title: Who will increase their physical activity? Predictors of change in objectively measured physical activity over 12 months in the ProActive cohort.
abstract: BACKGROUND
  The aim was to identify predictors of change in objectively measured physical activity over 12 months in the ProActive cohort to improve understanding of factors influencing change in physical activity.
  
  
  METHODS
  ProActive is a physical activity promotion trial that took place in Eastern England (1999-2004). 365 offspring of people with type 2 diabetes underwent measurement of physical activity energy expenditure (PAEE) using heart rate monitoring, fitness, and anthropometric and biochemical status at baseline and 1 year (n = 321). Linear regression was used to quantify the associations between baseline demographic, clinical, psychosocial and behavioural variables and change in PAEE over 12 months. This study is registered as ISRCTN61323766.
  
  
  RESULTS
  ProActive participants significantly increased their PAEE by 0.6 kj/min (SD 4.2, p = 0.006) over one year, the equivalent of around 20 minutes brisk walking/day. Male sex and higher fitness at baseline predicted increase in PAEE. No significant associations were found for any other variables. Very few baseline demographic, clinical, psychosocial and behavioural predictors were associated with change in objectively measured physical activity.
  
  
  CONCLUSIONS
  Traditional baseline determinants of self-reported physical activity targeted by behavioural interventions may be relatively weak predictors of change in objectively measured physical activity. Further research is needed to improve our understanding of factors influencing change in physical activity to inform the development and targeting of interventions.
authors.affiliation: MRC Epidemiology Unit, Institute of Metabolic Science, Box 285, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0QQ, UK. simon.griffin@mrc-epid.cam.ac.uk
authors.forename: Rebecca K
authors.initials: RK
authors.lastname: Simmons
authors.forename: Esther Mf
authors.initials: EM
authors.lastname: van Sluijs
authors.forename: Wendy
authors.initials: W
authors.lastname: Hardeman
authors.forename: Stephen
authors.initials: S
authors.lastname: Sutton
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Griffin
mesh_terms: D000328:Adult; D000886:Anthropometry; D001294:Attitude to Health; D018660:Blood Pressure Monitoring, Ambulatory; D003924:Diabetes Mellitus, Type 2 / Q000517:prevention & control; D004739:England; D015444:Exercise / Q000502:physiology* / Q000523:psychology; D005260:Female; D005500:Follow-Up Studies; D006293:Health Promotion / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010809:Physical Fitness; D012307:Risk Factors; D057185:Sedentary Behavior