title: Social cognitive theory mediators of physical activity in a lifestyle program for cancer survivors and carers: findings from the ENRICH randomized controlled trial.
abstract: BACKGROUND
  Despite increasing numbers of cancer survivors and evidence that diet and physical activity improves the health of cancer survivors, most do not meet guidelines. Some social cognitive theory (SCT)-based interventions have increased physical activity behavior, however few have used objective physical activity measures. The Exercise and Nutrition Routine Improving Cancer Health (ENRICH) randomized controlled trial reported a significant intervention effect for the primary outcome of pedometer-assessed step counts at post-test (8-weeks) and follow-up (20-weeks). The aim of this study was to test whether the SCT constructs operationalized in the ENRICH intervention were mediators of physical activity behavior change.
  
  
  METHODS
  Randomized controlled trial with 174 cancer survivors and carers assessed at baseline, post-test (8-weeks), and follow-up (20-weeks). Participants were randomized to the ENRICH six session face-to-face healthy lifestyle program, or to a wait-list control. Hypothesized SCT mediators of physical activity behavior change (self-efficacy, behavioral goal, outcome expectations, impediments, and social expectations) were assessed using valid and reliable scales. Mediation was assessed using the Preacher and Hayes SPSS INDIRECT macro.
  
  
  RESULTS
  At eight weeks, there was a significant intervention effect on behavioral goal (A = 9.12, p = 0.031) and outcome expectations (A = 0.25, p = 0.042). At 20 weeks, the intervention had a significant effect on self-efficacy (A = 0.31, p = 0.049) and behavioral goal (A = 13.15, p = 0.011). Only changes in social support were significantly associated with changes in step counts at eight weeks (B = 633.81, p = 0.023). Behavioral goal was the only SCT construct that had a significant mediating effect on step counts, and explained 22 % of the intervention effect at 20 weeks (AB = 397.9, 95 % CI 81.5-1025.5).
  
  
  CONCLUSIONS
  SCT constructs had limited impact on objectively-assessed step counts in a multiple health behavior change intervention for cancer survivors and their carers. Behavioral goal measured post-intervention was a significant mediator of pedometer-assessed step counts at 3-months after intervention completion, and explained 22 % of the intervention effect. Future research should examine the separate impact of goals and planning, as well as examining mediators of behavior maintenance in physical activity interventions targeting cancer survivors.
  
  
  BACKGROUND
  Australian and New Zealand Clinical Trials registry ANZCTRN1260901086257 .
authors.affiliation: School of Medicine and Public Health, The University of Newcastle, Hunter Medical Research Institute, Priority Research Centre for Health Behavior, Priority Research Centre in Physical Activity and Nutrition, Level 4 West, HMRI Building, Callaghan, NSW, 2308, Australia. fiona.stacey@uon.edu.au.
authors.forename: F G
authors.initials: FG
authors.lastname: Stacey
authors.affiliation: School of Medicine and Public Health, The University of Newcastle, Hunter Medical Research Institute, Priority Research Centre for Health Behavior, Priority Research Centre in Physical Activity and Nutrition, Level 4 West, HMRI Building, Callaghan, NSW, 2308, Australia.
authors.forename: E L
authors.initials: EL
authors.lastname: James
authors.affiliation: Cancer Council New South Wales, 153 Dowling St, Woolloomooloo, NSW, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Chapman
authors.affiliation: School of Education, and Priority Research Centre in Physical Activity and Nutrition, The University of Newcastle, ATC Building, Callaghan, NSW, 2308, Australia.
authors.forename: D R
authors.initials: DR
authors.lastname: Lubans
mesh_terms: D056044:Actigraphy; D000368:Aged; D001315:Australia; D017028:Caregivers; D003071:Cognition; D004032:Diet; D015444:Exercise; D005260:Female; D006040:Goals; D015438:Health Behavior; D006293:Health Promotion; D006801:Humans; D033182:Intention; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009369:Neoplasms; D009520:New Zealand; D011582:Psychological Theory; D020377:Self Efficacy; D012944:Social Support; D066269:Social Theory; D017741:Survivors / Q000523:psychology*; D016138:Walking
keywords: Cancer; Mediators; Physical activity; Social cognitive theory