L-arginine Lowers Blood Pressure and Improves Endurance

Summary
Improvement of exercise performance and stamina with specific dietary supplementation is an interesting area of research. Oxygen consumption increases during exercise. Nitrates are substances that are required in metabolizing oxygen. Recent research has shown that increasing dietary nitrate ingestion led to better exercise endurance and efficiency. The current study found that if taken before the beginning of exercise, L-arginine, an amino acid that gives rise to nitric oxide, also significantly improves exercise performance and tolerance to the level of intense exercise.

Introduction
Oxygen uptake by lungs increases proportional to the intensity of exercise. Effective utilization of oxygen by the body is the key to improved exercise performance. Nitric oxide (NO) is a molecule critical in the conversion of inhaled oxygen into chemicals that provide energy to muscles. The levels of nitric oxide influence exercise tolerance. Nitrates (NO3) are basic chemical substances from which nitric oxide is synthesized by the body. Substances rich in nitrates are known to yield more nitric oxide in the body. L-arginine is an amino acid rich in nitrates. This study was designed to test the idea that supplementation with L-arginine just before the starting exercise would be useful in improving exercise performance.

Methodology
•    Nine healthy recreationally active men, with a mean age of 26 years, participated in this study, during which they maintained their normal daily activities and diet.
•    Participants were randomly given two drinks to consume: (1) a solution containing 6 grams of L-arginine in 500 ml of water and (2) 500 ml of a blackcurrant-flavored cordial, containing no L-arginine.
•    One hour after having the drink, the subjects participated in baseline and high-intensity cycling exercises.
•    Blood pressure, heart rate, volume of inspired/expired air and the oxygen and carbon dioxide of expired air were measured. Levels of plasma nitrites (NO2), nitrous oxide and lactates were evaluated by blood tests.

Key findings
•    Plasma nitrite concentration was over three times greater in people receiving L-arginine than in the control group.
•    Systolic blood pressure was significantly reduced in the L-arginine group.
•    During moderate-intensity exercise, oxygen uptake was reduced by 7% in the L-arginine group as compared to the control group.
•    Exhaustion was delayed in L-arginine group, as compared to those in the placebo group, indicating increased endurance.

Shortcomings
This study is in contrast to past reports. Earlier studies utilized lower amount of L-arginine supplementation. It was taken frequently during the day rather than as one large dose of supplementation just before the exercise. These could be the reasons for the difference in the findings. A shortcoming is that there is a very small possibility that the L-arginine supplement used in this experiment contained trace amounts of other substances that may have contributed to the results.

Conclusions
Nitric oxide (NO) is critical in effective metabolism of the oxygen inhaled during exercise. Increased availability of nitric oxide through dietary L-arginine supplementation right before exercising extends the time to exhaustion during severe-intensity exercise. It also lowers blood pressure during exercise. The study authors state that though the exact means of this is not yet understood, it is probably due to an increased supply of oxygen to the muscles and the effect of nitric oxide on the efficiency of muscle contraction “and/or mitochondrial function.” Future studies could elucidate the precise mechanisms of this effect and present L-arginine as a wonderful dietary supplement.

For More Information:
L-arginine Supplementation Improves Endurance and Exercise Tolerance
Publication Journal: Journal of Applied Physiology, August 2010
By Stephen J. Bailey; Paul G. Winyard; School of Sport and Health Sciences and the Peninsula College of Medicine and Department of Dentistry, University of Exeter, UK

*FYI Living Lab Reports Are Summaries of the Original Research.
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