace for exposure t factors associated with musculoskeletal risks and that interventions can reduce this risk.

(Margaret Seminario, AFL-CIO)

Non-Biomechanical Factors That Can Affect Musculoskeletal Disorders

Presentation

Epidemiological Evidence that Non-Biomechanical Factors Can Cause Musculoskeletal Disorders

Julia Faucett and Robert A. Werner

Multiple occupational risk factors have been proposed for common musculoskeletal disorders, but a growing number of investigators around the world are reporting relationships between individual factors and non-biomechanical aspects of work and these disorders. Individual factors include age; ongoing medical conditions, such as diabetes or rheumatoid arthritis; weight and height; gender; levels of individual physical conditioning; and inherited anatomical variations, especially in the wrist. Non-biomechanical factors arise from the way work is organized, integrated, and controlled. These things can affect the psychological stress level of work, the degree of social support available, and the satisfaction workers obtain on the job.

Individual Factors

The ultimate mechanism of injury in carpal tunnel syndrome and cumulative trauma disorders is probably ischemia (or localized anemia due to contracted blood vessels) so that any individual factors influencing the health of the vascular system may compro-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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mise soft tissues. There is evidence from a number of well-designed studies to support a relationship between systemic disorders—especially diabetes and rheumatoid arthritis—and carpal tunnel syndrome and other disorders related to nerve compression and ischemia. These disorders, however, affect only a small percentage of active workers. Severe vitamin B6 deficiencies and gynecological conditions (pregnancy, use of oral contraceptives, surgery that affects hormones) have also been posed as risk factors, but the associations with carpal tunnel syndrome and related disorders, though statistically significant, are weak, and their clinical significance is low.

Increasing age has consistently been associated with the slowing of the median nerve across the wrist that is thought to be critical in carpal tunnel syndrome. The association between increased age and other cumulative trauma disorders and low back pain is weak. Studies have generally supported a relationship between obesity (as measured by body mass index ratios) and a diagnosis of carpal tunnel syndrome, but obesity explains less than 8 percent of the variance in such diagnoses. A relationship between obesity and other cumulative trauma disorders is not consistently found in studies of the industrial worker population. General fitness has been negatively associated with obesity and older age, but as an independent factor, it does not help to explain much of the variance in diagnoses of carpal tunnel syndrome, low back pain, or other cumulative trauma disorders.

Gender has also been suggested as an independent risk factor in carpal tunnel syndrome (that is, the prevalence of carpal tunnel syndrome is higher among women). Although there is some evidence supporting this higher prevalence, there are also inconsistencies among the gender study findings that require further investigation. Inherited characteristics of wrist shape and size, carpal tunnel size, and hand size have been investigated in carpal tunnel syndrome: there is strong evidence that a narrow carpal tunnel canal is associated with a diagnosis of carpal tunnel syndrome.

Organizational and Social Factors

Organizational, technological, environmental, and directly task-related features of work systems can influence workers' perceptions of work. These perceptions can, in turn, influence their performance of work in ways that may increase or decrease the likelihood of musculoskeletal disorders. For example, a managerial decision to increase production demands among data processors may evoke fear in an individual worker that he or she cannot complete the task on time. The result may be a change in that individual's work style that includes faster, harder key strokes, higher associated levels of catecholamines and cortisol, which may harm soft tissues, and detrimental delays in awareness of musculoskeletal discomfort.

Studies of non-biomechanical factors in the workplace can be categorized according to the factor emphasized in the investigation: job demands (work load, pace, fluctuations); job content (task variability, meaningfulness, and integration); job control (decision latitude, control over work pace and breaks); work role ambiguity; social relationships and support; and job satisfaction. Workplace investigations provide mod-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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erate support for relationships between job demands, job content, and job control and musculoskeletal outcomes. Generally speaking, poorly designed job content, unpredictable and heavy job demands, and lack of decision latitude or control are associated with higher incidence of musculoskeletal disorders. Studies of social relationships have shown that worker support, especially supervisory support, can moderate psychological stress on the job.

The scientific evidence on non-biomechanical factors varies considerably in method, making direct comparisons across studies difficult. Longitudinal studies are sparse. Data on worker perceptions were most frequently measured through worker self-reports, although observational methods have also been used. Outcome measures were sometimes clinical and sometimes reported symptoms, and surveys of non-biomechanical factors used a diversity of measures. Few studies investigated interactions among non-biomechanical factors. Despite these methodological weaknesses, there were moderate, but significant relationships between non-biomechanical factors and the incidence of musculoskeletal disorders across studies. Such consistency suggests that non-biomechanical factors must be considered in investigation of work-related musculoskeletal disorders.

Discussion

Individual, organizational, and social factors (see Figure 1) are possible influences on the physiological pathways that lead from soft tissue loading to the impairment and disability of musculoskeletal disorders. In reviewing the scientific literature on non-biomechanical factors, both the paper authors and the workshop discussants universally acknowledged that the number of such factors is potentially unlimited and thus any review has to narrow the factor set to a manageable number. The broad range of non-biomechanical factors also leads to a range of study methods and measures that complicates comparisons across studies. Diversity, however, can be a strength in evaluating evidence if findings from such different kinds of studies reinforce one another. The workshop authors and discussants generally agreed that there was sufficient mutually reinforcing evidence from these studies to support several findings:

  • Individuals vary in their susceptibilities to musculoskeletal disorders, especially along the dimensions of systemic vascular disorders (diabetes, rheumatoid arthritis), age, and to a more limited extent, body mass, genetics, and general conditioning.
  • Organizational and psychosocial factors associated with work design, work social supports, and individual responses to workplace stress can be reasonably assumed as risk factors for higher rates of work-related musculoskeletal disorders. Studies have demonstrated that poorly designed jobs, highly demanding workloads and pace, and low levels of worker control on the job can be associated with higher rates of musculoskeletal disorders. Social support at work can lower these rates.
  • Non-biomechanical factors can be thought of as moderators, but no one suggests
Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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  • that they are the primary causes of injury. However, they may change the likelihood of the severity of injury.

* Non-biomechanical factors must be considered if understanding of the relationship between biomechanical work factors and musculoskeletal disorders is to expand and inform the design of workplace interventions to reduce or prevent such disorders.

There was less consensus among workshop discussants about the relative importance of non-biomechanical and biomechanical factors as risk factors in workplace musculoskeletal disorders. The paper authors and several discussants agreed that non-biomechanical factors had modest effects in explaining differences in the rates of musculoskeletal disorders reported in the workplace. Others disagreed. Peter Nathan, Portland Hand Surgery Rehabilitation Center, Oregon, observed that it is essential to observe the patterns of musculoskeletal disease in the general population and ask how those individuals who are at risk perform when challenged at work. General health risk factors must take primacy in modeling the etiology of bodily discomfort. Samuel Moon, Duke University Medical Center, offered the view that the research offers little guidance as to which factors should be most heavily weighted.

This research base does not resolve questions of directionality. It provides ample warning that workplace musculoskeletal disorder prevention programs should not ignore psychosocial factors. . . (Samuel Moon, Duke University Medical Center)

Others agreed in qualified ways with the notion that non-biomechanical factors play a modest role in workplace musculoskeletal disorders. For example, Robert Gatchel, University of Texas, Dallas, noted that the importance of non-biomechanical factors in studying workplace musculoskeletal disorders cannot be well understood without looking beyond primary risk factors to secondary and tertiary risk factors. Primary prediction of musculoskeletal disorders only looks at questions about which factors constitute risk for injuries. Secondary prediction examines questions about which workers are at risk. Tertiary prediction explores which workers with chronic injuries can be effectively returned to work. The highest costs to employers, workers, and the medical system are incurred with chronically injured workers, especially those who cannot be effectively treated to return to work. Non-biomechanical factors can play an important role in secondary and tertiary prediction.

Several discussants noted the lack of attention in the paper to musculoskeletal disorders involving the lower extremities. Paulien Bongers, TNO Prevention and Health, Netherlands, noted that individual factors (especially smoking) and psychosocial factors have been shown in several systematic studies to be related to low back pain. Robert Gatchel, University of Texas, Dallas, noted that workers' compensation status or personal injury status (not covered in the papers) should be considered an

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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important predictor of the rates of musculoskeletal disorders, since it is an important predictor of related chronic disorders.

Overall, the majority of discussants and the paper authors agreed that more research integrating biomechanical and non-biomechanical factors would be useful and that more attention should be paid to multi-trait, multi-method approaches in designing systematic studies of predictor factors.

Intervention to Control Musculoskeletal Disorders

Presentation

The Research on Interventions to Control Musculoskeletal Disorders

Michael J. Smith, Ben-Tzion Karsh, and Francisco B.P. Moro

The purpose of interventions to control musculoskeletal disorders in the workplace is to reduce or eliminate stresses that overload the individual worker's capacity to accommodate or adapt without musculoskeletal strain and eventual disorders. Such loads can come from a variety of sources that have been discussed in other papers (see Figure 1).

There are a variety of workplace interventions that have been used to reduce or eliminate work-related musculoskeletal disorders, including: engineering redesign, changes in work methods, administrative controls, training, organized exercise and work "hardening," protective equipment, and medical management to reduce exposure. Engineering redesigns include the redesign of machinery or tools and the provision of ways to assist work. An example of machinery redesign is realignment of work station controls to allow for more natural body postures. A tool redesign example is the reduction of hand tool weight or an improved grip, both of which reduce loads on the body. Ways to assist work include lifting tables or hoists, such as those used in hospitals to lift patients. Engineering redesigns primarily involve ways to reduce biomechanical risk factors.

Work methods improvements, administrative controls, and employee training can also reduce biomechanical risk factors, and they can also influence the psychosocial work environment. An example is retraining employees in improved meat cutting techniques to reduce the frequency of cutting motions and improve body postures while cutting. Administrative control changes are designed to reduce risks by rotating workers through different jobs and tasks and by prudent use of rest breaks. Personal protective equipment is designed to block employees from contact with hazards: examples are the required use of gloves to protect against hand injuries from vibrating tools and the use of back belts in jobs that involve lifting. Finally, exercise and work hardening

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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programs are meant to increase the capacity of employees to adapt to work conditions by increasing strength, flexibility, or tolerance of pain.

Of 720 identified intervention research articles, 43 were selected for detailed examination. Conservative criteria were followed in selecting this small group of studies: the use of controls, an accounting for confounding factors, relevant measures, randomized trials, and a blind evaluation. Although not all the examined studies met all these criteria, all met basic conditions for methodological soundness. Fifteen laboratory studies, 15 field studies of injured employees, and 13 field studies of healthy employees were examined. All the studies involved deliberate manipulation of work conditions factors to reduce exposure and risk.

Laboratory studies have the advantage of randomized trials, control over the interventions and other experimental conditions, and, often, the use of control groups. However, these studies may suffer from the use of study subjects who are different from workers of interest, they may not always involve representative work tasks, and they may involve duration and intensity of exposure to risk that is often much lower than is typical in workplaces. On the other side, field study results are often difficult to interpret because they may involve multiple interventions, low levels of control over potentially confounding factors that occur naturally in the work environment, and limited availability of true control groups not treated with the intervention(s). Given the tradeoffs between laboratory and field studies, it is clear that both are needed to gain a more complete picture of the effectiveness of interventions to control work-related musculoskeletal disorders.

Several findings can be drawn from the 43 studies examined:

  1. Alternative tools designed to improve hand and wrist postures and reduce forces on the palm and fingers can reduce the risk of upper extremity musculoskeletal disorders. Weight handling devices such as hoists can also reduce these risks.
  2. The evidence on both proper lifting posture and the use of backbelts is unclear.
  3. Exercise, back school, and physical therapy interventions for injured workers can reduce musculoskeletal pain and symptoms, reduce the use of sick leave, and result in earlier return to work. Exercise interventions seem especially promising. However, most studies involved multiple interventions, and it is not possible to determine the effects of any one intervention.
  4. Among healthy workers, ergonomic interventions appear to have positive effects on the incidence of musculoskeletal discomfort, cumulative trauma disorders, and accidents.
  5. Despite recognized weaknesses and gaps, the intervention literature suggests that some interventions can influence the occurrence, recurrence, and severity of low back disorders and can reduce the risks associated with low back and upper extremity disorders. Physical exercise programs and hand tool and hoist designs, in particular, have shown benefits. There is value in pursuing research on interventions, especially re-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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search that deals with such questions as: Which interventions can be most beneficial for which circumstances? What are the mechanisms through which interventions produce benefits? How are multiple interventions related to each other and to the success of reducing or preventing musculoskeletal disorders?

Discussion

Workshop discussants generally agreed with the authors of invited papers that there is considerable diversity in the nature and quality of the research conducted on interventions. Martin Cherniack, University of Connecticut Health Center, noted that it is "a rapidly growing and unruly literature that highlights essential contradictions and logical inconsistencies in laboratory based and applied survey methods." Many discussants were willing to go beyond the paper authors in considering a broader range of studies as evidence that work-related musculoskeletal disorders can be reduced or prevented with interventions. Several discussants noted the many practical ergonomic programs in place at work sites around the globe that offer evidence of results. Thorough case studies of such programs, accepted for publication under peer review, meet many of the criteria set forth by well-respected methodologists.

The etiology of work-related musculoskeletal disorders indicates that multiple biomechanical, psychosocial, and personal factors interact , resulting in injury. Effective ergonomic interventions will need to be analyzed from a multidisciplinary approach, as well as in terms of individual effects from specific interventions. (Linda Cocchiarella, American Medical Association)

Other discussants went even further in saying that the requirements of research for regulatory purposes are different from those of research that meets strictly methodological criteria. For example, Scott Schneider, Laborers' Health and Safety Fund of North America, noted that intervention research is hard to conduct and hard to get funded. Clinical trials, randomized controls, full-scale epidemiological investigations, and 2-year follow-up studies are not needed to say that an intervention is successful. Schneider offered several examples from an earlier NIOSH review of ergonomic interventions of engineering controls. One study showed improvements in electromyographic measurements, which had previously indicated dysfunction, and increased productivity among truck drivers using a new cab design. Schneider then posed the question: "If this type of information is sufficient for most employers to decide whether interventions are effective enough to make purchasing decisions, shouldn't they then be sufficient for us?" Several company representatives (Thomas Albin, 3M; Brad Joseph, Ford Motor Company; Wendi Latko, Xerox; and Robert Morency, L.L. Bean) offered examples of their companies' ergonomic interventions that have yielded benefits and driven company interest in further interventions.

Several discussants noted that neither technology nor industry stands still for inter-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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vention studies. Stephen Burastero, Lawrence Livermore National Laboratory, observed that ergonomic product cycles outpace the publication of intervention research. Industry has often already acted on new products.

Finally, many discussants suggested that the paper authors had not examined psychosocial factors as mediators of interventions to the extent needed. They suggested that the multiple factors influencing the success of interventions should be addressed in future studies. For example, the extent of employee involvement in ergonomic interventions and the support of supervisors for using the interventions can influence their effectiveness.

Conclusion: Integration and Overview

The final session of the workshop was organized around a panel invited to offer an overview of perspectives voiced throughout the workshop. Chaired by steering committee cochair Colin Drury, the panel included Jacqueline Agnew, Sidney Blair, Donald Bloswick, Fredric Gerr, W. Monroe Keyserling, Susan Mackinnon, Steven Moore, Peter Nathan, Barbara Silverstein, Richard Szabo, and Richard Wells.

Panel Comments

Substantially all of the panel's major comments and observations reinforced points previously made throughout the workshop:

  • Musculoskeletal disorders are multifactorial, with work and the biomechanical aspects of work being important contributing factors. Research, especially integrative research, must continue.
  • Work factors that can contribute to musculoskeletal disorders include factors beyond the boundaries of a specific job or task. They include social and organizational factors, ranging from supervisory support to redesign of work to the involvement of employees in intervention design and delivery.
  • Individual factors also contribute to the incidence of musculoskeletal disorders seen in the workplace and in the general populations. This is especially true for systemic disorders (such as diabetes and rheumatoid arthritis) and age.
  • Interventions to reduce or eliminate the risks of musculoskeletal disorders in the workplace have been shown to be effective in some circumstances.
  • Physical conditioning programs appear to be especially promising. Ergonomic redesign of tools, workstations, and postural sequences have also been effective.

Jacqueline Agnew identified four particular issues raised during the workshop. First, with respect to interventions, there is interest in more than just primary interventions; secondary and tertiary interventions merit inquiry as well. Second, a question exists as to the outcomes that should be considered—that is, should the focus remain on medi-

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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cal diagnoses or also embrace reported symptoms? Third, are the musculoskeletal disorders under consideration serious enough to merit attention in a public forum and as a matter of public policy? Finally, she noted the differences that exist between the public health perspective and the clinical perspective, pointing out that during the workshop clinicians presented somewhat different viewpoints and emphasized somewhat different concerns than those of public health researchers.

Several other panelists echoed Agnew's questions about the seriousness of the musculoskeletal disorders that were the focus in the workshop (the emphasis on carpal tunnel syndrome and repetitive stress injuries had been denoted by several participants). Donald Bloswick, for example, urged that musculoskeletal disorders not be defined just in terms of carpal tunnel syndrome or upper extremity cumulative trauma disorder. He noted that the NIOSH report indicated that 700,000 workdays per year are lost due to musculoskeletal disorders, only 100,000 of which are upper extremity or repetitive trauma disorders. Susan Mackinnon suggested the need to educate the American public that keyboarding has not been shown to cause anything and that neuromusculoskeletal disorders are not dangerous and should not cause permanent disability. W. Monroe Keyserling noted that the focus of the workshop had been on injuries that result from repetitive job requirements, but that musculoskeletal disorders can result from irregular and sometimes unexpected events, which should also be seriously considered.

The importance of secondary and tertiary, as well as primary, conditions in understanding and intervening in the workplace were also reinforced and expanded on by other panelists, especially with regard to interventions. Richard Wells, for example, advocated a more applied research focus, particularly with respect to intervention research, so that ongoing changes can be better monitored and reported. Barbara Silverstein suggested that intervention research would gain from better feedback from employers and scientists to designers and manufacturers. More broadly, Peter Nathan argued that monies being spent on ergonomic assessments and many workplace interventions would be better spent on focusing and improving the overall health of workers.

General Discussion

The workshop ended with a number of comments from invited participants and the attending public. Several participants highlighted employers' perspectives. David Roy, Travelers Insurance, noted that employers must ask and get answers to questions about what to fix and how to fix it. He noted employers' uneasiness with the medical community's diagnosis of musculoskeletal disorders, especially in terms of numbers of such disorders reported, and employer concern with costs from faulty diagnosis and overreporting (coverage) above and beyond the costs of workplace preventive measures. Wendy Latko, Xerox Corporation, noted that employers cannot wait for research to be perfected before taking action in dealing with injuries and illnesses in the workplace. Xerox, for example, has taken a two-pronged approach emphasizing both wellness programs to enhance general fitness levels and the incorporation of sound

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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ergonomic principles in job and product design. Barbara Silverstein, Washington State Department of Labor and Industries, added that her department's surveys of employers in the state indicated that approximately one-third were directly dealing with workplace injuries and illnesses through engineering, organizational, and personal fitness education programs. Waldemar Karwowski, University of Louisville, emphasized that ergonomics does indeed offer principles that enable employers to design better work places and reduce work-related injuries.

Charles Barrett, International Union of Electronic and Electrical Workers, Margaret Seminario, AFL-CIO, and Scott Schneider, Laborers Health and Safety Fund, all emphasized the employees' perspective through the lens of organized labor. They noted that work-related musculoskeletal disorders are real and that they account for many days of lost work in addition to disabling injuries and suffering at work. Seminario echoed the view of many other participants that the workshop presentation and discussions were valuable because they enabled people from different perspectives to share information and interpretations.

References

Adams, M.A., W.C. Hutton, and J.R.R. Stott 1980 The resistance to flexion of the lumbar intervertebral joint. Spine 4:245-253.

Armstrong, T.J., and D.B. Chaffin 1979 Some biomechanical aspects of the carpal tunnel. Journal of Biomechanics 12:567-570.


Bernard, B.P., ed. 1997 Musculoskeletal Disorders and Workplace Factors : A Critical Review of Epidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back. Cincinnati, OH: U.S. Department of Health and Human Services.


Chaffin, D.B., and G.B.J. Andersson 1991 Occupational Biomechanics . Second Edition. New York, NY: John Wiley and Sons.


National Research Council 1998 Work-Related Musculoskeletal Disorders : A Review of the Evidence. Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries: The Research Base. Washington, DC: National Academy Press. [Part I of this volume]

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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Appendix A
Invitees and Participants, Workshop on Work-Related Musculoskeletal Injuries: Examining the Research Base

Participants

Jacqueline Agnew, Johns Hopkins University

Thomas Albin, 3M Company, St. Paul, Minnesota

Kai-Nan An, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Gunnar Andersson,* Rush Presbyterian-St. Luke's Medical Center, Chicago, Illinois

Thomas Armstrong,* University of Michigan, Ann Arbor

James Ashton-Miller, University of Michigan, Ann Arbor

Bruce Bernard, National Institute for Occupational Safety and Health, U.S. Department of Health and Human Services, Cincinnati, Ohio

Sidney Blair, Loyola University Medical Center

Donald Bloswick, University of Utah, Salt Lake City

Paulien Bongers, TNO Prevention and Health, Leiden, Netherlands

Stephen Burastero, Lawrence Livermore National Laboratory, Livermore, California

Dennis Carter, Stanford University

Martin Cherniack, University of Connecticut Health Center, Farmington

Linda Cocchiarella, American Medical Association, Chicago, Illinois

David Cochran, Occupational Safety and Health Administration, U.S. Department of Labor, Washington, DC

David Cordray,* Vanderbilt University

Theodore Courtney, Liberty Mutual Insurance Company, Hopkinton, Massachusetts

Mark Cullen,* Yale University School of Medicine

Carlo De Luca, Neuro Muscular Research Center, Boston, Massachusetts

Raymond Donnelly, Occupational Safety and Health Administration, U.S. Department of Labor, Washington, DC

Colin Drury,* State University of New York, Buffalo

Bradley Evanoff, Washington University School of Medicine

Julia Faucett, University of California, San Francisco

Lawrence Fine, National Institute for Occupational Safety and Health, U.S. Department of Health and Human Services, Cincinnati, Ohio

Baruch Fischhoff,* Carnegie Mellon University

David Florence, American Academy of Orthopedic Surgeons, Rosemont, Illinois

*  

Member, Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries: The Research Base

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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Alfred Franzblau, University of Michigan, Ann Arbor

Steven Garfin, University of California, San Diego

Arun Garg, University of Wisconsin-Milwaukee

Robert Gatchel, University of Texas, Dallas

Fredric Gerr, Emory University

Ronald Gray, Johns Hopkins University

Manny Halpern, New York University Medical Center

Steven Johnson, University of Arkansas, Fayetteville

Brad Joseph, Ford Motor Company, Dearborn, Michigan

Bentzi Karsh, University of Wisconsin-Madison

Waldemar Karwowski, University of Louisville

Michael Kerr, Institute for Work and Health, Toronto, Ontario, Canada

W. Monroe Keyserling, University of Michigan, Ann Arbor

Karl Kroemer, Virginia Tech

Mary Laedtke, U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, Maryland

Wendi Latko, Xerox Corporation, Webster, New York

Steven Lavender, Rush Presbyterian-St. Luke's Medical Center, Chicago, Illinois

Steven Lehman, University of California, Berkeley

Thomas Mayer, PRIDE, Dallas, Texas

Susan Mackinnon, Washington University School of Medicine

William Marras,* Ohio State University, Columbus

Gary Mirka, North Carolina State University, Raleigh

Samuel Moon, Duke University Medical Center

Steven Moore, Texas A&M University, College Station

Robert Morency, L.L. Bean, Inc., Freeport, Maine

Francisco Moro, University of Wisconsin-Madison

Peter Nathan, Portland Hand Surgery Rehabilitation Center, Portland, Oregon

Robert Norman, University of Waterloo, Ontario, Canada

Lida Orta-Anés, United Automobile Aerospace and Agricultural Implement Workers of America, UAW, Detroit, Michigan

Richard Pew,* Independent Consultant, Cambridge, Massachusetts

Malcolm Pope, University of Iowa

Laura Punnett, University of Massachusetts, Lowell

Robert Radwin, University of Wisconsin-Madison

Mark Redfern, University of Pittsburgh

David Rempel, University of California, San Francisco

David Roy, Travelers Insurance, Hartford, Connecticut

Howard Sandler, Sandler Occupational Medicine Associates, Inc., Melville, New York

Scott Schneider, Laborers' Health and Safety Fund of North America, Washington, DC

Margaret Seminario, AFL-CIO, Washington, DC

Barbara Silverstein, Washington State Department of Labor and Industries, Olympia

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

Mary Lou Skovron, Genentech, Inc., South San Francisco, California, and New York University School of Medicine

Michael Smith, University of Wisconsin-Madison

Moshe Solomonow, Louisiana State University Medical Center, New Orleans

Carolyn Sommerich, North Carolina State University, Raleigh

Robert Szabo, University of California, Davis

David Wegman, University of Massachusetts, Lowell

Richard Wells, University of Waterloo, Ontario, Canada

Robert Werner, University of Michigan, Ann Arbor

Invitees Who Were Unable to Attend

Peter C. Amadio, Mayo Clinic, Rochester, Minnesota

Mohamed M. Ayoub, Texas Tech University

Susan Baker, Johns Hopkins University

Stanley J. Bigos, University of Washington

Claire Bombardier, Institute for Work and Health, Toronto, Ontario, Canada

Patricia Buffler, University of California, Berkeley

Donald B. Chaffin, University of Michigan, Ann Arbor

Harvey Checkoway, University of Washington

Jerome Congleton, Texas A&M University

Thomas Cook, University of Iowa

Marvin J. Dainoff, Miami University, Oxford, Ohio

Richard Deyo, University of Washington

Michael Feuerstein, Uniformed Services University of the Health Services, Bethesda, Maryland, and Georgetown University School of Medicine

Adam Finkel, Occupational Safety and Health Administration, U.S. Department of Labor, Washington, DC

Gary Franklin, University of Washington

Andris Freivalds, Pennsylvania State University

John Frymoyer, University of Vermont

Nortin Hadler, University of North Carolina School of Medicine, Chapel Hill

Hal Hendrick, Consultant, Englewood, Colorado

William Howell,* Arizona State University, Tempe

Morton Kasdan, Physician, Louisville, Kentucky

Jeffrey Katz, Brigham and Women's Hospital, Boston, Massachusetts

Jennifer Kelsey, Stanford University

Jess F. Kraus, University of California, Los Angeles

Steven Lamm, Consultants in Epidemiology and Occupational Health, Inc., Washington, DC

Tom Leamon, Liberty Mutual Insurance Company, Hopkinton, Massachusetts

Steven Linton, Orebro Medical Center Hospital, Orebro, Sweden

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

Paul Marxhausen, University of Nebraska at Lincoln

Stuart McGill, University of Waterloo, Ontario, Canada

Steven Newell, Organization Resources Counselors, Washington, DC

Robert Ochsman, Consumer Products Safety Commission, Lovettsville, Virginia

Suzanne Rodgers, Consultant, Rochester, New York

Steven L. Sauter, National Institute for Occupational Safety and Health, U.S. Department of Health and Human Services, Cincinnati, Ohio

Stover H. Snook, Harvard School of Public Health

Carol Stuart-Buttle, Stuart-Buttle Ergonomics, Philadelphia, Pennsylvania

David Vlahov,* Johns Hopkins University

Kathryn G. Vogel, University of New Mexico

Laura Welch, Washington Hospital Center, Washington, DC

Savio Woo, University of Pittsburgh

Craig Zwerling, University of Iowa

Staff

E. William Colglazier, Executive Officer, National Research Council

Barbara Boyle Torrey, Executive Director, Commission on Behavioral and Social Sciences and Education

Alexandra Wigdor, Director, Division on Education, Labor, and Human Performance

Anne Mavor, Study Director, Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries

James McGee, Senior Research Associate, Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries

Renae Broderick, Writer/Editor, Cornell University, Ithaca, New York

Susan Coke, Administrative Associate, Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries

Susan McCutchen, Senior Project Assistant, Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries

Nat Tipton, Senior Project Assistant, Division on Education, Labor, and Human Performance

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

Appendix B

Workshop on Work-Related Musculoskeletal Injuries: Examining the Research Base

August 20-21, 1998 Auditorium,

National Academy of Sciences

2101 Constitution Avenue, N.W., Washington, DC

AGENDA

Thursday, August 20

7:30 a.m.

Continental Breakfast

Room 250: Participants A-J

Room 280: Participants K-Z

Public: Cafeteria is available to purchase breakfast

8:30 a.m.

Welcome and Introduction

William Colglazier and Richard Pew

8:50 a.m.

BIOLOGICAL RESPONSE OF TISSUES TO STRESSES: MUSCLES, TENDONS, AND NERVES

INVITED PAPER ON MUSCLES AND TENDONS: James Ashton-Miller

Panel Discussion: Kai-Nan An, Sidney Blair, Dennis Carter, Carlo De Luca, Steven Lehman, Steven Moore, Moshe Solomonow,

Questions from Invited Participants

INVITED PAPER ON NERVES: David Rempel

Panel Discussion: David Florence, Steven Garfin, Thomas Mayer, Susan Mackinnon, Robert Szabo

Questions from Invited Participants

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

10:50 a.m.

Break

11:15 a.m.

WORK FACTORS, INDIVIDUAL HOST FACTORS, AND INTERNAL LOADS: BIOMECHANICS OF WORK STRESSORS

INVITED PAPER: Robert Radwin and Steven Lavender

Panel Discussion: Arun Garg, W.Monroe Keyserling, Robert Norman, Mark Redfern, Carolyn Sommerich, Richard Wells

Questions from Invited Participants

12:30 p.m.

Lunch

Room 250: Participants A-J

Room 280: Participants K-Z

Public: Cafeteria is available to purchase lunch

1:30 p.m.

EPIDEMIOLOGY: PHYSICAL FACTORS

Panel Discussion

Moderator: Ronald Gray

Panelists: Bradley Evanoff, Alfred Franzblau, Fredric Gerr, Laura Punnett , Howard Sandler, David Wegman

Questions from Invited Participants

3:30 p.m.

Break

4:00 p.m.

General Discussion with Paper Presenters: Invited Participants and Public

Friday, August 21

8:00 a.m.

Continental Breakfast

Room 250: Participants A-J

Room 280: Participants K-Z

Public: Cafeteria is available to purchase breakfast

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
×

9:00 a.m.

NON-BIOMECHANICAL FACTORS POTENTIALLY AFFECTING MUSCULOSKELETAL DISORDERS

INVITED PAPER: Julia Faucett and Robert Werner

Panel Discussion: Jacqueline Agnew, Paulien Bongers, Robert Gatchel, Michael Kerr, Samuel Moon, Peter Nathan

Questions from Invited Participants

10:15 a.m.

Break

10:45 a.m.

INTERVENTIONS TO CONTROL MUSCULOSKELETAL DISORDERS

INVITED PAPER: Michael Smith

Panel Discussion: Donald Bloswick, Stephen Burastero, Martin Cherniack , Linda Cocchiarella, Brad Joseph, Lida Orta-Anés, Scott Schneider, Barbara Silverstein

Questions from Invited Participants

12:00 p.m.

Lunch

Room 250: Participants A-J

Room 280: Participants K-Z

Public: Cafeteria is available to purchase lunch

1:00 p.m.

Panel on the Integration of Workshop Presentations and Discussions Chair: Colin Drury Panelists: Jacqueline Agnew, Sidney Blair, Donald Bloswick, Alfred Franzblau, Fredric Gerr, W.Monroe Keyserling, Susan Mackinnon, Steven Moore, Peter Nathan, Barbara Silverstein, Robert Szabo , Richard Wells

2:00 p.m.

Questions and Comments from Invited Participants and Public

Suggested Citation:"II Workshop Summary." National Research Council. 1999. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press. doi: 10.17226/6431.
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Estimated costs associated with lost days and compensation claims related to musculoskeletal disorders—including back pains and repetitive motion injuries—range from $13 billion to $20 billion annually. This is a serious national problem that has spurred considerable debate about the causal links between such disorders and risk factors in the workplace.

This book presents a preliminary assessment of what is known about the relationship between musculoskeletal disorders and what may cause them. It includes papers and a workshop summary of findings from orthopedic surgery, public health, occupational medicine, epidemiology, risk analysis, ergonomics, and human factors. Topics covered include the biological responses of tissues to stress, the biomechanics of work stressors, the epidemiology of physical work factors, and the contributions of individual, recreational, and social factors to such disorders. The book also considers the relative success of various workplace interventions for prevention and rehabilitation.

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