Synchronized exposure and image presentation:: Analysis of digital EMG and video recordings of work sequences

In ergonomic analysis of work involving manual materials handling, there is a need to relate ergonomic assessment to specific situations or tasks performed in the course of work; it may be important to identify particularly strenuous tasks, as a basis for interventions, or analyze the mix of high and low load periods. Ergonomic analysis methods include observation methods as well as physiological measurements, like electromyography (EMG). This paper describes a method, called SEIP (Synchronized Exposure and Image Presentation), which integrates video recordings with simultaneously recorded exposure signals, on a regular PC display. An illustrative example includes a sequence from a car assembly plant where EMG was recorded from the trapezius and the wrist extensor muscles of a worker, while he was video recorded when performing his regular work. A computerized implementation of the Cube Model was used to access an estimated ergonomic load value versus time. This value was plotted next to the EMGs amplitude rectified values. It was concluded that the developed method, SEIP, is easy to use, and pedagogic when comparing different work methods. It unites observational methods and direct physiological measurements, offering the practicing ergonomist a more complete picture of the work being studied.