{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T16:47:01Z","timestamp":1791391621445,"version":"4.3.3"},"reference-count":28,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T00:00:00Z","timestamp":1774396800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000780","name":"European Union","doi-asserted-by":"publisher","award":["101083595"],"award-info":[{"award-number":["101083595"]}],"id":[{"id":"10.13039\/501100000780","id-type":"DOI","asserted-by":"publisher"}]},{"award":["101083595"],"award-info":[{"award-number":["101083595"]}],"id":[{"id":"https:\/\/ror.org\/019w4f821","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Accurately monitoring physical activity, including stationary cycling on an exercise bike, is important in managing chronic diseases and rehabilitation after lower limb surgery. This study aimed to validate a new smartphone-based sensor application (the BeSAFE+) for activity recognition and step counting across five phone placements, using the SENS Motion\u00ae system as a reference standard, and observed activity time as ground truth. In a laboratory-based study, 20 participants performed walking, brisk walking, running, high- and low-intensity cycling, sitting, standing, and lying activities while carrying five smartphones placed in the front and back trouser pockets, a backpack, a running armband, and a fanny pack, and wearing the activity tracker. The front pocket placement had the most accurate classification during cycling activities (89\u201393%) versus SENS Motion\u00ae (96\u201398%). For other activities, the highest overall classification accuracy was achieved with the phone in the back pocket. Overall, the SENS Motion\u00ae activity tracker demonstrated higher classification accuracy than most smartphone placements across all activities, except for running. Nevertheless, several smartphone placements and Application Programming Interface (API) approaches achieved activity recognition and step count estimates that were not significantly different from the SENS Motion\u00ae activity tracker, indicating that smartphone-based activity recognition can be valid under specific conditions.<\/jats:p>","DOI":"10.3390\/s26072033","type":"journal-article","created":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T09:11:14Z","timestamp":1774429874000},"page":"2033","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Placement-Dependent Accuracy of a Smartphone-Based Sensor Application Compared to an Accelerometer-Based System for Measuring Physical Activity in Healthy Adults: A Validation Study"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0684-0997","authenticated-orcid":false,"given":"Mette","family":"Garval","sequence":"first","affiliation":[{"name":"Elective Surgery Center, University Clinic for Interdisciplinary Orthopaedic Pathways, Regional Hospital Central Jutland, Falkevej 1, 8600 Silkeborg, Denmark"},{"name":"Department of Clinical Medicine, Aarhus University, Vennelyst Boulevard 4, 8000 Aarhus, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-0877-7235","authenticated-orcid":false,"given":"Louise","family":"Pedersen","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, Aarhus University, Finlandsgade 22, 8200 Aarhus, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lars M.","family":"Pedersen","sequence":"additional","affiliation":[{"name":"Department of Electrical and Computer Engineering, Aarhus University, Finlandsgade 22, 8200 Aarhus, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ane Kathrine W. d. 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Rev."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2040622319880392","DOI":"10.1177\/2040622319880392","article-title":"Common risk factors for major noncommunicable disease, a systematic overview of reviews and commentary: The implied potential for targeted risk reduction","volume":"10","author":"Peters","year":"2019","journal-title":"Ther. Adv. Chronic Dis."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Shephard, R.J., and Tudor-Locke, C. (2016). Self-Report and Direct Measures of Health: Bias and Implications. The Objective Monitoring of Physical Activity: Contributions of Accelerometry to Epidemiology, Exercise Science and Rehabilitation, Springer International Publishing.","DOI":"10.1007\/978-3-319-29577-0"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"56","DOI":"10.1186\/1479-5868-5-56","article-title":"A comparison of direct versus self-report measures for assessing physical activity in adults: A systematic review","volume":"5","author":"Prince","year":"2008","journal-title":"Int. J. Behav. Nutr. Phys. Act."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1080\/00336297.2001.10491746","article-title":"Measurement of Physical Activity","volume":"53","author":"Dishman","year":"2001","journal-title":"Quest"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1092","DOI":"10.1123\/jpah.2024-0259","article-title":"Assessing the Accuracy of Activity Classification Using Thigh-Worn Accelerometry: A Validation Study of ActiPASS in School-Aged Children","volume":"21","author":"Lendt","year":"2024","journal-title":"J. Phys. Act. Health"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2595","DOI":"10.1249\/MSS.0000000000001717","article-title":"A Dual-Accelerometer System for Classifying Physical Activity in Children and Adults","volume":"50","author":"Stewart","year":"2018","journal-title":"Med. Sci. Sports Exerc."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"224","DOI":"10.1123\/jmpb.2022-0024","article-title":"Integrity and Performance of Four Tape Solutions for Mounting Accelerometry Devices: Lolland-Falster Health Study","volume":"5","author":"Petersen","year":"2022","journal-title":"J. Meas. Phys. Behav."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Sousa Lima, W., Souto, E., El-Khatib, K., Jalali, R., and Gama, J. (2019). Human Activity Recognition Using Inertial Sensors in a Smartphone: An Overview. Sensors, 19.","DOI":"10.3390\/s19143213"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"148","DOI":"10.1038\/s41746-021-00514-4","article-title":"A systematic review of smartphone-based human activity recognition methods for health research","volume":"4","author":"Straczkiewicz","year":"2021","journal-title":"NPJ Digit. Med."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"288","DOI":"10.1108\/SR-11-2017-0245","article-title":"An overview of human activity recognition based on smartphone","volume":"39","author":"Yuan","year":"2018","journal-title":"Sens. Rev."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"3095","DOI":"10.1109\/ACCESS.2017.2676168","article-title":"Performance Analysis of Smartphone-Sensor Behavior for Human Activity Recognition","volume":"5","author":"Chen","year":"2017","journal-title":"IEEE Access"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1186\/s12938-024-01213-3","article-title":"The effectiveness of simple heuristic features in sensor orientation and placement problems in human activity recognition using a single smartphone accelerometer","volume":"23","author":"Barua","year":"2024","journal-title":"Biomed. Eng. Online"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"22","DOI":"10.1016\/j.jneumeth.2013.09.015","article-title":"Hand, belt, pocket or bag: Practical activity tracking with mobile phones","volume":"231","author":"Antos","year":"2014","journal-title":"J. Neurosci. Methods"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"e36","DOI":"10.2196\/mhealth.3505","article-title":"Validation of Physical Activity Tracking via Android Smartphones Compared to ActiGraph Accelerometer: Laboratory-Based and Free-Living Validation Studies","volume":"3","author":"Hekler","year":"2015","journal-title":"JMIR mHealth uHealth"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Minh, N.C., Dao, T.H., Tran, D.N., Huy, N.Q., Thu, N.T., and Tran, D.T. (2021). Evaluation of Smartphone and Smartwatch Accelerometer Data in Activity Classification. 2021 8th NAFOSTED Conference on Information and Computer Science (NICS), IEEE.","DOI":"10.1109\/NICS54270.2021.9701528"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"814","DOI":"10.2106\/JBJS.H.01359","article-title":"Ergometer cycling after hip or knee replacement surgery: A randomized controlled trial","volume":"92","author":"Liebs","year":"2010","journal-title":"J. Bone Jt. Surg. Am."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1186\/s11556-015-0152-9","article-title":"Health benefits of cycle ergometer training for older adults over 70: A review","volume":"12","author":"Bouaziz","year":"2015","journal-title":"Eur. Rev. Aging Phys. Act."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"522","DOI":"10.1177\/0269215520971795","article-title":"Stationary cycling exercise for knee osteoarthritis: A systematic review and meta-analysis","volume":"35","author":"Luan","year":"2021","journal-title":"Clin. Rehabil."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"496","DOI":"10.1111\/j.1600-0838.2011.01299.x","article-title":"Health benefits of cycling: A systematic review","volume":"21","author":"Oja","year":"2011","journal-title":"Scand. J. Med. Sci. Sports"},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Wagner, S.R., Gregersen, R.R., Henriksen, L., Hauge, E.M., and Keller, K.K. (2022). Smartphone Pedometer Sensor Application for Evaluating Disease Activity and Predicting Comorbidities in Patients with Rheumatoid Arthritis: A Validation Study. Sensors, 22.","DOI":"10.3390\/s22239396"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"377","DOI":"10.1016\/j.jbi.2008.08.010","article-title":"Research electronic data capture (REDCap)\u2014A metadata-driven methodology and workflow process for providing translational research informatics support","volume":"42","author":"Harris","year":"2009","journal-title":"J. Biomed. Inform."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"76","DOI":"10.1123\/jpah.2011-0347","article-title":"Detection of physical activity types using triaxial accelerometers","volume":"11","author":"Skotte","year":"2014","journal-title":"J. Phys. Act. Health"},{"key":"ref_25","first-page":"9230081","article-title":"Validation of Two Activity Monitors in Slow and Fast Walking Hospitalized Patients","volume":"2022","author":"Pedersen","year":"2022","journal-title":"Rehabil. Res. Pract."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"6596278","DOI":"10.1155\/2018\/6596278","article-title":"Reliability and Construct Validity of the SENS Motion\u00ae Activity Measurement System as a Tool to Detect Sedentary Behaviour in Patients with Knee Osteoarthritis","volume":"2018","author":"Bartholdy","year":"2018","journal-title":"Arthritis"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"3639","DOI":"10.1007\/s00431-023-05014-z","article-title":"Validation of an accelerometer system for measuring physical activity and sedentary behavior in healthy children and adolescents","volume":"182","author":"Milther","year":"2023","journal-title":"Eur. J. Pediatr."},{"key":"ref_28","unstructured":"Greenwood MC (2025, October 03). One-WayANOVA. 2022. In Intermediate Statistics with R [Internet]. Available online: https:\/\/greenwood-stat.github.io\/GreenwoodBookHTML\/chapter3.html#section3-6."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/7\/2033\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T15:50:27Z","timestamp":1775058627000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/7\/2033"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,25]]},"references-count":28,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2026,4]]}},"alternative-id":["s26072033"],"URL":"https:\/\/doi.org\/10.3390\/s26072033","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,25]]}}}