{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,14]],"date-time":"2026-10-14T20:06:17Z","timestamp":1792008377815,"version":"4.4.0"},"reference-count":26,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2022,9,13]],"date-time":"2022-09-13T00:00:00Z","timestamp":1663027200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Korea Institute of Industrial Technology (KITECH)","award":["2021R1A6A1A03043144"],"award-info":[{"award-number":["2021R1A6A1A03043144"]}]},{"name":"Korea Medical Development Fund (KMDF)","award":["2021R1A6A1A03043144"],"award-info":[{"award-number":["2021R1A6A1A03043144"]}]},{"name":"Basic Science Research Program through the National Research Foundation of Korea (NRF)","award":["2021R1A6A1A03043144"],"award-info":[{"award-number":["2021R1A6A1A03043144"]}]},{"DOI":"10.13039\/501100003725","name":"Ministry of Education","doi-asserted-by":"publisher","award":["2021R1A6A1A03043144"],"award-info":[{"award-number":["2021R1A6A1A03043144"]}],"id":[{"id":"10.13039\/501100003725","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>In the wake of COVID-19, the digital fitness market combining health equipment and ICT technologies is experiencing unexpected high growth. A smart trampoline fitness system is a new representative home exercise equipment for muscle strengthening and rehabilitation exercises. Recognizing the motions of the user and evaluating user activity is critical for implementing its self-guided exercising system. This study aimed to estimate the three-dimensional positions of the user\u2019s foot using deep learning-based image processing algorithms for footprint shadow images acquired from the system. The proposed system comprises a jumping fitness trampoline; an upward-looking camera with a wide-angle and fish-eye lens; and an embedded board to process deep learning algorithms. Compared with our previous approach, which suffered from a geometric calibration process, a camera calibration method for highly distorted images, and algorithmic sensitivity to environmental changes such as illumination conditions, the proposed deep learning algorithm utilizes end-to-end learning without calibration. The network is configured with a modified Fast-RCNN based on ResNet-50, where the region proposal network is modified to process location regression different from box regression. To verify the effectiveness and accuracy of the proposed algorithm, a series of experiments are performed using a prototype system with a robotic manipulator to handle a foot mockup. The three root mean square errors corresponding to X, Y, and Z directions were revealed to be 8.32, 15.14, and 4.05 mm, respectively. Thus, the system can be utilized for motion recognition and performance evaluation of jumping exercises.<\/jats:p>","DOI":"10.3390\/s22186922","type":"journal-article","created":{"date-parts":[[2022,9,13]],"date-time":"2022-09-13T22:37:28Z","timestamp":1663108648000},"page":"6922","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Three-Dimensional Foot Position Estimation Based on Footprint Shadow Image Processing and Deep Learning for Smart Trampoline Fitness System"],"prefix":"10.3390","volume":"22","author":[{"given":"Se-Kyung","family":"Park","sequence":"first","affiliation":[{"name":"Ansan R&D Campus, LG Innotek, Ansan 15588, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jun-Kyu","family":"Park","sequence":"additional","affiliation":[{"name":"Renewable Energy Solution Group, Korea Electric Power Research Institute (KEPRI), Naju 58277, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1609-8447","authenticated-orcid":false,"given":"Hong-In","family":"Won","sequence":"additional","affiliation":[{"name":"Advanced Mechatronics Research Group, Daegyeong Division, Korea Institute of Industrial Technology, Daegu 42994, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Seung-Hwan","family":"Choi","sequence":"additional","affiliation":[{"name":"Advanced Mechatronics Research Group, Daegyeong Division, Korea Institute of Industrial Technology, Daegu 42994, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chang-Hyun","family":"Kim","sequence":"additional","affiliation":[{"name":"Advanced Mechatronics Research Group, Daegyeong Division, Korea Institute of Industrial Technology, Daegu 42994, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Suwoong","family":"Lee","sequence":"additional","affiliation":[{"name":"Advanced Mechatronics Research Group, Daegyeong Division, Korea Institute of Industrial Technology, Daegu 42994, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7263-3403","authenticated-orcid":false,"given":"Min Young","family":"Kim","sequence":"additional","affiliation":[{"name":"School of Electronics Engineering, Kyungpook National University, Daegu 41566, Korea"},{"name":"Research Center for Neurosurgical Robotic System, Kyungpook National University, Daegu 41566, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,9,13]]},"reference":[{"key":"ref_1","unstructured":"(2022, August 25). World Health Organization. Available online: https:\/\/www.who.int\/campaigns\/connecting-the-world-to-combat-coronavirus\/healthyathome."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"S236","DOI":"10.1037\/tra0000840","article-title":"The psychological impact of preexisting mental and physical health conditions during the COVID-19 pandemic","volume":"12","author":"Alonzi","year":"2020","journal-title":"Psychol. Trauma Theory Res. Pract. Policy"},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Rodr\u00edguez-Nogueira, \u00d3., Leir\u00f3s-Rodr\u00edguez, R., Ben\u00edtez-Andrades, J.A., \u00c1lvarez-\u00c1lvarez, M.J., Marqu\u00e9s-S\u00e1nchez, P., and Pinto-Carral, A. (2020). Musculoskeletal Pain and Teleworking in Times of the COVID-19: Analysis of the Impact on the Workers at Two Spanish Universities. Int. J. Environ. Res. Public Health, 18.","DOI":"10.3390\/ijerph18010031"},{"key":"ref_4","unstructured":"(2022, August 08). Peloton. Available online: https:\/\/www.onepeloton.com\/bike."},{"key":"ref_5","unstructured":"(2022, August 08). Tonal. Available online: https:\/\/www.tonal.com\/intelligence."},{"key":"ref_6","unstructured":"Allied Market Research USA (2019). Fitness Equipment Market by Type, End User: Opportunity Analysis and Industry Forecast, Allied Market Research U.S."},{"key":"ref_7","first-page":"1","article-title":"Jumping into a Healthier Future: Trampolining for Increasing Physical Activity in Children","volume":"7","author":"Ehrlich","year":"2021","journal-title":"Sports Med. Open"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"91","DOI":"10.4103\/2008-7802.186225","article-title":"Effect of a trampoline exercise on the anthropometric measures and motor performance of adolescent students","volume":"7","author":"Aalizadeh","year":"2016","journal-title":"Int. J. Prev. Med."},{"key":"ref_9","first-page":"1","article-title":"Does mini-trampoline training more effective than running on body weight, body fat, VO2 max and Vertical Jump in Young Men","volume":"6","author":"Demir","year":"2016","journal-title":"Int. J. Sports Sci."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"512","DOI":"10.1016\/j.jelekin.2011.01.003","article-title":"Mini-trampoline exercise related to mechanisms of dynamic stability improves the ability to regain balance in elderly","volume":"21","author":"Karamanidis","year":"2011","journal-title":"J. Electromyogr. Kinesiol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"131","DOI":"10.4103\/ijpvm.IJPVM_527_18","article-title":"Comparison of the effect of 8-week rebound therapy-based exercise program and weight-supported exercises on the range of motion, proprioception, and the quality of life in patients with Parkinson\u2019s disease","volume":"10","author":"Daneshvar","year":"2019","journal-title":"Int. J. Prev. Med."},{"key":"ref_12","unstructured":"(2021, September 06). Jumping Fitness. Available online: https:\/\/www.jumping-fitness.com."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1007\/s12283-011-0081-4","article-title":"Classification of trampoline jumps using inertial sensors","volume":"14","author":"Helten","year":"2011","journal-title":"Sports Eng."},{"key":"ref_14","unstructured":"David, E., Chapman, C., and Bondoc, K. (2012, January 9\u201312). Characterisation of trampoline bounce using acceleration. Proceedings of the 7th Australasian Congress on Applied Mechanics (ACAM 7), Adelaide, Australia."},{"key":"ref_15","unstructured":"Connolly, P.W., Silvestre, G.C., and Bleakley, C.J. (September, January 30). Automated Identification of Trampoline Skills Using Computer Vision Extracted Pose Estimation. Proceedings of the 2017 Irish Machine Vision and Image Processing Conference (IMVIP), Maynooth, Ireland."},{"key":"ref_16","unstructured":"Kazuhito, S., Mori, H., and Hoshino, J. (2009, January 14). The trampoline entertainment system for aiding exercise. Proceedings of the 8th International Conference on Virtual Reality Continuum and Its Applications in Industry, Online."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Mori, H., Shiratori, K., Fujieda, T., and Hoshino, J.I. (2009, January 3). Versatile training field: The wellness entertainment system using trampoline interface. Proceedings of the ACM SIGGRAPH 2009 Emerging Technologies, Online.","DOI":"10.1145\/1597956.1597981"},{"key":"ref_18","first-page":"6","article-title":"Empowering the exercise: A body-controlled trampoline training game","volume":"13","author":"Raine","year":"2014","journal-title":"Int. J. Comput. Sci. Sport"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Tiator, M., K\u00f6se, O., Wiche, R., Geiger, C., and Dorn, F. (2017, January 20\u201322). Trampoline jumping with a head-mounted display in virtual reality entertainment. Proceedings of the International Conference on Intelligent Technologies for Interactive Entertainment, Funchal, Portugal.","DOI":"10.1007\/978-3-319-73062-2_8"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Park, S., Park, J., Ahn, J., Cho, B., Lee, S., and Kim, M. (2021, January 17\u201320). Three-dimensional Foot Contact Position on a Smart Fitness Trampoline with a Upward Looking Wide View Imaging System. Proceedings of the 2021 International Conference on Ubiquitous and Future Networks (ICUFN2021), Jeju Island, Korea.","DOI":"10.1109\/ICUFN49451.2021.9528679"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1137","DOI":"10.1109\/TPAMI.2016.2577031","article-title":"Faster R-CNN: Towards real-time object detection with region proposal networks","volume":"39","author":"Ren","year":"2016","journal-title":"IEEE Trans. Pattern Anal. Mach. Intell."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"He, K., Zhang, X., Ren, S., and Sun, J. (2016, January 27\u201330). Deep residual learning for image recognition. Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, Las Vegas, Nevada, USA.","DOI":"10.1109\/CVPR.2016.90"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"102589","DOI":"10.1016\/j.humov.2020.102589","article-title":"Gaze behavior of trampoline gymnasts during a back tuck somersault","volume":"70","author":"Natrup","year":"2020","journal-title":"Hum. Mov. Sci."},{"key":"ref_24","unstructured":"AAU Trampoline and Tumbling (2021). Trampoline & Tumbling Code of Points, AAU Trampoline and Tumbling."},{"key":"ref_25","unstructured":"(2022, August 25). BBC. Available online: https:\/\/www.bbc.co.uk\/bitesize\/guides\/zp99j6f\/revision\/3."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"141","DOI":"10.1080\/17461391.2020.1728390","article-title":"Developing a mathematical model to predict energy expenditure while bouncing on a trampoline","volume":"21","author":"Keith","year":"2021","journal-title":"Eur. J. 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