Do you find yourself continually starting exercise programs only to quit just weeks later? If so, you could be asking too much of yourself in terms of motivation.

Studies show that most people need to stick with a plan for 30 to 60 days before their commitment to exercise takes hold. Unfortunately, many of us give up sooner, discouraged if we don't approach each workout with zeal.

Perhaps one answer is to look at motivation as another "muscle." Just as biceps, abs and glutes gradually strengthen as they are exercised over time, so does motivation grow stronger with practice.

Also critical: Choose workouts you like. (It's extra hard to motivate yourself do to exercise you don't enjoy.)