Caffeine is a performance-enhancing drug. Dozens of scientific studies have shown that moderate caffeine consumption prior to exercise measurably improves speed and endurance across a range of athletic activities. There's little debate these days that caffeine has an ergogenic, or work-enhancing, effect on athletes. The question instead revolves around how to optimize caffeine's impact— how much to take, when to take it, and how to develop a caffeine strategy that works best for you.

A Legal Boost
Numerous studies have examined the effects of caffeine on athletes like cyclists, swimmers, runners, and rowers. "There's no question that caffeine has an ergogenic effect, especially if you're out there doing an endurance-type sport, like long-distance cycling, running, or even hiking," says Nancy Clark, MS, RD, and author of Nancy Clark's Sports Nutrition Guidebook. A review of the scientific literature bears this out. On average, endurance athletes who ingest a moderate amount of caffeine prior to exercise see a 1 to 3 percent improvement in performance. Simply put, caffeinated athletes go farther when tested over a set time period and travel faster when measured over a set distance.

Pathways to Power
Though the ergogenic effects of caffeine are well documented, the reasons behind them are not fully understood. A primary effect is believed to be psychological: Your caffeine-stimulated mind is simply less aware of fatigue. "Caffeine makes athletic exercise seem easier," explains Clark. "In terms of perceived effort, you work harder without realizing it." Another possible factor is physiological. One area of research has focused on the body's use of glycogen, the primary fuel for muscles. Some studies have indicated that caffeine stimulates the body to better metabolize fat—a secondary fuel source—and thus improve endurance by extending the amount of time glycogen reserves are available.

Everything in Moderation
Low to moderate levels of caffeine are sufficient to gain its full performance benefits. Higher doses offer little to no advantage and the accompanying increase in side effects—anxiety, shakiness, jitters—may actually be detrimental. The standard recommendation is 1 to 3 milligrams of caffeine per kilogram of body weight (roughly 0.5 to 1.5 milligrams per pound). If you weigh 150 pounds, this translates to 75 to 225 milligrams, the rough equivalent of 1 to 3 cups of coffee. "Each person has such a different tolerance," Clark says. "Experiment during training and figure out which amount works best for you."

Delivery Systems
Caffeine is present in a wide range of products, including coffee, tea, soda, chocolate, caffeine pills, and some energy gels and drinks. Amounts vary by source. A typical 8-ounce cup of coffee contains 75 to 150 milligrams; an 8-ounce cup of tea, 10 to 50 milligrams; and a 12-ounce can of cola, 40 to 50 milligrams. (Coffee is perhaps the least desirable caffeine source due to its highly variable caffeine amounts.) Caffeine levels in the blood peak about 45 to 60 minutes after consumption and the effects continue for another four to six hours. In most studies, athletes were provided caffeine one hour before exercise, the usual recommendation for timing. It is unclear whether continued caffeine consumption during activity provides additional benefits or whether abstaining from caffeine prior to exercise enhances its effect.

Myth and Reality
There is a widespread belief that caffeine has a diuretic effect that results in dehydration. "This is one of the main myths about caffeine," Clark notes. "The Army has done extensive research on this and found that caffeine does not have a dehydrating effect." Finally, keep in mind that caffeine won't turn a couch potato into an Olympic athlete. Caffeine will almost certainly improve your performance to at least some degree, regardless of your fitness level, but its effects pale in comparison to the impact of other factors. "The bottom line is that sleep, proper fueling, and proper training are the most crucial aspects of athletic performance," Clark concludes. "No amount of caffeine can compensate for a lack of those."