Oxygenation and neuromuscular activation of the quadriceps femoris including the vastus intermedius during a fatiguing contraction

Summary Introduction The purpose of this study was to assess oxygenation and neuromuscular activation of the quadriceps femoris muscle group, including the vastus intermedius (VI), during a fatiguing contraction. Methods Eleven healthy men performed an isometric knee extension at 50% of the maximum voluntary contraction until failure. Near‐infrared spectroscopy was used to measure tissue oxygen saturation (StO2), and surface electromyography was used to quantify the median frequency (MF) of the four individual quadriceps femoris muscles. Results A significant decrease in StO2 began at 25% of time to exhaustion in all four muscles, and StO2 of the VI was significantly higher than StO2 of the vastus medialis (VM) from 25% of time to exhaustion until 95% of time to exhaustion. The MF of the VI did not significantly decrease during the fatiguing task. We found a significant correlation between ∆MF and ∆StO2 in the VI (r = 0·745, P