Effect of contraction frequency on leg blood flow during knee extension exercise in humans

Previous studies in isolated muscle preparations have shown that muscle blo od flow becomes compromised at higher contraction frequencies. The purpose of this study was to examine the effect of increases in contraction frequen cy and muscle tension on mean blood flow (MBF) during voluntary exercise in humans. Nine male subjects [23.6 +/- 3.7 (SD) yr] performed incremental kn ee extension exercise to exhaustion in the supine position at three contrac tion frequencies [40, 60, and 80 contractions/min (cpm)]. Mean blood veloci ty of the femoral artery was determined beat by beat using Doppler ultrasou nd. MBF was calculated by using the diameter of the femoral artery determin ed at rest using echo Doppler ultrasound. The work rate (WR) achieved at ex haustion was decreased (P < 0.05) as contraction frequency increased (40 cp m, 16.2 +/- 1.4 W; 60 cpm, 14.8 +/- 1.4 W; 80 cpm, 13.2 +/- 1.3 W). MBF was similar across the contraction frequencies at rest and during the first WR stage but was higher (P, 0.05) at 40 than 80 cpm at exercise intensities > 5 W. MBF was similar among contraction frequencies at exhaustion. In humans performing knee extension exercise in the supine position, muscle contract ion frequency and/or muscle tension development may appreciably affect both the MBF and the amplitude of the contraction-to-contraction oscillations i n muscle blood flow.