When you think of carnitine, do fat- burning properties and ripped abs come immediately to mind? Great - you go to the head of the class. But don't rest too comfortably; the world of science has recent]y found that carol- tine may have an effect that's even more important to bodybuilders and strength- power athletes: It could increase your bodyweight and muscle mass. Carnitine is essentially an amino acid that's involved in moving long-chain fats into the "powerhouses" of your cells, the mitochondria. Your body uses these fats as fuel, so carnitine acts like a shuttle, but is not itself directly involved in energy production. As far as the two forms of carnitine are concerned, L-carnitine is the physiologically active form and is the type generally used as a dietary supplement; D-carnitine is of little value to the athlete.