Repetitive Strain Injury (RSI) gives rise to a high level of absenteeism and, to an increasing extent, ends in full incapacity for work. Making frequent repetitive movements, particularly of wrist, elbow, and shoulder joints, for a protracted period of time, is one of the main causes of RSI. The Department of Ergonomics of the University of Lisbon has been called upon to investigate RSI symptoms of employees working in a large car-assembly plant.

The ergonomists have opted in favor of detailed systematic observation of employees' tasks with The Observer Video-Pro (figure 1), using a timing resolution of 0.04 seconds. Although these tasks only last for an average of 11 seconds, the number of movements of the wrist, elbow and shoulder joints can easily run into hundreds, particularly when the employee has to manipulate pliers or other tools. This kind of detailed behavioral observation makes systematic video analysis an extraordinarily appropriate method of research.

Figure 1. The application window of The Observer Video-Pro, showing part of a detailed data file associated with its corresponding video file. Click on the bitmap to zoom in.

Analysis results revealed repetitive movements, occurring at a high frequency, not only during the task as a whole, but particularly during movements at which a considerable amount of force had to be applied. In addition, the frequency of transitions between several wrist positions turned out to be extremely high. These results enabled the researchers to identify those parts of the tasks that most urgently call for ergonomic enhancements.