title: Fast Regulation of Vertical Squat Jump during Push-Off in Skilled Jumpers.
abstract: The height of a maximum Vertical Squat Jump (VSJ) reflects the useful power produced by a jumper during the push-off phase. In turn this partly depends on the coordination of the jumper's segmental rotations at each instant. The physical system constituted by the jumper has been shown to be very sensitive to perturbations and furthermore the movement is realized in a very short time (ca. 300 ms), compared to the timing of known feedback loops. However, the dynamics of the segmental coordination and its efficiency in relation to energetics at each instant of the push-off phase still remained to be clarified. Their study was the main purpose of the present research. Eight young adult volunteers (males) performed maximal VSJ. They were skilled in jumping according to their sport activities (track and field or volleyball). A video analysis on the kinematics of the jump determined the influence of the jumpers' segments rotation on the vertical velocity and acceleration of the body mass center (MC). The efficiency in the production of useful power at the jumpers' MC level, by the rotation of the segments, was measured in consequence. The results showed a great variability in the segmental movements of the eight jumpers, but homogeneity in the overall evolution of these movements with three consecutive types of coordination in the second part of the push-off (lasting roughly 0.16 s). Further analyses gave insights on the regulation of the push-off, suggesting that very fast regulation(s) of the VSJ may be supported by: (a) the adaptation of the motor cerebral programming to the jumper's physical characteristics; (b) the control of the initial posture; and
authors.affiliation: Inter-University Laboratory on Human Movement Biology (EA 7424), Centre for Interdisciplinary Research in Sport (FED 4272), University of Lyon, University Claude Bernard Lyon 1 Villeurbanne, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Fargier
authors.affiliation: Inter-University Laboratory on Human Movement Biology (EA 7424), Centre for Interdisciplinary Research in Sport (FED 4272), University of Lyon, University Claude Bernard Lyon 1 Villeurbanne, France.
authors.forename: Raphael
authors.initials: R
authors.lastname: Massarelli
authors.affiliation: Inter-University Laboratory on Human Movement Biology (EA 7424), Centre for Interdisciplinary Research in Sport (FED 4272), University of Lyon, University Claude Bernard Lyon 1Villeurbanne, France; Laboratoire de Conception, Optimisation et Modélisation des Systèmes équipe émotion-action (EA 7306), Université de LorraineIle du Saulcy, Metz, France.
authors.forename: Tahar
authors.initials: T
authors.lastname: Rabahi
authors.affiliation: Dipartimento di Patologia Chirurgica, Medica, Molecolare et dell'Area Critica, Università degli Studi Pisa, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Gemignani
authors.affiliation: Inter-University Laboratory on Human Movement Biology (EA 7424), Centre for Interdisciplinary Research in Sport (FED 4272), University of Lyon, University Claude Bernard Lyon 1 Villeurbanne, France.
authors.forename: Emile
authors.initials: E
authors.lastname: Fargier
keywords: explosive movement; intersegment coordination; motor control; power; vertical squat jump