Estimating changes in physical behaviour during lockdowns using accelerometry‐based simulations in a large UK cohort

To contain the recent COVID-19 outbreak restrictions have been imposed, which has limited outdoor activity. These physical behaviour changes can have serious health implications, but there is little objective information quantifying these changes. This study aimed to estimate the change in physical behaviour levels during full lockdown conditions using objective data collected from a thigh-worn activity monitor. Data used was from 6,492 individuals in the 1970 British Cohort Study, collected between 2016 and 2018. Using walking bout characteristics, days were classified as either "indoor only" (n=861), "indoor and exercise" (n=167) and "outdoor active" (n=31,934). When compared to "outdoor active" days, “indoor only” days had 6,590 fewer steps per day (2,320 vs 8,876, p < 0.001), a longer sedentary time (1.5 hours, p < 0.001), longer lying time (1.4 hours, p < 0.001) and shorter standing (1.9 hours, p < 0.001) and stepping (1.3 hours, p < 0.001) times. The "indoor and exercise" days had a smaller number of steps compared to "outdoor active" (7,932 vs 8,876, p < 0.05). There is a strong relationship between reduced daily stepping, and increased sedentary time, with a range of poor health outcomes. This has important implications for public health policy and messaging during pandemics