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ACT24: Activities Completed over Time in 24 Hours

Activities Completed over Time in 24-hours (ACT24) is a web-based previous-day recall instrument that was designed to estimate daily summary values for physical activity and sedentary behavior, including energy expenditure, time spent sitting and in different types and intensities of physical activity. ACT24 has been examined for validity in middle-aged and older adults and has been used to provide detailed portraits of human time-use and energy expenditure at the population level.  

ACT24 is freely available for use by researcher, teachers, clinicians and others interested in assessing daily physical activity levels. The system is composed of two distinct sites, one for researchers and another for participants.

The Researcher Site is used to register projects and generate log-in keys for participants. Participants use researcher-provided login information to access the Participant Site and enter their recall data. Once the recall data is entered it is processed in real-time and made available for download on the Researcher Site. An Application Programming Interface (API) is available to link ACT24 to researchers' study management systems to facilitate automated data collection.  

Details regarding the ACT24 system (e.g., access, FAQs, scoring methods) can be found on the Researcher Site.  

ACT24 was developed by National Cancer Institute (NCI) investigators in the Division of Cancer Epidemiology and Genetics and the Division of Cancer Control and Population Sciences.

For more information, contact Charles E. Matthews.


Matthews CE Measurement of active and sedentary behavior in context of large epidemiologic studiesMed Sci Sports Exerc, 2018.

Keadle, et al. Validation of ACT24 version 2.0 for estimating behavioral domains, active and sedentary timeMed Sci Sports Exerc, 2023.

Matthews et al. Physical activity levels (PAL) in U.S. Adults–2019. Med Sci Sports Exerc, 2023