Intramuscular blood flow and muscle oxygenation of the vastus lateralis response to intermittent incremental muscle contractions.

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 knee extensions at 30%, 40%, 50%, 60% and 70% of maximal voluntary contraction (MVC) until task failure. Intramuscular blood flow and muscle oxygen saturation (StO2${{S}_{{\mathrm{t}}{{{\mathrm{O}}}_2}}}$) 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 from 0.5 ± 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${{S}_{{\mathrm{t}}{{{\mathrm{O}}}_2}}}$ significantly decreased from 30% to 70% MVC (P = 0.004). These results indicate that intramuscular blood flow and StO2${{S}_{{\mathrm{t}}{{{\mathrm{O}}}_2}}}$ 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. What is the central question of this study?How do intramuscular blood flow and muscle oxygenation change with intermittent and incremental muscle contractions?What is the main finding and its importance?Intramuscular blood flow reached a plateau above moderate exercise intensities, but muscle oxygen saturation continued to decrease. These results indicate that the contribution of intramuscular blood flow to oxygen supply varies with exercise intensity. [ABSTRACT FROM AUTHOR]