According to estimates, over fifty percent of dietary leucine may be used for energy in exercising muscles. Leucine may also stimulate the release of insulin, which increases protein synthesis and inhibits protein breakdown.
L-leucine is the only Branch-Chained Amino Acid (BCAA) that can be completely oxidised by muscles for energy. During strenuous exercise, L-leucine is oxidised at a greatly accelerated pace. Supplemental amounts of L-leucine act to compensate for those losses. In addition, L-leucine has the benefits of conserving glucose (blood sugar), the body's primary energy source, as well as sparing the other amino acids in muscle.
The result is greater endurance throughout the duration of a strenuous workout, and a net increase in muscle growth (due to diminished catabolism of muscle protein both during and after a workout). Ironically, well-conditioned athletes and bodybuilders have an even greater need for supplemental L-leucine, since trained muscle uses more L-leucine than untrained muscle.
Recommended dosage is 5-10 grams during a workout and another 5-10 grams post-workout. Including the other BCAAs along with glutamine will further enhance the muscle-building effects of L-leucine.