INTRODUCTION: The study of the mechanical energy (ME) fluctuations of the center of mass and/or body has recently been applied to cross-country (XC) skiing techniques (1,2). Pellegrini et. al. (2) argued that double poling (DP) is similar to that of the inverted pendulum mechanism as seen in walking, where the kinetic (Ekin) and gravitational potential (Epot) energies fluctuates out-ofphase. The present study investigated these energy fluctuations in DP and included instantaneous measurements of external work (Wext) generation. We, in contradiction with Pellegrini et al. (2), hypothesized that Ekin and Epot would fluctuate more in-phase, and that Ekin+pot (i.e. total ME) would show large fluctuations over the movement cycle, increasing in retrieval and decreasing in the poling phase. In that way, body ME can directly be transferred to do Wext as the main mechanism of propulsion in DP. METHOD: Nine male XC skiers completed tests on a DP ski ergometer at low, moderate, high and maximal intensity. Qualisys motion capture analysis and force cell recordings were used to obtain body dynamics and kinematics, including Wext and ME and their time differentials (power, P). Ptot was defined as the sum of Pkin+pot and Pext, and interpreted as the rate of energy absorption or generation by muscle-tendon systems. RESULTS: After fluctuating out-of-phase in the start of the movement cycle, Ekin and Epot then became in-phase, simultaneously decreasing around where Wext generation started. Ekin+pot showed large fluctuations over the movement cycle, increasing in retrieval and decreasing in the poling phase (Fig. 1). Pkin+pot fluctuated almost perfectly out-of-phase with Pext (Fig. 2). A brief period of muscle-tendon energy absorption took place at the onset of poling. For the rest of the poling and throughout the retrieval phase, muscle-tendons generated energy both to do Wext and to increase Ekin+pot. ~50 % of total Ptot was done during retrieval at all intensities. DISCUSSION: The present examination of the DP technique demonstrates that the functionality and mechanism of the large fluctuations of Ekin+pot over the movement cycle is to increase the body ME during the retrieval phase. Here, ~50 % of total muscletendon work is done. This is followed by a direct transfer of body ME to do external work during the subsequent poling phase. Overall, these out-of-phase fluctuations between Ekin+pot and external work generation indicate that neither the spring-mass or the inverted pendulum type of locomotion is utilized in DP. --- The hosting University of Jyväskylä is planning to publish conference proceedings "Science and Nordic Skiing III". In case you are interested in this publication please contact the editors (Anni Hakkarainen anni.s.j.hakkarainen@jyu.fi) to become registered for the book.
© Copyright 2015 3rd International Congress on Science and Nordic Skiing - ICSNS 2015. 5-8 June 2015, Vuokatti, Finland. Veröffentlicht von University of Jyväskylä; University of Salzburg. Alle Rechte vorbehalten. / Übersetzt mit https://www.DeepL.com/Translator