Habit strength moderates the effects of daily action planning prompts on physical activity but not sedentary behavior

This study was designed to examine the moderating influence of habit strength on daily action planning effects on physical activity and sedentary behavior. A 2 by 2 design was used with experimental factors corresponding to action planning interventions for (a) engaging in physical activity and (b) limiting or interrupting sedentary behavior. At the end of each day for 1 week, university students (n = 195) completed (a) a questionnaire about their behavior during the day and behavioral intentions for the following day and (b) a planning intervention(s) corresponding to their randomly assigned experimental condition. Action planning increased physical activity in those with weak habits but decreased physical activity in those with strong habits compared with those who did not create action plans. Action planning did not impact sedentary behavior. Action planning was a useful behavior change technique for increasing physical activity in people with weak habits, but may be iatrogenic for those with strong habits.