title: Physical activity and fatigue in breast cancer survivors: a panel model examining the role of self-efficacy and depression.
abstract: BACKGROUND
  Physical activity is associated with reductions in fatigue in breast cancer survivors. However, mechanisms underlying this relationship are not well-understood. The purpose of this study was to longitudinally test a model examining the role of self-efficacy and depression as potential mediators of the relationship between physical activity and fatigue in a sample of breast cancer survivors using both self-report and objective measures of physical activity.
  
  
  METHODS
  All participants (N = 1,527) completed self-report measures of physical activity, self-efficacy, depression, and fatigue at baseline and 6 months. A subsample was randomly selected to wear an accelerometer at both time points. It was hypothesized that physical activity indirectly influences fatigue via self-efficacy and depression. Relationships among model constructs were examined over the 6-month period using panel analysis within a covariance modeling framework.
  
  
  RESULTS
  The hypothesized model provided a good model-data fit (χ(2) = 599.66, df = 105, P ≤ 0.001; CFI = 0.96; SRMR = 0.02) in the full sample when controlling for covariates. At baseline, physical activity indirectly influenced fatigue via self-efficacy and depression. These relationships were also supported across time. In addition, the majority of the hypothesized relationships were supported in the subsample with accelerometer data (χ(2) = 387.48, df = 147, P ≤ 0.001, CFI = 0.94, SRMR = 0.04).
  
  
  CONCLUSIONS
  This study provides evidence to suggest the relationship between physical activity and fatigue in breast cancer survivors may be mediated by more proximal, modifiable outcomes of physical activity participation.
  
  
  CONCLUSIONS
  Recommendations are made relative to future applications and research concerning these relationships.
authors: Office of Cancer Survivorship, Division of Cancer Control and Population Sciences, National Cancer Institute, 6116 Executive Blvd., Suite 404, Bethesda, MD 20892, USA. siobhan.phillips@nih.gov
authors: Siobhan M
authors: SM
authors: Phillips
authors: Edward
authors: E
authors: McAuley
mesh_terms: D061725:Accelerometry / Q000295:instrumentation; D001943:Breast Neoplasms / Q000503:physiopathology* / Q000523:psychology*; D003625:Data Collection; D003866:Depressive Disorder / Q000209:etiology* / Q000503:physiopathology; D005221:Fatigue / Q000209:etiology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D011788:Quality of Life; D020377:Self Efficacy; D057566:Self Report; D011795:Surveys and Questionnaires; D017741:Survivors