• Jacob D Meyer, Laura D Ellingson, Matthew P Buman, Robin P Shook, Gregory A Hand, and Steven N Blair.
• Department of Kinesiology, Iowa State University, Ames, Iowa. Electronic address: jdmeyer3@iastate.edu.
• Am J Prev Med. 2020 Jul 1; 59 (1): 12-20.

IntroductionSedentary time is inversely associated with health. Capturing 24 hours of behavior (i.e., sleep, sedentary, light physical activity, and moderate-to-vigorous physical activity) is necessary to understand behavior-health associations.MethodsHealthy young adults aged 20-35 years (n=423) completed the Profile of Mood States, the Perceived Stress Scale, and dual-energy x-ray absorptiometry and anthropometric measures at baseline and 12 months. Time spent sedentary (total, in prolonged [>30 minutes] and short [≤30 minutes] bouts), in light physical activity (1.5-3.0 METs), moderate-to-vigorous physical activity (>3.0 METs), and asleep, were assessed through SenseWear armband worn 24 hours/day for 10 days at baseline. Isotemporal substitution modeling evaluated cross-sectional and longitudinal psychological and physical health associations of substituting sedentary time with sleep, light physical activity, or moderate-to-vigorous physical activity. Data were collected from 2010 to 2015 and analyzed in 2019.ResultsCross-sectional analyses revealed substituting prolonged sedentary time for sleep was associated with lower stress (standardized β= -0.11), better mood (-0.12), and lower BMI (-0.10). Substituting total or prolonged sedentary for moderate-to-vigorous physical activity was associated with lower body fat percentage (total, -0.22; prolonged, -0.23) and BMI (-0.40; -0.42). Higher BMI was associated with substituting total or prolonged sedentary for light physical activity (0.15; 0.17); lower BMI with substituting prolonged sedentary for short bouts (-0.09). Prospective analyses indicated substituting total or prolonged sedentary with light physical activity was associated with improved mood (-0.16; -0.14) and lower BMI (-0.15; -0.16); substituting with moderate-to-vigorous physical activity was associated with improved mood (-0.15; -0.15).ConclusionsShort- and long-term psychological benefits may result from transitioning sedentary time to light physical activity or sleep, whereas increasing moderate-to-vigorous physical activity may be required to influence physical health.Trial RegistrationThis study is registered at www.clinicaltrials.gov NCT01746186.Copyright © 2020 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.

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