In large scale cohort studies sedentary behaviour has been routinely measured using self-report or devices that apply count-based threshold. We employed a gold standard postural allocation technique using thigh inclination and acceleration to capture free-living sedentary behaviour . Participants (n=5,346, aged 46.8 ± 0.7 yrs) from the 1970 British Cohort study (U.K.) were fitted with a water-proofed thigh mounted accelerometer device (activPAL3 micro) worn continuously over 7 days, collected 2016 – 2018. Useable data were retrieved in 83.0% of the devices fitted, with 79.6% of the sample recording at least 6 full days of wear (at least 10 waking hours). Total daily sitting time (average 9.5±2.0 hr/d men and 9.0±2.0 hr/d women) accounted for 59.4% and 57.3% of waking hours in men and women respectively; 73.8% of the sample recorded ≥8hr/d of sitting. Sitting in prolonged bouts of more than 60 continuous minutes accounted for 25.3 % and 24.4% of total daily sitting in men and women respectively. In mutually adjusted models, male sex, underweight and obesity, education, poor self-rated health, TV-viewing time and a sitting occupation were associated with higher device measured sitting times. Thigh worn accelerometry was feasibly deployed and should be considered for larger scale national surveys
