One Week of L-Citrulline Supplementation Improves Performance in Trained Cyclists.

2019-12-19
Journal of strength and conditioning research 34(3)
- Sean T Stanelle
- Kelsey L McLaughlin
- Stephen F Crouse

PubMed: 31860534
DOI: 10.1519/jsc.0000000000003418

Study Design

Type: Randomized Controlled Trial (RCT)
Population: nine trained male cyclists (24 ± 3 years; 181 ± 7 cm; 76 ± 13 kg; 4.18 ± 0.51 L·min V̇O2max)
Methods: randomized, double-blind, crossover design; 7-day supplementation periods (6 g·d of CIT or PLAC) separated by a 7-day washout
Blinding: Double-blind
Duration: 7-day supplementation periods
Funding: Unclear

Stanelle, ST, McLaughlin, KL, and Crouse, SF. One week of L-citrulline supplementation improves performance in trained cyclists. J Strength Cond Res 34(3): 647-652, 2020-L-citrulline (CIT) is a nonessential amino acid that is touted as an ergogenic aid for athletic performance because of its purported ability to stimulate nitric oxide production. Although previous research has demonstrated that CIT supplementation over a period of days improves physiological factors such as V[Combining Dot Above]O2 kinetics, no studies to date have explored whether there is a direct benefit to endurance performance. This study used a randomized, double-blind, crossover design to test whether chronic supplementation with pure CIT improves cycling performance over a maltodextrin placebo (PLAC). Nine trained male cyclists (24 ± 3 years; 181 ± 7 cm; 76 ± 13 kg; 4.18 ± 0.51 L·min V[Combining Dot Above]O2max) completed two 7-day supplementation periods (6 g·d of CIT or PLAC) separated by a 7-day washout. Subjects consumed the final 6-g dose 2 hours before the cycling performance evaluation, which consisted of a 40-km time trial (TT) followed by a supramaximal sprint repeat task (SRT). Paired t-tests and repeated-measures analysis of variance (α = 0.05) were used to analyze TT and SRT data, respectively. CIT supplementation produced an improvement in TT time of 5.2% that trended toward significance (p = 0.08). Furthermore, CIT promoted a significant increase in average heart rate, average rating of perceived exertion, and average power throughout the TT (p < 0.05). However, supplementation with CIT did not prevent fatigue during the SRT. Overall, this study is the first to demonstrate that CIT supplementation may provide a modest improvement to endurance cycling performance in trained athletes.

Research Insights

L-Citrulline→Improved Cycling Time Trial Performance
CIT supplementation produced an improvement in TT time of 5.2% that trended toward significance (p = 0.08).
Effect
Neutral
Effect size
Small
Dose
6 g/day
L-Citrulline→Improved Sprint Repeat Task Performance
However, supplementation with CIT did not prevent fatigue during the SRT.
Effect
Neutral
Effect size
Small
Dose
6 g/day
L-Citrulline→Improved Time-Trial Performance
CIT supplementation produced an improvement in TT time of 5.2% that trended toward significance (p = 0.08).
Effect
Neutral
Effect size
Small
Dose
6 g/day
L-Citrulline→Increased Heart Rate
CIT promoted a significant increase in average heart rate, average rating of perceived exertion, and average power throughout the TT (p < 0.05).
Effect
Beneficial
Effect size
Small
Dose
6 g/day
L-Citrulline→Increased Perceived Exertion
CIT promoted a significant increase in average heart rate, average rating of perceived exertion, and average power throughout the TT (p < 0.05).
Effect
Beneficial
Effect size
Moderate
Dose
6 g/day
L-Citrulline→Increased Power Output
CIT promoted a significant increase in average heart rate, average rating of perceived exertion, and average power throughout the TT (p < 0.05).
Effect
Beneficial
Effect size
Small
Dose
6 g/day
L-Citrulline→Increased Rating of Perceived Exertion
CIT promoted a significant increase in average heart rate, average rating of perceived exertion, and average power throughout the TT (p < 0.05).
Effect
Beneficial
Effect size
Small
Dose
6 g/day
L-Citrulline→Reduced Fatigue During Sprint Repeat Task
However, supplementation with CIT did not prevent fatigue during the SRT.
Effect
Neutral
Effect size
Small
Dose
6 g/day