RT Journal Article SR Electronic T1 Nation-wide cohort of device-measured sedentary time and physical activity in the USA—the Cancer Prevention Study-3 (CPS-3) Accelerometry Substudy: cohort profile JF BMJ Open JO BMJ Open FD British Medical Journal Publishing Group SP e085896 DO 10.1136/bmjopen-2024-085896 VO 15 IS 1 A1 Rees-Punia, Erika A1 Nelson, Jillian A1 Briggs, Peter J A1 Joiner, Nance A1 Hodge, James M A1 Bontemps-Jones, Jeuneviette E A1 Bloodworth, Den E A1 Yeager, Ashley A1 McCrary, Jeshondria A1 Patel, Alpa YR 2025 UL http://bmjopen.bmj.com/content/15/1/e085896.abstract AB Purpose This paper describes the data collection and management methods for the Cancer Prevention Study-3 (CPS-3) Accelerometry Substudy, a nested cohort of device-based physical activity and sedentary time data.Participants US-based CPS-3 participants (initially enrolled 2006–2013) who completed the 2018 follow-up survey and had a valid email address were invited to the Accelerometry Substudy (n=109 780). Among the 23 111 participants who registered and were shipped an ActiGraph GT3X+ accelerometer, 21 219 participants returned the device with a complete wear log (91.8%) and 20 950 (90.6%) provided at least three adherent days of data (eg, days with at least 10 hours of wear).Findings to date Participants with ≥3 adherent days were predominantly female (n=16 187, 77.3%), non-Latino white (n=17 977, 85.8%) and had an average age of 58 years (SD=9.8). The median daily wear time was 15.3 hours, which did not vary considerably by wear day. The median time spent in moderate-intensity aerobic physical activity was 29 min/day (IQR=36), and the median time in vigorous physical activity was 3 min/day (IQR=13). Participants were sedentary for 9.4 hours (564 min, IQR=171 min) and accumulated a median of 6474 steps per day (IQR=5348).Future plans The full CPS-3 cohort will be linked with the National Death Index and state cancer registries biennially. Participants will be sent triennial surveys for the next two decades. Future analyses within the CPS-3 Accelerometry Substudy more specifically aim to identify relationships between physical activity, sedentary time and health outcomes, primarily cancer incidence, survival and survivorship.Data are available upon reasonable request. Data are available from the American Cancer Society by following the ACS Data Access Procedures (https://www.cancer.org/research/population-science/research-collaboration.html) for researchers who meet the criteria for access to confidential data. Please email cohort.data@cancer.org to inquire about access.