title: Twitch potentiation induced by stimulated and voluntary isometric contractions at various torque levels in human knee extensor muscles.
abstract: The purpose of this study was to compare the extent of twitch potentiation (TP) after stimulated or voluntary contractions at identical intensities for the human knee extensor muscles. Isometric knee extensions of 10 s were performed at 20%, 40%, and 60% of maximal voluntary contraction (MVC) torque level, through percutaneous electrical stimulation of the quadriceps at 80 Hz or voluntary contraction. Twitch responses were evoked by stimulating the femoral nerve percutaneously with supramaximal intensity. The extent of TP after the stimulated contraction was greater than that after the voluntary contraction at the 20% MVC torque level, whereas a stimulated contraction induced a smaller extent of TP than did a voluntary contraction at contraction intensities higher than 40% MVC. We suggest that this contraction intensity dependence of differences in TP after stimulated and voluntary isometric conditioning contractions is responsible for differences in the recruitment pattern of motor units during the conditioning contractions.
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan. miyamoto@aoni.waseda.jp
authors.forename: Naokazu
authors.initials: N
authors.lastname: Miyamoto
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Yanai
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000502:physiology; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque; D055815:Young Adult