Our findings indicate that, compared to a maltodextrin placebo, none of the products tested in the present study result in effects that are statistically different with regards to exercise performance, skeletal muscle blood flow, muscle pump, HLa, NOx, or MDA. These findings clearly refute the advertisement claims for these products, at least in the context of their use to impact acute exercise performance, blood flow, muscle pump, and NOx within a controlled laboratory environment. Of course, it is possible that 1) routine use of these products may result in favorable effects in our chosen variables over time (this is especially true for such ingredients as creatine and beta alanine) and/or 2) the products may influence variables that were not measured within the present design (e.g., those influencing exercise recovery; lower body exercise performance; exercise performance assessed at a higher relative intensity). Additional study would be needed to generate such data.
It is interesting to note that the single ingredient GlycoCarn® (in addition to 16 grams of maltodextrin as used in the present design) results in similar or more-favorable effects in terms of blood flow (StO2 start of exercise; as measured by NIRS), as well as the total volume load measured during the 10 set bench press protocol. Although not of statistical significance, from a practical standpoint, the percent increases in volume load above placebo and the other supplements may be of importance to serious athletes desiring a slight performance advantage. Moreover, while a slight to moderate increase in lipid specific oxidative stress (as measured by MDA) was observed with all other conditions, the noted decrease with GlycoCarn® may be of interest to those seeking antioxidant support within a pre-workout dietary supplement. Admittedly, the importance of these subtle differences in blood flow, total volume load, and MDA in relation to exercise performance and recovery are unknown at the present time and require additional study. Hence, athletes will need to consider the cost to benefit ratio when making such a decision as to whether or not to use an ingredient such as GlycoCarn®.
While several anecdotal reports exist indicating a performance benefit when using the products tested in the current study, we are unaware of any peer reviewed scientific manuscripts that examine any of these products. Based on the caffeine and other supposed performance aids contained within these products, we believed that it would be possible that a performance effect would be observed. However, because the actual dosage of ingredients contained within the products is unknown within a proprietary blend (see Figures 1, 2, and 3), it is possible that the actual amount of caffeine and other ingredients is simply too low to promote an ergogenic effect. In fact, studies using caffeine to improve resistance exercise performance have been mixed, as noted in a recent comprehensive review . One recent study found no effect of a caffeine containing dietary supplement on resistance exercise performance, despite using a relatively high dosage of caffeine (400mg) . Even this amount, which may not be adequate for many individuals, would correlate to approximately 5mg∙kg-1 for subjects in the present study (based on a mean body mass of 80kg). Although not possible to determine from looking at the product labels, based on the lack of a performance effect, it is doubtful that the caffeine dosage contained within the tested products is adequate.
Aside from caffeine (and agents such as creatine and beta alanine--which need to be consumed on a regular basis in order to provide ergogenic effects), the tested products contain very few additional ingredients that have been shown in human clinical research studies to provide an ergogenic effect. Moreover, as with caffeine, the dosage of each specific ingredient may be too low to provide any benefit. Logic dictates that if a single serving has a weight of 20 grams and half of the serving is comprised of carbohydrate and flavoring, little weight remains for each of the additional 30-60 ingredients. Our data clearly show that ingredient number has no influence on product effectiveness. In fact, the use of a very inexpensive maltodextrin powder yields similar effects as all products used for comparison in this design. Considering a per-serving cost of approximately $2 (when using the amount of powder included within the present design), the reasonable choice for an athlete may simply be to use a carbohydrate powder. That being said, it should be reiterated that the tested products may provide benefit outside of the measures tested in the present design, and because of this, they may in fact be superior to maltodextrin with regards to other measures (as well as our included measures, albeit tested using a different study design). This important issue should be considered by athletes and sport nutritionists when making such a decision.
Pertaining to ingredients, the amino acid L-arginine is a component of all three supplements used in the present study, as well as most other "nitric oxide stimulating" dietary supplements sold on the market today. While L-arginine is indeed the precursor to nitric oxide biosynthesis and has been associated with enhanced vasodilatation [27, 28], the rationale for inclusion of L-arginine within pre-workout supplements is primarily based on research using intravenous L-arginine, often at dosages as high as 20-30 grams, and not oral intake of L-arginine at a dosage of 3-5 grams. Studies comparing intravenous and oral L-arginine indicate no effect of oral L-arginine on vasodilatation, possibly due to variance in oral L-arginine bioavailability . Additionally, studies involving oral intake of L-arginine at dosages from 10-20 grams indicate no benefit with regards to increasing nitric oxide or enhancing blood flow [30–32].
A further problem with the use of L-arginine as a nitric oxide stimulator is that L-arginine availability is likely not the rate limiting component in this reaction. Rather, nitric oxide synthase enzymes appear most important . Two recent investigations provide support for this point. In one study, 3 grams per day of L-arginine was used and found not to increase nitric oxide availability, but rather reduced exercise time to fatigue in patients with peripheral arterial disease . Another study involved supplementation with 6 grams per day of L-arginine in exercise trained men, and noted no effect on nitric oxide production, lactate and ammonia metabolism, or performance in intermittent anaerobic exercise . Based on the above, adding L-arginine to a pre-workout powder for purposes of increasing nitric oxide is not supported by the available literature.
One final consideration is the knowledge that while brief production of nitric oxide at low (nanomolar) concentrations favor enhanced blood flow, high concentrations favor cell cycle arrest and apoptosis. Moreover, it is important to keep in mind that high levels of nitric oxide can react with superoxide anion to form peroxynitrite, a very harmful chemical  involved in nitrosative stress . Therefore, dramatically increasing nitric oxide via use of nutritional supplements, assuming this is actually possible, does not appear desirable. Considering the findings presented here indicating a lack of increase in nitrate/nitrite, none of the tested supplements would be thought to promote an increase in peroxynitrite.
A few previous studies have used the measure of NIRS to assess tissue blood flow during resistance exercise [19–21]. Our findings are similar to those previously presented, indicating a significant decrease in StO2 from the start to the end of the exercise set, with a return to pre-set values within one minute of exercise recovery (data not shown). We also show here that as an exercise session continues, blood flow to the muscle is increased, as evidenced by the increase in StO2 at the start of exercise from set one to set two and beyond (Table 4). However, despite popular writings within fitness and bodybuilding publications indicating that nitric oxide controls skeletal muscle blood flow during exercise, scientific evidence refutes this notion, demonstrating that nitric oxide plays only a non-obligatory role in exercise hyperemia . Our data support this notion, in that blood flow as measured using StO2 (start of exercise) increased approximately 10% from set one to set 10, despite the finding that NOx remained essentially unchanged from pre- to post-exercise (Table 7). As an aside, we believe that the inclusion of NIRS allows for the accurate measure of muscle tissue oxygen saturation, with very little error. This device may have value in future experiments designed to approximate muscle tissue blood flow with and without the use of dietary supplements.
In relation to muscle blood flow, many anecdotal reports indicate a more robust muscle pump when using pre-workout products designed to increase nitric oxide. Our data using a subjective rating scale for muscle pump, in addition to circumference measures, indicate that no such effect is observed in a controlled laboratory environment. In this regard, a placebo effect is certainly possible , leading individuals to believe that such an effect is absolute; as many individuals using such products are inundated with advertisements claiming increased blood flow and muscle pump. At the present time, these claims remain unsubstantiated. This phenomenon is described in detail within a recent review of nitric oxide dietary supplements for sports . Admittedly, our measures of muscle pump, although performed to the best of our known abilities, are rather crude. Perhaps if a more sophisticated measure were available to assess muscle pump, we may have noted condition differences. However, even if this were the case, the main findings of no difference in performance measures may overshadow any potential effects for muscle pump.
Our findings for no change in NOx with GlycoCarn® refute our initial work, in which we have noted an increase in both resting  and stress-induced NOx . The discrepancies in findings may be due to the fact that in the present design we simply provide a single serving of GlycoCarn® prior to exercise, whereas our prior work involved four  or eight  weeks of GlycoCarn® treatment. Likewise, our data are in opposition to the work of Jacobs and colleagues  who recently reported an improvement of 2.6-15% in high intensity cycle sprint performance with 4.5 grams of GlycoCarn® compared to a placebo. In this same study these investigators also noted an approximate 16% decrease in post-exercise blood HLa with GlycoCarn® compared to placebo. Differences in the exercise protocol likely contributed to the discrepancy in findings between the two studies. Finally, we have noted previously that GlycoCarn® results in lower resting MDA following chronic intake . The present study extends those findings by noting a decrease, albeit statistically insignificant, in MDA from pre- to post-exercise, indicating a potential antioxidant effect. Interesting to note, this favorable effect of GlycoCarn® on MDA reduction was associated with the highest StO2 at the start of exercise, indicating a possible association between increased blood flow and decreased lipid peroxidation. The converse was also true, as SUPP1 demonstrated the greatest increase in MDA from pre- to post-exercise, while displaying the lowest StO2 at the start of exercise and the greatest drop in StO2 from the start to the end of exercise. These findings support the idea that exercise-induced hypoxia is associated with increased lipid peroxidation, likely due to increased free radical production .
It is possible that chronic treatment of GlycoCarn® may result in more robust changes in MDA or other markers of oxidative stress. Using a different stress protocol (handgrip dynamometry vs. resistance exercise), we have reported recently that four weeks of GlycoCarn® treatment at a daily dosage of 4.5 grams in resistance trained men results in a 45% decrease in oxidized to total glutathione ratio . Additional work is needed to determine the antioxidant effect of chronic GlycoCarn® administration following resistance exercise, and to determine whether or not such an effect translates into improved post-exercise recovery.
One explanation for our lack of a performance effect for the chosen supplements, in addition to GlycoCarn®, could be our specific sample of subjects. That is, they may have been non-responders to treatment, as has been reported previously for a variety of sport supplements including caffeine , creatine , and GlycoCarn®, in terms of nitrate/nitrite . If this were true, it is possible that a different group of subjects may have responded positively to treatment. This should be considered when athletes are contemplating the use of such products. For example, of our 19 subjects, 11 responded positively to GlycoCarn® in terms of total volume load, with a mean improvement above placebo of 12.6%. This is in opposition to the 3.3% improvement above placebo when including all 19 subjects in the analysis. Of course, serial studies are needed to note the number of individuals who consistently and reliably respond to treatment. As with most nutritional supplements, the simple reality is that some individuals will likely respond well to treatment (i.e., experience a noted improvement in performance and/or some other variable of interest), while others will likely experience no benefit. In this case, individual experimentation is needed.