{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,10]],"date-time":"2025-12-10T08:22:24Z","timestamp":1765354944089,"version":"build-2065373602"},"reference-count":87,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2023,5,27]],"date-time":"2023-05-27T00:00:00Z","timestamp":1685145600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"The Alan Turing Institute"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Measures of stepping volume and rate are common outputs from wearable devices, such as accelerometers. It has been proposed that biomedical technologies, including accelerometers and their algorithms, should undergo rigorous verification as well as analytical and clinical validation to demonstrate that they are fit for purpose. The aim of this study was to use the V3 framework to assess the analytical and clinical validity of a wrist-worn measurement system of stepping volume and rate, formed by the GENEActiv accelerometer and GENEAcount step counting algorithm. The analytical validity was assessed by measuring the level of agreement between the wrist-worn system and a thigh-worn system (activPAL), the reference measure. The clinical validity was assessed by establishing the prospective association between the changes in stepping volume and rate with changes in physical function (SPPB score). The agreement of the thigh-worn reference system and the wrist-worn system was excellent for total daily steps (CCC = 0.88, 95% CI 0.83\u20130.91) and moderate for walking steps and faster-paced walking steps (CCC = 0.61, 95% CI 0.53\u20130.68 and 0.55, 95% CI 0.46\u20130.64, respectively). A higher number of total steps and faster paced-walking steps was consistently associated with better physical function. After 24 months, an increase of 1000 daily faster-paced walking steps was associated with a clinically meaningful increase in physical function (0.53 SPPB score, 95% CI 0.32\u20130.74). We have validated a digital susceptibility\/risk biomarker\u2014pfSTEP\u2014that identifies an associated risk of low physical function in community-dwelling older adults using a wrist-worn accelerometer and its accompanying open-source step counting algorithm.<\/jats:p>","DOI":"10.3390\/s23115122","type":"journal-article","created":{"date-parts":[[2023,5,27]],"date-time":"2023-05-27T16:18:43Z","timestamp":1685204323000},"page":"5122","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["The Analytical and Clinical Validity of the pfSTEP Digital Biomarker of the Susceptibility\/Risk of Declining Physical Function in Community-Dwelling Older Adults"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0009-0009-1647-5311","authenticated-orcid":false,"given":"Alexander","family":"Schoenfelder","sequence":"first","affiliation":[{"name":"Institute for Data Science and AI, University of Exeter, Exeter EX4 4QJ, UK"}]},{"given":"Brad","family":"Metcalf","sequence":"additional","affiliation":[{"name":"Sports and Health Sciences, University of Exeter, Exeter EX1 2LU, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3204-5866","authenticated-orcid":false,"given":"Joss","family":"Langford","sequence":"additional","affiliation":[{"name":"Sports and Health Sciences, University of Exeter, Exeter EX1 2LU, UK"},{"name":"Activinsights Ltd., Huntingdon PE28 0NJ, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2162-777X","authenticated-orcid":false,"given":"Afroditi","family":"Stathi","sequence":"additional","affiliation":[{"name":"School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham B15 2TT, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1107-8498","authenticated-orcid":false,"given":"Max J.","family":"Western","sequence":"additional","affiliation":[{"name":"Department of Health, University of Bath, Bath BA2 7AY, UK"}]},{"given":"Melvyn","family":"Hillsdon","sequence":"additional","affiliation":[{"name":"Sports and Health Sciences, University of Exeter, Exeter EX1 2LU, UK"}]}],"member":"1968","published-online":{"date-parts":[[2023,5,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"78","DOI":"10.1186\/s12966-020-00978-9","article-title":"Systematic Review of the Prospective Association of Daily Step Counts with Risk of Mortality, Cardiovascular Disease, and Dysglycemia","volume":"17","author":"Hall","year":"2020","journal-title":"Int. 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