Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Page numbers: 833-837
doi (if applicable):
Summary of Background and Research Design
Background: L-arginine supplements are marketed with claims that they can increase strength and endurance. It has been speculated that L-arginine works by virtue of its metabolic byproduct nitric oxide (NO). Indeed, chronic arginine supplementation has been shown to improve oxygen consumption (VO2) for patients with impaired endothelial function; however, there have been few studies evaluating the ergogenic potential for L-arginine in trained athletes.
Hypothesis/purpose of study: To determine if supplementation with L-arginine for 28 days would improve maximal VO2 (VO2max) and/or delay ventilatory threshold (VT) in endurance-trained male cyclists.
Subjects: Eighteen endurance-trained male cyclists participated in this study (mean age, 36.3 ± 7.9 yr; height, 182.4 ± 4.6 cm; body mass, 79.5 ± 4.7 kg).
Experimental design: Randomized, double-blind, independent groups (n = 9 for arginine and n = 9 for placebo)
Treatments and protocol: Subjects completed 2 graded exercise tests (50W + 25W/min) using their own bikes before and after 28 days of supplementation with arginine (6 g twice daily) or placebo. Cyclists maintained a chosen cadence of 70 to 100 rpm throughout the testing, with VO2 continuously recorded. Subjects were asked to maintain their dietary regimens and be adequately hydrated for the 48 hours preceding each test.
Summary of research findings:
- At 28 days, there was no significant difference in VO2max measures of arginine-treated vs placebo-treated subjects (61.1 vs 58.9 mL/kg/min, respectively; P = .65). The mean VO2max values at baseline for the arginine-treated group (63.5 ? 7.3 mL/kg/min) and the placebo group (58.7 ? 7.1 mL/kg/min) were also not significantly different from each other.
- At 28 days, there was no significant difference in VT measures of arginine-treated vs placebo-treated subjects (74.2% vs 74.3% VO2 max, respectively; P = .91). The mean VT values at baseline for the arginine-treated group (76.0% ? 5.3% VO2max) and the placebo group (75.7% ? 4.6% VO2max) were also not significantly different from each other.
Interpretation of findings/Key practice applications:
L-arginine supplementation has been hypothesized as a potential ergogenic aid via production of NO. This study, however, did not show an improvement in the key measures of aerobic endurance. It is possible that these results were confounded by increased NO production that has been documented in resting athletes and also during exercise for all individuals. Other research suggests that endurance performance (eg, time to exhaustion) can be enhanced without affecting markers of aerobic capacity, such as VO2max or VT. However, at this time it appears that L-arginine supplementation does not improve aerobic variables; therefore, use as an ergogenic aid should not be encouraged.