Abstract BackgroundIndividuals’ physical activity (PA) has been shown to be related to self-efficacy. However, few studies have assessed change in PA related to change in self-efficacy. We examined this in the ENABLE London study, a natural experiment which recruited adults seeking to move to social, intermediate and market-rent accommodation in East Village, a neighbourhood designed for healthy active living.Methods1278 participants were recruited. Self-report exercise self-efficacy (mean score over nine questions) and objective measures of PA from 7-day accelerometry (average daily step count and daily minutes of moderate-to-vigorous PA in ≥10 minute bouts (MVPA bouts)) were obtained at baseline and 2-year follow-up. Associations between change in PA and change in self-efficacy were assessed by regressing 2-year PA outcome on baseline value, change in self-efficacy and adjusted for age, sex, ethnicity, housing sector and whether the participant had moved to East Village.Results877 (69%) participants provided data at 2-year follow-up. Change in each PA outcome was positively associated with change in self-efficacy: a SD increase in self-efficacy (SD=0.8) was associated with an extra 253 steps per day (95% CI 74,431 p=0.006) and an extra 11 minutes per week of MVPA bouts (95% CI 3,18 p=0.005).ConclusionAn increase in an individual’s exercise self-efficacy was related to an increase in PA. Whilst the increases in PA were modest, interventions designed to increase self-efficacy could be effective in increasing PA levels. External funding details MRC National Prevention Research Initiative (MR/J000345/1) and National Institute for Health Research (12/211/69).