Abstract
An investigation was conducted on the actual diving conditions of 2, 996 divers in Japan except those engaged in fishery. Results of analysis made on the diving profiles and actual working conditions showed that some of their jobs required heavy load and that the burden was excessively large.
Little study has been made for the proper evaluation of diving stress or work loads, but it has been assumed from these limited studies that the load is not so heavy. The load has beeng enerally estimated to be about 1.8l/min STPD of oxygen consumption (Vo2) during 40l/min STPD of expiratory gas volume/min (VE). In our examination of their actual diving work, their work load was far greater than our expectation. It was in practice not only difficult to obtain the actual Vo2 but also very difficult to determine their actual fatigue. Instead of these, it is necessary to establish an adequate index for evaluating diving work load. Studies have been made in our laboratory since 1981 and regression equations have been finally obtained, by which load during diving work can be determined using heart rate as index.
Seven healthy males were chosen as subjects of the present study having a mean age of 34.4 yr and a mean diving history of 7.3 yr. First, performance time was acquired in each subject by bicycle ergometer exercise and the maximalen oxygen consumption (Vo2-max) was obtained. In the second step, Vo2-max was obtained by using the regulator apparatus for breathing during SCUBA diving. This value was 86.1% of the first step. The third step was made in a swimming pool. Subjects were fully equipped with a SCUBA tank for fin-swimming. Vo2-max by fin-swimming was found to be only 72.4% of their first Vo2-max. Fin-swimming was so excessively strenuous that they became exhausted.
Three different Vo2-max was thus obtained. This implies that Vo2 during diving work (fin-swimming) is determined by local kinetic energy (skeletal muscle metabolism) of the legs and not by whole body work, and that they become exhausted before the actual Vo2-max of whole body activity is attained. It is therefore not appropriate to evaluate that the diving load is not heavy because the obtained Vo2 value is lower that their actual Vo2-max.
As they became exhausted before the real Vo2 could be reached, it should be recommended in the evaluation of diving work load that the relation between % of Vo2-max and heart rate should be first obtained and secondarily the value of % Vo2-max should be determined by the regression equation.
When the heart rate is assumed to be 140 beats/min, it is estimated to be 47.3% of their real Vo2-max by the regression equation, but the value becomes 64% when compared with their Vo2-max by the regression equation of fin-swimming.
Based on the real physiological calculation of oxygen consumption, this value becomes 1.52l/min or light to moderate work load, but it reaches a high value of 2.06l/min when the value is recalculated according to Vo2-max by fin-swimming. This is a heavy work load, which is in agreement with their actual fatigue.
It is rather difficult to calculate Vo2 during diving and moreover the value obtained is not proportional to their actual fatigue. There is a tendency to estimate the work load at a lower level. This method of calculating their % of Vo2-max is very simple and convenient and the value obtained is in close agreement with their fatigue. The actual Vo2-max differs from Vo2 by fin-swimming. We must determine the proper work load to divers for their safe diving and provide control to prevent excessive work load.
