Journal Title (Medline/Pubmed accepted abbreviation): J Nutr
Page numbers: 195-200
doi (if applicable): 10.3945/jn.110.130138
Summary of Background and Research Design
Background:Increasing extracellular amino acid concentrations induce muscle protein synthesis (MPS). The synthesis rate is influenced by the type and quantity of amino acids, ingestion with other nutrients, and blood flow (availability). Arginine (ARG), a nonessential amino acid with no effect on MPS, potentially increases nitric oxide and, therefore, muscle blood flow. However, ingestion of 8 to 10 g of essential amino acids can maximally induce MPS both at rest and following resistance exercise.
Hypothesis/purpose of study: The null hypothesis was that arginine added to an amino acid drink would not affect muscle blood flow or MPS rate. The study evaluated the effect of adding 10 g of ARG to 10 g of essential amino acids on MPS rate at rest and following resistance exercise.
Subjects: The study included 8 recreationally active males 22.1 ± 2.6 years of age, 1.79 ± 0.06 m tall, and 76.6 ± 6.2 kg in weight.
Experimental design: Cross-over, double-blind, unilateral exercise study
Treatments and protocol:Individuals completed 3 exercise sessions separated by at least 1 week consisting of a familiarization session and 2 experimental sessions. Exercises consisted of unilateral 10-repetition maximum seated leg press and knee extensions. Dietary diaries were completed before the first session, and diets were replicated before each subsequent session. Following each unilateral resistance exercise, individuals consumed a drink containing 10 g of essential amino acids, 8% phenylalanine (a tracer), and 10 g of ARG or an isonitrogenous amount of glycine (CON). Drink order and exercised leg were randomized and counter-balanced. Femoral arterial blood flow was measured. Blood samples were collected 30 to 180 minutes after drink consumption at 30-minute intervals for amino acid, endothelin-1, nitrate, nitrite, and growth hormone levels. A muscle biopsy was obtained from both the exercised and nonexercised leg 180 minutes after drink ingestion.
Summary of research findings:
- Essential amino acid concentrations peaked at 30 minutes following ingestion for both ARG and CON drinks.
– The peak was higher for ARG than for CON (P < .05), but baseline levels returned sooner for ARG than for CON (P < .001).
– The essential amino acid areas under the curve after ARG and CON ingestion were not different.
- In both drink groups, femoral artery blood flow increased by ~270% in the exercised leg and returned to baseline within 15 minutes.
- Plasma endothelin-1, nitrate, and nitrite levels did not change during the experiment and were not different between the drink groups.
- Growth hormone levels increased at 30 minutes in both drink groups (higher in ARG; P < .05), but returned to baseline faster in CON (P < .05).
- Both mixed and myofibrillar muscle protein fractional synthesis rates increased with exercise
– There were no differences between ARG and CON either at rest or after exercise.
Interpretation of findings/Key practice applications:
Arginine supplementation had no effect on femoral artery blood flow, markers of vascular vasodilation, or muscle synthesis rate in mixed or myofibrillar fibers at rest or after resistance exercise. One limitation of the study is that the peak ARG concentration achieved was 225 µmol/L, which is lower than the reported level needed to induce vasodilation (6,223 µmol/L). In addition, the dose of essential amino acids used in this study is known to maximally induce MPS at rest or after exercise, suggesting that blood flow was not a limiting factor for MPS. Moreover, the clinical importance of the elevated growth hormone levels with ARG ingestion is currently not known. Growth hormone levels increase with resistance exercise and, in healthy adults, may be involved in collagen synthesis but not myofibrillar protein. Therefore, this study suggests that ARG supplementation to increase muscle protein synthesis after resistance exercise is of questionable value when adequate amounts of essential amino acids are available.