The purpose of this study was to elucidate if the m. quadriceps femoris was fully activated during the first contractions of a series of repetitive maximal contractions and if there was any difference in the development of fatigue between sexes. To do this sixteen untrained subjects performed two series of contractions in an isokinetic dynamometer: one series of single maximum contractions and one series of repetitive maximum contractions. The EMG activity of m. vastus lateralis, m. vastus medialis and m. rectus femoris was recorded. The subjects were unable to perform maximum effort during the first repetitions of each trial, which might influence the results of fatigue studies, if these contractions are chosen as reference. We also found in contrast to other studies a decrease in RMS between the reference contraction and the fatigue level. We have not been able to display any difference between males and females during fatigue either in relative mechanical output nor in electromyographic parameters or experience in fatigue during isokinetic knee-extensions.