The purpose of this study was to summarize findings from empirical applications of the transtheoretical model (TTM) (Prochaska & DiClemente, 1983) in the physical activity domain by using the quantitative method of meta-analysis. Ninety-one independent samples from 71 published reports were located that present empirical data on at least one core construct of the TTM applied to exercise and physical activity. In general, results support the application because core constructs differ across stages and most changes are in the direction predicted by the theory. Three general conclusions are offered. First, existing data are unable to confirm whether physical activity behavior change occurs in a series of stages that are qualitatively different or along adjacent segments of an underlying continuum. Second, the growing number of studies that incorporate TTM concepts means that there is an increasing need to standardize and improve the reliability of measurement. Finally, the role of processes of change needs reexamining because the higher order constructs are not apparent in the physical activity domain and stage-by-process interactions are not evident. There now are sufficient data to confirm that stage membership is associated with different levels of physical activity, self-efficacy, pros and cons, and processes of change. Further studies that simply stage participants or examine cross-sectional differences between core constructs of the TTM are of limited use. Future research should examine the moderators and mediators of stage transition. https://link.springer.com/article/10.1207/S15324796ABM2304_2 Marshall, S.J., Biddle, S.J.H. The transtheoretical model of behavior change: a meta-analysis of applications to physical activity and exercise. ann. behav. med. 23, 229–246 (2001). https://doi.org/10.1207/S15324796ABM2304_2 Abstract The Transtheoretical Model (TTM) is an integrative framework for understanding how individuals and populations progress toward adopting and maintaining health behavior change for optimal health. The Transtheoretical Model uses stages of change to integrate processes and principles of change from across major theories of intervention, hence the name "Transtheoretical." This model emerged from a comparative analysis of leading theories of psychotherapy and behavior change. The search was for a systematic integration of a field that had fragmented into more than 300 theories of psychotherapy. The comparative analysis identified only 10 processes of change, such as consciousness raising from the Freudian tradition, contingency management from the Skinnerian tradition, and helping relationships from the Rogerian tradition. From the initial studies of smoking, the stage model rapidly expanded in scope to include investigations of and applications to a broad range of health and mental health behaviors. These include alcohol and substance abuse, anxiety and panic disorders, stress and depression, partner violence and bullying, delinquency, eating disorders and obesity, high-fat diets, exercise, HIV/AIDS, use of mammography screening, medication compliance, unplanned pregnancy, pregnancy and smoking, radon testing, sedentary lifestyles, sun exposure, and the practice of preventive medicine. Over time, these studies have expanded, validated, applied, and challenged the core constructs of the Transtheoretical Model. (PsycInfo Database Record (c) 2020 APA, all rights reserved) https://psycnet.apa.org/record/2008-17602-004 Prochaska, J. O., Johnson, S., & Lee, P. (2009). The Transtheoretical Model of behavior change. In S. A. Shumaker, J. K. Ockene, & K. A. Riekert (Eds.), The handbook of health behavior change (p. 59–83). Springer Publishing Company.