(64) ACUTE EFFECT OF L-CITRULLINE SUPPLEMENTATION ON MUSCLE OXYGENATION DURING RESISTANCE EXERCISE IN RECREATIONALLY RESISTANCE TRAINED MEN AND WOMEN

Oral supplementation with L-citrulline has been demonstrated to augment plasma concentrations of L-arginine, and in turn, nitric oxide, a potent signaler of vasodilation. Consequently, L-citrulline has gained popularity as an ergogenic aid due to its potential to enhance blood flow to working muscle tissue during exercise at a minimum effective dose of 3g. However, few studies have examined the acute effect of a higher dose (8g) of L-citrulline on muscle oxygenation during resistance exercise.  

Purpose: The purpose of this study was to evaluate the acute effect of L-citrulline supplementation on muscle oxygenation parameters during a strength-endurance bench press protocol in recreationally resistance-trained men and women.

Methods: In a cross-over design fashion, 18 recreationally resistance-trained men (n=11) and women (n=7) (21.4 ± 1.8 years; 172.3 ± 7.5 cm; 76.9 ± 10.8 kg) were randomly assigned to supplement with a beverage containing 8 grams of L-citrulline or a placebo one hour prior to completing a strength-endurance bench press protocol consisting of 5 repetition-maximum sets at 75% 1RM. A near-infrared spectroscopy muscle oxygen sensor was placed on the participants’ muscle belly of the anterior deltoid to continuously measure the concentration of oxygenated hemoglobin (HbO2) relative to total hemoglobin (tHb).  Muscle oxygen saturation (SmO₂) was calculated using the equation: SmO₂ (%) = HbO₂/tHb.  Muscle oxygenation dynamics were assessed via the percent change in SmO₂ during each set (∆%SmO₂), muscle oxygen resaturation rate (SmO₂RecSlope), and the highest measured SmO₂ value achieved during each recovery period between sets (SmO₂peak). Muscle oxygenation data were evaluated on a set-to-set basis using both a frequentist and Bayesian 2 (sex) x 2 (condition) x 5 (set) three-way analysis of variance (ANOVA) with significance accepted an alpha (p) level ≤ 0.05.  Significant main effects were evaluated with a Bonferroni post-hoc correction.

Results: No significant main effect of sex, main effect of condition, or interaction of any type was present. However, significant main effects of time (p < 0.001) were observed for SmO₂RecSlope and SmO₂peak such that SmO₂RecSlope during set 5 was significantly reduced when compared to sets 1-3 (p < 0.05). Additionally, SmO₂peak was significantly decreased during set 5 compared to sets 1-4 (p < 0.05) and during set 4 compared to set 1 (p = 0.044).

Conclusion: Although muscle oxygenation dynamics were attenuated  during later sets of the strength-endurance bench press protocol, a single 8-gram dose of L-citrulline had no ergogenic effect in recreationally resistance-trained men and women. PRACTICAL APPLICATION: These data suggest that acute L-citrulline supplementation does not enhance muscle oxygenation dynamics during strength-endurance upper-body resistance exercise. Further research should evaluate the effect of chronic or short-term L-citrulline supplementation on muscle oxygenation dynamics and resistance exercise performance.

Acknowledgements: None