The purpose of this study was to elucidate how long it takes to reach peak blood flow after muscle contractions in consideration of the cardiac cycle. Seven healthy female subjects performed two successive dynamic plantar flexions of 1-s duration at 30, 50 and 70% of maximal voluntary contraction (MVC). Based upon the blood flow response after a single contraction, we set up intervals during two successive contractions each corresponding to 10% (10 I), 30% (30 I) and 50% (50 I) of the time required to reach peak blood flow. Upon cessation of contraction, the popliteal artery blood flow (Qpa) increased progressive, beat-by-beat increase and peaked by the 5th cardiac cycle, for all conditions. The highest peak blood flow among the cardiac cycle was at 3rd cycle in overall data. Peak Qpa values reached after exercise did not differ among intervals, whereas peak Qpa value attained after exercise was significantly greater in 50 and 70%MVC than 30%MVC (p<0.05). The result indicates that the augmentation of the Qpa after exercise with short duration differed with the exercise intensity but the timing for reaching peak post-exercise value did not differ in terms of the number of cardiac cycles.
