title: The activation time-course of contractile elements estimated from in vivo fascicle behaviours during twitch contractions.
abstract: To better understand the cascade from neural activation up to force production within in vivo contracting muscle-tendon units, we estimated activation of contractile elements from experimentally measured human fascicle length change and force using a Hill-type muscle model. The experiment was conducted with respect to twitch contractions of the tibialis anterior muscle at three joint angles. As muscle contractile element force is a function of its length and velocity, the activation of contractile elements was calculated using a Hill-type muscle model and measured data. The results were able to reproduce the continuous rising activation of contractile elements after termination of electromyographic activity, the earlier shift of peak activation in time compared to twitch force, and the differences in time-course activation at three different joint angles. These findings are consistent with the predicted change in the activation of contractile elements from previous reports. Also, the results suggest that the time-course of the activation of contractile elements was greatly influenced by the change in force generating capacities related to both length and velocity, even in fixed end contractions, which could result from muscle-tendon interaction.
authors.affiliation: Hyogo University of Teacher Education, Faculty of Physical Education, Kato, Japan. toda@hyogo-u.ac.jp
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Oda
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Himeno
authors.forename: Dean C
authors.initials: DC
authors.lastname: Hay
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kanehisa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukunaga
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
mesh_terms: D000328:Adult; D000818:Animals; D001696:Biomechanical Phenomena; D006801:Humans; D007596:Joints / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D013710:Tendons / Q000502:physiology*; D055815:Young Adult