title: Adaptive goal setting and financial incentives: a 2 × 2 factorial randomized controlled trial to increase adults' physical activity.
abstract: Emerging interventions that rely on and harness variability in behavior to adapt to individual performance over time may outperform interventions that prescribe static goals (e.g., 10,000 steps/day). The purpose of this factorial trial was to compare adaptive vs. static goal setting and immediate vs. delayed, non-contingent financial rewards for increasing free-living physical activity (PA).
  
  
  
  A 4-month 2 × 2 factorial randomized controlled trial tested main effects for goal setting (adaptive vs. static goals) and rewards (immediate vs. delayed) and interactions between factors to increase steps/day as measured by a Fitbit Zip. Moderate-to-vigorous PA (MVPA) minutes/day was examined as a secondary outcome.
  
  
  
  Participants (N = 96) were mainly female (77%), aged 41 ± 9.5 years, and all were insufficiently active and overweight/obese (mean BMI = 34.1 ± 6.2). Participants across all groups increased by 2389 steps/day on average from baseline to intervention phase (p < .001). Participants receiving static goals showed a stronger increase in steps per day from baseline phase to intervention phase (2630 steps/day) than those receiving adaptive goals (2149 steps/day; difference = 482 steps/day, p = .095). Participants receiving immediate rewards showed stronger improvement (2762 step/day increase) from baseline to intervention phase than those receiving delayed rewards (2016 steps/day increase; difference = 746 steps/day, p = .009). However, the adaptive goals group showed a slower decrease in steps/day from the beginning of the intervention phase to the end of the intervention phase (i.e. less than half the rate) compared to the static goals group (-7.7 steps vs. -18.3 steps each day; difference = 10.7 steps/day, p < .001) resulting in better improvements for the adaptive goals group by study end. Rate of change over the intervention phase did not differ between reward groups. Significant goal phase x goal setting x reward interactions were observed.
  
  
  
  Adaptive goals outperformed static goals (i.e., 10,000 steps) over a 4-month period. Small immediate rewards outperformed larger, delayed rewards. Adaptive goals with either immediate or delayed rewards should be preferred for promoting PA.
  
  
  
  ClinicalTrials.gov ID: NCT02053259 registered prospectively on January 31, 2014.
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA. marc.adams@asu.edu.|Global Institute of Sustainability (GIOS), Arizona State University, Tempe, AZ, 85287, USA. marc.adams@asu.edu.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Adams
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.
authors.forename: Jane C
authors.initials: JC
authors.lastname: Hurley
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.|College of Nursing and Health Innovation, Arizona State University, 500 N. 3rd Street, Phoenix, AZ, 85004, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Todd
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.
authors.forename: Nishat
authors.initials: N
authors.lastname: Bhuiyan
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Jarrett
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.
authors.forename: Wesley J
authors.initials: WJ
authors.lastname: Tucker
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Hollingshead
authors.affiliation: College of Health Solutions, Arizona State University, 425 North 5th Street (MC9020), Phoenix, AZ, 85004, USA.
authors.forename: Siddhartha S
authors.initials: SS
authors.lastname: Angadi
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D000328:Adult; D015444:Exercise; D005260:Female; D006040:Goals; D006801:Humans; D008297:Male; D008875:Middle Aged; D009042:Motivation; D009765:Obesity / Q000517:prevention & control*; D012201:Reward; D060145:Text Messaging; D016896:Treatment Outcome; D055815:Young Adult
keywords: Adaptive interventions; Fitbit; Goals; Pedometer; Reward; Text messaging; mHealth