{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T00:57:50Z","timestamp":1760230670472,"version":"build-2065373602"},"reference-count":32,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2022,8,8]],"date-time":"2022-08-08T00:00:00Z","timestamp":1659916800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004955","name":"FFG","doi-asserted-by":"publisher","award":["881844"],"award-info":[{"award-number":["881844"]}],"id":[{"id":"10.13039\/501100004955","id-type":"DOI","asserted-by":"publisher"}]},{"name":"University of Linz","award":["881844"],"award-info":[{"award-number":["881844"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Many studies on alpine skiing are limited to a few gates or collected data in controlled conditions. In contrast, it is more functional to have a sensor setup and a fast algorithm that can work in any situation, collect data, and distinguish alpine skiing activities for further analysis. This study aims to detect alpine skiing activities via smartphone inertial measurement units (IMU) in an unsupervised manner that is feasible for daily use. Data of full skiing sessions from novice to expert skiers were collected in varied conditions using smartphone IMU. The recorded data is preprocessed and analyzed using unsupervised algorithms to distinguish skiing activities from the other possible activities during a day of skiing. We employed a windowing strategy to extract features from different combinations of window size and sliding rate. To reduce the dimensionality of extracted features, we used Principal Component Analysis. Three unsupervised techniques were examined and compared: KMeans, Ward\u2019s methods, and Gaussian Mixture Model. The results show that unsupervised learning can detect alpine skiing activities accurately independent of skiers\u2019 skill level in any condition. Among the studied methods and settings, the best model had 99.25% accuracy.<\/jats:p>","DOI":"10.3390\/s22155922","type":"journal-article","created":{"date-parts":[[2022,8,9]],"date-time":"2022-08-09T04:16:55Z","timestamp":1660018615000},"page":"5922","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":13,"title":["Alpine Skiing Activity Recognition Using Smartphone\u2019s IMUs"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6160-341X","authenticated-orcid":false,"given":"Behrooz","family":"Azadi","sequence":"first","affiliation":[{"name":"Pro2Future GmbH, Altenberger Strasse 69, 4040 Linz, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6817-9639","authenticated-orcid":false,"given":"Michael","family":"Haslgr\u00fcbler","sequence":"additional","affiliation":[{"name":"Pro2Future GmbH, Altenberger Strasse 69, 4040 Linz, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Bernhard","family":"Anzengruber-Tanase","sequence":"additional","affiliation":[{"name":"Pro2Future GmbH, Altenberger Strasse 69, 4040 Linz, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4801-5223","authenticated-orcid":false,"given":"Stefan","family":"Gr\u00fcnberger","sequence":"additional","affiliation":[{"name":"Institute of Pervasive Computing, Johannes Kepler University, Altenberger Stra\u00dfe 69, 4040 Linz, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alois","family":"Ferscha","sequence":"additional","affiliation":[{"name":"Institute of Pervasive Computing, Johannes Kepler University, Altenberger Stra\u00dfe 69, 4040 Linz, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,8,8]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"111","DOI":"10.3389\/fphys.2019.00111","article-title":"Recent kinematic and kinetic advances in olympic alpine skiing: Pyeongchang and beyond","volume":"10","author":"Supej","year":"2019","journal-title":"Front. 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