New research into three amino acids in particular––leucine, alanine and proline––suggests they can enhance muscle recovery, improve endurance, and build muscle mass more efficiently when taken in combination with other amino acids, carbohydrates, or whey protein. Substantial evidence suggests that, for both endurance and strength, athletes require more protein than non-active individuals. Approximately one to six percent of the energy used by muscles to fuel endurance exercise comes from amino acids. After endurance exercise, amino acid requirements are increased. Both highly trained athletes and everyday fitness enthusiasts often supplement with branched-chain amino acids (BCAAs). Some evidence shows that BCAAs may help build muscle, reduce workout fatigue, and decrease muscle soreness after exercise.