Nitric oxide (NO) plays an important role in vascular homeostasis as a chemical mediator that leads to vasodilation. Present study aims at measuring the urinary variables such as NOX (NO₂⁻ and NO₃⁻), bicarbonate (HCO₃⁻) and pH, in order to estimate the physiological responses to maximal loading during continuous knee extension. We recruited male volleyball athletes aged 18 or 19 yrs. (n=9) currently in good health. Subjects performed 30% of a one repetition maximum (RM) knee extension until complete fatigue; 2 weeks later they performed 80% of the same protocol. On the day of the experiment, the subjects' nutritional intake consisted only of water. The urine samples were collected at beginning of experiment and then three times every one hour. We measured the levels of urinary NOX, HCO₃⁻, creatinine and urinary pH and estimated the changes in these variables during exercise loading. The levels of urinary HCO₃⁻ and urinary pH decreased, 30 min after cessation of 30% 1 RM (repetition maximum) loading, but increased significantly and continuously for 2 hours, thereafter. However, the level of NOX was not significantly changed. When 80% 1 RM loading was given, drastic changes in urinary HCO₃⁻ and pH were observed after the cessation of the loading, i.e. urinary HCO₃⁻ and pH increased 7 times and 1.13 times as much as those of the controls (before exercise loading), respectively, 150 min after the loading. In this case, the level of urinary NOX was also increased by 1.19 times as much as that of the control, however with no significant differencees. These results indicate that the changes in urinary NOX, bicarbonate and pH reflect the changes in blood nitric oxide (NO), bicarbonate and pH which are important humoral factors in the blood to maintain the physiological homeostasis in the body. It was also suggested that the measurement of urinary NOX, bicarbonate and pH may be useful for the estimation of the events in the body after the extreme exercise loading.

DESCENTE SPORTS SCIENCE Vol.23/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE