Workout Extender #3:
Rest or Rest Less
You can alter the effect of your workout tremendously in a matter of seconds. In fact, you can change the entire goal of any program simply by adjusting the length of your rest periods. Longer rests are needed when your sets are heavy, as your muscles must be almost fully recovered in order to lift a heavy load for successive sets. Greater muscular endurance comes from keeping rests to a minimum, which forces your muscles to adapt to longer work bouts with less recovery. In the middle lies the key to muscle gain and fat loss: short-to-moderate rest periods that elicit the greatest release of the body's testosterone and growth hormone.
While fat-loss training can be organized in many different ways, one particularly effective method is circuit training, in which you perform one set each of several exercises back-to-back with little or no rest in between. In this case, the lack of full rest keeps your metabolism stoked, so you burn calories at an accelerated rate. Circuit training also saves time, moving you through your workout much more quickly than performing straight sets.