Ma et al. 2023, habit-formation interventions for physical activity (meta-analysis)

Meta-analysis and meta-regression in the International Journal of Behavioral Nutrition and Physical Activity, pooling 10 randomised trials (2,349 participants) of interventions designed to build physical-activity habits. Habit-formation interventions produced a small-to-moderate increase in physical-activity habit strength versus control (SMD ≈ 0.31, 95% CI 0.14 to 0.48). Effects were larger at follow-ups of 12 weeks or less and weaker beyond that, suggesting habit strength can plateau or fade without continued support. Interventions that taught problem-solving were associated with better results, whereas those relying on social or external rewards were associated with worse outcomes, echoing self-determination theory’s warning that external rewards can undermine intrinsic motivation. The strongest quantitative synthesis on the topic, but built on only 10 trials.