Pro Performance L-Carnitine provides 500 mg of this important nutrient per pill. L-Carnitine is a popular amino acid among bodybuilders, weight trainers and serious athletes. Found abundantly in red meats, carnitine is stored in skeletal muscles where it is needed to transform fatty acids into energy for muscular activity. Amino acids are the building blocks of protein and help fuel skeletal muscles. Recently, deficiencies of carnitine have been seen in people who avoid eating red meats in the diet.