Coffee, Tea and Me

The effects of caffeine on running performance

Monday, March 1, 2004, 12:00 am

Caffeine is a ubiquitous drug that you almost undoubtedly consume in coffee, soft drinks, tea or chocolate. Caffeine has a wide variety of effects on the body, some of which may enhance running performance. But, like any drug, caffeine also has side effects, and some of them can be detrimental, particularly in high doses.

Can caffeine help you race better? Several hundred studies have been conducted on the effects of caffeine on sport performance, and the answer is: probably. Studies with runners and cyclists have shown that caffeine can improve performance in the lab during simulated events lasting from five minutes to several hours. Extrapolating from run-to-exhaustion studies in the lab, the likely benefit of taking caffeine is in the range of 1 to 2 percent (20 to 50 seconds in a 10K, 90 seconds to four minutes in a marathon).


Hardly any studies have investigated the effects of caffeine on race performance, however, so we do not really know if it can help improve your next 10K or marathon. One reason that caffeine may not work as well during races as in lab tests is that caffeine increases epinephrine (adrenaline) levels, which are also stimulated by the excitement of competition, so the caffeine may be redundant during a race.

How does caffeine affect running performance? Despite all the research, no one is sure. The conventional wisdom is that caffeine improves endurance performance by increasing the activity of enzymes for fat metabolism. By using relatively more fat, the runner’s glycogen stores are used more slowly, so they last longer. This theory is under question, however, because caffeine also improves performance in events that last only a few minutes, in which glycogen depletion is not a factor.

The primary effect of caffeine in improving endurance performance may be stimulation of the central nervous system, which increases alertness and concentration. There is intriguing evidence that central nervous system stimulation reduces perception of effort so that a given pace feels easier. Determining how caffeine improves running performance is difficult because the metabolism of caffeine in the body is complicated, with caffeine quickly broken down into three other compounds that have a variety of effects on the mind and body.

How much caffeine is required to enhance running performance? Most of the studies that have found caffeine to improve endurance performance used 3 to 6 mg of caffeine per kg body weight taken one hour before exercise (for a 147-pound [67-kg] runner, 3 mg per kg body weight would require 200 mg of caffeine). Recent studies have also found that ingesting 1 to 2 mg per kg body weight has a positive result. Doses above 6 mg per kg body weight have increased negative side effects and do not lead to greater improvements in performance.

Coffee contains many chemicals other than caffeine, and a 1998 study found that drinking coffee did not have the same performance-enhancing effects as pure caffeine. Energy drinks are not a good choice because they typically contain many other substances and may not be readily absorbed. If you choose to take caffeine for performance enhancement, it is probably better to take a caffeine tablet so you can regulate the dose more precisely.

What are the risks? As of January 2004, caffeine is no longer a restricted drug by the World Anti-Doping Agency. There are risks, however, in taking caffeine before a race. The side effects include headaches, dizziness, anxiety, gastrointestinal distress, and heart palpitations. Caffeine is also a mild laxative, which can be particularly inconvenient during a race.

The side effect that is most likely to reduce running performance is caffeine’s diuretic (urine producing) effect. Caffeine may increase dehydration, which would cancel out its performance-enhancing benefits. Interestingly, taking caffeine during exercise does not seem to increase urine formation, and caffeine is less of a diuretic in individuals who are regular caffeine users.

The positives and negatives of caffeine vary between individuals. A dose that has few side effects and improves performance for one runner may cause marked side effects and reduce performance in you (and the effects may even vary from day-to-day). If you have any medical conditions, such as high blood pressure, check with your doctor before using caffeine.

My view is that runners should only consider using caffeine if they are already training hard and intelligently, have an excellent diet, and are working to optimize various other aspects of their lifestyle. If you decide to try caffeine to improve your race performance, start with a low dose and do not experiment in an important race.