title: Overestimation of physical activity level is associated with lower BMI: a cross-sectional analysis.
abstract: BACKGROUND
  Poor recognition of physical inactivity may be an important barrier to healthy behaviour change, but little is known about this phenomenon. We aimed to characterize a high-risk population according to the discrepancies between objective and self-rated physical activity (PA), defined as awareness.
  
  
  METHODS
  An exploratory cross-sectional analysis of PA awareness using baseline data collected from 365 ProActive participants between 2001 and 2003 in East Anglia, England. Self-rated PA was defined as 'active' or 'inactive' (assessed via questionnaire). Objective PA was defined according to achievement of guideline activity levels (≥30 minutes or <30 minutes spent at least moderate intensity PA, assessed by heart rate monitoring). Four awareness groups were created: 'Realistic Actives', 'Realistic Inactives', 'Overestimators' and 'Underestimators'. Logistic regression was used to assess associations between awareness group and 17 personal, social and biological correlates.
  
  
  RESULTS
  63.3% of participants (N = 231) were inactive according to objective measurement. Of these, 45.9% rated themselves as active ('Overestimators'). In a multiple logistic regression model adjusted for age and smoking, males (OR = 2.11, 95% CI = 1.12, 3.98), those with lower BMI (OR = 0.89, 95% CI = 0.84, 0.95), younger age at completion of full-time education (OR = 0.83, 95% CI = 0.74, 0.93) and higher general health perception (OR = 1.02 CI = 1.00, 1.04) were more likely to overestimate their PA.
  
  
  CONCLUSIONS
  Overestimation of PA is associated with favourable indicators of relative slimness and general health. Feedback about PA levels could help reverse misperceptions.
authors.affiliation: MRC Epidemiology Unit, Institute of Metabolic Science, Addenbrookes Hospital, Hills Road, Cambridge, UK. simon.griffin@mrc-epid.cam.ac.uk.
authors.forename: Clare
authors.initials: C
authors.lastname: Watkinson
authors.forename: Esther Mf
authors.initials: EM
authors.lastname: van Sluijs
authors.forename: Stephen
authors.initials: S
authors.lastname: Sutton
authors.forename: Wendy
authors.initials: W
authors.lastname: Hardeman
authors.forename: Kirsten
authors.initials: K
authors.lastname: Corder
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Griffin