Once a decision has been made to initiate an ergonomics program, a necessary step is to gather information to determine the scope and characteristics of the problem or potential problem. A variety of techniques and tools have been used; many provide the basis for developing solutions to identified problems.

Health and Medical Indicators

Following up of worker reports

Assuring that employees feel free to report, as early as possible, symptoms of physical stress is a key component of any ergonomics program. Early reporting allows corrective measures to be implemented before the effects of a job problem worsen. As mentioned earlier, individual worker complaints that certain jobs cause undue physical fatigue, stress, or discomfort may be signs of ergonomic problems. Following up on these reports, particularly reports of WMSDs, is essential. Such reports indicate a need to evaluate the jobs to identify any ergonomic risk factors that may contribute to the cause of the symptoms or disorders. Techniques to evaluate jobs are described later.

Reviewing OSHA Logs and Other Existing Records

Inspecting the logs of injuries and illnesses required by OSHA and plant medical records can yield information about the nature of WMSDs, as can workers compensation claims, insurance claims, absentee records, and job transfer applications. Finding workers in certain departments or operations presenting more of these problems than others (and exhibiting the same types of musculoskeletal disorders) would suggest some immediate areas for study with regard to possible risk factors. Jobs with elevated rates of low back musculoskeletal disorders often also have higher risks for acute injuries due to slips and trips or other safety hazards. In these cases, acute musculoskeletal injuries may also be an important problem. NIOSH evaluations of alleged work-related musculoskeletal problems begin with an examination of OSHA and medical records to understand the magnitude and seriousness of such problems. These records may also offer leads to jobs or operations that may cause or contribute to musculoskeletal disorders. Exhibits 7 and 8 illustrate the kind of data one might find, the evaluations made to judge the significance of the data, and their use in targeting jobs for ergonomic risk analysis.

Conducting Symptom Surveys

In Exhibit 8, entries from OSHA records and other medical reports documented worker disorders, and information from interviews with workers linked the disorders to workplace factors. Interviews or symptom surveys have been used to identify possible WMSDs that might otherwise go unnoticed. In addition to questions about the type, onset, and duration of symptoms, symptom survey forms may include a body map [Corlett and Bishop 1976; Hales and Bertsche 1992] wherein the respondent is asked to locate and rate the level of discomfort experienced in different areas of his or her body. The assumption is that any discomfort or symptoms may be associated with some increased risk for WMSDs. Compared with OSHA logs, symptom surveys provide a more sensitive way to determine who has symptoms and who does not. A disadvantage of symptom questionnaires is their reliance on self-reports. Other factors besides the presence or absence of WMSDs may influence the reporting of symptoms, and the analysis and interpretation of questionnaire data can be complex. Hales and Bertsche [1992] offer one example of a symptom survey form (see Tray 4-B of the Toolbox). Such data collection can help identify specific jobs or job elements deserving an ergonomic analysis. Also needed are other questions dealing with the worker s perception of job tasks that induce the discomfort. Exhibit 9 describes a NIOSH health hazard evaluation that used a questionnaire to gather relevant symptom data.

Using Periodic Medical Examinations

A disadvantage of using OSHA logs or company medical information to identify possible cases of WMSDs is the lack of specific or uniform medical information. This limitation may make the identification of WMSDs difficult. One optional approach to overcome this limitation is to have each worker undergo a periodic standardized examination that includes a history and physical examination. Such an examination program should be designed and administered by a health care provider. NIOSH has undertaken studies in which physical examinations were given to workers to establish the prevalence of upper extremity musculoskeletal disorders and to establish whether evidence of excessive numbers of cases could be related to certain working conditions. One such study is described in Exhibit 10.

Identifying Risk Factors in Jobs

Screening Jobs for Risk Factors

Health records or medical examinations and symptom surveys may indicate the nature and extent of musculoskeletal problems in the workforce. Efforts to identify jobs or tasks having known risk factors for musculoskeletal problems can provide the groundwork for changes aimed at risk reduction. Even without clear medical evidence, screening jobs for musculoskeletal risk factors can offer a basis for early interventions. (See the "Proactive Ergonomics" section of this primer.)

A great deal of ergonomic research has been conducted to identify workplace factors that contribute to the development of musculoskeletal disorders [Kourinka and Forcier 1995; Riihmaki 1991; Garg and Moore 1992; Silverstein et al. 1986; Salvendy and Smith 1981]. NIOSH has recently summarized the epidemiological scientific studies that show a relationship between specific work activities and the development of musculoskeletal disorders [NIOSH 1997]. A variety of nonepidemiological research, including clinical, biomechanical, and psychophysical studies, supports these findings [Pope et al. 1991; Ranney et al. 1995; Szabo and Chidgey 1989; Waters et al. 1993; Chaffin and Andersson 1984; Fransson-Hall et al. 1995; Ulin et al. 1993].

According to the scientific literature, the following are recognized as important risk factors for musculoskeletal disorders, especially when occurring at high levels and in combination. Figure 1 provides illustrations of some of these risk factor conditions. In general, knowledge of the relationships between risk factors and the level of risk is still incomplete. Also, individuals vary in their capacity to adjust to the same job demands. Some may be more affected than others.

• Awkward postures Body postures determine which joints and muscles are used in an activity and the amount of force or stresses that are generated or tolerated. For example, more stress is placed on the spinal discs when lifting, lowering, or handling objects with the back bent or twisted, compared with when the back is straight. Manipulative or other tasks requiring repeated or sustained bending or twisting of the wrists, knees, hips, or shoulders also impose increased stresses on these joints. Activities requiring frequent or prolonged work over shoulder height can be particularly stressful.
  
  
• Forceful exertions (including lifting, pushing, and pulling) Tasks that require forceful exertions place higher loads on the muscles, tendons, ligaments, and joints. Increasing force means increasing body demands such as greater muscle exertion along with other physiological changes necessary to sustain an increased effort. Prolonged or recurrent experiences of this type can give rise to not only feelings of fatigue but may also lead to musculoskeletal problems when there is inadequate time for rest or recovery. Force requirements may increase with increased weight of a load handled or lifted,
  
  
  • increased bulkiness of the load handled or lifted,
    
    
  • use of an awkward posture,
    
    
  • the speeding up of movements, increased slipperiness of the objects handled (requiring increased grip force),
    
    
  • the presence of vibration (e.g., localized vibration from power handtools leads to use of an increased grip force),
    
    
  • use of the index finger and thumb to forcefully grip an object (i.e., a pinch grip compared with gripping the object with your whole hand), and
    
    
  • use of small or narrow tool handles that lessen grip capacity.
    
    
• Repetitive motions If motions are repeated frequently (e.g., every few seconds) and for prolonged periods such as an 8-hour shift, fatigue and muscle-tendon strain can accumulate. Tendons and muscles can often recover from the effects of stretching or forceful exertions if sufficient time is allotted between exertions. Effects of repetitive motions from performing the same work activities are increased when awkward postures and forceful exertions are involved. Repetitive actions as a risk factor can also depend on the body area and specific act being performed. (See Table 4 in the main text and Tray 6-B in the Toolbox.)
  
  

Table 4. Reference levels used in rating job risk factors for musculoskeletal disorders

• Duration Duration refers to the amount of time a person is continually exposed to a risk factor. Job tasks that require use of the same muscles or motions for long durations increase the likelihood of both localized and general fatigue. In general, the longer the period of continuous work (e.g., tasks requiring sustained muscle contraction), the longer the recovery or rest time required.
  
  
• Contact stresses Repeated or continuous contact with hard or sharp objects such as non-rounded desk edges or unpadded, narrow tool handles may create pressure over one area of the body (e.g., the forearm or sides of the fingers) that can inhibit nerve function and blood flow.
  
  
• Vibration Exposure to local vibration occurs when a specific part of the body comes in contact with a vibrating object, such as a power handtool. Exposure to whole-body vibration can occur while standing or sitting in vibrating environments or objects, such as when operating heavy-duty vehicles or large machinery.
  
  
• Other conditions Workplace conditions that can influence the presence and magnitude of the risk factors for WMSDs can include cold temperatures,
  
  
  • insufficient pauses and rest breaks for recovery,
    
    
  • machine paced work, and
    
    
  • unfamiliar or unaccustomed work.

In addition to the above conditions, other aspects of organization of work may not only contribute to physical stress but psychological stress as well. Scientific research is examining work factors such as performance monitoring, incentive pay systems, or lack of control by the worker to determine whether these factors have a negative effect on the musculoskeletal system [Moon and Sauter 1996]. Another related area of research is to determine which personal, work, or societal factors contribute to acute musculoskeletal disorders developing into chronic or disabling problems.

Screening jobs for these risk factors may involve the following:

• Walk-through observational surveys of the work facilities to detect obvious risk factors
  
  
• Interviews with workers and supervisors to obtain the above information and other data not apparent in walk-through observations, such as time and workload pressures, length of rest breaks, etc.
  
  
• Use of checklists for scoring job features against a list of risk factors

Of the above three methods, the checklist procedure provides the most formal and orderly procedure for screening jobs. Numerous versions of checklists exist in ergonomics manuals. When checklist data are gathered by persons familiar with the job, task, or processes involved, the quality of the data is generally better. Checklist procedures are also typically used in more complete job analyses (described below). Samples of checklists are found in Tray 5 of the Toolbox. While screening tools such as checklists have been widely and successfully used in many ergonomics programs, most have not been scientifically validated. Combining checklist observations with symptoms data offers a means of overcoming uncertainty.

Integrating efforts to identify risk factors for musculoskeletal disorders with efforts to identify common safety hazards such as slips and trips should be considered. Jobs with risk factors for musculoskeletal disorders also may have safety hazards.

Performing Job Analyses

Job analysis breaks a job into its various elements or actions, describes them, measures and quantifies risk factors inherent in the elements, and identifies conditions contributing to the risk factors [Putz-Anderson 1988; Keyserling et al. 1993; Grant et al. 1995; ANSI 1996].

Job analyses are usually done by persons with considerable experience and training in these areas. While most job analyses have common approaches, such as a focus on the same set of risk factors described above, no "standard" protocol exists for conducting a job analysis to assess ergonomic hazards.

Most job analyses have several common steps. A complete description of the job is obtained. Employees are often interviewed in order to determine if the way the job is done changes over time. During the job analysis, the job is divided into a number of discrete tasks. Each task is then studied to determine the specific risk factors that occur during the task. Sometimes each risk factor is evaluated in terms of its magnitude, the number of times it occurs during the task, and how long the risk factor lasts each time it occurs.

The tasks of most jobs can be described in terms of (1) the tools, equipment, and materials used to perform the job, (2) the workstation layout and physical environment, and (3) the task demands and organizational climate in which the work is performed. Job screening, as described above, provides some of these data. More definitive procedures for collecting information on these components can include the following:

• Observing the workers performing the tasks in order to furnish time-activity analysis and job or task cycle data; videotaping the workers is typically done for this purpose
  
  
• Still photos of work postures, workstation layouts, tools, etc., to illustrate the job
  
  
• Workstation measurements (e.g., work surface heights, reach distances)
  
  
• Measuring tool handle sizes, weighing tools and parts, and measuring tool vibration and part dimensions
  
  
• Determining characteristics of work surfaces such as slip resistance, hardness, and surface edges
  
  
• Measuring exposures to heat, cold, and whole body vibration
  
  
• Biomechanical calculations (e.g., muscle force required to accomplish a task or the pressure put on a spinal disc based on the weight of a load lifted, pulled, or pushed)
  
  
• Physiological measures (e.g., oxygen consumption, heart rate)
• Special questionnaires, interviews, and subjective rating procedures to determine the amount of perceived exertion and the psychological factors influencing work performance

Exhibits 11, 12, 13, and 14 illustrate the varied approaches that NIOSH has taken in analyzing and evaluating jobs for apparent risk factors.

While a job analysis enables a person to characterize ergonomic risk factors, the question of what level or amount of exposure is harmful to the musculoskeletal system is a difficult one. Some have argued against the overuse of simple guidelines [Buckle et al. 1992; Leamon 1994], while others have recognized that, despite the limitations of current guidelines, many contain sufficiently useful information to identify potentially risky work activities [Karwowski 1993; Waters et al. 1993; Winkel et al. 1992]. While acknowledging the limitations of current knowledge, NIOSH and others conducting job analyses have used a variety of approaches to provide answers best suited for the specific workplaces under study. One approach calculates the muscle strength required to perform a certain job task and estimates the fraction of the working population that possesses the required strength. A second approach asks workers in the laboratory to judge acceptable work conditions by engaging them in tasks that impose different physical demands. A third method compares the forces generated in a part of the body when performing specific work tasks and compares it with a level believed to be harmful. Tray 6 of the Toolbox section contains references to and information about these and other approaches.

NIOSH recommends the use of the NIOSH lifting equation as one useful approach in both the design of new lifting tasks and in the evaluation of existing lifting tasks [Waters et al. 1993; Waters et al. 1994]. Other assessment tools are also available for evaluating such tasks [Chaffin and Andersson 1991; Marras et al. 1993, 1995; Hidalgo et al. 1995]. Population data depicting human strength capacities can be helpful in designing and evaluating jobs [Snook and Ciriello 1991]. Tables indicating standing and seated height and reach distances that can accommodate various proportions of the worker population [Kroemer and Kroemer-Elbert 1994] can also be helpful. Comparing job analysis results with such references can yield estimates of the percentage of the population that may be especially affected by these job conditions. In some NIOSH evaluations, efforts have been made to duplicate the specific stresses observed in the job to calculate forces on joints and limbs and to arrive at risk determinations [Habes and Grant, in press]. Computerized 2- and 3-dimensional biomechanical models can predict the percentage of males and females capable of exerting static forces in certain postures [Chaffin and Andersson 1991]. Westgaard and Winkel [1996, p. 87] recently summarized the strengths and weaknesses of current guidelines by concluding that "at present, guidelines to prevent musculoskeletal disorders can only give directions, not absolute limits." These authors believe the best guidelines must consider the level, duration, and frequency of exposure.

Table 4 presents the reference levels or limiting conditions used by NIOSH to rate risk factors of consequence to the musculoskeletal problems under investigation. (For the scientific justification of each guideline or approach, the reader is referred to the references indicated in Table 4.) In some instances these determinations were based on more than one rating procedure. For example, judgments of problematic lifting conditions in many NIOSH investigations have been derived both from use of the NIOSH lifting equation [Waters et al. 1993; Waters et al. 1994] as well as the Michigan computerized 2- and 3-dimensional analyses [Chaffin and Andersson 1991].

The entries in Table 4 are offered as illustrative examples of reference levels or guidelines. The actual risk to each worker depends not only on the current level of exposure to risk factors, but also on their physical capability, their past medical history, concurrent non work exposures, and many other factors. These reference levels have varying degrees of scientific justification. Each was useful in a specific NIOSH workplace investigation aimed at reducing WMSDs.

Setting Priorities

In Exhibits 11 to 14, certain job tasks were targeted for more intensive analysis to verify the existence of risk factors for musculoskeletal disorders.

• In Exhibits 11 and 12, finding cases of musculoskeletal disorders prompted the follow up analysis.
  
  
• In Exhibit 14, complaints of musculoskeletal discomfort, established through questionnaires, were the basis for sorting out possible work-related causes.
  
  
• The physical demands or risk factors of the job described in Exhibit 13, even without medical or symptom data, presented strong risk implications for potential WMSDs, thus triggering the analysis.

These three scenarios offer a basis for setting priorities for undertaking risk factor analyses and implementing control measures. Specifically, jobs associated with cases of musculoskeletal problems deserve the highest consideration in follow up efforts to identify risk factors and implement control actions. Jobs in which current cases have been identified should receive immediate attention, followed by those in which past records have noted a high incidence or severity of WMSDs despite the lack of current cases. Priority for job analysis and intervention should be given to those jobs in which most people are affected or in which work method changes are going to be taking place anyway.

Jobs associated with worker complaints of fatigue and discomfort should be ranked next in deciding needs for follow up job analysis and possible interventions.

Finally, where screening efforts suggest the presence of significant risk factors for musculoskeletal disorders, more detailed job analyses should be done to assess the problem potential. Ratings of high or extreme levels of risk factors, especially occurring in combination, may indicate a need for control actions. While appearing last in the priority order, taking steps to reduce apparent risk factors for musculoskeletal disorders is a preventative approach.

Table 5 summarizes the priority considerations in deciding about the need for job analyses and consequent control interventions for addressing WMSDs.

Table 5. Determining priorities for job analyses and control actions