Key result
L-citrulline supplementation (6 g for 7 days) increased exhaled NO by 26% (p<0.001) but did not improve respiratory muscle performance, fatigue, or oxygenation in healthy older males.
Why the study?
Nitric oxide precursors like L-citrulline are used to enhance bioavailability as an ergogenic aid, but its effect on respiratory muscle performance, fatigue, and oxygenation in older adults required examination.
Does short-term L-citrulline supplementation improve respiratory muscle performance and oxygenation in healthy older males?
RCT (n=14)
Double-blind
Does short-term L-citrulline supplementation improve respiratory muscle performance and oxygenation in healthy older males?
Short-term L-citrulline supplementation increases exhaled nitric oxide but does not provide ergogenic benefits for respiratory muscle performance or oxygenation in healthy older males.
No ergogenic benefit on respiratory muscle performance despite raised NO; challenges L-citrulline use and leaves open effects in clinical populations.
In sports nutrition, nitric oxide (NO•) precursors such as L-citrulline are widely used to enhance NO• bioavailability, which is considered an ergogenic aid. Our study aimed to examine the effect of short-term L-citrulline supplementation on respiratory muscles’ performance, fatigue, and oxygenation in older adults. Fourteen healthy older males took 6 g of L-citrulline or a placebo for seven days in a double-blind crossover design. Pulmonary function via spirometry (i.e., forced expired volume in 1 s (FEV1), forced vital capacity (FVC), and their ratio)), fractional exhaled nitric oxide (NO•), maximal inspiratory pressure (MIP), rate of perceived exertion, and sternocleidomastoid muscle oxygenation (i.e., oxyhemoglobin (Δ[O2Hb]) and de-oxyhemoglobin (Δ[HHb]), total hemoglobin concentration (Δ[tHb]), and tissue saturation index (TSI%)) were evaluated at baseline, after seven days of L-citrulline supplementation, and after incremental resistive breathing to task failure of the respiratory muscles. The exhaled NO• value was only significantly increased after the supplementation (26% p < 0.001) in the L-citrulline condition. Pulmonary function, MIP, rate of perceived exertion, and sternocleidomastoid muscle oxygenation were not affected by the L-citrulline supplementation. In the present study, although short-term L-citrulline supplementation increased exhaled NO•, no ergogenic aids were found on the examined parameters at rest and after resistive breathing to task failure in older adults.
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Theodorou et al. (2023) conducted an RCT in Healthy (n=14). L-citrulline vs. Placebo was evaluated on Respiratory muscles' performance, fatigue, and oxygenation. L-citrulline supplementation (6 g for 7 days) increased exhaled NO by 26% (p<0.001) but did not improve respiratory muscle performance, fatigue, or oxygenation in healthy older males.
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