A number of studies have shown significant performance increases in various endurance disciplines, including running, following caffeine ingestion. In one study, elite runners improved their time in a treadmill run to exhaustion by 1.9 percent with caffeine. Caffeine boosted time to exhaustion in a cycling test by 15 minutes in another study. And in a study involving swimmers, caffeine was found to enhance performance in maximal-effort swims of up to 25 minutes' duration.

How does the world's most widely used drug achieve these effects? It appears caffeine enhances performance in shorter events by stimulating the nervous system in ways that enable the muscles to contract faster and more efficiently. In longer events, caffeine delays fatigue by reducing the athlete's perception of effort. Specifically, it increases the concentration of hormone-like substances in the brain called ß-endorphins during exercise. The endorphins affect mood state, reduce perception of pain, and create a sense of well-being.

Caffeine has also been found to delay fatigue during exercise by increasing the level of free fatty acids in the bloodstream and thereby boosting fat burning and conserving muscle glycogen (which is the limiting fuel source for muscle work). This latter effect of caffeine used to be considered the major mechanism by which it enhanced endurance performance, but it is now known to be a minor factor. In fact, for those who normally maintain a high-carbohydrate diet, it is virtually a non-factor.

Caffeine is a diuretic, meaning that it increases urine production, which could theoretically exacerbate dehydration during exercise. However, exercise negates this effect. In a recent scientific review, researchers from the University of Connecticut wrote, "Dietitians, exercise physiologists, athletic trainers and other sports medicine personnel commonly recommend that exercising adults and athletes refrain from caffeine use because it is a diuretic, and it may exacerbate dehydration and hyperthermia." However, "contrary to popular beliefs... caffeine consumption does not result in... water-electrolyte imbalances or hyperthermia and... reduced exercise-heat tolerance."

When and How

Runners commonly take caffeine in pill form (proven to be more effective than equal amounts of caffeine consumed in coffee) 30 to 60 minutes before races to enhance competitive performance. What's the optimal amount? The ergogenic effect of caffeine is dose-dependent. The maximum effect is seen with doses of 5 to 6 milligrams per kilogram of body weight. For a 150-lb runner this translates to roughly 340 to 400 mg, or the amount of caffeine you'd get in 14 to 17 oz. of drip brewed coffee. The minimum amount of caffeine the average runner must consume for a measurable ergogenic effect is about two mg per kilogram of body weight.

It makes less sense to use caffeine as a daily workout performance enhancer, for two reasons. First, workouts are seldom maximal efforts, and the rationale for caffeine supplementation is to enhance maximal performance. Second, the ergogenic effects of caffeine consumption decrease with habituation. For this reason, if you are a regular coffee drinker, you should cease coffee consumption four to six days before participating in a race.

Caffeine and Health

In moderation, caffeine consumption does not cause any health problems. In fact, a daily cup of joe is good for you. The health benefits of coffee come from its caffeine content and its unique blend of antioxidants. According to Harvard Medical School, "Studies show that the risk for type two diabetes is lower among regular coffee drinkers than among those who don't drink it. Also, coffee may reduce the risk of developing gallstones, discourage the development of colon cancer, improve cognitive function, reduce the risk of liver damage in people at high risk for liver disease, and reduce the risk of Parkinson's disease."

However, heavy caffeine use can cause or exacerbate problems ranging from headache to insomnia, and it is possible to become physically dependent on the drug. Caffeine is especially harmful when used as a means to stimulate artificial wakefulness or energy in those suffering from conditions such as chronic fatigue. So if you do like caffeine, limit yourself to one mug of coffee or green tea in the morning. Those who rely on regular "caffeine injections" throughout the day are well advised to cut back.

Caffeine and Sports Drinks

A new alternative to taking a single large dose of caffeine prior to racing is to consume a caffeinated sports drink throughout races. In a recent study, conducted at the University of Birmingham in England, researchers looked at the effect of caffeine on exogenous carbohydrate oxidation (i.e. the rate at which carbs consumed in a supplement are burned) during exercise. Cyclists received either a six percent glucose solution, a six percent glucose solution plus caffeine, or plain water during a two-hour indoor cycling test. Researchers used indirect calorimetry to measure the amounts and proportions of fat and carbohydrate oxidized during the test.

They found that the rate of exogenous carbohydrate oxidation was 26 percent higher in the cyclists receiving carbs with caffeine than in those receiving carbs without caffeine. The study's authors concluded that caffeine may have increased the rate of glucose absorption in the intestine, providing fuel to the working muscles more quickly. The likely effect on performance is the ability to work harder for a longer period of time without becoming fatigued.

Another recent study looked at the effects of consuming a caffeinated sports drink on performance in a warm environment. Sixteen highly trained cyclists completed three trials. Subjects cycled for 135 minutes, alternating between 60 percent and 75 percent VO2max every 15 minutes for the first 120 minutes, followed by a 15-minute performance ride. In one trial they consumed flavored water; in another, a conventional carbohydrate sports drink; and in another, a caffeinated sports drink.

The cyclists completed 15 percent to 23 percent more work during the caffeine trial than in the other two trials. Ratings of perceived exertion were lower with the caffeinated sports drink than with the placebo and the conventional sports drink. After cycling, maximal strength loss was found to be two-thirds less for the caffeinated drink than for the other beverages.

This new research suggests that using a caffeinated sports drink may be the best way to go in races.