{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,16]],"date-time":"2026-05-16T16:20:24Z","timestamp":1778948424493,"version":"3.51.4"},"reference-count":29,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2014,10,13]],"date-time":"2014-10-13T00:00:00Z","timestamp":1413158400000},"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>High precision Global Navigation Satellite System (GNSS) measurements are becoming more and more popular in alpine skiing due to the relatively undemanding setup and excellent performance. However, GNSS provides only single-point measurements that are defined with the antenna placed typically behind the skier\u2019s neck. A key issue is how to estimate other more relevant parameters of the skier\u2019s body, like the center of mass (COM) and ski trajectories. Previously, these parameters were estimated by modeling the skier\u2019s body with an inverted-pendulum model that oversimplified the skier\u2019s body. In this study, we propose two machine learning methods that overcome this shortcoming and estimate COM and skis trajectories based on a more faithful approximation of the skier\u2019s body with nine degrees-of-freedom. The first method utilizes a well-established approach of artificial neural networks, while the second method is based on a state-of-the-art statistical generalization method. Both methods were evaluated using the reference measurements obtained on a typical giant slalom course and compared with the inverted-pendulum method. Our results outperform the results of commonly used inverted-pendulum methods and demonstrate the applicability of machine learning techniques in biomechanical measurements of alpine skiing.<\/jats:p>","DOI":"10.3390\/s141018898","type":"journal-article","created":{"date-parts":[[2014,10,14]],"date-time":"2014-10-14T02:13:08Z","timestamp":1413252788000},"page":"18898-18914","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":24,"title":["Estimation of Alpine Skier Posture Using Machine Learning Techniques"],"prefix":"10.3390","volume":"14","author":[{"given":"Bojan","family":"Nemec","sequence":"first","affiliation":[{"name":"Department of Automation, Biocybernetics and Robotics, Jo\u017eef Stefan Institute, Ljubljana 1000, Slovenia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tadej","family":"Petri\u010d","sequence":"additional","affiliation":[{"name":"Department of Automation, Biocybernetics and Robotics, Jo\u017eef Stefan Institute, Ljubljana 1000, Slovenia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jan","family":"Babi\u010d","sequence":"additional","affiliation":[{"name":"Department of Automation, Biocybernetics and Robotics, Jo\u017eef Stefan Institute, Ljubljana 1000, Slovenia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Matej","family":"Supej","sequence":"additional","affiliation":[{"name":"Faculty of Sport, University of Ljubljana, Ljubljana 1000, Slovenia"},{"name":"Faculty of Mathematics, Natural Sciences and Information Technologies, University of Primorska, Koper SI-6101, Slovenia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2014,10,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1093","DOI":"10.2165\/00007256-200333150-00002","article-title":"Global positioning system and sport-specific testing","volume":"33","author":"Larsson","year":"2003","journal-title":"Sports Med."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1016\/j.jsams.2008.09.015","article-title":"Validity and reliability of GPS devices for measuring movement demands of team sports","volume":"13","author":"Coutts","year":"2010","journal-title":"J. Sci. Med. Sport"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1123\/ijspp.6.3.295","article-title":"Applications of GPS Technologies to Field Sports","volume":"6","author":"Aughey","year":"2011","journal-title":"Int. J. Sports Phys. Perform."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"759","DOI":"10.1080\/02640411003716934","article-title":"3D measurements of alpine skiing with an inertial sensor motion capture suit and GNSS RTK system","volume":"28","author":"Supej","year":"2010","journal-title":"J. Sports Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"470","DOI":"10.1016\/j.proeng.2011.05.116","article-title":"Evaluation of the use of a GPS data-logging device in a snowsport environment","volume":"13","author":"Dickson","year":"2011","journal-title":"Procedia Eng."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"9821","DOI":"10.3390\/s130809821","article-title":"Determination of external forces in alpine skiing using a differential global navigation satellite system","volume":"13","author":"Gilgien","year":"2013","journal-title":"Sensors"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"17","DOI":"10.1080\/19346182.2008.9648447","article-title":"Fusion motion capture: A prototype system using inertial measurement units and GPS for the biomechanical analysis of ski racing","volume":"1","author":"Brodie","year":"2008","journal-title":"Sports Tech."},{"key":"ref_8","unstructured":"Shiefermueller, C., Lindinger, S., and Mueller, E. (2005). Science and Skiing III, Meyer & Meyer Sport."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1123\/jab.24.2.121","article-title":"Differential specific mechanical energy as a quality parameter in racing alpine skiing","volume":"24","author":"Supej","year":"2008","journal-title":"J.Appl. Biomech."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"72","DOI":"10.1111\/j.1600-0838.2010.01159.x","article-title":"Mechanical parameters as predictors of performance in alpine World Cup slalom racing","volume":"21","author":"Supej","year":"2011","journal-title":"Scand. J. Med. Sci. Sports"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1063","DOI":"10.1080\/02640414.2012.690073","article-title":"Quantifying instantaneous performance in alpine ski racing","volume":"30","author":"Federolf","year":"2012","journal-title":"J. Sports Sci."},{"key":"ref_12","unstructured":"Supej, M., Kugovnik, O., and Nemec, B. (2008, January 4\u20137). DGPS measurement system in alpine skiing track and center of mass estimation. Nanjing, China."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"38","DOI":"10.1111\/sms.12007","article-title":"\u0160arabon, N.; Nemec, B.; Holmberg, H.C. Aerodynamic drag is not the major determinant of performance during giant slalom skiing at the elite level","volume":"23","author":"Supej","year":"2013","journal-title":"Scand. J. Med. Sci. Sports"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"400","DOI":"10.1080\/02701367.2011.10599772","article-title":"A new time measurement method using a high-end global navigation satellite system to analyze alpine skiing","volume":"82","author":"Supej","year":"2011","journal-title":"Res. Q. Exerc. Sport"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"516","DOI":"10.1123\/jab.26.4.516","article-title":"Application of a full body inertial measurement system in alpine skiing: A comparison with an optical video based system","volume":"26","author":"Kruger","year":"2010","journal-title":"J. Appl. Biomech."},{"key":"ref_16","unstructured":"The Mass and Inertia Characteristics of the Main Segments of the Human Body. Available online: http:\/\/www.dh.aist.go.jp\/bodyDB\/m\/e-k-05.html."},{"key":"ref_17","unstructured":"Spivak, M. (2006). Calculus, Cambridge University Press."},{"key":"ref_18","first-page":"2","article-title":"Neural Networks: A Review from a Statistical Perspective","volume":"9","author":"Cheng","year":"1994","journal-title":"Stat. Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"585","DOI":"10.1109\/TIE.2003.812470","article-title":"A Comprehensive Review for Industrial Applicability of Artificial Neural Networks","volume":"50","author":"Meireles","year":"2003","journal-title":"IEEE Trans. Ind. Electron."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2","DOI":"10.1016\/j.eswa.2007.10.005","article-title":"Neural networks and statistical techniques: A review of applications","volume":"36","author":"Paliwal","year":"2009","journal-title":"Expert Syst. Appl."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1016\/S0167-7012(00)00201-3","article-title":"Artificial neural networks: Fundamentals, computing, design, and application","volume":"43","author":"Basheer","year":"2000","journal-title":"J. Microbiol. Methods"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1613\/jair.295","article-title":"Active Learning with Statistical Models","volume":"4","author":"Cohn","year":"1996","journal-title":"J. Artif. Intell. Res."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"596","DOI":"10.1080\/01621459.1988.10478639","article-title":"Locally Weighted Regression: An Approach to Regression Analysis by Local Fitting","volume":"83","author":"Cleveland","year":"1988","journal-title":"J. Am. Stat. Assoc."},{"key":"ref_24","unstructured":"Atkeson, C., Moore, A., and Schaal, S. Locally Weighted Learning. Available online: http:\/\/www.ias.informatik.tu-darmstadt.de\/uploads\/Teaching\/AutonomousLearningSystems\/Englert_ALS_2012.pdf."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"49","DOI":"10.1023\/A:1015727715131","article-title":"Scalable Techniques from Nonparametric Statistics for Real Time Robot Learning","volume":"17","author":"Schaal","year":"2002","journal-title":"Appl. Intell."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Domany, E., van Hemmen, J., and Schulten, K. (1996). Models of Neural Networks III, Springer.","DOI":"10.1007\/978-1-4612-0723-8"},{"key":"ref_27","unstructured":"Vijayakumar, S. Locally Weighted Projection Regression: Matlab Code. Available online: http:\/\/homepages.inf.ed.ac.uk\/svijayak\/software\/LWPR\/."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"679","DOI":"10.1080\/0264041031000140284","article-title":"Biomechanical aspects of new techniques in alpine skiing and ski-jumping","volume":"21","author":"Schwameder","year":"2003","journal-title":"J. Sports Sci."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1123\/jab.28.1.41","article-title":"Kinetic analysis of ski turns based on measured ground reaction forces","volume":"28","author":"Vaverka","year":"2012","journal-title":"J. Appl. Biomech."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/14\/10\/18898\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:16:48Z","timestamp":1760217408000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/14\/10\/18898"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,10,13]]},"references-count":29,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2014,10]]}},"alternative-id":["s141018898"],"URL":"https:\/\/doi.org\/10.3390\/s141018898","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,10,13]]}}}