In this study, we examined usefulness of α−AMY activity value in saliva as a non−invasive stress marker in the enduring exercise. In experiment 1, nine high school students participated in the measurement of the day−to−day variation and diurnal variation of saliva α−AMY activity value at rest. In experiment 2, seven adult male athletes participated in the measurement of α−AMY activity value in saliva during gradually increased or decreased exercise test. In Experiment 3, two adult males of identical twins and fraternal twins who specialize in long−distance run, we verified the constitutional impact on α−AMY activity value change in saliva during gradually increased or decreased exercise test. Summaries of knowledge obtained from these experiments are as follows. 1．A day change of α−AMY activity value in saliva at rest showed transition reflecting circadian rhythm. 2．Diurnal change for four days of α−AMY activity value in saliva at rest didn’t show significant change. 3．A strongly positive correlation was observed between α−AMY activity value in saliva and heart rate in endurance exercise. 4．The α−AMY activity value in saliva during endurance exercise changed reflecting the exercise intensity, but large individual differences were also observed. 5．From the ups and downs of α−AMY activity value in saliva of identical twins during endurance exercise, constitutional influence was little suggested. From the above results, α−AMY activity value in saliva was suggested to be useful as a non−invasive stress marker in enduring exercise. However, the change is observed to correspond to individual differences, and personal factors such as physical condition and characteristics of the subject seem to be related to, which will be the future work to verify
