Effects of L-Citrulline or Citrulline-malate on Neuromuscular Performance in Resistance-trained Adults

Nitric oxide (NO) is a ubiquitous gaseous molecule that plays a critical role in the regulation of cardiovascular function and in the signaling of multiple cellular processes. Specifically, NO could reduce the oxygen cost of exercise and adenosine triphosphate (ATP) in the production of muscle contractile force, improving calcium handling, glucose uptake and mitochondrial efficiency in muscle fibers. Therefore, it has been suggested that increasing the availability of NO through the oral intake of food and nutritional supplements may be useful to delay the onset of fatigue and improve performance in high-intensity efforts.

L-citrulline is a nonessential amino acid involved in the urea cycle that acts as an endogenous precursor of L-arginine, being a more efficient alternative to L-arginine to increase the plasma concentration of L-arginine through the nitric oxide synthase (NOS) pathway.

On the other hand, citrulline malate is an organic salt of L-citrulline and malate which has been shown to exert a small but significant ergogenic effect in different high-intensity efforts compared to a placebo. However, no study to date has compared L-citrulline VS. citrulline malate to assess whether there is an additive effect from malate to exercise performance.

50 resistance-trained adults (50% women) will be randomized into three conditions (L-citrulline, citrulline-malate and placebo conditions) with 48 hours of separation between conditions. 48h previous to the randomization the participants will perform a familiarization to avoid the learning effects.

Each evaluation day will conform to the following tests:

• Maximal dynamic strength of lower- and upper-body
• Maximal endurance strength of lower- and upper-body

Inclusion criteria

• Healthy male or female
• Ages 18-30years
• BMI: 18-30.0 kg/m2
• Stable weight over the last 3 months (body weight changes<3kg)
• Previous experience in resistance training (i.e., at least 1 year with a frequency of two or more training sessions per week),
• Participant must be capable and willing to provide consent, understand exclusion criteria, instructions and protocols.

Exclusion criteria

• History of chronic diseases (renal disease, diabetes, cardiovascular disease, cancer, VIH, hepatic disease, food disorders)
• Pregnant, planning to become pregnant, or breastfeeding
• Have been treated previously or during the study period with prescription drugs:

antihypertensive, lipid lowering, acid uric lowering, glucose lowering, beta blockers or any drug that under the investigator's judged could influence the results.

• Allergy/intolerance to any ingredient of the dietary supplements.
• Chronic consumers of dietary NO-precursors dietary supplements (citrulline malate, arginine, nitrates).
• Any non-controlled medical condition which could influence results or could be worsened by the participation in the study.
• Are deemed unsuitable by the investigator for any other reason, that prevent data collection.