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.

Regional differences in oxygen supply-demand balance in active muscles may be related to exercise tolerance. However, the dynamics of oxygen supply-demand balance and its regional differences within active muscles have not been clarified. The purpose of this study was to evaluate regional differences in the patterns of change in the relationship between intramuscular blood flow and muscle deoxygenation along the vastus lateralis length during submaximal isometric knee extension. Thirteen healthy young males (19.4 ± 0.9 years) performed intermittent (5-s contraction and 5-s relaxation) isometric knee extension at 50% of maximal voluntary contraction for 18 contractions. Intramuscular blood flow and deoxy-[hemoglobin+myoglobin] (deoxy-[Hb+Mb]) were simultaneously measured using power Doppler ultrasonography and near-infrared spectroscopy, respectively, at the proximal, middle and distal sites of the vastus lateralis. The ratio of intramuscular blood flow to deoxy-[Hb+Mb] (intramuscular blood flow/deoxy-[Hb+Mb]) was calculated. There was no significant interaction (measurement site × time) for intramuscular blood flow/deoxy-[Hb+Mb] (proximal; 256 ± 138 a.u., middle; 384 ± 228 a.u., distal; 291 ± 197 a.u., F = 1.683, p = 0.076). These results suggest that the balance between oxygen supply and demand is uniformly regulated in the vastus lateralis along its length during intermittent submaximal isometric knee extension.

Purpose: The purpose of this study was to evaluate blood flow changes in femoral artery and skeletal muscle microvasculature during intermittent submaximal isometric knee extension. Methods: Seventeen healthy young males (19.7 ± 1.2 years) performed intermittent (5 s on, 5 s off) isometric knee exten- sion. Five contractions were performed at each force level of 10%, 30%, 50%, and 70% of maximal voluntary contraction (MVC) at random with a 10-min rest between sets. We measured right femoral artery blood flow by pulsed-wave Doppler ultrasonography and intramuscular blood flow in the vastus lateralis of the right mid-thigh by power Doppler ultrasonography, simultaneously. Both femoral artery and intramuscular blood flow were normalized by the peak value for each participant and represented as %Peak. Time-to-peak was defined as the time from the end of exercise to the peak. Results: %Peak of femoral artery blood flow was significantly higher than that of intramuscular blood flow at the baseline and following contractions at 10% MVC (P < 0.01). The time-to-peak during the post-exercise of intramuscular blood flow was significantly longer than that of femoral artery blood flow following contractions at 70% MVC (P < 0.01). Conclusions: These results indicate that blood flow increases appeared slowly in skeletal muscle microvasculature than in femoral artery after intermittent submaximal isometric knee extension, suggesting that differences in vascular reactivity and blood flow regulation could exist between femoral artery and skeletal muscle microvasculature in healthy young males. Keywords

Power Doppler ultrasonography is used to measure blood flow within a given muscle, otherwise known as intramuscular blood flow. However, it is not fully understood how intramuscular blood flow and muscle oxygenation change with repetitive muscle contraction. The present study was conducted to assess changes in intramuscular blood flow and muscle oxygenation of the vastus lateralis (VL) during intermittent and incremental contractions. Fifteen healthy male subjects (21.7 ± 2.6 years) performed intermittent (5 s contraction, 5 s relaxation) and incremental isometric kneeextensions at 30%, 40%, 50%, 60% and 70% of maximal voluntary contraction (MVC) until task failure. Intramuscular blood flow and muscle oxygen saturation (StO2 ) were simultaneously measured using power Doppler ultrasonography and near-infrared spectroscopy, respectively, from the right VL of the mid-thigh. Intramuscular blood flow was increased from0.5 ±0.5% at rest to 13.9±9.5% at task failure. Intramuscular blood flow significantly increased from rest to 30% and 40%MVC (P = 0.001), and StO2 significantly decreased from 30% to 70%MVC (P = 0.004). These results indicate that intramuscular blood flow and StO2 show different patterns of change, suggesting that the contribution of intramuscular blood flow to oxygen supply decreases within the VL at moderate and higher exercise intensities.