{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T17:57:04Z","timestamp":1790791024887,"version":"4.1.0"},"reference-count":39,"publisher":"JMIR Publications Inc.","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JMIR Cardio"],"abstract":"Abstract<\/jats:title>\n \n Background<\/jats:title>\n Wearable monitoring of sedentary behavior is increasingly used in digital cardiovascular care, but the validity of consumer-grade wrist-worn trackers in older patients with cardiac issues is unclear.<\/jats:p>\n <\/jats:sec>\n \n Objective<\/jats:title>\n This study aimed to evaluate the agreement between sedentary time measured by a consumer-grade wrist-worn tracker (Fitbit Inspire 3; Fitbit LLC) and a research-grade waist-worn accelerometer (ActiveStyle Pro HJA-750C; Omron Healthcare Co, Ltd) used as the comparator, in Japanese outpatients with cardiac issues under free-living conditions.<\/jats:p>\n <\/jats:sec>\n \n Methods<\/jats:title>\n Fifty-one outpatients with heart failure (28\/51, 55%) or ischemic heart disease (23\/51, 45%; mean age 78.4, SD 9.0 years; 25\/51, 49% male) simultaneously wore both devices for 7 consecutive days. Sedentary time was assessed within a standardized 12-hour daytime window (9 AM to 9 PM) at 1-minute epochs. Agreement was examined using Pearson correlation, Bland-Altman analysis (after confirming normality of the paired differences), Lin concordance correlation coefficient (CCC), and Cohen kappa for distribution-based tertile classification. A constant bias correction was applied, with leave-one-out cross-validation (LOOCV) used as an internal-consistency check on the stability of the sample mean bias. Moderators of the bias were explored using multivariable regression.<\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n \n Mean sedentary time within the 12-hour window was 497.9 (SD 86.5) minutes for the comparator and 559.9 (SD 84.3) minutes for the Fitbit. The devices were strongly correlated (\n r<\/jats:italic>\n =0.905, 95% CI 0.838\u20100.945;\n P<\/jats:italic>\n <.001). The Fitbit showed a significant fixed bias of 62.0 minutes (95% CI 51.5\u201072.5;\n P<\/jats:italic>\n <.001) with no proportional bias (slope \u22120.03;\n P<\/jats:italic>\n =.67); the 95% limits of agreement were wide (\u221211.3 to 135.2 minutes). Uncorrected concordance was moderate (CCC=0.71, 95% CI 0.57\u20100.80) and improved to high after subtracting the 62-minute bias (CCC=0.904, 95% CI 0.84\u20100.94); LOOCV indicated that this in-sample improvement was internally stable (out-of-sample CCC=0.90). No candidate factor (sex, age, diagnosis, and musculoskeletal disorder) significantly moderated the bias (model\n P<\/jats:italic>\n =.12). Tertile classification showed moderate agreement (\u03ba=0.588, 95% CI 0.405\u20100.772; 37\/51, 72.5% agreement), with all misclassifications between adjacent categories.\n <\/jats:p>\n <\/jats:sec>\n \n Conclusions<\/jats:title>\n In older Japanese outpatients with cardiac issues, a consumer-grade wrist-worn tracker overestimated sedentary time by approximately 62 minutes within a standardized 12-hour daytime window compared with a waist-worn comparator, with fixed but no proportional bias. A simple constant correction markedly improved group-level concordance (cross-validated CCC\u22480.90), supporting calibrated use of consumer wearables for scalable monitoring in ambulatory cardiac care. However, wide limits of agreement constrain individual-level precision, and the population-specific correction factor requires independent validation before transfer to other settings.<\/jats:p>\n <\/jats:sec>","DOI":"10.2196\/91104","type":"journal-article","created":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T16:45:11Z","timestamp":1787330711000},"page":"e91104-e91104","source":"Crossref","is-referenced-by-count":0,"title":["Assessment of Wrist-Worn Activity Tracker Accuracy for Measuring Sedentary Behavior in Outpatients With Cardiovascular Disease: Validation Study"],"prefix":"10.2196","volume":"10","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5092-686X","authenticated-orcid":false,"given":"Koichi","family":"Naito","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7262-8903","authenticated-orcid":false,"given":"Kazuhiro 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