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By Bryan Bergman, PhD, Associate Professor of Medicine and Scientific Advisory Board Member for GU Energy Labs
The truth about caffeine
Caffeine is the most commonly-used performance aid in the world. The research indicates caffeine ingestion increases performance in both endurance, sustained high intensity, and stop-and-go, team-based sports. It has long been thought that caffeine increases performance by promoting fat mobilization from adipose tissue. Although this does happen, enhanced free fatty acid availability does not substantially change fat or carbohydrate oxidation (usage as fuel) in working muscle.
Most data suggests that caffeine actually works by stimulating the central nervous system, effectively decreasing perception of pain or effort during exercise. Additionally, caffeine can decrease fatigue during very intense exercise bouts. The combination of improved performance, decreased pain perception, and decreased fatigue make caffeine consumption an effective way to improve performance during training.
Many historical studies have found that caffeine dosing at 3-6 mg/kg body mass enhanced performance, however more recent studies showed performance benefit from more modest doses (of 1-3 mg/kg body weight). Further, several studies have reported a "dose response plateau"--or point at which its effect stabilizes--at 3 mg/kg. Therefore, modest amounts of caffeine can result in improved performance, but its incorporation into your training should not follow a “more is better” philosophy. Studies have also shown that caffeine is effective at various times--when consumed before exercise, during exercise, or after the onset of fatigue.
Does caffeine improve sports performance even when athletes habitually consume it? While this question is filled with anecdotal responses, a recent study confirmed an earlier report, answering this all-important question for the coffee junkie crowd. In 2011, Irwin et al., performed a double blind placebo controlled crossover design study in 12 male cyclists, who withdrew from caffeine for four days, or consumed a controlled amount of caffeine for four days (1.5 mg/kg body weight). Subjects then received an acute dose of caffeine (3mg/kg) 90 min before a cycling time trial. Performance time during the time trial was increased by 3 percent during acute caffeine ingestion following the four-day withdrawal period, and by 3.6 percent without the withdrawal period. These two responses were not significantly different from one another. The conclusion was that withdrawal from caffeine was not required to benefit from its performance-enhancing effects.
Coffee, of course, isn’t the only (or necessarily the best) source of caffeine. Though it plays a large cultural role in the daily lives of many athletes, it's not necessarily the best way to consume caffeine prior to exercise. An interesting study was designed to answer this question, comparing caffeine ingestion in coffee compared to caffeine ingested as a capsule. This was a well-designed, double-blind study with all the proper controls. It found that the same dose of caffeine ingested as coffee or as a capsule (4.45 mg/kg body weight) resulted in similar blood caffeine concentrations. However, only the caffeine capsule increased performance during a run to exhaustion at 85 percent VO2max! The authors concluded that there must be components of coffee that counteract caffeine's chief benefits. While these are results from only one study, it suggests that not all caffeine is created equal. The take home? Athletes may want to consider consuming caffeine in a form other than coffee in order to improve performance.
Some of you may be wondering whether caffeine in a sports drink promotes dehydration. Several studies have shown that caffeine ingested during exercise does not influence weight loss, sweat rates, urine output and plasma volume compared to water alone. This may be due to decreased kidney blood flow during exercise which is proportional to exercise intensity, leading to minimized urine production. Therefore, it appears that caffeine will not lead to diuresis if consumed during exercise, and will not contribute to dehydration.
Another ergogenic compound which has substantial data supporting its use in endurance sports is taurine--an amino acid found in most mammalian tissues, synthesized from the amino acids methionine and cysteine. It is found in highest concentrations in excitable tissues such as skeletal and cardiac muscle. Taurine has been reported to increase calcium storage and handling in muscle, resulting in the increased ability of the heart to pump blood per beat (myocardial contractility), the amount of blood pumped by the left ventricle per minute (cardiac output), and skeletal muscle function. All of these functions are helpful in endurance sports. During prolonged endurance exercise, myocardial contractility decreases and consuming taurine during this time may actually offer a remedy.
The perfect marriage
Caffeine and taurine have great potential to increase endurance-based athletic performance by decreasing perceived effort and pain perception, stimulating the central nervous system, and increasing myocardial contractility and cardiac output. An intriguing study was performed in mice, where researchers were able to isolate the individual impact of caffeine or taurine, as well as the combination of the two on running performance. They found that two weeks of daily caffeine and taurine ingestion increased running performance more than caffeine or taurine individually, as well as a placebo. The increase in running performance occurred with a decrease in circulating lactate concentration as well. This showed that caffeine and taurine together improve performance more than either ingredient alone; the combination of the two may make a potent cocktail for increased performance.
In humans, consuming caffeine, taurine, and carbohydrates increased cycling performance compared to a flavored water placebo. This study did not control for the well-known ergogenic effect of carbohydrate consumption on performance, so it is unknown which of the three and in what combination was responsible for the increased performance. Another study did not measure exercise performance, but rather examined cardiac performance during an incremental exercise test to exhaustion. Importantly, this study examined three beverages: one with carbohydrate only, another with carbohydrate and caffeine, and another with carbohydrate, caffeine and taurine. Interestingly, they reported increased stroke volume at rest after exercise with the drink containing carbohydrates, caffeine and taurine compared to the other two drinks. While we do not know if this drink also promoted increased stroke volume during exercise, the data suggests a benefit. The data is sparse for the potential benefit of taurine and caffeine on human exercise performance. However, animal studies show clear benefit, and there is circumstantial evidence supporting the combination of caffeine, taurine, and carbohydrates in a drink to improve exercise performance in humans.
The overwhelming majority of evidence suggests that caffeine and taurine individually may improve exercise performance. Several studies also suggest that consuming caffeine and taurine together during exercise will have a more positive effect on performance compared to each consumed individually. Therefore, there is solid evidence supporting the use of both caffeine and taurine to enhance performance in endurance sports.
Stay tuned for monthly "GU Fuels You" articles from our Official Nutrition Partner, GUenergy.com. Full Disclosure: GU is a paying sponsor of certain Ironman® events and/or an advertiser on certain Ironman® media properties. The foregoing article has been prepared and published here as promotional consideration under an agreement regarding such sponsorship and/or advertisement.