title: Affective mediators of a physical activity intervention for depression in multiple sclerosis.
abstract: OBJECTIVE
  Previous analyses showed that a telephone-based intervention to increase physical activity in individuals with multiple sclerosis (MS) and depression resulted in significantly improved depressive symptoms compared to a wait-list control group. The aim of this study was to test positive affect and negative affect as mediators of the effect of the physical activity counseling on depressive symptoms.
  
  
  METHODS
  Ninety-two adults with MS, who met diagnostic criteria for either major depression or dysthymia and who reported low levels of physical activity, were randomized 1:1 to a 12-week telephone-based motivational interviewing (MI) intervention to improve physical activity (n = 44) or to a 12-week wait-list control group (n = 48). Self-reported positive and negative affect, physical activity, and depressive symptoms were gathered at baseline and postintervention. Path-analysis was used to test whether positive affect and negative affect mediated the positive effects of the intervention on depressive symptoms.
  
  
  RESULTS
  Both positive and negative affect were significant mediators of the effects of the intervention on depressive symptoms; however, only positive affect mediated the association between changes in physical activity and improved depressive symptoms.
  
  
  CONCLUSIONS
  Findings support physical activity and positive affect as key mediators of the MI treatment effect on improved mood. Decreases in negative affect were also evident in the treatment group, but were not related to improved physical activity. Findings may suggest the use of exercise-based interventions in conjunction with treatments that specifically target negative affective mechanisms for depression.
authors.affiliation: Department of Physical Medicine & Rehabilitation, University of Michigan.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Kratz
authors.affiliation: Department of Rehabilitation Medicine, University of Washington School of Medicine.
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Ehde
authors.affiliation: Department of Rehabilitation Medicine, University of Washington School of Medicine.
authors.forename: Charles H
authors.initials: CH
authors.lastname: Bombardier
mesh_terms: D000293:Adolescent; D000328:Adult; D000339:Affect / Q000502:physiology*; D000368:Aged; D003866:Depressive Disorder / Q000150:complications / Q000523:psychology* / Q000534:rehabilitation*; D005081:Exercise Therapy / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D062405:Motivational Interviewing / Q000379:methods; D009043:Motor Activity / Q000502:physiology; D009103:Multiple Sclerosis / Q000150:complications / Q000523:psychology* / Q000534:rehabilitation*; D016896:Treatment Outcome; D055815:Young Adult