title: An adaptive physical activity intervention for overweight adults: a randomized controlled trial.
abstract: BACKGROUND
  Physical activity (PA) interventions typically include components or doses that are static across participants. Adaptive interventions are dynamic; components or doses change in response to short-term variations in participant's performance. Emerging theory and technologies make adaptive goal setting and feedback interventions feasible.
  
  
  OBJECTIVE
  To test an adaptive intervention for PA based on Operant and Behavior Economic principles and a percentile-based algorithm. The adaptive intervention was hypothesized to result in greater increases in steps per day than the static intervention.
  
  
  METHODS
  Participants (N = 20) were randomized to one of two 6-month treatments: 1) static intervention (SI) or 2) adaptive intervention (AI). Inactive overweight adults (85% women, M = 36.9 ± 9.2 years, 35% non-white) in both groups received a pedometer, email and text message communication, brief health information, and biweekly motivational prompts. The AI group received daily step goals that adjusted up and down based on the percentile-rank algorithm and micro-incentives for goal attainment. This algorithm adjusted goals based on a moving window; an approach that responded to each individual's performance and ensured goals were always challenging but within participants' abilities. The SI group received a static 10,000 steps/day goal with incentives linked to uploading the pedometer's data.
  
  
  RESULTS
  A random-effects repeated-measures model accounted for 180 repeated measures and autocorrelation. After adjusting for covariates, the treatment phase showed greater steps/day relative to the baseline phase (p<.001) and a group by study phase interaction was observed (p  .017). The SI group increased by 1,598 steps/day on average between baseline and treatment while the AI group increased by 2,728 steps/day on average between baseline and treatment; a significant between-group difference of 1,130 steps/day (Cohen's d = .74).
  
  
  CONCLUSIONS
  The adaptive intervention outperformed the static intervention for increasing PA. The adaptive goal and feedback algorithm is a "behavior change technology" that could be incorporated into mHealth technologies and scaled to reach large populations.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT01793064.
authors.affiliation: School of Nutrition and Health Promotion, Arizona State University, Phoenix, Arizona, United States of America ; Graduate School of Public Health, San Diego State University, San Diego, California, United States of America.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Adams
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, San Diego, California, United States of America ; Department of Psychology, San Diego State University, San Diego, California, United States of America.
authors.forename: James F
authors.initials: JF
authors.lastname: Sallis
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, San Diego, California, United States of America.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Norman
authors.affiliation: Graduate School of Public Health, San Diego State University, San Diego, California, United States of America.
authors.forename: Melbourne F
authors.initials: MF
authors.lastname: Hovell
authors.affiliation: School of Nutrition and Health Promotion, Arizona State University, Phoenix, Arizona, United States of America.
authors.forename: Eric B
authors.initials: EB
authors.lastname: Hekler
authors.affiliation: College of Education and Allied Studies, California State University East Bay, Hayward, California, United States of America.
authors.forename: Elyse
authors.initials: E
authors.lastname: Perata
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D005081:Exercise Therapy / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009043:Motor Activity; D050177:Overweight / Q000503:physiopathology / Q000628:therapy; D013997:Time Factors