The mechanics of running while approaching and jumping over an obstacle
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ORIGINAL ARTICLE
The mechanics of running while approaching and jumping over an obstacle G. Mauroy • B. Schepens • P. A. Willems
Received: 4 July 2012 / Accepted: 28 September 2012 / Published online: 14 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract When leaping an obstacle, the runner increases the vertical velocity of his/her centre of mass (COM) at takeoff to augment the amplitude and duration of the aerial phase over it. This study analyses the modification of the bouncing mechanism of running when approaching a barrier. The forces exerted by the feet on the ground are measured by a 13-m-long force platform during the four to nine running steps preceding the jump over a 0.45- to 0.85-m-high barrier, at an approaching speed between 9 and 21 km h-1. The movements of the COM are evaluated by time-integration of the forces and the stiffness of the bouncing system by computer simulation. The running mechanism is modified during the two steps preceding the barrier. During the contact period, two steps before the barrier, the leg-spring stiffness decreases; consequently, the COM is lowered and accelerated forward. Then during the contact period preceding the obstacle, the leg-spring stiffness increases and the COM is raised and accelerated upwards, whereas its forward velocity is reduced. During this phase, the leg-spring acts like a pole, which stores elastic energy and changes the direction of the velocity vector to release this energy in a vertical direction. At high speeds, this storage–release mechanism of elastic energy is sufficient to provide the energy necessary to leap the
Communicated by Jean-Rene´ Lacour.
Electronic supplementary material The online version of this article (doi:10.1007/s00421-012-2519-1) contains supplementary material, which is available to authorized users. G. Mauroy B. Schepens P. A. Willems (&) Universite´ catholique de Louvain-Institute of NeuroScience, Laboratoire de physiologie et biome´canique de la locomotion, Place Pierre de Coubertin 1, 1348 Louvain-la-Neuve, Belgium e-mail: [email protected]
obstacle. On the contrary, at low speeds, the amount of elastic energy stored and released in the leg-spring is not sufficient to jump over the obstacle and additional positive muscular work must be done. Keywords Mechanical work Locomotion Running Jump Muscular stiffness
Introduction When running, the human body can be compared to a spring–mass system bouncing on the ground (Alexander 1992; Blickhan 1989; Cavagna et al. 1988; McMahon and Cheng 1990). Muscles, tendons and ligaments of the lower limb act like a single linear spring, storing and releasing elastic energy during the contact phase. In the simplest bouncing model of running, the leg is assimilated to a linear spring bouncing vertically on the ground (Cavagna et al. 1988). In this case, the natural frequency of the body bouncing system increases with the stiffness of the elastic structures responsible for the vertical rebound. This model gives accurate predictions of the running step fr
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