Abstract

In ergonomics, the concept of margin of manoeuvre is defined as the freedom workers have to develop different ways of working in order to meet production targets without adverse effects on their health. This freedom allows them to vary their ways of operating.

Though it is an established concept in ergonomics, there are no quantitative data to support the link between this freedom and the risk of developing musculoskeletal disorders. From the standpoint of human motor skills, a repeated movement varies, from one instance to the next, in terms of amplitude and time. Current knowledge about the operating methods of workers forced to perform repeated movements on a daily basis is inadequate to assess these variations from the start to the end of each movement.

Some researchers hypothesize that there is a relationship between the variations that occur over the course of a movement (manifested through a variability in ways of operating) and a risk of developing a musculoskeletal disorder. According to this hypothesis, people who adopt a work method with little variation, or who are forced to perform a job in a work setting that allows little variation, would put more demand on and overuse the same biological structures, whereas people who vary their ways of performing the same movement would spread the burden differently, from one time to the next, on the various structures involved.

The purpose of this study is to test the hypothesis by analysing the intra- and interindividual variability of different ways of working, taking the case of materials handlers working in a controlled work environment as an example.

The results will help improve understanding of the management of the ways of performing a repetitive job over time.