Joseph A. Chromiak

Use of amino acids as growth hormone-releasing agents by athletes

Specific amino acids, such as arginine, lysine and ornithine, can stimulate growth hormone (GH) release when infused intravenously or administered orally. Many individuals consume amino acids before strength training workouts, believing this practice accentuates the exercise-induced GH release, thereby promoting greater gains in muscle mass and strength. The GH response to amino acid administration has a high degree of interindividual variability and may be altered by training status, sex, age, and diet. Although parenteral administration consistently leads to increased circulating GH concentration, oral doses that are great enough to induce significant GH release are likely to cause stomach discomfort and diarrhea. During exercise, intensity is a major determinant of GH release. Although one study showed that arginine infusion can heighten the GH response to exercise, no studies found that pre-exercise oral amino acid supplementation augments GH release. Further, no appropriately conducted scientific studies found that oral supplementation with amino acids, which are capable of inducing GH release, before strength training increases muscle mass and strength to a greater extent than strength training alone. The use of specific amino acids to stimulate GH release by athletes is not recommended.

Skeletal Muscle Plasticity

Skeletal muscle is a highly organized tissue designed to produce force for postural control, movement, and even breathing. Various architectural designs, varying amounts of muscle proteins (e.g., enzymes or myosin), and different isoforms of many muscle proteins provide for a wide range of force-producing, biochemieal, and metabolic characteristics. Additionally, the ability of skeletal muscle to adapt to the demands placed upon it, such as increased mitochondrial volume associated with endurance training or increased muscle fiber cross-sectional area as a result of strength training, demonstrates a tremendous plasticity. For the sports nutritionist, a fundamental understanding of the structure and function of skeletal muscle is important inasmuch as the adaptive response to various contractile and nutritional perturbations are manifest in this tissue. It should be noted that there is a large variation among individuals with regard to the magnitude of muscle adaptability to various types of training. Differing muscle characteristics, such as muscle pennation and fiber type, and variation in degree of adaptability among individuals partially explain the wide range of differences in aspects of exercise performance, such as muscular endurance or strength.