This study investigated the relationship between exercise intensity and energy contribution in shortduration intensive exercise. Two competitive university sprinters performed 30-s pedaling tests at 4 high intensity levels, following a submaximal test to determine the energy contribution during the 30-s pedaling tests by using the linear regression between exercise power and O2 demand. The energy contribution in each subject was almost constant during the 30-s pedaling tests at the 4 high intensity levels. Furthermore, O2 uptake and peak blood lactate concentration increased with increasing O2 demand in each subject. These results suggest that the energy contribution during short-duration intensive exercise at different high intensity levels is almost constant and that aerobic and anaerobic energy increase with increasing exercise intensity in each individual.