The purpose of this study is to develop a new method for evaluating workload by comparing the ratio of working heart rate (HRw) to the heart rate of the step-stress test (HRst). We carried out two experiments. In the first experiment, the heart rate and the volume of oxygen consumption (VO2) were measured while a subject carried a 10kg box at 3km/h on a treadmill. In the second experiment, HR and VO2 were recorded while a subject shoveled 1.7-2.2kg of soil at a time and moved it about 1.5m.
The results were as follows:
1) In both experiments, interpersonal variation and drift (variations in an individual) of the resting HR were larger than those of the step-stress test and work. The HR values in the rest period were easily effected by mental stress.
2) In the first experiment, the variations of HR and VO2 among individuals were larger than the drift. The interpersonal variation and drift of VO2 were also larger than those of the HR.
3) The coefficient of interpersonal variation (4.8-5.4%)of the HR ratio (HRW/HRST) based on the step-stress test was smaller than the coefficient of resting HR (10.1-11.6%).
4) In both experiments, the coefficients of interpersonal variation for VO2 per unit weight in work ranged from 6.6-19.4%. In contrast, the coefficients of the relative metabolic rate showed large values ranging from 17.6 to 31.5%.
5) These results prove that the HR ratio based on the stepstress test is much better than conventional indexes for evaluating workload.