**A Unified Deep-Learning Model for Classifying the Cross-Country Skiing Techniques Using Wearable Gyroscope Sensors**

**Jihyeok Jang 1,†, Ankit Ankit 2,†, Jinhyeok Kim 1, Young Jae Jang 1, Hye Young Kim 3, Jin Hae Kim <sup>4</sup> and Shuping Xiong 1,\***


Received: 31 August 2018; Accepted: 4 November 2018; Published: 7 November 2018

**Abstract:** The automatic classification of cross-country (XC) skiing techniques using data from wearable sensors has the potential to provide insights for optimizing the performance of professional skiers. In this paper, we propose a unified deep learning model for classifying eight techniques used in classical and skating styles XC-skiing and optimize this model for the number of gyroscope sensors by analyzing the results for five different configurations of sensors. We collected data of four professional skiers on outdoor flat and natural courses. The model is first trained over the flat course data of two skiers and tested over the flat and natural course data of a third skier in a leave-one-out fashion, resulting in a mean accuracy of ~80% over three combinations. Secondly, the model is trained over the flat course data of three skiers and tested over flat course and natural course data of one new skier, resulting in a mean accuracy of 87.2% and 95.1% respectively, using the optimal sensor configuration (five gyroscope sensors: both hands, both feet, and the pelvis). High classification accuracy obtained using both approaches indicates that this deep learning model has the potential to be deployed for real-time classification of skiing techniques by professional skiers and coaches.

**Keywords:** sports analytics; deep learning; classification; inertial sensor; cross-country skiing; classical style; skating style
