Some of the more common ingredients do show solid scientific evidence for efficacy when examined alone in various studies. Examples of this include creatine, amino acids, and beta alanine. But in the pre-workout supplements, the precise amount of these nutrients is rarely listed, and the studies showing their efficacy did use specific amounts, such as 5 grams a day of creatine, 4.5 grams a day of beta alanine and so on. The odds are that the products don't contain effective levels of these nutrients, since such levels aren't listed on the product labels.Perhaps the most popular of the pre-workout supplements are those touted to boost the production of nitric oxide (NO).
NO supplements are said to increase levels of nitric oxide in the blood, which is thought to boost exercise performance and recovery. The primary ingredient in NO boosters is the amino acid, L-arginine. Arginine is indeed the primary precursor for the synthesis of NO in the body, but it isn't the limiting factor. The limiting factor that determines just how much NO is synthesized from arginine are various nitric oxide synthesizing enzymes. You could ingest a pound of arginine, but if the NO enzymes aren't working, the answer is no for NO synthesis.The research that did show increased levels of NO from arginine intake involved Intravenous administration of large doses, 20-30 grams of arginine. The average dose in a NO boosting supplement is 3-5 grams, and studies have shown no increases in NO after oral intake of arginine, even at doses of 10-20 grams.
An overlooked aspect of NO supplements is that recent studies found that NO produced during exercise is not the main determinant of muscle blood flow during exercise.Thus, the entire premise of using NO boosting supplements appears to be questionable. But as we will see later, there is an advantage to boosting NO in a different manner than using NO supplements that may actually work to increase exercise efficiency. One other thing to consider is that you would never want to get an unusually high level of NO rapidly produced in the blood. High concentrations of NO promote cell cycle arrest and apoptosis. In simple terms, too much NO kills cells. In addition, high levels of NO react with free radicals called superoxides to form the potent radical, peroxynitrite, which is quite harmful to cells.
A new study compared three multi-ingredient pre-workout formulas with a supplement containing glycine propionyl L-carnitine or glycocarn, and a maltodextrin (carbohydrate) placebo. Glycocarn was used in the study for two reasons: 1) previous studies in which gycocarn was used for 4-8 weeks showed an 18% increase in NO; 2) the primary author of the study was a paid consultant for companies that sell glycocarn products. The study tested the effects of the products in 19 experienced resistance-trained men, who engaged in tests for muscular power and endurance before and after using the supplements or the placebo. The study included measurements of muscle oxygen saturation (MOS), blood nitrate and nitrite, which measures levels of NO; lactate, and a marker for oxidation of fats. The results showed that glycocarn increased muscle oxygen saturation more than the pre-workout supplements.None of the supplements showed any effects on blood NO levels, although the glycocarn lowered the level of the oxidation marker by 13.7%, while this marker increased with all the other supplements and the placebo.The Glycocarn also led to an increase in total exercise volume load greater than the other supplements and the placebo.None of the subjects reported any increase in muscle pump.
Another new study examined whether dietary precursors for NO synthesis in the body known as nitrates can affect exercise intensity. These nitrates are found in various fruits and particularly in vegetables. The study involved seven men, ages 19 to 38, who consumed either 500 milliliters of beet root juice or a placebo for six days prior to engaging in tests involving low and high exercise intensity levels. Beet root juice is rich in nitrates, and previous studies showed that it appears to increase exercise efficiency, an effect attributed to increased NO production. The study found that drinking beet juice resulted in a reduced oxygen cost during high and low exercise intensity, which led to a reduced ATP cost of muscle force production. In simple terms, drinking the beet juice provided an ergogenic effect through sparing the immediate source of energy for muscle contraction, ATP, along with sparing muscle levels of phosphocreatine, which explains the higher ATP levels. This would result in an increased ability to tolerate a high intensity level of exercise for a longer amount of time. And guess what: beet juice is a lot cheaper than those fancy pre-workout supplements!
RJ, et al. Comparison of pre-workout nitric oxide stimulating dietary supplements on skeletal muscle oxygen saturation, blood nitrate/nitrite, lipid peroxidation, and upper body exercise performance in resistance trained men.J Int Soc Sports Nutr 2010;7:16.
Bailey SJ, et al. Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercises in humans.
