title: Both the elongation of attached crossbridges and residual force enhancement contribute to joint torque enhancement by the stretch-shortening cycle.
abstract: This study examined the influence of the elongation of attached crossbridges and residual force enhancement on joint torque enhancement by the stretch-shortening cycle (SSC). Electrically evoked submaximal tetanic plantar flexions were adopted. Concentric contractions were evoked in the following three conditions: after 2 s isometric preactivation (ISO condition), after 1 s isometric then 1 s eccentric preactivation (ECC condition), and after 1 s eccentric then 1 s isometric preactivation (TRAN condition). Joint torque and fascicle length were measured during the concentric contraction phase. While no differences in fascicle length were observed among conditions at any time points, joint torque was significantly higher in the ECC than TRAN condition at the onset of concentric contraction. This difference would be caused by the dissipation of the elastic energy stored in the attached crossbridges induced by eccentric preactivation in TRAN condition due to 1 s transition phase. Furthermore, joint torques observed 0.3 and 0.6 s after concentric contraction were significantly larger in the ECC and TRAN conditions than in the ISO condition while no difference was observed between the ECC and TRAN conditions. Since the elastic energy stored in the attached crossbridges would have dissipated over this time frame, this result suggests that residual force enhancement induced by eccentric preactivation also contributes to joint torque enhancement by the SSC.
authors.affiliation: Faculty of Kinesiology, University of Calgary, 2500 University Drive, NW, Calgary, Alberta, CanadaT2N 1N4; Japan Society for the Promotion of Science, Postdoctoral Fellow for Research Abroad, 5-3-1, Chiyoda-ku, Tokyo 102-0083, Japan; Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Atsuki
authors.identifier: 0000-0002-8572-7940
authors.initials: A
authors.lastname: Fukutani
authors.affiliation: Graduate School of Sport and Health Science , Ritsumeikan University , 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577 , Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Misaki
authors.affiliation: Faculty of Sport and Health Science , Ritsumeikan University , 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577 , Japan.
authors.forename: Tadao
authors.initials: T
authors.lastname: Isaka
keywords: crossbridge; eccentric contraction; elastic energy; muscle; titin