Biomechanics of speed adaptation and functionality of arm swing in cross-country skiing

Skiing technique has a major impact on cross-country (XC) skiing performance and helps the athlete to ski as fast or as economic as possible depending on what is asked in the specific race situation. Four studies have been conducted, aiming to investigate speed adaptation mechanism in arm swing assisted XC-skiing techniques (I, II), to determine if and how arm swing contributes to XC-skiing speed (II, IV) and propulsion (IV), putting special emphasis on accessing the centre of mass (COM) acceleration and to reveal from which push-off the gained acceleration originates (III, IV). Highly skilled XC-skiers participated in the experiments. While study I was conducted during double poling with kick (DPK) and roller skiing on a treadmill, the studies II-IV investigated leg skating and V2-alternate skating (V2A) during natural skiing on snow. The results (I) indicate that adapting to submaximal DPK speeds athletes increased cycle length and cycle rate, producing greater forces. Thereby athletes who increased cycle length more across speeds emphasised poling with short poling and long arm swing times rather than leg-action. Studies II and IV revealed that athletes skied considerable faster when using arm swing. They realised greater cycle length at high submaximal skiing speed, a pattern which has been described as performance characteristic. A neuromuscular effect of arm swing was detected (II) in high submaximal speed as greater forces have been produced with lower neuromuscular activation in knee extensor muscles. The position of COM could be accessed and validated (III). By estimating COM acceleration from force and position data, it was feasible to determine how much each push-off contributes to overall propulsion (II) and that the amount of gained propulsion changed due to arm swing use (IV). It should be emphasised that greater propulsion could be generated during arm swing assisted push-offs in maximal speeds and regardless if one or both arms were swinging (IV). Main reason for this was the greater forward lean of the athletes during push-off. The additional linear momentum of the swinging arms and the transfer of momentum from braking arms to the rest of the body contributed to greater gain of linear momentum during push-off in arm swing trials. A faster arm swing directed more forward and less upward at the end of push-off together with a “long arm” pattern added to compensate the disadvantage of less swinging mass in single arm swing. This study provided first insights how arm swing should be conducted in V2A. The detected mechanism of speed adaptation in arm swing assisted skiing techniques together with the beneficial effects of arm swing offer new possibilities for diagnostic and training and should be considered in theory based technique training.by Mag. Caroline GöpfertLiteraturverzeichnis: Blatt 101-112Paris Lodron University of Salzburg, Dissertation, 2017OeBB(VLID)497120