Repeated or continuous adoption of awkward postures during work can lead to fatigue and eventually result in musculoskeletal disorders. The static or postural load is a critical factor to consider when evaluating working conditions, and reducing it is essential for improving workstations.
Several methods have been developed to assess the risk related to postural load at a workstation, each with its distinct application scope and result contributions. RPA is not a method that identifies risk factors linked to postural load but serves as a preliminary tool for a rough assessment of a worker's postures throughout the day. If an EPR study indicates a high static load, the evaluator should conduct a more comprehensive study of the workstation using specific postural evaluation methods such as RULA, OWAS, or REBA.
The method calculates static load by considering the types of postures a worker adopts and the duration they maintain them, providing a numerical value proportionate to the load level. Based on the static load value, the method suggests an Action Level ranging from 1 to 5.
RPA utilizes the static load valuation system of the LEST method, developed by F. Guélaud, M.N. Beauchesne, J. Gautrat, and G. Roustang, members of the Laboratoire de Economie et Sociologie du Travail (L.E.S.T.), of the CNRS, in Aix-en-Provence.
RPA focuses on an overall assessment of various postures and the duration they are maintained, rather than evaluating specific postures. The method assumes that a worker can adopt 14 possible generic postures, as listed Table 1.
| Posture table | |||||
| Sitting normally |
 |
Sitting leaning forward |
 |
Sitting with arms above shoulders |
 |
| Standing normally |
 |
Standing with arms in front extension |
 |
Standing with arms above shoulders |
 |
| Standing leaning forward |
 |
Standing heavily leaning forward |
 |
Kneeling normally |
 |
| Kneeling leaning forward |
 |
Kneeling with arms above shoulders |
 |
Lying down with arms above shoulders |
 |
| Squatting normally |
 |
Squatting with arms above shoulders |
|
The evaluation process starts with observing the worker for one hour while performing their tasks. During this time, the evaluator notes the different postures adopted (from Table 1) and the duration of each posture. If the work cycle is short and regular, the evaluator can measure the time each posture is adopted during a cycle and calculate the proportionate duration for one hour. For example, if an operator maintains the "Standing leaning forward" posture for 40 seconds in a 5-minute cycle, they will maintain that posture for 8 minutes in an hour of work.
Using this data, the method calculates the Postural Load value. The method then categorizes the final scores into action levels, which guide the evaluator in making decisions after the analysis. These action levels range from level 1, signifying that the evaluated postures are acceptable, to level 5, indicating that the static load is harmful to the worker and urgent measures must be taken to improve the workplace (Table 2).
| Score | Level | Action |
|---|---|---|
| 0, 1 or 2 | 1 | Satisfactory situation. |
| 3, 4 or 5 | 2 | Minor discomfort. Some improvements could provide more comfort to the worker. |
| 6 or 7 | 3 | Moderate discomfort. Risk of fatigue. |
| 8 or 9 | 4 | Severe discomfort. Fatigue. |
| 10 or more | 5 | Harmfulness. |
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