Effect of movement velocity and movement pattern on the root mean
square and the median frequency of the electromyographic activity of the
quadriceps during isokinetic testing
Affiliations: [a] Department of Kinesiology, University of New
Hampshire, Durham, NH 03824, USA
Abstract: 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.
Keywords: EMG, root mean square, median frequency, quadriceps
