Biomechanics in cross-country skiing skating technique and measurement techniques of force production

Abstract

Requirements of a successful skier have changed during last decades due to e.g. changes in race forms and developments of equipment. The purpose of this thesis was to clarify in four Articles (I-IV) what are the requests modern skate skiing sets for the athletes in a biomechanical point of view. Firstly, it was explained how skiers control speed from low to maximal speeds (I). Secondly, the effects of long simulated ski race were determined with traditional force measurement methods (III) as well as with novel propulsion methods (IV). During the work process a need for updated multi-dimensional leg force sensor appeared and it was materialized (II). During the thesis 16 national level athletes participated in the different experiments of the study. Measurements for controlling speed were carried out with 3D force sensor for legs and pole force sensor for arms. Conventional cycle, force and joint kinematic parameters were analysed (I). After, a need for reliable force sensor appeared especially for anterior- posterior forces. Two 2D force binding sensors (Skate binding: vertical and medio-lateral directions and Classic binding: vertical and anterior-posterior directions) were designed and built. Validation was done in different temperatures and mechanical stress situations as well as in diverse normal and sport specific jumping situations and skiing with both techniques (II). Effects of simulated ski skating race (20 km) on athletes’ performance were analysed by direct force measurements from legs with updated force binding and from arms with pole force sensors. In addition, EMG and cycle definitions were conducted (III). Novel analysing method for propulsion was tested on the same data using additional 3D movement analysis (IV). Skiers control their speed during V2- skating with cycle length and cycle rate while length is dominant with lower speeds and rate governs with higher speeds. Force production of the arms and legs with increasing speeds is aided by vertical oscillation of COM (I). New force binding system was verified to be valid for skate skiing while some improvements were needed for classic binding (II). Effects of long simulated race were detected with slower skiing speed at the end of race caused by lower EMG activity and force production as indications of fatigue (III). Propulsion analyses gave new insights on athlete diagnostics by revealing the decrement of force production especially with legs which was overlooked with traditional analysing methods (IV). Keywords: cross-country skiing, speed adaptation, force measurement, fatigue, propulsion