We know that heart disease and cancer are the two biggest killers, followed by stroke. We are quite accustomed to seeing ads telling us the dangers of smoking cigarettes. We hear gurus and diet experts tell us every day the importance of building good diet and exercise habits. Many people have stopped smoking, try to eat more healthfully, and exercise regularly--or at the very least know they need to do so. But there's another root cause of these killers that we don't often talk about--inactivity. Yes, those daily workouts and intentional exercise help. But that's not what we're talking about here. And this type of inactivity isn't due to laziness and personal choice.