Post Exercise Hyperemia Does Not Overshoot Peak Oscillatory Blood Flow During Exercise

Previous research in muscle blood flow suggested that, immediately following exercise, there is an overshoot of the blood flow to the working muscle, which has been interpreted to imply inadequate flow during exercise. The purpose of this study was to further characterize this post exercise hyperemia (PEH), specifically relative to the contraction-induced oscillations in blood flow observed during exercise. For the preliminary study, 5 male subjects performed discontinuous, incremental knee extension exercise under four conditions: supine and upright, with a long (22 cm), and short (10 cm) kicking length. Each increment consisted of 3 minutes of kicking with one minute of recovery. Exercise intensities ranged from 4–5% of maximum voluntary contraction at the lowest intensity to 30–40% at the highest intensity. The contraction frequency was set at 40 kicks/min. Mean blood velocity was continuously measure and averaged over a cardiac cycle using Doppler sonography and converted to flow using a cross sectional area of the femoral artery derived from ultrasound. Peak PEH early in recovery was invariably greater than the mean blood flow during the last 30 seconds of exercise, consistent with previous interpretations. However, when peak PEH was compared to the 10 highest individual values during exercise (which reflected the true oscillatory behavior of the blood flow response) in 88 of 96 trials (92%) PEH was no greater than these highest exercise values. The 8 exceptions occurred at the highest power outputs. Thus, in humans performing knee extension exercise, the post exercise blood flow response does not usually show an overshoot when compared to the peak blood flow oscillations observed during exercise, even at high exercise intensities.