In the context of sports nutrition the definition of “energy" can be provided with precision as it is linked to muscular, athletic and/or competitive sport performance but not, for example, to cognitive performance or alertness “energy" alone. Surveying the landscape of energy bioactives yields a large and broad territory. Thus, this small review of key research on energy bioactives will focus on acute, single-dose ingestion before exercise, defined by a select few modes of presumed action.

Citrulline: Solo or Malate Mated

L-citrulline, like creatine, is a non-protein amino acid yet with discovery origins in a vegan food source: watermelon. Much of the focus on L-citrulline has been on its presumed action of increasing muscle blood flow due to its possibly superior systemic delivery of arginine (a nitric oxide precursor), compared to arginine itself.5 L-citrulline also may influence the production of ATP from carbohydrate metabolism during intense exercise. Two studies have shown L-citrulline to confer no performance benefit—one of these two showed decreased performance treadmill running time to exhaustion (3 g, three hours before the run, or 9 g over 24 hours before the run).6 The other study had university athletes take watermelon juice (with an approximately 6-g payload of L-citrulline), 6 g of L-citrulline mixed into a drink with approximately 53 g of sucrose, or a sucrose placebo, one or two hours before bench pressing and treadmill running to exhaustion;7 blood flow also was unchanged by either L-citrulline source.

On the other hand, acute dosing with citrulline malate (8 g; one hour pre-workout) has been shown to improve leg-centric and pectoral/chest-centric resistance training performance among resistance trained males.8,9 Collectively, these studies reinforce the malate form of citrulline and intensively question any sports nutrition “energy" merit of L-citrulline alone.

For more information on energy bioactives applied to sports nutrition, read the full article, “Sports Nutrition: Energy Bioactives," in INSIDER’s free Sports Nutrition Energy Digital Issue.

Anthony L. Almada, MSc, FISSN, has collaborated on more than 50 university-based human studies assessing sports nutrition products. He was the co-founder of EAS (which introduced creatine to North America in 1993) and is the CEO of Vitargo Global Sciences Inc.

References

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3. Antonio J and Ciccone V. “The effects of pre versus post workout supplementation of creatine monohydrate on body composition and strength." J Int Soc Sports Nutr 2013;10:36.

4. Candow DG et al. “Strategic creatine supplementation and resistance training in healthy older adults." Appl Physiol Nutr Metab. 2015;40:689-94.

5. Schwedhelm E, et al. “Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism." Br J Clin Pharmacol 2007;65:51-9.

6. Hickner R et al. “L-citrulline reduces time to exhaustion and insulin response to a graded exercise test."  Med Sci Sports Exerc. 2006 Apr;38(4):660-6.

7. Cutrufello PT et al. “The effect of l-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance." J Sports Sci 2015;33:1459-66.

8. Wax B, at al. Effects of supplemental citrulline malate ingestion during repeated bouts of lower-body exercise in advanced weight lifters. J Strength Cond Res 2015;29:786-92.

9. Perez-Guisado J, Jakeman PM. Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. J Strength Cond Res 2010;24:1215-22.

10. Beyond the obvious: Future innovations in sports nutrition. Almada AL. Nutritional Supplements in Sports and Exercise. Second edition. Greenwood M, et al., Eds. Springer International, New York, 2015.

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12. Childs E, de Wit H. Subjective, behavioral, and physiological effects of acute caffeine in light, nondependent caffeine users. Psychopharmacology 2006;185:514–13. The effects of supplementation with p-synephrine alone and in combination with caffeine on resistance exercise performance. J Int Soc Sports Nutr 201512:35.14.

14. Rainnie AS, et al. The efficacy of ingesting low-dose capsaicinoids for ergogenic benefit. Appl Physiol Nutr Metab 2015;40:S53-4.