The component proportions of energy expended on an industrial task

Abstract

The total metabolic cost of shovelling and tramming consists of three components of energy expenditure, namely, the effort of moving the body only, the effort of moving the empty shovel or empty mine car, and the effort of moving a load on the shovel or in the mine car. The relative proportions of these components of energy expenditure were estimated in a study on sixteen Bantu subjects engaged in various rates of shovelling and in tramming a mine car at a pre-determined speed while the cars contained different loads.

It was found that the movement of the worker's body during the tasks of shovelling and tramming with a load, accounted for a large proportion of the total energy expended. In both tasks about 50 per cent of the total energy (the metabolic cost of the task, in terms of oxygen consumption) is expended during movement of the operator's body and about 70 to 75 per cent in movement of his body and the shovel or mine car. The “true” energy expenditure required for productive work was found to be relatively small, being 25 to 30 per cent of the total metabolic cost of the task. Evidence was found in the study that in the various tasks the mechanical efficiency of the men (in a physiological sense) varied with body weight and the intensity of work.