Hypothesis
Combining a motivational component (mental simulation) with a volitional one (implementation intentions) would increase regular physical activity.
What failed
Neither trial found any significant main or interactive effect on physical activity: a cluster-randomised study of 92 students with self-reported activity at four weeks, and a 2 x 2 trial of 184 fitness-centre members with attendance records at four and nineteen weeks.
Broken assumption
Self-regulation techniques that worked in earlier studies transfer to sustained real-world physical activity.
Why
The authors emphasise that they followed protocols consistent with previous research, used an objective behavioural measure and had sufficient statistical power, and so suggest the components may not change physical activity and that format and moderators need testing.
From the published paper: Meslot et al. Frontiers in Psychology, 2016. ↗CC BY