Effect of heavy isokinetic intermittent exercise on acute neuromuscular fatigue in knee extensors

This study aimed at quantifying maximal voluntary force-generating capacity of the quadriceps femoris and its EMG output after an isokinetic concentric intermittent exercise. Another objective was to find out whether the amount of neuromuscular fatigue was velocity-dependent. Eight males judo players (age: 18.4 +/- 1.4 years; height: 1.80 +/- 0.03 m; body mass: 77.0 +/- 4.2 kg) performed a fatiguing exercise composed of five sets of ten maximal knee extension at 120 degrees/s, with 3min recovery in between. Peak torque (PT) at three angular velocities (60, 120 and 180 degrees/s) and EMG from the vastus lateralis, rectus femoris and vastus medialis were evaluated before and after the fatiguing exercise. EMG was analyzed for root mean square (RMS) and median frequency (MF). The fatiguing exercise induced PT decrement (P < 0.01) irrespective of the test velocity, in conjunction with decreased RMS (P < 0.001) and a decrease in MF (P < 0.01). In addition, although EMG activity demonstrated no velocity effect, the loss of PT after the fatiguing isokinetic intermittent exercise was more pronounced at the lower velocity (P < 0.05). The combination of decreased PT, RMS and MF suggests a reduction of the neural drive under the present fatiguing protocol.