Another popular nutritional ergogenic aid is the branched-chain amino acids (BCAAs): leucine, isoleucine, and valine. They are prevalent in both protein/meal replacement powders and energy drinks. Table 11.3 shows the typical amino acid composition of some common protein preparations. The RDA for BCAAs is less than 3 g per day, although supplementation studies frequently utilize 5–20 g per day in tablet form and 1–7 g per liter in solutions [40]. The theory behind BCAA supplements relates to a phenomenon known as central fatigue, which holds that mental fatigue in the brain can adversely affect physical performance in endurance events. The central fatigue hypothesis suggests that low blood levels of BCAAs may accelerate the production of the brain neurotransmitter serotonin, or 5-hydroxytryptamine (5-HTP), and prematurely lead to fatigue [41]. Tryptophan, an amino acid that circulates in the blood, is a precursor of serotonin and can be more easily transported into the brain to increase serotonin levels when BCAA levels in the blood are low because high blood levels of BCAAs can block tryptophan transport into the brain [42]. During endurance exercise, as muscle and liver glycogen are depleted for energy the blood levels of BCAAs also decrease, and fatty acid levels increase to serve as an additional energy source [43]. The issue with extra fatty acids in the blood is that they need to attach to albumin as a carrier protein for proper transport. In doing so, the fatty acids displace tryptophan from its place on albumin and facilitate the transport of tryptophan into the brain for conversion to serotonin [44]. Thus, the combination of reduced BCAAs and elevated fatty acids in the blood causes more tryptophan to enter the brain and more serotonin to be produced, leading to central fatigue [45].

For endurance athletes competing in long races (more than 2 h), BCAA supplements can help delay central fatigue and maintain mental performance [46]. One study looked at BCAA supplementation during a marathon and showed improved performance for slower runners (3+ hours) but no effect on faster runners (less than 3.05 h) [2]. Chronic BCAA supplementation (2 weeks) has also been shown to be effective in improving time-trial performance in trained cyclists [39]. In addition to their effects on prolonging endurance and delaying central fatigue, BCAA supplements have been associated with a reduced rate of protein and glycogen breakdown during exercise and an inhibition of muscle breakdown following exhaustive endurance exercise [41, 47]. A number of studies in trained and untrained subjects, however, have shown no effect of BCAA supplements on exercise performance or mental performance [48]. In some cases, BCAAs have been compared with carbohydrate supplementation during exercise, with results showing they both delay fatigue to similar degrees [43]. The data on BCAA supplements are mixed, but they clearly do not harm endurance performance. Some studies have shown positive adaptations, whereas others have displayed no effect. Biological variations may determine whether BCAAs are effective for the individual athlete and the particular sport or event.

Pharmacological sports ergogenics are drugs designed to function like hormones or neurotransmitter substances that are found naturally in the human body. Like some nutritional sports ergogenics, pharmacological sports ergogenics may enhance physical power by affecting various metabolic processes associated with sport success. The most popular pharmacological sports ergogenics used by endurance athletes today are caffeine and ephedrine. Caffeine is theorized to enhance endurance performance by first stimulating the central nervous system (CNS) and increasing psychological arousal. Caffeine also stimulates the release of epinephrine from the adrenal glad, which may further enhance physiological processes such as cardiovascular function and fuel utilization. The caffeine-mediated increase in free fatty acid mobilization and sparing of muscle glycogen is the primary theory underlying the ergogenic effects of caffeine on prolonged endurance activities. Lastly, caffeine increases myofilament affinity for calcium and/or increases the release of calcium from the sarcoplasmic reticulum in skeletal muscle, resulting in more efficient muscle contractions.

In one of the first studies conducted on caffeine’s ergogenic effect, subjects consumed decaffeinated coffee or decaffeinated coffee combined with 330 mg pure caffeine 60 min prior to exercise. Time to exhaustion was more than 19 % longer in the caffeine trial than in the decaffeinated trial [49]. The authors concluded that the performance increase was more likely due to the increase in fat oxidation, as muscle glycogen was not measured. Another study measured muscle glycogen utilization and found that caffeine prior to exercise reduced muscle glycogen utilization by 30 % [50]. A later study supported the muscle glycogen-sparing hypothesis by reporting a 55 % decrease in muscle glycogenolysis during the first 15 min of exercise in the caffeine trial [51]. The decrease in glycogenolysis during the initial stages of exercise allowed more glycogen to be available during the final stages, subsequently leading to an increased time to exhaustion. Further support of caffeine supplementation was demonstrated in a study examining the effects of acute caffeine ingestion (6 mg/kg) on prolonged, intermittent sprint performance on a cycle ergometer. The total amount of sprint work performed during the caffeine trial was 8.5 % greater than that performed during the placebo trial [52]. The authors concluded that acute caffeine ingestion can significantly enhance performance of prolonged, intermittent sprint ability in competitive male, team-sport athletes.

Despite the overwhelming ergogenic evidence of caffeine supplementation, caution should be exercised when considering its use. A recent study showed that in healthy volunteers a caffeine dose corresponding to two cups of coffee (200 mg) significantly decreased blood flow to the heart during exercise by 22 %. That percentage increased to 39 % for people exercising in a high-altitude chamber, which the researchers used to simulate the way coronary artery disease (CAD) limits the amount of oxygen that gets to the heart [53]. Because an increase in blood to the heart is necessary for aerobic activity, the findings theoretically suggest that caffeine could slow the body down. The study’s purpose, however, was not to look at whether caffeine could help athletes go faster or farther. Instead, it set out to investigate the effect caffeine has on blood flow to the heart. It can thus be concluded that people with CAD or those at a high risk for heart disease should avoid loading up on caffeine before a run or at least check with their primary care physician first.

Though a popular concern of caffeine ingestion has been for dehydration, recent research by Killer et al. (2014) appears to dispel this myth [54]. Using a counterbalanced, crossover design, 50 male coffee drinkers consumed either 4 × 200 mL of coffee containing 4 mg/kg caffeine or water. By examining total body water and deuterium oxide techniques, no significant changes in total body water were noted between trials across any hematological markers or in 24 h urine volume following caffeine ingestion; thus coffee provides similar hydrating qualities to water when consumed in moderation [54].

A final note in regard to caffeine supplementation is that the International Olympic Committee lists caffeine as a banned substance. Although some amount of caffeine is allowed because of its occurrence in foods, a urinary level that exceeds 12 μg/ml results in a doping violation and possible disqualification or suspension. Therefore, it is recommended to keep the daily caffeine intake to less than 3 mg/kg body weight (i.e., 50–200 mg of caffeine). Table 11.4 lists typical caffeine content in common beverages, pills, and other products.