Effects of Knee Joint Angle on Intramuscular Blood Flow and Muscle Deoxygenation During Fatiguing Isometric Contractions

The purpose of this study was to investigate the effect of the knee joint angle on intramuscular blood flow and muscle deoxygenation during fatiguing intermittent isometric knee extensions. Seventeen healthy young male participants (19.6 ± 1.3 years) performed intermittent (5 s contraction, 5 s relaxation) and incremental isometric knee extensions at 30%, 40%, 50%, 60%, and 70% of maximal voluntary contraction (MVC) consecutively until task failure. Exercise was performed at flexed (90°) and extended (140°; full extension = 180°) knee joint angles. Intramuscular blood flow and muscle oxygen saturation (StO2) were measured using power Doppler ultrasonography and near-infrared spectroscopy, respectively, in the right vastus lateralis at mid-thigh. Although MVC torque did not differ significantly between knee joint angles (p = 0.139), endurance time was significantly longer in the extended than in the flexed position (p = 0.002). There were no significant differences in intramuscular blood flow (p = 0.105) and StO2 (p = 0.292) between knee joint angles at baseline. The Δintramuscular blood flow was significantly higher in the flexed than in the extended position from 30% to 60% MVC (p = 0.006), and ΔStO2 was significantly lower in the flexed than in the extended position above 30% MVC (p = 0.026). These results indicate that changes in intramuscular blood flow and muscle deoxygenation are influenced by knee joint angle at submaximal intensities during intermittent isometric knee extension exercise.