The purpose of this study was twofold: 1) compare the effect of movement velocity and movement pattern on the electromyographic activity (EMG) of the quadriceps as measured by the Root Mean Square of the electromyogram(rmsEMG) and the Median Frequency of the electromyogram (mfEMG) during isokinetic testing and 2) compare the effect of movement pattern on the torque production of the quadriceps during isokinetic testing. Fourteen healthy adult females with no known knee pathologies and familiarity with isokinetic testing performed six continuous isokinetic movements at
$100^{0}·s^{-1}$
,
$200^{0}·s^{-1}$
,
$300^{0}·s^{-1}$
and
$400^{0}·s^{-1}$
. Movements were performed in a reciprocal pattern, (maximal knee extension followed by maximal knee flexion), and a non-reciprocal pattern (maximal extension followed by relaxation of the hamstrings). Statistical analyses revealed there was a difference in the rmsEMG for the quadriceps on the effect of velocity (F=3.2, P<0.05) with post hoc analysis revealing significant differences in the rmsEMG between 100 and
$300^{0}·s^{-1}$
(F= 5.6, P<0.05), and between 100 and
$400^{0}·s^{-1}$
(F = 6.7, P<0.01) with the highest rmsEMG being seen during the slowest velocities. For the mfEMG there were significant differences when comparing the velocity of movement F= 7.8, P<0.001), specifically when comparing the slowest velocity
$100^{0}·s^{-1}$
with
$200^{0}·s}^{-1}$
(F = 4.9, P<0.05),
$300^{0}·s}^{-1}$
(F= 8.8, P<0.005) and
$400^{0}·s}^{-1}$
(F = 22.7, P<0.001) with the highest mfEMG observed at the lower velocities. No difference was noted either in EMG or torque between the reciprocal and non-reciprocal movements. The results of this study suggests that during isokinetic testing the EMG activity of the quadriceps is altered as velocity changes with regard to the rmsEMG and mfEMG. Specifically as velocity increases overall muscle activity decreases as measured by the rmsEMG. In addition as velocity increases there is a shifting toward recruitment of slower velocity muscle fibers as measured by the mfEMG. These results also suggest that movement pattern (reciprocal vs. non reciprocal) does not effect the EMG for quadriceps activity during isokinetic knee extension.
