The Relationship between Energy Expenditure and Performance Index in the Task of Shovelling Sand

Abstract

An examination is made of the relationship between the energy expenditure in litres of oxygen consumed per minute, as measured by the physiologist, and the performance index, as assessed by the work-study engineer. The data used in the analysis were obtained from 16 Bantu labourers engaged in shovelling sand at four different rates of work into a mine car of 1 ton capacity.

A close relationship between mean oxygen consumption and mean performance index over the range of work levels was found. A linear model appeared to describe the relationship between these two variables adequately. The particular linear relationship between the variables was, however, dependent on the observer, i.e. the lines for the two work-study engineers were different from each other. A performance index value of about 75 was found to be equivalent to an oxygen consumption of about 1-5 litres per minute. This is 50 per cent of the average Bantu mine labourer's maximum oxygen intake and, on physiological grounds, this is the rate of work which the Bantu labourer can maintain easily for a shift of 6-8 hours. However, it appears from the results of these preliminary studies that men working at a performance index value of 100 (i.e. well motivated in the work-study sense) are liable to work at a rate which is about 70 per cent of the maximum oxygen intake. This would be excessive for the average labourer. The existence of this close relationship is most encouraging and means that the work-study engineer would be able to relate his assessments to rates of energy expenditure and hence estimate the physical effort of men engaged on heavy manual labour.