Answer:
The transtheoretical model of behavior change postulates that individuals engaging in a new behavior, such as adopting a regular exercise program, move through the stages of precontemplation, contemplation, preparation, action, and maintenance.
Step-by-step explanation:
The transtheoretical model of behavior change was developed in 1977. It is a result of analysis and application of several psychotherapy theories - hence the name "transtheoretical". Its purpose is to assess someone's readiness to change an unhealthy behavior, trading it for a healthier one. The stages are: 
1. Precontemplation 
2. Contemplation 
3. Preparation 
4. Action 
5. Maintenance 
6. Termination 
The stages vary from: a person not being ready to change a harmful behavior at all --> the person thinking of the possibility and beginning to admit his behavior is unhealthy --> the person taking small steps toward change and intending to do it for good --> the person modifying their behavior openly --> the person keeping the new behavior going for over six months --> the person feeling no temptation to return to the previous harmful behavior.