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Introduction: Intention to engage in physical activity (PA) is an important concept in behavior change theories. However, age, body mass index (BMI), and sleep may influence one’s intention to engage in PA and intention might not predict actual activity.Purpose: This secondary analysis examined predictors of intention to engage in PA and if the factors associated with intention predicted objectively measured moderate-to-vigorous physical activity (MVPA) in adults who were overweight or obese and enrolled in a weight loss study.Methods: We used 6- and 12-mo data from the EMPOWER Study, an observational study examining triggers of lapse following intentional weight loss. Objective measures included up to 7 days of overlapping accelerometer and actigraphy data to assess daily MVPA and sleep. Self-report data included responses to the question “Do you intend to be physically active today?” hereafter called intention, collected at the beginning of each day via ecological momentary assessment. Analyses were performed examining: 1) the effects of subject-level covariates (e.g., age, sex, race, BMI) on intention, 2) the effects of objectively measured sleep characteristics (e.g., total sleep time [TST], number of awakenings, sleep fragmentation) on intention, and 3) the relationships between sleep, intention, and MVPA. Logistic regression using generalized estimating equations and linear mixed-effect models were used.Results: The analyses included 680 person-days at 6 mo and 678 person-days at 12 mo. Participants (N=136) were mostly female (89.8%) and white (81.8%) with a mean (± SD) age of 51.5 ± 9.9 years and BMI of 33.5 ± 4.6. At 6 mo, participants intended to engage in PA on 81.2% of days, had a mean TST of 408.9 ± 81.8 min/night, and a mean of 32.4 ± 14.7 awakenings/night. At 12 mo, PA intention decreased to 80.6% of days, TST increased to 416.5 ± 82.5 min/night, and awakenings increased to 34.0 ± 14.4 per night (p = .089 for TST; p = .043 for awakenings). Mean daily MVPA decreased from 19.0 ± 23.9 min at 6 mo to 17.3 ± 23.4 min at 12 mo (p = .185). Intention increased with increasing age (odds ratio [OR] = 1.04; 95% confidence interval [95% CI] = 1.02 -1.07). At 6 mo, sleep fragmentation, after adjusting for age, negatively affected intention (OR = 0.96; 95% CI = 0.94 - 0.98); however, it did not significantly affect intention at 12 mo. When comparing days with no PA intention to days in which participants intended to engage in PA, mean MVPA nearly tripled from 7.4 min (95% CI = 3.6 - 11.2) to 21.2 min (95% CI = 18.4 - 24.0). Furthermore, when controlling for age, time of assessment, and intention, participants engaged in an estimated 0.135 (95% CI = 0.241 - 0.029) fewer min of MVPA for each awakening.Conclusions: Based on these findings, future weight loss programs should include interventions that improve sleep quality by reducing fragmentation and strengthen the link between intention and engagement in PA.