{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,12]],"date-time":"2026-02-12T18:06:44Z","timestamp":1770919604753,"version":"3.50.1"},"reference-count":29,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2021,4,12]],"date-time":"2021-04-12T00:00:00Z","timestamp":1618185600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Position\u2013time tracking of athletes during a race can provide useful information about tactics and performance. However, carrier-phase differential global navigation satellite system (dGNSS)-based tracking, which is accurate to about 5 cm, might also allow for the extraction of variables reflecting an athlete\u2019s technique. Such variables include cycle length, cycle frequency, and choice of sub-technique. The aim of this study was to develop a dGNSS-based method for automated determination of sub-technique and cycle characteristics in cross-country ski skating. Sub-technique classification was achieved using a combination of hard decision rules and a neural network classifier (NNC) on position measurements from a head-mounted dGNSS antenna. The NNC was trained to classify the three main sub-techniques (G2\u2013G4) using optical marker motion data of the head trajectory of six subjects during treadmill skiing. Hard decision rules, based on the head\u2019s sideways and vertical movement, were used to identify phases of turning, tucked position and G5 (skating without poles). Cycle length and duration were derived from the components of the head velocity vector. The classifier\u2019s performance was evaluated on two subjects during an in-field roller skiing test race by comparison with manual classification from video recordings. Classification accuracy was 92\u201397% for G2\u2013G4, 32% for G5, 75% for turning, and 88% for tucked position. Cycle duration and cycle length had a root mean square (RMS) deviation of 2\u20133%, which was reduced to &lt;1% when cycle duration and length were averaged over five cycles. In conclusion, accurate dGNSS measurements of the head\u2019s trajectory during cross-country skiing contain sufficient information to classify the three main skating sub-techniques and characterize cycle length and duration.<\/jats:p>","DOI":"10.3390\/s21082705","type":"journal-article","created":{"date-parts":[[2021,4,12]],"date-time":"2021-04-12T11:05:06Z","timestamp":1618225506000},"page":"2705","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Classification of Cross-Country Ski Skating Sub-Technique Can Be Automated Using Carrier-Phase Differential GNSS Measurements of the Head\u2019s Position"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5424-6183","authenticated-orcid":false,"given":"\u00d8yvind","family":"Gl\u00f8ersen","sequence":"first","affiliation":[{"name":"Department of Physical Performance, Norwegian School of Sport Sciences, 4014 Oslo, Norway"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Matthias","family":"Gilgien","sequence":"additional","affiliation":[{"name":"Department of Physical Performance, Norwegian School of Sport Sciences, 4014 Oslo, Norway"},{"name":"Center of Alpine Sports Biomechanics, Engadin Health and Innovation Foundation, 7503 Samedan, Switzerland"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1425","DOI":"10.3389\/fphys.2018.01425","article-title":"Tracking performance in endurance racing sports: Evaluation of the accuracy offered by three commercial GNSS receivers aimed at the sports market","volume":"9","author":"Kocbach","year":"2018","journal-title":"Front. Physiol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"239","DOI":"10.2165\/00007256-200838030-00004","article-title":"Describing and understanding pacing strategies during athletic competition","volume":"38","author":"Abbiss","year":"2008","journal-title":"Sports Med."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"983","DOI":"10.1249\/MSS.0000000000002209","article-title":"Oxygen demand, uptake, and deficits in elite cross-country skiers during a 15-km race","volume":"52","author":"Gilgien","year":"2020","journal-title":"Med. Sci. Sports Exerc."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"846","DOI":"10.3389\/fphys.2018.00846","article-title":"Exercise intensity during cross-country skiing described by oxygen demands in flat and uphill terrain","volume":"9","author":"Karlsson","year":"2018","journal-title":"Front. Physiol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3199","DOI":"10.1016\/j.jbiomech.2015.07.001","article-title":"An inertial sensor-based system for spatio-temporal analysis in classic cross-country skiing diagonal technique","volume":"48","author":"Fasel","year":"2015","journal-title":"J. Biomech."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"65","DOI":"10.3389\/fbioe.2020.00065","article-title":"Drift-free foot orientation estimation in running using wearable IMU","volume":"8","author":"Falbriard","year":"2020","journal-title":"Front. Bioeng. Biotechnol."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Fasel, B., Sp\u00f6rri, J., Sch\u00fctz, P., Lorenzetti, S., and Aminian, K. (2017). Validation of functional calibration and strap-down joint drift correction for computing 3D joint angles of knee, hip, and trunk in alpine skiing. PLoS ONE, 12.","DOI":"10.1371\/journal.pone.0181446"},{"key":"ref_8","first-page":"651","article-title":"Automated identification and evaluation of subtechniques in classical-style roller skiing","volume":"13","author":"Sakurai","year":"2014","journal-title":"J. Sports Sci. Med."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Rindal, O.M.H., Seeberg, T.M., Tjonnas, J., Haugnes, P., and Sandbakk, O. (2017). Automatic classification of sub-techniques in classical cross-country skiing using a machine learning algorithm on micro-sensor data. Sensors, 18.","DOI":"10.3390\/s18010075"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"313","DOI":"10.1007\/s12283-017-0252-z","article-title":"A multi-sensor system for automatic analysis of classical cross-country skiing techniques","volume":"20","author":"Seeberg","year":"2017","journal-title":"Sports Eng."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Jang, J., Ankit, A., Kim, J., Jang, Y.J., Kim, H.Y., Kim, J.H., and Xiong, S. (2018). A unified deep-learning model for classifying the cross-country skiing techniques using wearable gyroscope sensors. Sensors, 18.","DOI":"10.3390\/s18113819"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"5047","DOI":"10.3390\/s120405047","article-title":"Identification of cross-country skiing movement patterns using micro-sensors","volume":"12","author":"Marsland","year":"2012","journal-title":"Sensors"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Sakurai, Y., Fujita, Z., and Ishige, Y. (2016). Automatic identification of subtechniques in skating-style roller skiing using inertial sensors. Sensors, 16.","DOI":"10.3390\/s16040473"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"18433","DOI":"10.3390\/s141018433","article-title":"The effect of different global navigation satellite system methods on positioning accuracy in elite alpine skiing","volume":"14","author":"Gilgien","year":"2014","journal-title":"Sensors"},{"key":"ref_15","first-page":"1","article-title":"How useful is satellite positioning system (GPS) to track gait parameters?","volume":"2","author":"Terrier","year":"2005","journal-title":"A review. J. Neuroeng. Rehabil."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1631","DOI":"10.3389\/fphys.2018.01631","article-title":"Propulsive power in cross-country skiing: Application and limitations of a novel wearable sensor-based method during roller skiing","volume":"9","author":"Losnegard","year":"2018","journal-title":"Front. Physiol."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Takeda, M., Miyamoto, N., Endo, T., Ohtonen, O., Lindinger, S., Linnamo, V., and St\u00f6ggl, T. (2019). Cross-country skiing analysis and ski technique detection by high-precision kinematic global navigation satellite system. Sensors, 19.","DOI":"10.3390\/s19224947"},{"key":"ref_18","first-page":"229","article-title":"Technique analysis in elite athletes using principal component analysis","volume":"36","author":"Myklebust","year":"2017","journal-title":"J. Sports Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"492","DOI":"10.1123\/jab.2015-0081","article-title":"Validity of ski skating center of mass displacement measured by a single inertial measurement unit","volume":"31","author":"Myklebust","year":"2015","journal-title":"J. Appl. Biomech."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"85","DOI":"10.1080\/14763140408522832","article-title":"Effects of speed on temporal patterns in classical style and freestyle cross-country skiing","volume":"3","author":"Nilsson","year":"2004","journal-title":"Sports Biomech."},{"key":"ref_21","unstructured":"Skaloud, J., and Limpach, P. (2003, January 9\u201312). Synergy of CP-DGPS, accelerometry and magnetic sensors for precise trajectography in ski racing. Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS\/GNSS 2003), Portland, OR, USA."},{"key":"ref_22","first-page":"429","article-title":"Theory of communication","volume":"93","author":"Gabor","year":"1946","journal-title":"J. Inst. Electr. Eng."},{"key":"ref_23","unstructured":"Myklebust, H. (2016). Quantification of Movement Patterns in Cross-Country Skiing Using Inertial Measurement Units. [Ph.D. Thesis, Norwegian School of Sport Sciences]."},{"key":"ref_24","unstructured":"Nordmo, T.-A.S. (2018). Arctic HARE. A Machine Learning-Based System for Performance Analysis of Cross-Country Skiers. [Ph.D. Thesis, The Arctic University of Norway]."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"435","DOI":"10.1080\/14763141.2015.1084033","article-title":"Using micro-sensor data to quantify macro kinematics of classical cross-country skiing during on-snow training","volume":"14","author":"Marsland","year":"2015","journal-title":"Sports Biomech."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Marsland, F., Mackintosh, C., Holmberg, H.-C., Anson, J., Waddington, G., Lyons, K., and Chapman, D. (2017). Full course macro-kinematic analysis of a 10 km classical cross-country skiing competition. PLoS ONE, 12.","DOI":"10.1371\/journal.pone.0182262"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"20589","DOI":"10.3390\/s141120589","article-title":"Automatic classification of the sub-techniques (gears) used in cross-country ski skating employing a mobile phone","volume":"14","author":"Holst","year":"2014","journal-title":"Sensors"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"6908","DOI":"10.1109\/JSEN.2018.2857502","article-title":"Step length estimation methods based on inertial sensors: A review","volume":"18","author":"Bahillo","year":"2018","journal-title":"IEEE Sens. J."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"2330","DOI":"10.1016\/j.jbiomech.2009.06.025","article-title":"Functional calibration procedure for 3D knee joint angle description using inertial sensors","volume":"42","author":"Favre","year":"2009","journal-title":"J. Biomech."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/8\/2705\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T13:26:53Z","timestamp":1760362013000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/8\/2705"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,4,12]]},"references-count":29,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2021,4]]}},"alternative-id":["s21082705"],"URL":"https:\/\/doi.org\/10.3390\/s21082705","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,4,12]]}}}