Exercise: Get Your Facts Straight

Knowing that exercise is good for you isn't always enough. To get the most out of your fitness routine, it's important to have your facts straight.

For example, are sit-ups really the best way to get a flat tummy? Does exercise keep you awake or help you sleep? And just how much of a workout is healthy for older people?

Dr. Mallika Marshall joins The Saturday Early Show with questions and answers. Take our HealthWatch quiz.