Warfighters often experience physical overload, as the uniform and associated gear that they carry burdens them with substantial loads. The loads increase energy expenditure to levels that exceed a Warfighter's typical energy intake. The typical assault load is approximately 25 kg, although loads as high as 55 kg are often carried, which when combined with extreme energy expenditures can degrade health and performance, and increase the risk of injury. Branched-chain amino acid (leucine) supplementation may confer protection against the negative effects of operational stress by stimulating muscle protein synthesis and reducing degradation. This study will determine if leucine-enriched nutrition supplementation confers protection against the negative consequences of sustained load carriage exercise, and explore the mechanisms by which leucine might impart protection.

Inclusion Criteria:

• Weight stable (±5 lbs)with a body mass index between 22-29 kg/m2 and a VO2peak of 40 - 60 ml/kg/min
• Willing to refrain from taking any NSAIDS (i.e., aspirin, Advil®, Aleve®, Naprosyn®), or any aspirin-containing products, alchohol, and nicotine
• Females must be on oral contraception

Exclusion Criteria:

• Metabolic or cardiovascular abnormalities, gastrointestinal disorders
• Disease or medication that affects macronutrient metabolism or the ability to participate in strenuous exercise
• Allergies or intolerance to foods (e.g. lactose intolerance/milk allergy), vegetarian practices, or medications (including, but not limited to, lidocaine or phenylalanine) to be used in the study
• Anemia (HCT <38) and Sickle Cell Anemia/Trait, abnormal PT/PTT test or problems with blood clotting
• Present condition of alcoholism, use of nutritional/sports supplements, anabolic steroids, or other substance abuse issues
• Musculoskeletal injuries that compromise the ability to exercise
• Blood donation within 8 weeks of enrollment
• Pregnancy and women not on oral contraceptives