Time course and magnitude of blood flow changes in the human quadriceps muscles during and following rhythmic exercise.

1. Pulsed bidirectional Doppler‐ultrasound equipment was used to measure changes in blood velocities in the femoral artery on a beat to beat basis for consecutive contraction and relaxation phases during voluntary rhythmic exercise of the quadriceps muscle group in man. 2. Rapid and large fluctuations of blood velocities were found, being high during relaxation and low during contraction phases. At the onset of contraction phase, negative velocities were present, indicating retrograde flow. During the rest of the contraction phase, forward flow occurred comparable to the resting flow level even at high loads. 3. Estimated maximal flow to the whole leg during relaxation phase, calculated from these blood velocity measurements and vessel diameter (measured with echo‐ultrasound equipment with high resolution) was in two of the subjects 3.32 l min‐1 (female) and 5.97 l min‐1 (male). When using computer tomography to estimate the volume of the quadriceps muscle group, the calculated maximum flow to this muscle group was 243 (female) and 257 (male) ml min‐1 100 ml muscle‐1. The time‐averaged flow during exercise to the whole leg was 1.51 l min‐1 (female) and 2.47 l min‐1 (male). The calculated time‐averaged flow to the quadriceps muscle group was 101 (female) and 98 (male) ml min‐1 100 ml muscle‐1. 4. The duration of post‐contraction hyperaemia following such rhythmic exercise of up to 6 min duration and up to 75% maximum voluntary contraction was never in excess of 150 s.