Morphological Analysis of Acceleration Signals in Cross-country Skiing - Information Extraction and Technique Transitions Detection

Aims: Experience morphology of acceleration signals, extract useful information and classify time periods into defined techniques during cross-country skiing. Method: Three Norwegian cross-country skiers ski skated one lap in the 2011 world championship sprint track as fast as possible with 5 accelerometers attached to their body and equipment. Algorithms for detecting ski/pole hits and leaves and computing specific ski parameters like cycle times (CT), poling/pushing times (PT), recovery times (RT), symmetry between left and right side and technique transition times were developed based on thresholds and validated against video. Results: In stable and repeated techniques, pole hits/leaves and ski leaves were detected 99% correctly, while ski hits were more difficult to detect (77%). From these hit and leave values CT, PT, RT, symmetry and technique transitions were successfully calculated. Conclusion: Accelerometers can definitely contribute to biomechanical research in cross-country skiing and studies combining force, position and accelerometer data will probably be seen more frequently in the future.