Is your cup of coffee giving you an unfair edge?
The effects of caffeine on the performance of athletes have been studied and described for years. A number of hypotheses have been suggested to explain these effects within a range of sports. But is caffeine just a legal, and socially acceptable, form of doping? Should certain groups: elites, amateurs, or adolescents, be banned or discouraged from using caffeine?
The strongest evidence for the enhancing effects of caffeine on exercise is in endurance sports (hence, the personal interest I have in this topic). Studies have reported that 3-9 mg of caffeine per kilogram of body weight, consumed one hour prior to exercise, by highly trained runners and cyclists, enhanced their laboratory-measured endurance performances. Therefore, a 160 pound (72.6 kg) person would consume 218-653 mg of caffeine to get 3-9 mg of caffeine per kg of body weight. To put this in familiar terms, a 12 ounce (“tall”) Starbucks brewed coffee contains 260 mg caffeine and the same-sized Starbucks latte contains 75 mg. In contrast, a 12 ounce (“small”) McDonald’s coffee contains 109 mg of caffeine. One 12 ounce Starbucks brewed coffee or two 12 ounce McDonald’s brewed coffees would provide enough caffeine to be in the dosage range of 3-9 mg/kg for a 160 pound person.
The mechanism to explain these improvements in endurance is unclear. It has been demonstrated that muscle glycogen (an energy source) is spared early during submaximal exercise after caffeine doses at a range of 5-9 mg/kg. However, at the lower end of the range of caffeine doses described above (3 mg/kg), there is no evidence that muscle glycogen is spared. Therefore, glycogen sparing is not a complete explanation for the ergogenic effects of caffeine on endurance exercise.
In addition to effects on endurance exercise, caffeine has been shown to improve performance during short-term exercise, lasting approximately 5 minutes, at 90-100% maximal oxygen uptake, in laboratory tests. Hypotheses about the mechanisms underlying this improvement include enhancement in contraction of muscles, provision of anaerobic energy to muscles, or an effect upon the central nervous system related to sensation of effort. Sprint performances of up to 90 seconds of intense exercise do not appear to be affected by caffeine.
Caffeine is defined as a “controlled or restricted substance” by the International Olympic Committee, which limits the amount of caffeine in urine to 12 micrograms per milliliter of urine. It is also restricted by the US National Collegiate Athletic Association, which uses 15 micrograms per milliliter of urine as its limit. But these limits actually allow for the consumption of a great deal of caffeine. For example, if an athlete were to consume 9 mg of caffeine per kg of body weight one hour before exercise, then exercise for 60-90 minutes, and then submit a urine sample, this sample would only approach the limit of 12 micrograms per milliliter of urine. This is about 29 ounces of Starbucks brewed coffee or about 69 ounces of McDonald’s brewed coffee! On the other hand, doses of caffeine of greater than 6 mg/kg of body weight can lead to a higher chance of side effects such as anxiety, jitters, inability to focus, gastrointestinal upset, insomnia, irritability, and, at higher doses, hallucinations and heart arrhythmias. Therefore, the optimal dose to enhance performance and minimize side effects appears to be 3-6 mg of caffeine per kg of body weight.
With some basic information about dosing, it is easy for endurance athletes to use caffeine to enhance their performances “within the rules.” However, is this fair? What if athletes are at an unfair disadvantage because of religious beliefs, unusual sensitivity to caffeine (susceptibility to migraines, for instance), or, simply, not enjoying caffeinated products? Another concern is young endurance athletes. A Canadian survey of young (11-18 years old) athletes found that 27% consumed caffeine over the previous year for the specific purpose of enhancing athletic performance. Is this an indication that caffeine is a “gateway” drug to other, much more dangerous, performance-enhancing drugs?
Posted March 4, 2015.