title: Influences of tendon stiffness, joint stiffness, and electromyographic activity on jump performances using single joint.
abstract: The present study aimed to examine the influences of tendon stiffness, joint stiffness, and electromyographic activity on jump performances consisting of a single-joint movement. Twenty-four men performed three kinds of unilateral maximal jump using only the ankle joint (squat jump: SJ; countermovement jump: CMJ; drop jump: DJ) on the sledge apparatus. The relative differences in the jump height of CMJ and DJ compared to SJ were defined as pre-stretch augmentation. During jumping exercises, electromyographic activities (mEMG) were recorded from the plantar flexors. Ankle joint stiffness was calculated as the change in the joint torque divided by the change in ankle joint angle during the eccentric phase of DJ. Achilles tendon stiffness was measured using ultrasonography during isometric plantar flexion. No significant correlations were found between joint stiffness and pre-stretch augmentation in both CMJ and DJ. On the contrary, tendon stiffness was significantly correlated with pre-stretch augmentation in both CMJ (r = -0.471) and DJ (r = -0.502). The relative mEMG value of CMJ (to that of SJ) during the concentric phase was significantly correlated with pre-stretch augmentation (r = 0.481), although this relationship was not found in DJ. These results suggested that (1) the greater jump height in CMJ could be explained by both the tendon elasticity and the increased activation level of muscle, (2) tendon elasticity played a more significant role in the enhancement of jump height during DJ, and (3) joint stiffness was not related to either pre-stretch augmentation or tendon stiffness.
authors.affiliation: Department of Life Science, Sports Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, Japan. kubo@idaten.c.u-tokyo.ac.jp
authors.forename: Keitaro
authors.initials: K
authors.lastname: Kubo
authors.forename: Masanori
authors.initials: M
authors.lastname: Morimoto
authors.forename: Teruaki
authors.initials: T
authors.lastname: Komuro
authors.forename: Naoya
authors.initials: N
authors.lastname: Tsunoda
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kanehisa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukunaga
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D004548:Elasticity; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular; D013647:Task Performance and Analysis; D019415:Torque; D014463:Ultrasonography