Author(s): THEODOROU, A., CHRISTODOULOU, F., PAMBORIS, G., CHRISTODOULIDES, S., TRYFONOS, A., Institution: EUROPEAN UNIVERSITY CYPRUS, Country: CYPRUS, Abstract-ID: 2037

INTRODUCTION:
L-citrulline is a non-coded alpha-amino acid, synthesized from ornithine and metabolized by argininosuccinate synthetase. It is commonly used in sports nutrition to enhance nitric oxide synthesis. Nitric oxide represents a potent vasodilator regulating blood flow and oxygen delivery. In older adults, skeletal muscle oxygenation is reduced due to endothelial dysfunction and decreased nitric oxide activity. Thus, supplementation with nitric oxide precursors such as L-Citrulline might have favorable effects on muscle oxygen metabolism. Considering that muscle oxygenation directly affects performance, the present investigation aimed to examine the acute and short-term impact of L-Citrulline on older adults muscle oxygenation.
METHODS:
Following a counterbalanced crossover, double-blind, and placebo-controlled design, the researchers enrolled 12 older individuals in the present study [n=12, age 64 ± 5 years, body mass 78.4 ± 6.9 kg, height 173 ± 4 cm, body fat 26.8 ± 2.6 (mean ± standard deviation)]. Participants received 6 g of L-citrulline (Now, L-citrulline Pure Powder, Bloomingdale, IL) or a placebo (maltodextrin) daily for seven days. Using near-infrared spectroscopy, the microvascular concentrations of oxyhemoglobin and deoxyhemoglobin, which reflect the dynamic balance between muscle oxygen delivery and extraction, were measured at baseline 1 hour after the first intake of L-citrulline and at day seven after the end of the supplementation period. Additionally, total hemoglobin concentration was calculated as the sum of oxyhemoglobin and deoxyhemoglobin, representing changes in microvascular blood flow, and the tissue saturation index was also measured, reflecting muscle oxygenation and saturation balance at the same time points. For the statistical analysis of the data, a two-way repeated-measures ANOVA test [(condition (L-citrulline vs. placebo) × time (baseline, 1 hour after supplementation, and seven days post supplementation)] was performed.
RESULTS:
No significant condition-by-time interaction or main effect of condition (p>0.05) was found in any of the examined muscle oxygenation parameters (oxyhemoglobin, deoxyhemoglobin, total hemoglobin, tissue saturation index).
CONCLUSION:
As a nitric oxide precursor, we expected that L-citrulline supplementation would have enhanced nitric oxide bioavailability and improved muscle oxygenation. However, the results of the present investigation opposed our hypothesis, as acute and short-term L-citrulline supplementation had no effect on vastus lateralis oxygenation at rest in older adults. In the present investigation, muscle oxygenation indices were measured only at rest and not during a condition with an increased demand for oxygen for muscles, such as exercise. Perhaps this prevented us from finding any favorable impact of L-citrulline on muscle oxygenation. Thus, we suggest future studies to examine the effect of L-citrulline on muscle oxygenation during exercise.