Exercise protocol. We set up the time intervals based on the time taken to reach the peak value of blood flow. In the first experiment, we investigated popliteal artery blood flow after a single 1-second contraction of plantar flexion exercise. Immediately after the cessation of contraction, the blood flow began to increase markedly and reached its peak value. The intervals between the contractions used in this study were 50%, 100%, and 150% of the time taken to reach the peak value.