Science and Skiing

By E.Müller; H. Schwameder et al. | Go to book overview

23

TYPES OF MUSCLE ACTION OF LEG AND HIP EXTENSOR MUSCLES IN SLALOM

U.FRICK and D.SCHMIDTBLEICHER

Institute for Sport Sciences, Johann Wolfgang Goethe University Frankfurt, Germany


C.RASCHNER and E.MÜLLER

Institute for Sport Sciences, University of Salzburg, Austria

Keywords: concentric muscle action, eccentric muscle action, slalom skiing, stretch-shortening cycle, training device, alpine skiing.


1Introduction

During preparation and competition periods, specific strength training and exercises which simulate the slalom turn, are used to prepare, maintain or enhance performance in slalom. Common skills for this purpose are one-and two-footed vertical and horizontal jumps. One-footed alternating lateral jumps with landing and push-off on the outside leg are particularly often used. During all these movements performance is generated mainly by leg-and hip-extensor muscles, acting in a stretch-shortening cycle (SSC). Stretch-shortening cycle is characterised by the immediate succession of two movement phases during ground contact. During the first phase, external forces usually exceed (internal) muscle forces. Therefore the joints (here: ankle-, knee-, and hip-joint) are bent in this phase and the corresponding active extensor muscles are stretched, working eccentrically. Immediately after compensation of the external forces the second phase begins: the joints are extended and the extensor muscles shorten, working concentrically. As indicated from several studies [ 1 ] [ 2 ] [ 3 ], SSC is a specific type of muscle action (MA). The reason for this is that during the eccentric phase, energy is stored in elastic structures of the muscle-tendon complex and reutilized during the concentric phase [ 4 ] [ 5 ] [ 6 ]. This leads to the maximization of performance potential and to an enhanced efficiency of movements using SSC, compared to movements with pure concentric MA [ 1 ] [ 2 ] [ 7 ]. The potentiation of performance as well as the efficiency of SSC depend mainly on the quality of the regulation of muscle stiffness. In SSC movements muscle stiffness is regulated essentially via three mechanisms: the muscle

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