Development of a simple algorithm to detect different types of freestyle jumps and jumps during skiing

Christina Kranzinger, Aaron Martinez, Stefan Kranzinger, Thomas Stöggl (2023): Development of a simple algorithm to detect different types of freestyle jumps and jumps during skiing In: Abstract Book of the 9th International Congress on Science and Skiing.

INTRODUCTION: Jump detection via inertial measurement units (IMUs) to monitor athletes is of high interest in many sports (e.g. volleyball [1,2], figure skating [3], snowboarding [4], ski jumping [5]). This work aims to develop an algorithm that detects jumps under different skiing conditions: freestyle jumps (big air, jumping hills) and jumps during normal skiing based on IMU data. The IMUs are attached to the skiers’ boots, which allows stable and consistent data recording [6].
METHODS: The algorithm takes the mean of the absolute vertical accelerations and smooths this data using a moving average of the last 25 data points. These smoothed values are rounded to the nearest tenth. Finally, the ranges with zeros are identified as jumps. For the analysis of freestyle jumps, we used data from seven freestyle skiers, while we collected jumps while skiing from two recreational skiers. The experiment took place on big-air jumps and on an alpine skiing piste.
RESULTS: Our results show that the proposed method can detect 100% (35 jumps) of freestyle jumps. We divide jumps during skiing into small jumps (flight time < 500 ms) and medium jumps (flight time ≥ 500 ms). For small jumps, 22.2% (4 out of 18), and for medium jumps, 91.4% (32 out of 35) of the jumps were detected. DISCUSSION/CONCLUSION: The proposed algorithm works well for medium jumps during skiing and freestyle jumps but needs to be strengthened for jumps with a flight time of less than 500 ms. Future work should further develop the algorithm to detect additional events, such as the moment of take-off or landing, and to classify the type of jump.

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