Wavelet Decomposition of Wearable Sensor Measurement for Analysis of Nordic Skiing Double Poling

Introduction Nearly all Nordic ski coaching is still done verbally, supplemented with video analysis of the athlete. To date, there has been no quantifiable technique analysis largely accepted by the sport. This study seeks to advance a new approach based on direct measurement of athlete motion using wearable sensors. Specifically, we aimed to demonstrate that pole plant and pole off events can be reliably identified and used to quantify important kinematic variables from athletes spanning a range of ability levels. Methods Wearable sensor data were collected from sensors affixed to the sternum, pelvis, and bilaterally to thigh, shank and ski poles from three levels of skiers: beginner, intermediate-advanced, and advanced. Each skier completed 2, 50 m rollerski bouts of a double poling technique at three different speeds for a total of 6 trials per skier and 18 trials total. To determine pole plant and pole off events, data recorded by sensors affixed to the ski poles were processed using the continuous wavelet transform. Results The continuous wavelet transform provided a reliable method for identifying key pole plant and pole off events. Ideal double poling form at the time of pole plant is the forward angulation of the trunk parallel to the pole and shank, with the elbow angle approximately 45 degrees and the 5th finger at eyebrow height. Ongoing analysis will allow us to quantify the kinematics of each segment more precisely. Conclusions These results are the first step toward the development of a wearable sensor system that can be used to quantify and analyze Nordic skiing technique in real time. When used by the coach and athlete, the wearable sensor system could facilitate objective analysis of technique, a rarity in Nordic Skiing, which may result in faster technique adjustments and subsequent faster skiing