Motor Unit Activation Variability and Reliability during Maximal Voluntary Quadriceps Contractions

The ability of an individual to generate maximal quadriceps torque is dependent mainly upon motor unit activation characteristics. This assessment can often be considered invalid should its reproducibility be in question. Furthermore, the median frequency (MF) of sampled EMG signals during maximal voluntary efforts is inherently variable both within and between multiple trials. The purpose of the present investigation was to assess MF variability and reliability of the quadriceps during multiple trials of maximal voluntary efforts. A second purpose of this study was to examine MF differences between the 3 superficial portions of the quadriceps femoris muscles.