Goal setting and achievement for walking: A series of N-of-1 digital interventions.

Objective: Despite evidences that goal setting is valuable for physical activity promotion, recent research pointed out a risk of oversimplification in the application of this behavior change technique. While more difficult goals might trigger higher physical activity levels, higher goals might concurrently be more difficult to achieve, which could reduce long-term motivation. This study explores the associations between goal difficulty, physical activity, and goal achievement. Methods: This study used data from an e-Health intervention among inactive overweight adults (n = 20). The study duration included a 2-week baseline period and an intervention phase of 80 days. During the intervention, participants received a daily step goal experimentally manipulated by taking participants’ baseline physical activity median (i.e., number of steps) multiplied by a pseudo-random factor ranging from 1 to 2.6. A continuous measure of goal achievement was inferred for each day by dividing the daily number of steps by the goal prescribed that day. Generalized additive models were fit for each participant individually. Results: The results of the present study confirm that, for a majority of the participants involved in the present study, goal difficulty was positively and significantly associated with physical activity (n = 14 participants out of 20), but, concurrently, negatively and significantly associated with goal achievement (n = 19 participants out of 20). Conclusion: These results suggest the existence of an ‘optimal goal setting zone’ triggering challenging behavioral performances while being still doable. Practitioners or researchers involved in goal setting for physical activity should “tune” goal difficulty levels according to not only behavioral performance but also goal achievement.