Let's start with the obvious: Sex can be a great form of exercise, depending on how, um, involved you get. A half hour of sex can help you burn about 150 calories.

That means that having a half-hour sex session once a week for a year will burn off 7,800 calories, about the equivalent of jogging 75 miles at a moderate pace.

A bit of heavy breathing is good for you, too. Breathing deeply during sex will raise the amount of oxygen in your cells, helping all of your organs to function at their best.

Tips to help you vary your fitness routine:

• Quiz: What's your fitness personality?


• Running tips


• Pool aerobics

Next: Building sexual muscle