Muscle levels of L-CARNITINE determine the exercise capacity of muscles. L-CARNITINE forms the essential transport system for use of fats as an energy source. L-CARNITINE may help delay muscle fatigue and improve endurance. L-CARNITINE is essential for normal heart function. Performance horses recover more efficiently when supplemented with L-CARNITINE. L-CARNITINE is an amino acid which helps transport fats into muscle cells. It is essential in the transport of fats into muscle cells for energy production. The muscle levels of L-CARNITINE determine the exercise capacity of muscles.. By using fats as energy for muscle contractions, the body is sparing glycogen and delaying the accumulation of lactic acid.