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The ergonomics approach to manual materials handling (MMH) tasks defines a Man-Task-Environment System. A generally accepted means of minimizing MMH related injuries is to design MMH tasks so that the demands of the tasks are less than the capacities of the individuals performing these tasks. Task design is dependent, in part, on the availability of comparable data for task demands and worker capacities. The generation of the appropriate data is dependent, in part, on being able to identify the pertinent capacity parameters of manual materials handling activities.
In the past, a substantial effort has been directed at determining ‘safe’ lifting capacities for individuals and groups of individuals. The assumption used for these studies was that there is a relationship between an individual’s capacity and his or her injury potential. In other words, a person with a small capacity with respect to a given task demand is more likely to be injured than another person with larger capacities. For the measurement of a safe and permissible lifting capacity three approaches are commonly used. The first approach is the biomechanical approach, the second approach is the physiological approach, and the third is the psychophysical approach. These three approaches and the models developed using the selected criterion under each approach are discussed below.