*3.1. Classification by Knowledge Categories*

A particular classification [33] has been used to order the RULA studies according to the knowledge categories. Table 2 shows the different areas presented, the designated nomenclature and the number of published studies.


### **Table 2.** Knowledge categories [33].

\* The category "Other areas not previously included" is not part of the classification used; it is a section that encompasses studies that have not been considered in the other fields.

In total, 19 categories are differentiated. One can observe that "Manufacturing" stands out as having more studies than the rest, a total of 74. This is followed by 38 and 25 publications corresponding to "Human health and social work activities" and "Other areas not previously included ", respectively (Table 2).

In contrast, two fields are differentiated in which only one research study is recorded—"Water supply, sewerage, waste management and remediation activities" and "Financial and insurance activities" (Table 2).

Figure 4 shows the different areas of knowledge based on the frequency of the published studies.

**Figure 4.** Knowledge categories and frequency.

Below is a description of each of these categories [33].
