What are varying levels of intensity? What counts as aerobic activity?

In the Fitness #1 Module on Exercise and Physical Activity, you learned how much physical activity is needed to gain (greater) health benefits and it referred to moderate and vigorous aerobic activity. But, what is the difference between moderate and vigorous activity?

> Visit this CDC page (and scroll down about half way) to distinguish the difference.

>>>Proceed to the next menu link: “FITT Principle“