Efficacy and mechanisms of a brief adaptive goal-setting intervention for physical activity: A randomised pilot trial

Adaptive goal-setting (AGS) interventions, which tailor physical activity (PA) goals to changing individual capability over time, have previously shown efficacy for improving physical activity compared with more standard, static goal-setting (SGS). However, trials to date have been fully automated, which negatively impacts generalisability to more traditional coaching interventions providing human coach support. Furthermore, data on underlying mechanisms of action of AGS are lacking. The purpose of the current pilot trial was to address these two research gaps by preliminarily evaluating both efficacy and change in putative underlying mechanisms of AGS during a 6-week, coach-supplemented PA intervention. 38 sedentary adults (89.5% female) engaging in <150 min of moderate to vigorous physical activity per week and without medical or psychiatric conditions contraindicating increased PA, were randomised to receive 6 weeks of either AGS or SGS. PA was assessed daily and mechanistic variables were assessed up to once weekly. Results indicated that as expected, AGS produced a significantly greater initial PA increase relative to SGS (d = 0.14). However, the AGS group also showed a small (d = 0.01), unexpected, subsequent decrease in PA that was greater than under SGS. A non-significant trend towards greater improvement in implicit attitudes towards PA following AGS was also observed (d = 0.62) but change in implicit attitudes did not mediate intervention effects on PA. Findings suggest that a brief, coach-supplemented AGS intervention was not superior to SGS for increasing PA, but also highlight that implicit attitude variables may warrant further study as potential mechanisms of AGS.