Article

Stretch of activated muscles leads to enhanced forces compared to isometric
contractions at the same muscle length and the same level of activation. This
so-called residual force enhancement (RFE) is thought to be a property of all
muscles and preparations. However, observations concerning the existence, amount
and duration of RFE are inconsistent, especially for voluntary activated large
human muscles. Therefore, physiological relevance for daily activity is still
questionable and the purpose of this study was to examine whether RFE is present
in voluntary sub-maximal activated quadriceps femoris (QF). Seated in a
rotational dynamometer with EMG attached to superficial parts of QF, 30 subjects
performed isometric and isometric-eccentric-isometric contractions (20 degrees
stretch, omega=60 degrees s(-1)) at 30% and 60% of maximum voluntary activation
(MVA) and contraction (MVC). To account for the complexity of the multi-headed
QF, a compensation model based on physiological cross-sectional area and
individual EMG-torque relations was used to interpret EMG data. For both levels
of intensity and both feedback control strategies, ANOVA identified significant
RFE (at the same level of activation) and reduced activation (at the same level
of torque). Against expectations, RFE was independent of the level of activation.
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Langue : ANGLAIS