Affiliations: [a] Department of Kinesiology, University of New
Hampshire, Durham, NH 03824, USA
Note: [] Corresponding author: John P. Miller, Department of Kinesiology,
University of New Hamshire, Durham, NH 03824, USA. Tel.: +1 603 862-0263; Fax:
+1 603 862-0154; E-mail: jm@christa.unh.edu
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 300o.s-1 and 2) to examine
the changes in the mfEMG with fatigue at 300o.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 300o.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.
