The origins of MSDs - physical factors

Several factors can be at the origin of the appearance of MSDs: physical, organizational or psychosocial factors. This is the reason why we talk about "plurifactoriality" of MSDs, because they come from the combination of these different factors, at different levels, which makes them complicated to detect or measure.

Today our article concerns the physical factors, we will try to identify the various biomechanical parameters which favor the appearance of MSDs.

During the analysis of the work activity, the ergonomist analyzes the various gestures made during the execution of the task as well as the environment in which the man must work.

He identifies the postures, repetitive movements, muscular efforts or the elements of the environment which bring a physical constraint to the employees.

Awkward postures

Certain activities generate feelings of discomfort, especially if they have been maintained for a long period, or more generally if they force the employee to adopt an uncomfortable position for the performance of his task. Once the analysis has been carried out on the employee, the risk of the appearance of MSDs must be reduced by acting on the layout of the workstation to limit feelings of discomfort, pain or fatigue.

There are many possible solutions to overcome uncomfortable postures: organization of the workstation, organization of working time (plan rotations or breaks), adjustment of the pace of work (avoid sustained rhythms, etc.).

Repetitive gestures

The repetitiveness of a gesture is characterized by the same gesture performed for a long period. The repetitiveness is induced by the organization of work, which aims to optimize the “efficient” gesture of employees with a production rate imposed by a machine. It is therefore the fact of being constrained added to a small margin of maneuver that makes repetitiveness dangerous. Repetitive work causes damage to joints, muscles or tendons.

There are several physical symptoms linked to repetitiveness: muscle fatigue, feelings of discomfort during movements, pain or, in the most serious and advanced situations, an incapacity to work. There are other identifiable symptoms such as the automation of complex gestures or the loss of sense of work.

Handling

Manipulation includes manual manipulation actions (pushing, pulling, carrying, ...) that an employee can perform during his working time. Handling can be a risk factor if it requires significant employee effort. The standards appeared as the NF-x35-109 which aims to define a framework to limit the excesses on what can be asked of the employee. These standards should not be the “acceptable limit” as this limit may vary depending on the person or their abilities.

In the study of physical factors, it is interesting to question the subjectivity of employees and to take an interest in their personal stories, to understand how they carry out their work activities (for example, if an employee has a knee problem, he will promote ventral flexion rather than leg curls). That's why we need to put these physical factors in context, and never take what we see for granted.