Acute L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance


Journal Title (Medline/Pubmed accepted abbreviation): J Appl Physiol
 
Year: 2010
Volume: Published ahead of print
Number:
Page numbers:
doi (if applicable): 10.1152/japplphysiol.00503.2010
 

Summary of Background and Research Design

Hypothesis: Dietary supplementation with arginine, a substrate for nitric oxide synthesis, might reduce the O2 cost of moderate-intensity exercise and enhance exercise tolerance during severe intensity exercise.
 
Subjects: 9 healthy, non-smoking, recreationally active adult males (mean age 26 y, mean weight 84 kg)

Design: Randomized, double-blind, crossover

Treatments : 3 days of supplementation once per day with Arginine (ARG) or Placebo (PLA).
 
ARG treatment: 500 mL water solution containing 20 g of a commercial arginine preparation. The preparation contained 6 g L-arginine, trace amounts of vitamins (E, C, B6, and B12), other amino acids and related compounds (L-glutamine, L-leucine, L-valine, L-carnitine, L-citrulline, L-cysteine, and L-isoleucine), and fructose (11 g).
 
PLA treatment: 500 mL of a blackcurrant flavor cocktail
 
Exercise treatments: Subjects 1-h after supplement ingestion. Exercise consisted of cycling on an ergometer at either moderate intensity (87 W, or 22% of peak work rate) or severe intensity (274 W, or 75% of peak work rate). On the first day of supplementation, the subjects completed two 6-min periods of moderate intensity cycling. On the second day, the subjects completed one 6-min bout of moderate intensity cycling followed by 6 min at high intensity. On the third day, subjects completed a 6-min bout of moderate intensity cycling followed by cycling at high intensity until task failure.
 

Summary of Research Findings
  • Plasma nitrite concentrate doubled in ARG (331 nM) vs. PLA (159 nM) (P< 0.05)
  • Resting systolic blood pressure was significantly lower in ARG (123 mm Hg) vs. PLA (131 mm Hg) (P<0.01)
  • Steady-state VO2 during moderate intensity exercise was reduced 7% by ARG vs. PLA (P<0.05)
  • During severe intensity exercise, the amplitude for the slow component of VO2 was reduced by ARG and the time to exhaustion was significantly lower for ARG (707 sec) vs. PLA (562 sec) (P<0.05)

Interpretation of findings/Key practice applications:

These findings indicate potential benefits of acute arginine supplementation (6 g/d) on lowering the oxygen cost of activity and improvement of exercise tolerance at higher exercise intensity. The lowered blood pressure is another positive effect. The dose is in the physiological range and could be obtained using various arginine products on the market.
 
Key limitations or additional questions associated with this study are: 1) Small sample size; 2) Presence of compounds other than arginine in the ARG treatment group for which an effect, albeit unlikely, cannot be ruled out; 3) Subject population was basically untrained, so it is not clear if benefits would also apply to a trained population; 4) Study was not designed to examine long-term effects of arginine supplementation on exercise; 5) There were no meaningful treatment-related changes in blood lactate concentrations despite the measured changes in oxygen cost of activity. Given the change in oxygen kinetics, it is not clear why blood lactate levels were not altered (e.g., better O2 delivery to working muscles = lower lactate production)
 
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