Training

The best way to rapidly burn calories and shed excess bodyfat while maintaining muscle mass is low- to medium-intensity repetition training that promotes overall cardiovascular fitness.

There are other benefits (such as lowering blood pressure, reducing the risk of heart disease, improving respiration and decreasing stress), but most bodybuilders do cardio to get rid of fat. Many do a small amount year-round (one to two hours a week), but almost everyone steps up the volume closer to a contest (to as much as two hours per day).

If your only motivation in the gym is to put on size, you should probably do only a minimal amount of cardio, but everybody else can benefit from at least some occasional aerobic activity to keep metabolism high and safeguard against the conversion of excess calories into fat storage.