Hypothesis/background: Arginine is a precursor to the formation of nitric oxide in blood vessels. Because nitric oxide is associated with vasodilation, many athletes utilize arginine supplementation in the attempt to increase blood flow to exercising muscles. Further, some studies suggest that intravenous arginine administration can increase growth hormone response. The authors of this study hypothesized that high dose oral arginine supplementation would increase concentrates of nitric oxide metabolites and hormones (e.g., growth hormone (GH), insulin-like growth factor 1 (IGF-1), and insulin).

Subjects: 14 physically-active male participants (mean age: 25 y, mean weight: 78 kg, mean height: 179 cm, mean protein intake: 1.2 g/kg/day). Subjects were all nonsmokers, nonvegetarian and had not used any other dietary supplements for 12 weeks before the study.

Experimental design: Double-blind, repeated measures with each condition separated by 7 days

Treatments:There were 3 treatment conditions consisting of 500 mL water plus:  1) placebo (flour) in capsule form; 2) 0.075 g/kg body mass L-arginine (~5.9 g for a 78-kg subject); 3)  0.15 g/kg body mass L-arginine (~11.7 g for a 78-kg subject).

Protocol:This study involved the administration of a single dose of each of the above treatments, administered in random order. Subjects refrained from vigorous physical activity the day before testing and came to the laboratory on the morning of testing having fasted 10 h overnight. Blood samples were collected at baseline and at 30, 60, 90, 120, and 180 min following consumption of the test dose. Blood samples were analyzed for arginine, nitrate, nitrite, GH, glucose, IGF-1 and insulin.