Cardiac load should be taken into consideration as an exercise intensity in case of exercise prescription from the stand point of safety. Double product (product of systolic blood pressure and heart rate) was studied and evaluated for the index of cardiac load.
(1) Double product is a valid index of cardiac load, because it has a high positive correlation between myocardial oxygen consumption.
(2) Systolic blood pressure during exercise is a linear function of heart rate. This means double product can be expressed by the following equation;
　　　y=ax²+bx
　　　here, y: double product, x: heart rate
(3) The constant a sand b in this equation can be determined by an experimental procedure. Double product can be calculated from heart rate using the equation with predetermined a and b.
(4) Possibility of the development of a compact watch-type instrument which calculates and displays double product from heart rate in real time was discussed.

DESCENTE SPORTS SCIENCE Vol.8/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE