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Differences in activation patterns between eccentric and concentric quadriceps contractions
by
McHugh MP, Tyler TF, Greenberg SC, Gleim GW.
—
last modified
2009-10-09 15:16
J Sports Sci. 2002 Feb;20(2):83-91.
Previous studies analysing electromyograms (EMGs) from indwelling electrodes have
indicated that fast-twitch motor units are selectively recruited for
low-intensity eccentric contractions. The aim of this study was to compare the
frequency content of surface EMGs from quadriceps muscles during eccentric and
concentric contractions at various contraction intensities. Electromyograms were
recorded from the rectus femoris, vastus lateralis and vastus medialis muscles of
10 men during isokinetic (1.05 rad x s(-1)) eccentric and concentric knee
extension contractions at 25%, 50%, 75% and 100% of maximal voluntary contraction
(MVC) for each contraction mode. Additionally, isometric contractions (70
degrees) were performed at each intensity. The mean frequency and root mean
square (RMS) of the surface EMG were computed. Mean frequency was higher for
eccentric than concentric contractions at 25% (P < 0.01), 50% (P < 0.01) and 75%
(P < 0.05) but not at 100% MVC. It increased with increasing contraction
intensity for isometric (P < 0.001) and concentric (P < 0.01) contractions but
not for eccentric contractions (P = 0.27). The EMG amplitude (RMS) increased with
increasing contraction intensity similarly in each contraction mode (P < 0.0001).
Higher mean frequencies for eccentric than concentric contractions at submaximal
contraction intensities is consistent with more fast-twitch motor units being
active during eccentric contractions.