Assessing the energy cost of work

There is a fairly straightforward measttre of energy expenditure for typical tasks. The energy expenditure is given in either kcal/hr or watts. Table 11.3 shows this. 

Energy is provided in the body by a combination of processes which are independent of oxygen and those which are oxygen-dependent. Dynamic muscular activity is oxygen-dependent, while static muscular activity isn t. Moderate-intensity, continuous work 

Another way of assessing energy expenditure is to measure heart rate. Because VO2 varies between people, firstly the link between VO2 and heart rate has to be established by laboratory tests. Once this is done, heart rate alone can be used in the field to measure energy usage. 

There is also a subjective scale called the Borg RPE scale where workers are asked to rate their level of exertion from 6-20, based on heart rates of 60-200 beats/min. A sinprisirrgly good match between the rating and the heart rate has been foimd. 

Although rrot an energy cost measure, stressful situatiorrs where there is low physical activity can be assessed using certain types of measurement of CO2 in expired air. Where breathing due to stress exceeds the O2 demand of the body, the level of CO2 in the blood drops. Blood vessels constrict and this can cause dizziness and heart palpitations. 

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