Abstarct: Background and objectives: Background and Objectives: The aim of this study was to investigate the acute effect of a combination of nitric oxide precursor supplements on selected performance indicators in trained men. Materials and methods: In a randomized crossover design, 13 trained men (age: 22.00 ± 1.73 years; weight: 71.15 ± 6.86 kg; height: 181.76 ± 5.05 cm; BMI: 21.50 ± 1.53 kg/m²) were assigned to either a supplement or placebo group baxsed on their maximal oxygen uptake. A fatigue-inducing exercise protocol was used as the physical activity stimulus. In two separate sessions spaced one week apart, participants consumed a mixture of 3 g L-arginine, 3 g L-citrulline, and 300 ml beetroot juice or a placebo dissolved in 200 ml water, 60 minutes prior to exercise. Blood samples were collected at three time points: before supplementation, 60 minutes after ingestion, and immediately post-exercise, to measure blood lactate levels. Data were analyzed using SPSS version 27. Normality was assessed via the Shapiro-Wilk test, and repeated measures ANOVA along with paired t-tests were used to evaluate statistical significance at P < 0.05. Results: The analysis revealed no significant differences between the supplement and placebo conditions in terms of blood lactate levels and time to exhaustion (P > 0.05). However, significant improvements were observed in heart rate during exercise, respiratory exchange ratio, perceived exertion, and respiratory exchange ratio during the final three minutes of the fatigue-inducing activity in the supplement group compared to placebo (P < 0.05). Conclusion: Despite the findings of this study, it can be concluded that although the nitric oxide-enhancing supplements used in this research did not significantly affect serum lactate levels or time to exhaustion, they contributed to improved athletic performance and delayed central fatigue. Given the limitations of the study, further research in this area is recommended.