BACKGROUND: Emerging interventions that rely on and harness variability in behavior to adapt to individual performance over time may outperform interventions that prescribe static goals (eg, 10,000 steps/day). The purpose of this factorial trial was to compare adaptive versus static goal setting and immediate versus delayed, non-contingent financial rewards for increasing free-living physical activity (PA). METHODS: A 4-month 2x2 factorial randomized controlled trial tested main effects for goal setting (adaptive versus static goals) and rewards (immediate versus 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. RESULTS: 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 2,389 steps/day on average from baseline to intervention phase (p < 0.001). Participants receiving static goals showed a stronger increase in steps per day from baseline phase to intervention phase (2,630 steps/day) than those receiving adaptive goals (2,149 steps/day; difference 482 steps/day, p = 0.095). Participants receiving immediate rewards showed stronger improvement (2,762 step/day increase) from baseline to intervention phase than those receiving delayed rewards (2,016 steps/day increase; difference 746 steps/day, p = 0.009). 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 (ie, less than half the rate) compared to the static goals group (-7.7 steps versus -18.3 steps each day; difference 10.7 steps/day, p < 0.001) 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. CONCLUSIONS: Adaptive goals outperformed static goals (ie, 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. TRIAL REGISTRATION: ClinicalTrials.gov ID NCT02053259 registered prospectively on January 31, 2014.

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