and Their Limitations

Whether it’s about physical factors (mechanical exposure), or psychosocial factors related to work, there isn’t a unique method to identify and measure risk factors simultaneously. Each method presents advantages and disadvantages, and the decision should be taken based on: the work context and the activity to be studied, the level of accuracy and desired precision, the level of quality requested, the costs and the available resources and the multiplicity of factors to be measured at once.

In fact, some of the methods that allow to assess the physical factors used, for example, in a preliminary phase of the work, allow the collection of information about other risk factors, i.e., variables related to the workplace conception, design of work areas, anthropometry of the workplace, type of used tools, customized weights, etc. For the evaluation of psychosocial risk factors, the possibility of choice for the assessment methods is more limited, focusing frequently on the usage of questionnaires or scales.

The range of available methods varies from the subjective judgments to the direct quantitative measures. As we evolve in this matter, the level of accuracy for the analysis, as well as for the quality of the results, increases, being followed by incremental costs in terms of skill to data analysis.

Since there is a need to define strategies in order to access the exposure to the risk factors for the prevention of the musculoskeletal disorders, many authors have presented preventive approaches including several levels of analysis of exposure to the risk factors, using an evolutionary constructive logic for analysis, and taking in consideration different subjects of the company. These approaches differ in the number of levels to consider (two to four levels), but in accordance with the construction of the logical analysis and the agents evolved (workers, managers, workplace designers, ergonomists, biomechanics experts) depending on the level of approach.

Thus, we advocate a stratified approach that represents an agreement between the various presented approaches taking into account three levels of analysis:

  • First level – pre-assessment, where a qualitative analysis is carried out of the major risk factors presented in all labor situations, through observational methods with a quick and an easy implementation on the real-environment (checklists), and in the rate analysis of musculoskeletal disorders, through the methods of subjective judgments (symptom questionnaires) and database of health monitoring in the company. At this level, the results are, firstly, a scenario of global risk found in the various situations analyzed, establishing priorities for further analysis and, secondly, the calculation of prevalence rates and / or incidence of musculoskeletal disorders associated. In the case of a global approach, it is absolutely desirable to involve all stakeholders in the system (workers, direct chief, responsible for the production, occupational health and human resources, ergonomists, among other stakeholders in the organization).

  • Second level - systematic analysis of situations identified as problematic as a result of the data analysis from level 1, also qualitative, using methods of systematic observation more precise, with direct application or retrospective analysis of risk factors, and means of diagnostic symptoms and musculoskeletal disorders equally accurate (anamnestic and clinical examinations). As a result, we obtain an improved understanding of risk factors that underlie the development and/or aggravation of certain musculoskeletal disorders, facilitating decisions concerning the measures of job transformation; in this stage the number of players involved will be smaller and will fall primarily on the participation of workers, ergonomists and physicians.

  • Third level - the quantification of exposure to a range of situations, which by the nature of the risks, the specificity of situations and solutions to take, require the application of direct measurements (example: electromyography, accelerometry, image analysis-in situ or simulated), including a limited number of tasks or operations and the participation of experts.

Methodological approach for exposure assessment.

These levels succeed in space and time and should not be overtaken or rearranged. There is a conviction that the integrated approach of exposure evaluation is the right way for prevention, based on global and integrated understanding of the developed work.

The Need For Quantification

Accurate and precise methods of measuring the workload exposure are important pre-requisites to establish the exposure-response relationships, as well as to correctly interpret the intervention studies. The methods based on direct measurements of mechanical exposure are considered as those that provide data with higher quality, and therefore more recommended than the observational methods or subjective judgments which only provide classified information at intervals or ordinal scales.

Main characteristics of different methods of mechanical exposure evaluation (Winkel & Mathiassen, 1994, pag. 983).

The subjective judgments give the possibility of studying a large number of individuals at a modest cost, being the instruments most used in epidemiological studies. In addition, through a simple instrument we can obtain information about different exposure variables. In combination, the questions can be conceived to objectify exposure in general, whereas the direct methods only cover exposure information in a certain period of records. However, self-records present a valid record and a very low reproducibility concerning the needs of ergonomic intervention, while a more accurate and precise estimation operation appears to be offered by direct measurements.

There is a reasonable number of methods to assess mechanical exposure exerted on several body segments, when workers perform a certain task, which can be associated with measures that reflect physiological responses in a particular situation. Such methods include: a dynamometry (force), electromyography (electrical activity of muscle), goniometry (joint angles and frequency of movements) and accelerometry (vibrations).