Jan. 2 (HealthDay News) -- Before you make a New Year's resolution to get in shape, it might be a good idea to assess whether you're really ready to make that commitment, say experts at the American Council on Exercise (ACE).

Change isn't something that happens in a single stroke, it's a process that develops over time, they note.

"We all go through noticeable, obvious phases when making decisions to change habits. By taking the time to evaluate if you are ready to start exercising, you've thoughtfully planted yourself on the path to better health and fitness," Dr. Cedric Bryant, ACE chief science officer, said in a prepared statement.

Here are some of the stages:

• Pre-contemplation. You're in denial and not planning to change anytime soon (within six months). You're aware of and/or denying the need for lifestyle change. You're pessimistic, especially about your ability to change or the real benefits of becoming more active and modifying your diet.
• Contemplation. You're considering it and weighing the costs, effort, treatment and time commitment of joining a fitness or weight-loss program in the near future. This phase, often characterized by ambivalence, may last for months or even years.
• Preparation. You've made the first moves by starting to limit how much junk food you eat, joining a gym and exercising periodically, or making an appointment with a personal trainer.
• Action. You're changing your behavior. You're getting regular exercise, planning meals and/or keeping a diet record. But beware. At this stage, you're at high risk for relapsing back into your old, unhealthy habits.
• Maintenance. You've achieved sustained lifestyle modification and are actively using methods to monitor and control your behavior. You may be actively avoiding situations that could put you in danger of relapse.