Effect of movement velocity on the median frequency of the electromyographic activity of the quadriceps and hamstrings during isokinetic testing

Abstract

The purpose of this study was two-fold: 1) to examine the median frequency of the electromyographic activity (mfEMG) of the quadriceps and hamstrings during isokinetic movements at 60, 180 and 300° . s -1 and 2) to examine the changes in the mfEMG with fatigue at 300° . s -1 . Fourteen female athletes had their dominant limb tested on a Cybex II+ isokinetic dynamometer (Cybex, Ronkonkoma, NY). The mfEMG of the quadriceps and hamstring muscle groups was determined by placing bipolar surface electrodes on the vastus lateralis, vastus medialis, biceps femoris, and medial hamstrings. Repeated measures ANOVA indicated no effect of movement velocity on the mfEMG of the quadriceps. Significant differences were noted however in the mfEMG of the hamstrings with the higher movement velocities effecting significant upward shifts in the mfEMG. Significant differences were also noted in the mfEMG of both the quadriceps and the hamstrings within the 300° . s -1 trials with the mfEMG shifting downward as the muscles fatigued. These results suggest that there is a difference in motor recruitment strategies for the hamstrings between low, moderate and high speed isokinetic activity and for the quadriceps and the hamstrings during high velocity movement.