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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>S</mml:mi> <mml:mrow><mml:mi>t</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> <mml:annotation>${{S}_{{\mathrm{t}}{{{\mathrm{O}}}_2}}}$</mml:annotation></mml:semantics> </mml:math> ) 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>S</mml:mi> <mml:mrow><mml:mi>t</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> <mml:annotation>${{S}_{{\mathrm{t}}{{{\mathrm{O}}}_2}}}$</mml:annotation></mml:semantics> </mml:math> significantly decreased from 30% to 70% MVC (P = 0.004). These results indicate that intramuscular blood flow and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>S</mml:mi> <mml:mrow><mml:mi>t</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> <mml:annotation>${{S}_{{\mathrm{t}}{{{\mathrm{O}}}_2}}}$</mml:annotation></mml:semantics> </mml:math> 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.