title: Feedback controlled force enhancement and activation reduction of voluntarily activated quadriceps femoris during sub-maximal muscle action.
abstract: 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° stretch, ω=60°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.
authors: Technische Universität München, Faculty of Sport and Health Science, Department of Biomechanics in Sports, Germany. wolfgang.seiberl@tum.de
authors: Wolfgang
authors: W
authors: Seiberl
authors: Daniel
authors: D
authors: Hahn
authors: Walter
authors: W
authors: Herzog
authors: Ansgar
authors: A
authors: Schwirtz
mesh_terms: D000328:Adult; D056228:Feedback, Sensory / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D014836:Volition / Q000502:physiology*