Background On Nitric Oxide
Ergogenic aids are a huge market in the sports performance and fitness community. Every product is the advertised to benefit performance. Nitric oxide (NO) is a labile lipid soluble gas synthesized in many body locations which are believed to improve athletic performance. NO is an important modulator of blood flow and mitochondrial respiration during physical exercise. Moreover, the increase in oxygen is in blood flow may speed recovery.
Many of the supplements on the market are linked with NO production but are 'cocktails' of a variety of substances. In fact, the NO ingredients (L-arginine and L-citrulline) are typically low in many commercial products. Some natural foods (beetroot juice) also contain NO, but research is contradictory on its effectiveness.
This article attempts to focus on pathways and donors of NO synthesis and reviews the effectiveness of NO supplement on performance.
What was done
All the research article databases were searched for articles on NO and performance.
L-arginine is a proteinogenic amino acid found in seafood, watermelon juice, nuts, seeds, algae, meat, etc. L-arginine is transitioned in the body (kidney) to L-citrulline. L-arginine helps form NO as L-arginine combines with oxygen to for NOS. Little research has been done on L-arginine as a supplement alone, but the research done has found no improvement in performance. However, L-arginine in a combination of other components could induce benefit in untrained or moderately trained subjects.
L-citrulline is a non-essential alpha-amino acid is produced in the body by 1) synthesized from glutamine in enterocytes by condensation of orthithine and carbnyl phosphase in a reatinon catalyzed by orthinine carbaml-transferase 2) L-citrulline produced via the conversion of L-arginine to NO in a reaction catalyzed by NOS enzymes. Only one studied has assessed L-citrulline supplementation on performance and found it hinders performance. However, when L-citrulline is combined with malate, NO metabolites may increase, but this has not been correlated with improved performance.
Current data suggest that L-arginine supplementation, in a combination of other components, may be effective in moderate to untrained subjections for enhancing cardiorespiratory adaption and tolerance to exercise. However, no relationship between these findings and NO synthesis has been established.
It seems training status is an important variable for NO, as minimal improvement has been found in NO supplementation in highly trained athletes.
Also, almost all the studies have been done in young male subjects, therefore more research on diverse populations is necessary.
NO supplementation appears to not be beneficial for trained athletes, but may be mildly beneficial in low to untrained people.
- Bescós R, Sureda A, Tur JA, Pons A. The effect of nitric-oxide-related supplements on human performance. Sports Med. 2012 Feb 1;42(2):99-117.
Originally Posted June 2012