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 (VO
2) were measured while a subject carried a 10kg box at 3km/h on a treadmill. In the second experiment, HR and VO
2 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 VO
2 among individuals were larger than the drift. The interpersonal variation and drift of VO
2 were also larger than those of the HR.
3) The coefficient of interpersonal variation (4.8-5.4%)of the HR ratio (HR
W/HR
ST) 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 VO
2 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.
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