{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,11]],"date-time":"2026-10-11T04:46:46Z","timestamp":1791694006829,"version":"4.3.4"},"reference-count":23,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T00:00:00Z","timestamp":1790726400000},"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>Background: Traditional 3D gait analysis constrains natural movement variability due to artificial laboratory settings; thus, this study evaluated the intra- and inter-rater reliability of a low-cost, 2D markerless smartphone video protocol for assessing lower limb sagittal kinematics in an unconstrained environment. Methods: Forty-five healthy young adults walked at a self-selected speed in a non-laboratory corridor, where sagittal hip, knee, and ankle angles were recorded at 60 fps and analyzed using Kinovea\u00ae software by two independent raters, with one rater repeating measurements seven days later. Results: Inter-rater reliability ranged from moderate to good across most joint variables (ICC = 0.628\u20130.789), except for the ankle during loading response, which showed poor consistency (ICC = 0.381). Between-session intra-rater reliability was generally lower, ranging from poor to moderate (ICC = 0.278\u20130.580), with the lowest values observed at the hip (ICC = 0.278) and ankle (ICC = 0.391) during loading response. Minimal Detectable Change (MDC95) values ranged from 7.07\u00b0 to 8.95\u00b0 for inter-rater assessments and from 7.40\u00b0 to 16.55\u00b0 for intra-rater assessments, with Bland\u2013Altman analysis displaying wide limits of agreement longitudinally. Conclusions: In conclusion, while prior observer training standardizes criteria for immediate cross-sectional evaluations, the protocol\u2019s high sensitivity to measurement variability and unconstrained motor execution limits its clinical application for longitudinal tracking across different sessions. Between-session intra-rater variability reflects evaluator subjectivity in manual frame selection and landmark digitization over time when no physical markers are present, rather than biological gait fluctuations.<\/jats:p>","DOI":"10.3390\/s26196229","type":"journal-article","created":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T16:36:31Z","timestamp":1790786191000},"page":"6229","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Reliability of Markerless 2D Video Analysis for Calculating Gait Joint Angles in Uncontrolled Environments"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1684-1416","authenticated-orcid":false,"given":"Sagrario","family":"P\u00e9rez-de la Cruz","sequence":"first","affiliation":[{"name":"Department of Nursery, Physiotherapy and Medicine, University of Almer\u00eda, 04120 Almer\u00eda, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8616-5505","authenticated-orcid":false,"given":"Francisco","family":"Molina-Rueda","sequence":"additional","affiliation":[{"name":"Department of Physical Therapy, Occupational Therapy, Rehabilitation and Physical Medicine, Faculty of Health Sciences, Rey Juan Carlos University, 28922 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0113-9077","authenticated-orcid":false,"given":"Pilar","family":"Fern\u00e1ndez-Gonz\u00e1lez","sequence":"additional","affiliation":[{"name":"Department of Physical Therapy, Occupational Therapy, Rehabilitation and Physical Medicine, Faculty of Health Sciences, Rey Juan Carlos University, 28922 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,30]]},"reference":[{"key":"ref_1","unstructured":"Perry, J., and Burnfield, J.M. 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