Recognition of the role of exercise in health is changing as robots and automation now perform most of the laborious tasks that used to be done by muscle power. A cartoon in an American newspaper recently quipped, 'Time was when most men who finished a day's work needed rest. Now they need exercise!' It is encouraging to see this new wisdom grow in popular acceptance.
(R. S. Paffenbarger, quoted from Noakes, 1992)
Central to the drive for productivity improvement is the challenge of finding an acceptable work rate for a given job. Industrial engineers have developed methods for designing manual jobs in a systematic way (Barnes, 1963). These techniques enable them to specify standard times for the completion of tasks and to describe the physical load of tasks by means of performance rating, providing industry with a way of organising work in which standard levels of production can be defined and output can be monitored. These methods rely on observation of worker behaviour by the industrial engineer rather than objective measurement of physiological variables.
In this chapter, the application of physiological methods in industry will be described. In addition to the measurement of workload itself, physiological methods also offer the possibility of investigating mental stress and dealing with wider issues such as nutrition and employees' levels of fitness for a given job.
In principle, any increase in oxygen uptake over and above that required for basal metabolism can be used as an index of physiological cost to an individual. When an individual begins a work task from rest, heart rate and oxygen consumption increase to meet the new demands. Because this response is not instantaneous, the immediate requirements for energy are met by local (i.e. muscular) energy stores. When work stops, heart rate and oxygen consumption return to their initial levels slowly because extra oxygen is still required to replenish the muscle stores and to oxidise the waste products of oxygen-independent processes (Figure 8.1) - to pay back the oxygen debt.
In many industrial tasks there is a warm-up period in which physiological processes adjust to meet the new demands. This is followed by a period of steady-state work and a recovery period (Manenica and Corlett, 1977). The total physiological cost of work includes the energy expenditure during both the working and the recovery periods. Assessment of the physical demands of work using physiological measures must begin with the subject completely at rest and continue until the physiological variables return to the resting levels measured previously.