A lifetime of fitness relies on you starting new workout programs at regular intervals throughout your life, based on changes in your fitness levels, as well as changes in your life and schedule.

For instance, let's say you've been going along for six months, regularly taking walks in the afternoon and attending yoga classes twice a week. After this amount of time, your body has become used to this program and no longer gets the same fitness kick from the activity that it used to. So if you want to continue to see results or if you want to continue challenging yourself, you'll need to change your routine, and you can change it in big ways or small.

You might, for example, add short jogs or faster walks to your walking program to add a little intensity. Or you could try harder poses with your yoga routine, or maybe add a third class each week. Another alternative would be to change your program in a more extreme way, such as taking bike rides rather than walking, or adding a third activity to your program, such as weight training.

While you should be very proud of yourself for sticking to a program for six months, that's actually a long time to stay with one program. Your body gets used to a routine in four to eight weeks (depending on your fitness level before you began working out).

Now, try to keep in mind that these changes are based on your success as an exerciser, not on any type of failure. Due to homeostasis, the body is resistant to change, which is why it took so much effort to alter both the psychological and physical differences you've achieved.

Unfortunately, as a self-regulating machine, once you've achieved those results, the body holds onto this routine and stops making those same steps of progress.