THE INEFFECTIVENESS OF ACUTE L-ARGININE SUPPLEMENTATION ON MUSCLE STRENGTH: A SYSTEMATIC REVIEW AND META-ANALYSIS WITH GRADE ASSESSMENT

Resumo

L-arginine (L-arg) supplementation is widely used by individuals engaged in resistance training due to its proposed role in nitric oxide production and its potential to enhance muscle perfusion and strength performance. Despite its popularity, evidence supporting its acute ergogenic effects remains inconsistent and controversial. Objective: To synthesize and critically examine the available randomized evidence on acute L-arginine supplementation and strength performance in resistance training. Methods: A systematic review and meta-analysis were conducted following the PRISMA and PICO frameworks. Electronic searches were performed in PubMed, SciELO, MEDLINE, and LILACS databases. Randomized controlled trials investigating acute isolated L-arginine supplementation and strength-related outcomes were included. A random-effects model was pre-specified to account for clinical heterogeneity across different age groups and muscle protocols. The overall certainty of evidence was evaluated using the GRADE framework. Results: Out of 265 full-text articles assessed, only four studies met the strict inclusion criteria for qualitative synthesis, and three provided data for meta-analysis (k=3). The random-effects model showed no significant improvement in strength performance compared to placebo, with a pooled SMD of 0.168 (95% CI: -0.145 to 0.481; p = 0.292). Although the risk of individual bias was low, the overall certainty of evidence was classified as moderate. This classification was primarily due to imprecision stemming from the small cumulative sample size (n=30), which increases the risk of Type II error. Conclusion: The current body of randomized evidence indicates that acute L-arginine supplementation (6–8g) does not elicit significant improvements in maximal strength or peak torque in resistance-trained individuals. The lack of ergogenic effect is likely attributed to extensive first-pass metabolism and the inherent physiological 'ceiling effect' in active populations. Consequently, athletes and healthcare professionals should prioritize alternative ergogenic strategies or nitric oxide precursors with superior bioavailability, such as L-citrulline, for acute strength gains, as the oral L-arginine pathway appears insufficient to acutely alter muscular mechanics in performance-oriented settings.