title: The Walking Interventions Through Texting (WalkIT) Trial: Rationale, Design, and Protocol for a Factorial Randomized Controlled Trial of Adaptive Interventions for Overweight and Obese, Inactive Adults.
abstract: BACKGROUND
  Walking is a widely accepted and frequently targeted health promotion approach to increase physical activity (PA). Interventions to increase PA have produced only small improvements. Stronger and more potent behavioral intervention components are needed to increase time spent in PA, improve cardiometabolic risk markers, and optimize health.
  
  
  OBJECTIVE
  Our aim is to present the rationale and methods from the WalkIT Trial, a 4-month factorial randomized controlled trial (RCT) in inactive, overweight/obese adults. The main purpose of the study was to evaluate whether intensive adaptive components result in greater improvements to adults' PA compared to the static intervention components.
  
  
  METHODS
  Participants enrolled in a 2x2 factorial RCT and were assigned to one of four semi-automated, text message-based walking interventions. Experimental components included adaptive versus static steps/day goals, and immediate versus delayed reinforcement. Principles of percentile shaping and behavioral economics were used to operationalize experimental components. A Fitbit Zip measured the main outcome: participants' daily physical activity (steps and cadence) over the 4-month duration of the study. Secondary outcomes included self-reported PA, psychosocial outcomes, aerobic fitness, and cardiorespiratory risk factors assessed pre/post in a laboratory setting. Participants were recruited through email listservs and websites affiliated with the university campus, community businesses and local government, social groups, and social media advertising.
  
  
  RESULTS
  This study has completed data collection as of December 2014, but data cleaning and preliminary analyses are still in progress. We expect to complete analysis of the main outcomes in late 2015 to early 2016.
  
  
  CONCLUSIONS
  The Walking Interventions through Texting (WalkIT) Trial will further the understanding of theory-based intervention components to increase the PA of men and women who are healthy, insufficiently active and are overweight or obese. WalkIT is one of the first studies focusing on the individual components of combined goal setting and reward structures in a factorial design to increase walking. The trial is expected to produce results useful to future research interventions and perhaps industry initiatives, primarily focused on mHealth, goal setting, and those looking to promote behavior change through performance-based incentives.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT02053259; https://clinicaltrials.gov/ct2/show/NCT02053259 (Archived by WebCite at http://www.webcitation.org/6b65xLvmg).
authors.affiliation: Exercise Science and Health Promotion, School of Nutrition and Health Promotion, Arizona State University, Phoenix, AZ, United States.
authors.forename: Jane C
authors.identifier: http://orcid.org/0000-0002-1197-0585
authors.initials: JC
authors.lastname: Hurley
authors.forename: Kevin E
authors.identifier: http://orcid.org/0000-0001-9136-5459
authors.initials: KE
authors.lastname: Hollingshead
authors.forename: Michael
authors.identifier: http://orcid.org/0000-0002-1981-4245
authors.initials: M
authors.lastname: Todd
authors.forename: Catherine L
authors.identifier: http://orcid.org/0000-0001-5131-7858
authors.initials: CL
authors.lastname: Jarrett
authors.forename: Wesley J
authors.identifier: http://orcid.org/0000-0003-3728-3000
authors.initials: WJ
authors.lastname: Tucker
authors.forename: Siddhartha S
authors.identifier: http://orcid.org/0000-0002-2932-7926
authors.initials: SS
authors.lastname: Angadi
authors.forename: Marc A
authors.identifier: http://orcid.org/0000-0001-6310-1472
authors.initials: MA
authors.lastname: Adams
keywords: Fitbit; SMS; exercise; inactive; just in time adaptive interventions; mHealth; overweight; percentile schedule of reinforcement; text messaging